Environmental Aspects of Construction with Waste Materials

ENVIRONMENTAL ASPECTS OF CONSTRUCTION WITH WASTE MATERIALS PROCEEDING OF THE INTERNATIONALCONFERENCE ON ENVIRONMENTAL I...

Author: Th.G. Aalbers | H.A. van der Sloot | J.J.J.M. Goumans

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ENVIRONMENTAL ASPECTS OF CONSTRUCTION WITH WASTE MATERIALS PROCEEDING OF THE INTERNATIONALCONFERENCE ON ENVIRONMENTAL IMPLICATIONS OF CONSTRUCTIONMATERIALS AND TECHNOLOGY DEVELOPMENTS, MAASTRICHT, THE NETHERLANDS, 1-3 JUNE 1994

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Studies in Environmental Science 60

ENVIRONMENTAL ASPECTS OF CONSTRUCTION WITH WASTE MATERIALS PROCEEDING OF THE INTERNATIONAL CONFERENCE ON ENVIRONMENTAL IMPLICATIONS OF CONSTRUCTION MATERIALS AND TECHNOLOGY DEVELOPMENTS, MAASTRICHT, THE NETHERLANDS, 1-3 JUNE 1994

Edited by

J.J.J.M. Goumans Netherlands Agency for Energy and the Environment (NOVEM), P.0. Box 8242, 3503 RE Utrecht, The Netherlands

H.A. van der Sloot Netherlands Energy Research Foundation (ECN), P.0.Box 1, 1755ZG Petten, The Netherlands

Th. G. Aalbers National Institute of Public Health and Environmental Protection (RI VM), P.O. Box 1, 3720 BA Bilthoven, The Netherlands

ELSEVIER Amsterdam

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London

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NewYork

- Tokyo

1994

ELSEVIER SCIENCE B.V. Molenwerf 1 P.O. Box 21 1,1000 AE Amsterdam, The Netherlands

ISBN 0-444-81853-7

01994 Elsevier Science B.V. All rights reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science B.V., Copyright & Permissions Department, P.O. Box 521, 1000 AM Amsterdam, The Netherlands. Special regulations for readers in the U.S.A. - This publication has been registered with the Copyright Clearance Center Inc. (CCC), Salem, Massachusetts. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the U.S.A. All other copyright questions, including photocopying outside of the U.S.A., should be referred to the publisher. No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. This book is printed on acid-free paper. Printed in The Netherlands

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33

Atmospheric Pollution 1978 edited by M.M. Benarie Air Pollution ReferenceMeasurement Methods and Systems edited by T. Schneider, H.W. de Koning and L.J. Brasser Biogeochemical Cycling of Mineral-Forming Elements edited by P.A. Trudinger and D.J. Swaine PotentialIndustrialCarcinogensand Mutagens by L. Fishbein IndustrialWaste Management by S.E. Jergensen Tradeand Environment: ATheoretical Enquiry by H. Siebert, J. Eichberger, R. Gronych and R. Pethig Field Worker Exposure during Pesticide Application edited by W.F. Tordoir and E.A.H. van Heemstra-Lequin Atmospheric Pollution1980 edited by M.M. Benarie Energetics and Technology of Biological Eliminationof Wastes edited by G. Milazzo Bioengineering,ThermalPhysiologyand Comfort edited by K. Cena and J.A. Clark Atmospheric Chemistry. Fundamental Aspects by E. Meszaros Watersupply and Health edited by H. van Lelyveld and B.C.J. Zoeteman Man under Vibration. Sufferingand Protection edited by G. Bianchi, K.V. Frolov and A. Oledzki Principlesof Environmental Science and Technology by S.E.Jergensen and I. Johnsen Disposalof RadioactiveWastes by Z. Dlouhy Mankind and Energy edited by A. Blanc-Lapierre Quality of Groundwater edited by W. van Duijvenbooden, P. Glasbergen and H. van Lelyveld Educationand Safe Handlingin PesticideApplication edited by E.A.H. van Heemstra-Lequin and W.F. Tordoir PhysicochemicalMethods for Water and Wastewater Treatment edited by L. Pawlowski Atmospheric Pollution 1982 edited by M.M. Benarie Air Pollution by NRrogenOxides edited by T. Schneider and L. Grant Environmental Radioanalysis by H.A. Das, A. Faanhof and H.A. van der Sloot Chemistry for Protectionof the Environment edited by L. Pawlowski, A.J. Verdier and W.J. Lacy Determination and Assessment of PesticideExposureedited by M. Siewierski The Biosphere: Problems and Solutions edited by T.N. VezirMlu Chemical Events in the Atmosphere and their Impacton the Environment edited by G.B. Marini-Bettolo Fluoride Research 1985 edited by H. Tsunoda and Ming-Ho Yu Algal Biofouling edited by L.V. Evans and K.D. Hoagland Chemistryfor Protectionof the Environment 1985 edited by L. Pawlowski, G. Alaerts and W.J. Lacy Acidification and its Policy Implicationsedited by T. Schneider Teratogens: Chemicals which Cause Birth Defects edited by V. Kolb Meyers Pesticidechemistryby G. Matolcsy, M. Nadasy and Y. Andriska Principlesof EnvironmentalScience and Technology (secondrevisededition) by S.E. Jergensen and I. Johnsen

34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

57 58 59

Chemistry for Protectionof the Environment 1987 edited by L. Pawlowski, E. Mentasti, W.J. Lacy and C. Sarzanini Atmospheric Ozone Researchand its Policy Implicationsedited by T. Schneider, S.D. Lee, G.J.R. Wolters and L.D. Grant Valuation Methods and Policy Making in Environmental Economics edited by H. Folmer and E. van lerland Asbestos in Natural Environment by H. Schreier How to Conquer Air Pollution.A Japanese Experience edited by H. Nishimura Aquatic BioenvironmentalStudies: The HanfordExperience, 1944-1984 by C.D. Becker Radon in the Environment by M. Wilkening Evaluationof Environmental Data for Regulatory and ImpactAssessment by S. Ramamoorthy and E. Baddaloo EnvironmentalBiotechnology edited by A. Blazej and V. Privarova Applied Isotope Hydrogeology by F.J. Pearson Jr., W. Balderer, H.H. Loosli, B.E. Lehmann, A. Matter, Tj. Peters, H. Schmassmann and A. Gautschi Highway Pollutionedited by R.S. Hamilton and R.M. Harrison Freight Transport and the Environment edited by M. Kroon, R. Smit and J.van Ham Acidification Research inThe Netherlands edited by G.J. Heij and T. Schneider Handbook of RadioactiveContamination and Decontamination by J. Severa and J. Bar Waste Materials in Construction edited by J.J.J.M. Goumans, H.A. van der Sloot and Th.G. Aalbers Statistical Methods in Water Resources by D.R. Helsel and R.M. Hirsch Acidification Research: Evaluationand Policy Applications edited by TSchneider Biotechniques for Air PollutionAbatement and Odour Control Policies edited by A.J. Dragt and J. van Ham EnvironmentalScience Theory. Concepts and Methods in a OneWorld, Problem-OrientedParadigm by W.T. de Groot Chemistry and Biology of Water, Air and Soil. Environmental Aspects edited by J. Tolgyessy The Removalof NitrogenCompoundsfrom Wastewater by B. Halling-Serensen and S.E. Jergensen EnvironmentalContamination edited by J.-P. Vernet The Reclamation of Former Coal Mines and Steelworks by I.G. Richards, J.P. Palmer and P.A. Barratt Natural Analogue Studies in the GeologicalDisposalof Radioactive Wastes by W. Miller, R. Alexander, N. Chapman, I. McKinley and J. Smellie Water and Peace in the Middle East edited by J. Isaac and H. Shuval Environmental Oriented Electrochemistry edited by C.A.C. Sequiera

vii

mREw0RD The Organizing and Scientific Committees of the Second International Conference on Environmental Implications of Construction Materials and Technology Developments, WASCON '94, present herewith the Proceedings of this Conference, which will be held from 1-3 June, 1994 in Maastricht, The Netherlands.

SCOPE OF THE CONFERENCE The concept of "Sustainable Development", implicating the protection of soil and groundwater, the limitation of waste production and the re-use of solid waste materials is still the leading theme of WASCON '94. Although it is clearly recognized in most countries that products derived from solid waste materials can be applied as construction materials, research is still needed to assess various environmental problems. With respect to the prediction and control of release of contaminants, there is a trend towards consensus on the usage of the various leaching tests which have been developed. In addition, scientific research regarding, e.g., speciation of chemical elements is generating results which can be transferred to technical studies and also to more general studies dealing with environmental and life cycle analysis. As is reflected in the amount of contributions, two topics are currently the subject of study in many countries. Firstly, there is the problem of municipal waste, stabilization of waste materials and their use in civil works is the subject of research and legislation. Within these fields it can be seen that transfer of knowledge and know-how is helping to find environmentally acceptable solutions, also with respect to establishing criteria and standards. Secondly, as far as technology development is concerned, it can be seen that research has encompassed a wider variety of materials. Furthermore, quality control and standardization has been applied to these types of materials. The incorporation of environmental quality standards is the next step to be taken, and is already the subject of some studies. In general, technical studies are often already accompanied by environmental aspects as an integral part of research. The Organizing Committee hopes that WASCON '94 will contribute to the solution of environmental and technical problems concerning the re-use of waste materials and, thus, to sustainable development in building practice.

SCIENTIFIC COOPERATION

The International Society for Construction with Alternative Materials (ISCOWA) was founded as a result of the First Conference, held in 1991. To date over 110 members from 15 different countries have been registered, and the Society is still growing. ISCOWA is actively participating in the scientific committee and in the organization of WASCON '94. Many ISCOWA members have submitted contributions to the Conference, arid the Chairmen of the ISCOWA working groups have prepared state-of-the-art documents.

viii

ACKNOWLEDGEMENT Organizing an international conference means a lot of work for many people, we therefore wish to express our thanks to the following: The members of the Honorary Committee and the Scientific Committee. The Dutch National Institute of Public Health and Environmental Protection (RIVM), the Netherlands Energy Research Foundation (ECN), Environment Canada, The United States Environmental Protection Agency (USA-EPA), Community Bureau of References, Commission of the European Community (BCR), The Danish National Agency for Environmental Protection, European Association for Use of the By-products of Coal Fired Power Stations E.V. (ECOBA), the Center for Applied Research, Norway, and the Netherlands Agency for Energy and the Environment (NOVEM) for supporting the Conference. The Netherlands Ministries of Housing, Physical Planning and the Environment and of Economic Affairs, which have sponsored the Conference. Van Namen and Westerlaken Congress Organization Services, De Boer and Van TeyIingen Public Relations and the staff of Elsevier Science B.V. All Authors, Participants of the Conference, and all others who have contributed to WASCON '94. On behalf of the Organizing Committee, Dr J.J.J.M. Goumans Chairman of ISCOWA Utrecht, The Netherlands, 21 March 1994

ix CONTENTS Preface

...................................................................................................

vii

SECTION 1: Opening The International Ash Working Group: A Treatise on Residues from MSW Incinerators .............................................................................................. S.E. SAWELL, A.J. CHANDLER, T.T. EIGHMY, J. HARTLEN, 0. HJELMAR, D. KOSSON, H.A. VAN DER SLOOT and J. VEHLOW

3

International Progress in Solid Waste Management J.H. SKINNER

..............................................

7

Life Cycle Analyses; Results of Some Case Studies J. CRAMER

.............................................

17

SECTION 2: Environmental Aspects Chemical Processes Controlling the Mobility of Waste Material Contaminants in Soils L.G. WESSELINK, P.M. DEKKER and T.G. AALBERS

..

31

Leaching of Slags and Ashes - Controlling Factors in Field Experiments versus Laboratory Tests ....................................................................................... A.-M. FALLMAN and J. HARTLEN

39

Validation of Leaching Model on Actual Structures ............................................. G . VAN DER WEGEN and C. VAN DER PLAS

55

Intercompanson of Leaching Tests for Stabilized Waste ...................................... H.A. VAN DER SLOOT, G.J.L. VAN DER WEGEN, D. HOEDE and G.J. DE GROOT

63

Immobilisation Potential of Cementitious Materials F.P. GLASSER

...............................................

Coal Fly-Ash Leaching Behaviour and Solubility Controlling Solids R. GARAVAGLIA and P. CARAMUSCIO Modelling Ca-Solubility in MSWI Bottom Ash Leachates R.N.J. COMANS and J.A. MEIMA

........................

87

....................................

Particle Petrogenesis and Speciation of Elements in MSW Incineration Bottom Ashes T.T. EIGHMY, J.D. EUSDEN, JR., K. MARSELLA, J. HOGAN, D. DOMINGO, J.E. KRZANOWSKI and D. STAMPFLI

77

103

..

111

X

An Approach to the Assessment of the Environmental Impacts of Marine Applications of Municipal Solid Waste Combustion Residues ................................................. 0. HJELMAR, E.A. HANSEN, K.J. ANDERSEN, J.B. ANDERSEN and E. BJ0RNESTAD Quality Assessment of Granular Combustion Residues by a Standard Column Test: Prediction versus Reality ............................................................................. M. JANSSEN-JURKOVICOVA, G.G. HOLLMAN, M.M. NASS and R.D. SCHUILING

137

161

Geochemical Factors Controlling the Mobilization of Major Elements during Weathering of MSWI Bottom Ash .................................................................. C. ZEVENBERGEN and R.N.J. COMANS

179

Leaching Behaviour of Building Materials with Byproducts under Practical Conditions ............................................................................................... P.J.C. BLOEM, F.L.M. LAMERS and L. TAMBOER

195

FGD Gypsum Definitions and Legislation in the European Communities, in the OECD and in Germany ........................................................................................ F. WIRSCHING, R. HULLER and R. OLEJNIK

205

In-situ Utilization of Waste Bentonite Slurry N. UCHIYAMA and S. HORIUCHI

.....................................................

217

..................................

227

The use of MWI Fly Ash in Asphalt for Road Construction J.B.M. HUDALES

Enhanced Natural Stabilization of MSW Bottom Ash: A Method for Minimization of Leaching ............................................................................................. J.J. STEKETEE and L.G.C.M. URLINGS Immobilization of Slag Material by Foam Bitumen J.H. DIJKINK

233

.............................................

239

..........................

247

Immobilisation of Phenol and PAH by Special Hydraulic Binders P. VOGEL and M. SCHMIDT

Leaching of Organic Contaminants from Contaminated Soils and Waste Materials ...... M. WAHLSTROM, H. THOMASSEN, J. FLYVBJERG, A.C. VELTKAMP, C. OSCARSSON, J . - 0 . SUNDQVIST and G.A. ROOD

257

Investigating a Leaching Test for PCBs and Organochlorine Pesticides in Waste and Building Materials ................................................................................ G.A. ROOD, M.H. BROEKMAN and T.G. AALBERS

27 1

French Qualification Procedure for Solidification Processes ................................... J. MEHU, P. MOSZKOWICZ, R. BARNA. P. PHILIPPE and V. MAYEUX

281

xi Utilization Status, Issues and Criteria Development for Municipal Waste Combustor Residues in the United States ....................................................................... D.S. KOSSON, B.A. CLAY, H.A. VAN DER SLOOT and T.T. KOSSON

293

........................

305

Validation of Dutch Standard Leaching Tests Using NEN-IS0 5725 G.J. DE GROOT and D. HOEDE

The Laconia, New Hampshire Bottom Ash Paving Project ..................................... C.N. MUSSELMAN, M.P. KILLEEN, D. CRIMI, S. HASAN, X. ZHANG, D.L. GRESS and T.T. EIGHMY

315

Application of Fly Ash and other Waste Materials for the Construction of an Off-Shore Island Opposite the Coast of Tel-Aviv ............................................................. Y. ZIMMELS, G. SHELEF and A. BOAS

329

Fly Ash Utilisation in Civil Engineering .......................................................... J.G. CABRERA and G.R. WOOLLEY

345

High Pressure Mixing: A New Technology to Re-use Waste Materials Containing CaO and/or MgO ...................................................................................... R. HAVERKORT, W. DEKKER and J. SENDEN

357

Environmental Compatibility of Cement and Concrete ......................................... S. SPRUNG, W. RECHENBERG and G. BACHMANN

369

.................................................

387

European Standardization of Additions for Concrete ........................................... J.M.J.M. BIJEN

397

State of the Art of Waste Characterization on European Level ............................... A. TUKKER. M. VAN DEN BERG and H.A. V A N DER SLOOT

409

Leaching Properties of Cement-bound Materials I. HOHBERG and R. RANKERS

Leaching Behavior Assessment of Wastes Solidified with Hydraulic Binders: Critical Study of Diffusional Approach ............................................................ P. MOSZKOWICZ, R. BARNA, J . MEHU, H. VAN DER SLOOT and D. HOEDE Burning of Hazardous Wastes as Co-Fuel in a Cement Kiln Does it Affect the Environmental Quality of Cement? .......................................... K.H. KARSTENSEN Approach towards International Standardization: A Concise Scheme for Testing of Granular Waste Leachability ..................................................................... H.A. VAN DER SLOOT, D.S. KOSSON, T.T. EIGHMY, R.N.J. COMANS and 0. HJELMAR Speciation of As and Se during Leaching of Fly Ash E.E. VAN DER HOEK and R.N.J. COMANS

..........................................

42 1

433

453

467

xii Measurement of Redox Potential During Standardized Column Tests J. KEIJZER and A.J. ORBONS

.......................

477

The Influence of Reducing Properties on Leaching of Elements from Waste Materials and Construction Materials ........................................................................... H.A. VAN DER SLOOT, D. HOEDE and R.N.J. COMANS Hydrology and Chemistry of Pulverized Fuel Ash in a Lysimeter or the Translation of the Results of the Dutch Column Leaching Test into Field Conditions ..................

483

49 1

R. MEIJ and H.P.C. SCHAFTENAAR Role of Facilitated Transport in the Emissions of Secondary Raw Materials J.J. STEKETEE, J.C.M. DE WIT, G.J. VAN ROSSUM and L. G. C.M. URLINGS

...............

507

Immobilization of Heavy Metal Ions by the Alkali Activated Slag Cementitious Materials ................................................................................................. J. MALOLEPSZY and J. DEJA

5 19

Integrated Treatment of MSWI-residues: Treatment of Fly Ash in View of Metal Recovery ......................................................................................... B. LAETHEM, P. VAN HERCK, P. GEUZENS and C. VANDECASTEELE

525

Life Cycle Assessment of a Road Embankment in Phosphogypsum: Preliminary Results .................................................................................... J.W. BROERS, F.E.T. HOEFNAGELS and H.L. ROSKAMP

539

Co-combustion of Coal and Waste Wood, Consequences for the By-product Quality M.L. BEEKES, C.H. GAST and A.J.A. KONINGS

.....

543

SECTION 3: Technical Aspects Use of Demolition Concrete to produce Durable Structural Concrete P.J. WAINWRIGHT and J.C. CABRERA

.......................

553

Improvement of Portland Cement/Fly Ash Mortar Strength using Classified Fly Ashes ............................................................................................... J. PAYA, V. BORRACHERO, E. PERIS-MORA, A. ALIAGA and J. MONZd

563

Ground Fly Ashes: Characteristics and their Influence on Fresh and Hardened Mortars .................................................................................................. J. PAYA, V. BORRACHERO, J. MONZO, E. PERIS-MORA and A. ALIAGA

571

Development of Cementitious Products using Industrial Process Wastes as Sources of Reactive Sulfate and Alumina ......................................................... G. BELZ, J. BERETKA, R. CIOFFI, L. SANTORO, N. SHERMAN and G.L. VALENTI

579

xiii Potentials for Utilisation of PFBC Ash ............................................................ J. ROGBECK and P. ELANDER

589

..................................

599

Recycling of Magnesium Slags in Construction Block Form M. COURTIAL, R. CABRILLAC and R. DUVAL

Improving the MSWI Bottom Ash Quality by Simple In-Plant Measures I. SCHNEIDER, J. VEHLOW and H. VOGG

...................

Potentials in Quality Improvement of Processed Building Rubble by Demolition and Treatment Technics .............................................................................. J.O.V. TRANKLER and I. WALKER Quantities and Qualities of Municipal Waste Incinerator Residues in the Netherlands J.G.P. BORN

605

62 1

....

Upgrading Techniques for the Quality Improvement of Municipal Waste Incineration Residues ................................................................................. F.J.M. LAMERS and J.G.P. BORN Re-use of Colliery Spoils in Construction Materials using Fluidized Bed Combustion J.J.M. HEYNEN, H.N.J. A. BOLK, G.J. SENDEN and P.J. TUMMERS

...

633

645

655

Recovery of Raw Materials from Reclaimed Asphalt Pavement .............................. E. MULDER, C. DE GROOT, C. JONKER and J. VAN DER ZWAN

665

.............................

673

Applications for Coal-use Residues: An International Overview L.B. CLARKE

Specifications and the Use of Wastes in Construction in the United Kingdom ............. R.J. COLLINS and C.J. ATKINSON Overview of Coal Ash Use in the USA S.S. TYSON

..........................................................

687

699

Environmental Life Cycle Analysis of Construction Products with and without Recycling ................................................................................................ M.S. A.M. SCHUURMANS-STEHMANN

709

Assessment of the Environmental Compatibility of Industrial By-products and Recycled Materials .................................................................................... R. BIALUCHA, J. GEISELER and K. KRASS

719

...................................

727

Environmental Management in Large Construction Projects E.K. LAURITZEN

A Concept for the Environmental Evaluation of Waste Management Benefits A. TUKKER and D.J. GIELEN

.............

737

......

749

Technological and Environmental Properties of Concretes with High PFA Content H.A.W. CORNELISSEN and R.E. HELLEWAARD

xiv Towards Sustainability with Construction and Demolition Waste in Belgium? G. DESMYTER, B. LAETHEM, B. SIMONS, J. VAN DESSEL and J. VYNCKE Disintegration of Fly Ashes i? the Rotary-vibration Mill J.SIDOR and M.A. WOJCIK

.............

.......................................

759

775

Release of Heavy Metals from a Municipal Solid Waste Incineration Residue Stabilized in Non-traditional Matrices ............................................................. V. ALBINO, R. CIOFFI, B. DE VITO, M. MARROCCOLI and L. SANTORO

789

Applications of By-products from Coal Gasification Power Plants: Quality- and Environment-Related Aspects ........................................................................ M.L. BEEKES, J.W. VAN DEN BERG and A.J.A. KONINGS

80 1

Quality Improvement of MSW Fly Ash and APC Residue from MSW Incinerator Amsterdam-West using Different Iinmobilisation Processes ................................... H.T.M. VAN DE LAAR, J. SLAGTER, R.F. DUZIJN and J.H. DE ZEEUW

81 1

Certification System for Aggregates Produced from Building Waste and Demolished Buildings ................................................................................................ C.F. HENDRIKS

82 1

Sampling and Sub-sampling of Primary and Secondary Building Materials: A Statistical Treatise .................................................................................. A.M.H. VAN DER VEEN and D.A.G. NATER

835

Industrial Scale Application of the Alkali Activated Slag Ceinentitious Materials in the Injection Sealing Works ...................................................................... W. BRYLICKI, J. MALOLEPSZY and S. STRYCZEK

84 1

The use of MSWI Bottom Ash in Asphalt Concrete ............................................. M.M.T. EYMAEL, W. DE WIJS and D. MAHADEW

85 1

How to Prevent Expansion of MSWI Bottom Ash in Road Constructions? ................. M.M.C. ALKEMADE, M.M.T. EYMAEL, E. MULDER and W. DE WIJS

863

Microstructure of Concretes Containing Artificial and Recycled Aggregates J.A. LARBI and P. STEIJAERT Frost Susceptibility of Recycled Aggregate M.M. O’MAHONY

................

877

.......................................................

889

...............................

897

Use of Crushed Tile and Concrete as Filling in Pipe Trenches J. FOLKENBERG

XV

Use of Ashes from MSW Incineration in Cementitious Building Materials A. GERDES and F.H. WITTMANN

................. 905

Effect of Grain Size Composition of the Calcium-sulphate Fly Ashes on the Properties of Autoclaved Building Materials ..................................................... Z. PYTEL and J. MALOLEPSZY Sulphate and Acid Attack on Concrete i n Ground and Landfill C. PLOWMAN

...............................

909 917

Contaminated Soil Cement Stabilizations for Application as a Construction Material .................................................................................................. P.J. KROES and J . VAN LEEUWEN

925

The Assessment of a Pollutant Charge of Dredged Sediments as a Tool to Minimize Adverse Environmental Effects ...................................................................... E. PERIS-MORA, J. MONZO, J. PAYA and J.M. MESA

929

Minestone Substraturn,Behaviour under Loading ................................................ K.M. SKARZYNSKA and E. ZAWISZA

939

Ecological and Energy-saving Advantages and Benefits of Building with Earth .......... H. HOUBEN

94 1

Fly Ash and Slag Reactivity in Cements - TEM Evidence and Application of Thermodynamic Modelling ........................................................................... H.S. PIETERSEN and J.M.J.M. BlJEN

949

SECTION 4: Closing State of the Art Report: Use of Waste Materials in Construction Technological Development .......................................................................... G.R. WOOLLEY

963

...............................

979

A Unified Approach to Leaching Behavior of Waste Materials T.T. EIGHMY and H.A. VAN DER SLOOT

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SECTION 1: Opening


Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, HA.van der SIoot and Th.G. Aalbers (Editors) @I994 Elsevier Science B. V. All rights resewed.

3

THE INTERNATIONAL ASH WORKING GROUP A TREATISE ON RESIDUES FROM MSW INCINERATORS

S.E. Sawell', A.J. Chandler*, T.T. Eighmy3, J. HartlCn4, 0. Hjelmars, D. Kosson6, H.A. van der Sloot' and J. Vehlow8 'Compass Environmental Inc., Burlington,Ontario; 2 k J . Chandler C Associates Ltd., Willowdale, Ontario; Wniversity of New Hampshire, Durham, N H 4SwedishGeotechnical Institute, Linkoping, Sweden; SDanishWater Quality Institute, H0rsholm, Denmark; 6RutgersUniversity, Piscataway, NJ; 'Netherlands Energy Research Foundation,Petten NL; and *KernforschungszentrumKarlsruhe, Germany. INTRODUCTION Historically, public opposition to the siting and operation of MSW incinerators has been based on concerns over emissions of contaminants to the atmosphere. During the late seventies and early eighties, much of this concern was justifiable in light of the poor performance of inadequately designed and operated facilities. In addition, the enhanced ability of scientists to detect trace contaminants a t very low concentrations placed further pressure on the industry to reduce emissions. During the last decade, the industry has responded positively. Most of the concerns related to emissions have been addressed by optimizing incinerator design and operation through improved combustion control. This and the implementation of new air pollution control technologies has dramatically reduced atmospheric emissions. The advent of more efficient incinerator operation and better designed air pollution control systems has resulted in concern shifting from air emissions to the disposal of the captured residues. Today, ash disposal is one of the major issues limiting the acceptance of new incinerator facilities.

The Incinerator Ash Issue In 1988, several individuals actively involved with ash research were prompted to suggest that the global data base on incinerator ash needed to be compiled, reviewed and critically evaluated. The major concern over incinerator ash centred on the potential for human exposure to contaminants, specifically trace metals in the ash. The potential exposure routes were deemed to be either through the inhalation of fugitive dust or the ingestion of contaminated groundwater. While the industry was moving to address these issues, environmental groups continued to push for more stringent regulations for the disposal of the residues. Several factors contributed to this situation:

o The heterogeneity of the ash characteristics often resulted in contradictory laboratory results; o Residue sampling and analytical protocols were not well established, thereby compounding the variability of the data; o Different combustion technologies and air pollution control systems produce additional variations in the quality of the residues, and thus the data bases exhibit large variations;

4

o Cursory groundwater studies provided an inadequate data base on the long-term effects of monofills on groundwater; and, o The management of these residues had to consider the contentious issue of potential long-term effects, particularly in view of the changing nature of the MSW stream. All of these factors contributed to a highly fragmented data base, which in turn, had resulted in much confusion and a preponderance of misconceptions. The researchers thought that a critical review of the data would provide an opportunity to clarify many of the issues. Thus, in April of 1989, a proposal entitled: "MUNICIPALWASTE INCINERATION: AN INTERNATIONAL PERSPECTIVE ON THE CHARACTERISTICS, DISPOSAL, TREATMENT and UTILIZATION OF RESIDUALS"

was submitted to the International Energy Agency (IEA) for consideration and this led to the establishment of an International Ash Working Group (IAWG). OBJECTIVES While the general purpose of the project was to put the MSW incinerator ash issue into proper perspective, the project had some specific objectives. 1. Provide a compilation of existing knowledge concerning MSW incinerator residues;

2. Define uniform protocols for the sampling and full characterization (including defining chemical, physical, and leaching properties) of incinerator residues; 3. Describe the fate and behaviour of contaminants during the incineration process including documenting the effects of different incinerator designs, air pollution control systems, incinerator operations and refuse feedstocks; 4. Evaluate and develop recommendations with regard to current or proposed disposal, treatment

utilization and recovery practices; 5. Provide regulators with recommended standard performance criteria for the residues under

different management scenarios; 6. Identify areas for further research and development.

APPROACH

The IAWG has formally met 12 times over the past four years. In addition, international seminars have been held on several occasions to bring together regulators and researchers to discuss economically and environmentally sound ash management practices. For example, the IAWG has held two major seminars on leaching protocols, one in Europe and the other in North America. Most of each meeting was devoted to review of specific topics as selected from the original outline. Members of the group prepared for the meetings by gathering together information on the selected subject(s) and provided this material to the group at the meetings. The discussions that ensued lead

5

to the development of draft chapter outlines, which were used to develop the full chapters. Draft chapters were then distributed to the sponsoring agencies for review and comment. In addition to the original mandate of the Group, the IAWG has been designated as a full Activity under the International Energy Agency’s Bioenergy Agreement - Conversion of MSW to Energy Task XI. Consequently, the IAWG now has a mandate to meet through 1994 to consider revisions to the final report based on the review of any new evidence from current research topics.

Benefits

The IAWG is committed to providing the sponsors with the information necessary to make sound decisions regarding MSW incinerator residue management. 1. Outline criteria for data gathering to assist other researchers with project development and generation of quality comparable data; 2. Develop a framework on which to build characterization protocols for assessing incinerator residues;

3. Provide a bench-mark for other researchers by compiling the data and identifying areas requiring further research; 4. Enable regulators, the public and industry to make decisions on the environmental acceptability

of alternative management options for the residues; 5. Develop a framework for international collaboration on managing other wastes.

Sponsorship In order to ensure objectivity, the IAWG sought out funding based on equal contributions from a large number of government agencies, private organizations and companies. The IAWG gratefully acknowledges the support provided by: Maior Soonsors Asea Brown Boveri Ltd Danish Ministry of Energy Energy, Mines & Resources Canada Environment Canada European Economic Community KernforschungszentrumKarlsruhe International Energy Agency Integrated Waste Services Association Minor SDonsors American Society of Mechanical Engineers Greater Vancouver Regional District Northeast Waste ManagementOfficiabAssociation

International Lead Zinc Research Organization LAB France

NOVEMlRIVM Netherlands Swedish National Board for Industrial & Technical Development United Kingdom Department of the Environment United States Environmental Protection Agency Wheelabrator EnvironmentalSystems Inc.

New Jersey - Solid Waste Administration Waste Processing Association Netherlands

6 REPORT OUTLINE In order to develop better options for the management of MSW incinerator ash, full characterisation of the different residues and knowledge of the factors which influence those characteristics are necessary. Consequently, the scope of the report was expanded far beyond that originally anticipated. The current document now includes discussions on a wide range of topics directly related to ash management, including:

o the physical and chemical composition of municipal solid waste, and a summary of how it is managed in the various countries;

o the variations in incinerator and air pollution control technology and how these will influence the characteristics of the residues; o the regulations governing the operation of incinerator facilities and residue disposal; o recommended sampling and analysis methodologies for the residues; o the characteristics of various residue streams based upon the recommended characterisation protocol; o the fate of elements during incineration as a function of waste feed input, incinerator/APC technologies and operation; o the leaching of residues, including a discussion of fundamental physical and chemical aspects, as well as interpretation of appropriate test methods, leaching modelling and detailed discussions of laboratory and field leaching data; o the potential fate of elements in the environment as a function of management practices; o the treatment and modification of residues including a generic outline of possible alternatives and detailed discussions of solidification/stabilization,separation, and thermal treatment. o the chemical, physical and leaching properties of products made from treated incinerator residues; o the disposal or utilization of residues, including a review of the alternatives available and the influence of fate and transport systems, i.e., short and long term impacts; and o identification of areas for further study.

Overall, the report represents a comprehensive examination of the complex issues pertaining to MSW incinerator residues. The IAWG has prepared a summary of the full report which will be distributed in conjunction with this conference. It is anticipated that the full document will be published in hard-cover form and made available to the public in the near future.

Environmental Aspects of Conshuction with Waste Materials JJJM Goumans, HA.VM der S I w t and l71.G.Aalbers (Editors) @I994 Elsevier Science B.K AN rights reserved.

7

International Progress in Solid Waete Management John H. Skinner, Ph.D. President of ISWA the International Solid Waste Association Bremerholm 1, Copenhagen K, Denmark DK 1069

Introduction: Solid Waste Management, The Environmental Issue of the '90's. Solid waste management has moved to the forefront of the environmental agenda. The level of activity and concern by citizens and governments worldwide have reached unprecedented levels. Nations are considering restrictions on packaging and controls on products in order to reduce solid waste generation rates. Local and regional governments are requiring wastes to be separated for recycling, and some have even established mandatory recycling targets. Concerns about emissions from incinerators and waste-to-energy plants have resulted in imposition of state-of-the-art air pollution controls. Landfills are being equipped with liners, impervious caps and leachate collection systems, and gas and groundwater is being routinely monitored. There is wide scale public opposition to siting of new solid waste treatment and disposal facilities. As a result, the costs of solid waste management are increasing rapidly. Previously considered a local issue, it is now clear that solid waste management has international and global implications. Concerns about transboundry shipment of hazardous waste has led to the adoption of the Base1 Convention by the United Nations. Recognizing the interrelationship between solid waste standards and economic development, the European Community is moving forward to harmonize waste disposal requirements in member countries. Around the globe countries are discovering thousands of sites where hazardous wastes have been spilled, dumped or otherwise discarded resulting in contamination of soils, surface waters and ground water. The economic costs of clean-up these sites will stress national economies and at the same time offer enormous international business opportunities. Solid waste management in countries with developing economies poses a special set of problems. In these countries quite often financing is not available for the construction of waste treatment facilities, and there is a lack of trained personnel to operate waste management systems. Also, there are generally no regulations or control systems, no administrative body responsible for solid waste control and no obligation for industry to dispose of wastes properly. The United Nations Environment Programme has focused on solid waste management in developing economies as a priority concern. More than ever before, solid waste management policy makers world wide need sound and reliable information on the technical performance, environmental impact and costs of solid waste

8

collection, recycling, treatment and disposal systems. ISWA, the International Solid Wastes and Public Cleansing Association is putting forward a number of programs that are trying to address that need.

The Mission and Organization of ISWA. The objective of ISWA is to promote the adoption of effective and economically sound solid waste management practices that protect the environment and conserve materials and energy resources. ISWA is a professional association open to members from all countries in the world. Its activity is solely in the public interest through professional development of its members; it does not pursue any commercial or political aims. ISWA is truly an international organization in that its governing body, the General Assembly, is made up of National Members from 20 countries around the world. Most countries with an established solid waste management infrastructure hold National Membership in ISWA. National Members must be national organizations representing all professional activities related to solid waste management in the member country. National Members are encouraged to form national committees of solid waste professional associations within their countries to assure a broad representation in ISWA. It is this international network of National Member organizations that provides ISWA the ability to reach thousands of solid waste professionals throughout the world. ISWA also has over 700 individual and organizational members in over 60 countries. Recognizing the special solid waste management problems in developing countries, ISWA also provides a Development Membership category pending the establishment of a fully functioning National Member organization.

ISWA Programe. ISWA carries out its mission through a series of efforts to collect and disseminate information to its members. The ISWA Journal, Waste Management and Research is published six times a year by Academic Press and has a ten year history of successful issues containing high quality peer reviewed articles. Our newsletter, the ISWA Times is published quarterly and provides practical and useful information to its readers. The ISWA Yearbook, the International Directory of Solid Waste Management and Public Cleansing, provides extensive listings of companies and organizations in the solid waste field, as well as a wide range of articles summarizing activity throughout the industry. ISWA sponsors and cosponsors a number of conferences, workshops and symposia. Important ISWA conferences and congresses for the next several years include: 1994 ISWA Annual Conference, in conjunction with the UK Institute of Wastes Management, Torbay, UK, June 14-17, 1994.

9

ISWA 25th Anniversity Congress, Vienna, Austria, October 16-20, 1995. ISWA Quadrennial Congress, Yokohama, Japan, October 27November 1, 1996. In order to provide the opportunity for the development of specialized ISWA activities, working groups on the following seven subjects have been established: Hazardous Waste Sanitary Landfill Incineration Recycling and Waste Minimization Collection and Transport Sewage and Water Works Sludge Biological Waste Treatment. ISWA members can belong to these working groups and engage in practical information exchanges with members from other countries. Through these working groups ISWA holds many specialized symposia and workshops and has developed an international solid waste professional book and report series.

Integrated Solid Waste Management. ISWA members and most other solid waste management professionals recognize that there is no single, simple solution to solid waste problems. Instead an integrated approach is necessary combining the elements of several techniques. In the United States, the Environmental Protection Agency published The Solid Waste Dilemma: An Agenda for Action, which outlines an integrated set of strategies for dealing with solid waste management. These strategies are very similar to those recommended by the European Commission, the United Nations Environment Programme and countries around the world. Integrated solid waste management is a comprehensive strategy involving four key elements applied in a hierarchial manner: 1.

Reducing the volume and toxicity of the solid waste that is generated,

2.

Recycling or reusing as much as possible of what is generated,

3.

Recovering energy from the remaining waste through combustion systems equipped with the best available pollution control technology, and

4.

Utilizing landfills with adequate environmental controls.

In the following sections each of the elements of this strategy will be discussed in turn. Also recent data on U.S. practices will be presented for purposes of illustration.

10

Waste Reduction. Waste reduction activities are important to halt or slow down the increasing rate of waste generation per-capita. For example, the most recent data from the U . S . indicates the total amount of municipal solid waste increased from 180 million tons in 1988 to 196 million tons in 1990, which represents an increase in the per capita generation rate from 1.82 to 1.95 kg. per person per day. Waste reduction has several aspects, all of which should be addressed. One is toxicity reduction, in which the nature of waste is changed by reducing manufacturer's use of toxic materials in consumer products. Another is volume reduction-cutting the amount of waste generated by using less material in the first place. A prime example of this is a reduction in packaging. Waste reduction also includes encouraging the production of products that can be recycled more easily, such as shifting from multimaterial to one-material packaging. Other options to reduce wastes include the redesign of products, material use changes, and restrictions on specific product types. The approach to reducing waste must be broadly based incorporating actions that can be taken by industries, individuals, commercial enterprises and governmental agencies. Industry can reduce waste through raw material substitution and redesign of products and processes. Individuals, commercial enterprises and agencies can use their purchasing power to create a demand for low waste products or items produced from recycled materials. Governments should investigate the use of economic and other incentives to encourage waste reduction. Waste reduction efforts also need to focus on consumer behavior. Education and information dissemination programs can be effective means of causing desired behavioral and attitudinal changes. There are many cases of successful reduction of wastes produced by industrial processes. Experience has shown that modifications to industrial processes that reduce waste also result in lower raw material, energy and waste disposal costs. Productivity is often enhanced and liabilities related to release of hazardous substances are reduced. The fact that waste reduction quite often pays has been demonstrated repeatedly.

Recycling. There are two basic approaches to recycling solid wastes. The first involves separating recyclable materials by the waste generator and separately collecting and transporting these materials to recycling markets. The second involves collecting mixed wastes or commingled recyclable materials and separating them at a central processing facility. In the U.S., through a combination of these practices the percentage of the municipal solid waste stream recovered for recycling or composting increased from 13 percent in 1988 to 17 percent in 1990. Prior separation of recyclable materials has the advantage that the materials are not contaminated by other wastes.

11

However, this requires the waste generator (e.g. householder) to separate the wastes correctly and store them in separated form. Also, the generator needs to transport the separated material to recycling centers or separate or compartmentalized collection vehicles need to be used. Key factors in success of preseparation efforts are the cooperation and willingness of the generator to participate in the program over the long tern, and the additional collection and transport costs that may be required. Mixed solid waste can be separated for recycling at local processing centers or materials recovery facilities (MRFs). Inn the U.S. for example, there are over 200 MRFs in operation, construction, or advance planning stages. Some plants process segregated recyclables; others separate mixtures of glass bottles, aluminum cans and steel cans; still others process mixed residential or commercial wastes, separating the recyclable materials. The success of these plants depends on the processing costs and the quality of the recyclable material produced. A major factor affecting recycling economics is the difference in cost between disposal and recycling. In many locales this cost difference is narrowing. For example, in the U.S. the disposal fee for landfills and waste-to-energy plants has increased dramatically over the past 10 years. Today, on the average, a solid waste management system in the U.S. can avoid $25 to $40 per ton in disposal costs for every ton it recycles, whether or not it gets paid for the recycled material. In some locations the savings are even higher. A major recycling impediment is the question of continued viability and availability of secondary materials markets. Can manufacturers expand markets so they can accept all of the material that is being collected by the new residential programs? Topping the list of problematic waste material markets is the market for old newspaper. In the late 1980s, there was dislocation in markets due to an oversupply created by the large number of municipal collection programs that were all bringing new supplies to markets simultaneously. Many U.S. municipalities were forced to pay to recycle collected newspapers. Current market figures show that the value of old newspaper varies from $40/ton to a -(negative) $4O/ton. Problems are also being experienced in other recycled material markets, including those for glass, plastic and for compost produced from yard waste and mixed municipal solid waste. There are some encouraging trends that suggest the problem of oversupply of old newspaper could be reduced. Some newsprint producers in the U.S. and Canada have announced plans for new facilities to make use of recycled fiber. Others have undertaken feasibility studies for new facilities. It is important to understand that separation of materials from the solid waste stream in itself does not constitute recycling. Recycling only occurs when these materials are incorporated into products that enter commerce. Therefore requirements to separate certain fractions of materials from waste may produce a supply of materials, but these requirements

12

in themselves will not ensure recycling. In fact, if markets for these materials are not found, and the materials are subsequently disposed of, all of the costs of recycling are experienced with none of the benefits. Similarly, requirements to incorporate separated waste materials in products will not result in recycling unless these products are of a quality and price that they successfully compete in the marketplace. To analyze the economic feasibility of recycling one must consider the price received for the recycled material, the solid waste collection and disposal costs avoided and the costs of separation, collection and processing the separated materials. In making these cost comparisons it is important that all environmental costs and benefits are internalized. Also, the benefits to future generations in terms of natural resources conserved or landfill space conserved must be considered. Any virgin raw material subsidy that artificially drives down the price must be accounted for so that virgin materials and recycled materials compete in an equitable manner. Similarly, procurement specifications that arbitrarily discriminate against recycled materials should be eliminated. In order to effectively carry out successful recycling programs, solid waste managers must operate in a business-like manner as raw material suppliers. They must treat the users of their materials as customers. This means they must produce recyclable materials meeting the customer's material quality requirements, and offer recyclable materials at a price competitive with other material supplies. They must operate their separation, collection and processing systems to produce competitively priced, quality materials at the lowest possible costs. The elements of success of a recycling operation are the same as for any successful business; staying close to the customer, understanding and meeting their quality needs and operating in a cost effective manner to produce a competitively priced product.

Combustion with Energy Recovery. Waste-to-energy facilities can achieve an 85% volume reduction in the waste burned. In the U.S. these plants have increased their handling of solid wastes from a negligible percentage of the municipal solid waste stream in the early 1980s to almost 16% of municipal solid waste today. Waste-to-energy plants have faced two main problems in their fight to win public acceptance: air pollution concerns and the heavy metal content of the ash generated in the combustion process. On January 14, 1991, the U.S. EPA issued regulations for new municipal (New Source Performance Standards, or NSPS) and guidelines for existing plants. These standards incorporate good combustion practices, emissions monitoring and highly efficient air pollution control systems to control organic emissions (dioxins and furans), metals, acid gases and other pollutants. The standards are similar to those used in other countries to regulate incinerators. EPA estimated that in 1994 the national costs of these rules will be $170 million a year for new

13

facilities and $302 million a year for existing facilities. Therefore in the U.S. there will be a substantial financial investment to upgrade the environmental performance of municipal incinerators. Another environmental concern that has developed over the past several years involves the disposal of ash residues from municipal waste incinerators. Usually significant amounts of lead, cadmium, zinc, mercury, arsenic, and other metals are found in incinerator ash, especially fly ash. The environmental concern is the potential for these metals to leach out of the residue when disposed of with other wastes in a sanitary landfill. This has led to the utilization of monofills or landfills used solely for ash disposal. In September 1992, the U . S . EPA issued an opinion that ash generated by solid waste-toenergy incinerators is not considered a hazardous waste under Federal law and that the new requirements for solid waste landfills will ensure that ash is disposed of in a manner that protects human health and the environment. Also, technologies have been developed to chemically extract metals from incinerator ash or to solidify and stabilize the ash by adding cement or kiln dust to create a concrete like substance. While these technologies are effective in removing or stabilizing metals, they do result in added disposal costs. Some of these costs can be offset if the ash is treated to the extent that it can be used safely and sold as an aggregate or building material. In the U.S. over 8 million tons of incinerator ash are produced annually.

Landf i 11s. Landfill technology has advanced very rapidly over the past decade. Today's state-of-the-art landfills are equipped with leachate collection systems, liner systems, systems for control of landfill gas, groundwater monitoring, closure and post-closure care and much more. The objective is to ensure that landfilling is performed in a manner that greatly reduces the change of environmental degradation--and also, that any degradation that occurs is quickly detected and remediated. In the U . S . the number of landfills continues to decrease, two main consequences are seen: first, communities face longer transport distances to deliver their solid waste to disposal sites; secondly, several large facilities, designed to serve a limited number of communities for a given number of years, are seeing their lifespans drastically foreshortened by the influx of waste from outside their service areas. Due to more stringent landfill regulations, many small facilities will shut down because they will be unable to meet the new requirements. A hoped-for-result is a decrease in opposition to landfills, stemming from greater public faith in the environmental soundness of facilities that are allowed to operate.

14

Some observers believe the combination of continued strong public opposition and tougher landfill rules will result in a system of large, remotely located regional landfills. Signs of this can be seen already.

A Strategy for Continuous Improvement. Over the past 20 years there has been substantial progress in addressing solid waste problems. However, many problems still exist and we understand them to be very complex. To deal with them, the strategies that have been used in the past will not be enough. As we move towards the 21st Century, a number of forces must come together to lead to continuous improvement in solid waste management. These include:

Continued, Rigorous Enforcement of Environmental Laws and Environmental standards must be rigorously Regulations. enforced in order to assure the public that our solid waste systems are operated in ways that protect human health and the environment. Enforcement must create an incentive for compliance with environmental standards. It must level the playing field so that violators are not at a competitive economic advantage to the good citizens that comply. Waste Reduction as the Strategy of Choice. The traditional approach to solid waste management has been a pollution control strategy where wastes are collected and treated or disposed of after they are generated, or waste is cleaned up after it has occurred. A waste reduction strategy is different, it means not creating the waste in the first place. This can be accomplished through changing product designs, increasing process efficiencies, and extending product lifetimes. Waste reduction results in reduction in waste treatment and disposal costs, reduced liability for environmental damages, lower raw material costs and process efficiencies. Risk-Based Decision Making. Solid waste management decision-making must be based on a comparative analysis of the relative environmental risks of the various options available. Quite often there is public opposition to a particular facility because of concern about environmental risk. While the public expresses a preference for recycling over waste-to-energy or landfill, it is often forgotten that the recycling process itself produces waste or residuals that must be managed or disposed of (eg. waterborne wastes produced from the deinking of recycled newsprint or increased air pollution from additional collection vehicles). In order to make an informed decision, the risk of one option must be compared to the alternatives. Priorities must be based on relative environmental risk. In order to do this we need to develop better and more reliable risk assessment methodologies and put them to use. Significant advances need to be made in our capabilities to assess the risks to ecological systems. An investment in risk assessment research will certainly pay off. Public Information to Encourage Voluntary Action. Providing data and information to those who make or influence decisions can

15

lead to voluntary actions with significant environmental benefits. A good example is the Toxic Release Inventory (TRI) in the US. Each year industries are required to publish the total release of certain toxic wastes to the environment and make this information publicly available. When the public for the first time realized the total environmental releases from all of these plants and facilities, they demanded that something be done about it. This led to the establishment of the 33/50 Program. Under this program companies voluntarily agree to reduce their waste discharges of by 33 percent by the end of 1992 and 50 percent by the end of 1995. Over 700 companies have made written commitments which will reduce the discharge to the environment of 150,000 tons of toxic chemicals by 1995. Information is a powerful tool which can stimulate real results.

Environmental Education. As the above example shows an informed public can be an effective force in environmental protection. However, professionals in the field must do a much better job in explaining to the public the true nature of environmental risks and what can be done about them. The National Environmental Education Act which was passed in the US in 1991 provides some excellent vehicles for doing this including (1) support for environmental curriculum development, (2) assistance for teacher training and ( 3 ) scholarships and fellowships for environmental science and engineering. It is very important to increase environmental literacy to build public support for environmental programs and train future generations of environmental professionals. Economic Incentivee. Market based economic incentives can be used as an alternate to regulation or as a means of making regulations more effective. For example, the liability standards under the US Superfund legislation make a waste generator liable for environmental damages caused by that waste. This produces a very strong economic incentive for waste reduction and on-site waste treatment. Other economic incentives such as pollution charges and deposit systems should also be evaluated for future solid waste management policies. Research and Development. A sustained, long term research and development effort is necessary to improve our understanding of the environmental impacts of solid waste management systems and develop solutions. What are the health effects of environmental releases from solid waste management systems. How do pollutants move through the environment and change in their physical and chemical form? What are the routes of exposure for human populations and ecological systems? How can we monitor and detect pollutant levels in real time? What are the most cost effective approaches to waste reduction, recycling, combustion nd disposal. These are just a few of the questions that research must address. However, research should not be limited to technological and physical science issues. Research into the social and economic aspects of solid waste management is necessary to understand and better design economic incentives and information and education programs.

16

-

Technology Transfer Domestic and International. Research and development alone is not enough, the results must be transferred into the field as new and improved solid waste management systems are developed. Therefore, outreach efforts to apply the results of research are essential. This is especially true on an international basis where there are potentially large market opportunities for cost effective environmental technologies. Technology transfer to countries with developing economies is especially important, if we expect these countries to be able to participate effectively in improving the global environment. Integration of Solid Waste Management Policy With Other Policies. Other national and international policies can have as strong or stronger influence on solid waste management as can environmental policies. Consider the effect of: (1) energy policy on the incentives for waste-to-energy facilities, (2) transportation policy on freight charges for recycled materials, (3) agricultural policy on the uses of sludges as fertilizers or soil conditioners. Other examples include the effect of financial policy on investment into environmental technologies and military policy's effect on clean-up of defense installations. Solid waste management professionals must play a role assuring the solid waste management implications of these policies are assessed in national and international forum. These are the issues that will be facing the solid waste professional of the future. There remains a tremendous opportunity to improve waste management through technological development. However it will be necessary to combine technical and engineering skills with risk assessment, market forces, public information and education, enforcement strategies, pollution prevention, research and development and technology transfer. Solid waste management professionals must show leadership in developing broad based strategic initiatives to bring about continuous improvement in integrated solid waste management. To find out more about ISWA programs and activities including membership information contact the General Secretariat in Copenhagen Denmark.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, H A van der Sloot and Th.G. Aalbers (Edtors) 01994 Elsevier Science B.V. All rights resewed.

17

LIFE CYCLE ANALYSES; RESULTS OF SOME C A S E STUDIES

J . Cramer, TNO Centre for Technology and Policy Studies,

P . 0 . Box 541, 7300 AM Apeldoorn, The Netherlands

INTRODUCTION

Environment-oriented product policy has become a central focus of Dutch environmental policies. The aim of this policy is Yo prevent, or at least reduce, the effects on the environment caused by products in the various phases of the product life cycle'. Up to now the government has placed the emphasis mainly on developing methods of analyzing the environment-friendliness

of

products

(environmental life

cycle

analyses). Experience has been gained in the application of life cycle analysis for various purposes. Of particular interest a r e four different applications :

-

the use of life cycle analysis in 'eco-design'

-

the use of life cycle analysis in 'integrated chain management'

-

the use of life cycle analysis in information exchange between

the use of life cycle analysis in product comparisons

producers in a product chain

In this contribution the experiences with these four types of application will be discussed on the basis of case studies. Many of these case studies have been conducted on behalf of the Netherlands Company for Energy and the Environment (NOVEM) (often together with the State Institute for Public Health and Environmental Hygiene (RIVM))

.

18 LIFE CYCLE ANALYSIS

Before dwelling upon the various applications of life cycle analysis I shall first explain in more detail the principles of life cycle analysis. A

life cycle analysis of a product is the systematic analysis of the environmental impact of a product, calculated over the entire life cycle of a product ('from cradle to grave'). Life cycle analysis is often combined with an assessment of the environmental impact of a product (together called 'life cycle assessment' ( L C A )

.

A full life cycle assessment is made up of five components which

together form a comprehensive structure. These components are (Heijungs et al. , 1992):

*

goal definition, including a consideration of the type of potential application;

* *

inventory analysis of environmental interventions ; classification and modelling of environmental interventions on the basis of their potential environmental effects;

*

evaluation of the product based on its potential environmental effects ;

*

improvement analysis aimed at changes which are desirable on environmental grounds.

There are various bottlenecks standing in the way of the further development and application of the LCA method, principally relating to its complexity. In practice, setting up an extensive LCA is extremely time-consuming , especially for individual companies. The development of environmental indicators has been promoted as a way of reducing the complexity of the LCA method. Environmental indicators are index numbers that express the environmental impact of

19 particular products in terms of a limited number of relevant units, specifically raw materials,

energy,

emissions, nuisance,

waste,

recyclability, reparability and the product's life. They a r e intended for communication purposes, for initiating an increase in environmental awareness and for regulation purposes (TAUW Infra Consult, 1992). Four main stages can be distinguished in the process of establishing environmental indicators (TAUW Infra Consult, 1992). Stage one involves setting the objectives : what a r e we establishing environmental indicators for? Stage two consists of the stock-taking: the entire chain is described and checked for impacts on the environment. Stage three

involves the classification: all the pieces of information obtained a r e classified according to workable categories. Finally, stage four consists of the evaluation: the data collected is evaluated, assessed and translated into environmental indicators.

I n principle, the purpose of environmental indicators is to present the

data from a LCA in a clear and simple form and so to simplify the exchange of information between the parties in the market. In a number of recent trial projects, for instance, environmental indicators have been drawn up for paper, plant trays, margarines, printer ribbons, paints, light sources, insulating plates and a particular make of high performance heating boiler.

It proved possible, in principle, to present L C A data in terms of environmental indicators. However, i t did not usually reduce the workload. In order to establish environmental indicators one still needs some form of life cycle assessment. A s a result, environmental indica-

20 tors a r e regarded as the results of a particular type of L C A , although the approach adopted for the LCA may vary.

THE USE OF LIFE CYCLE ANALYSIS IN PRODUCT COMPARISONS Up to now, a great deal of time and energy has been devoted to applying L C A to product comparison. For instance, what a r e the effects on the

environment of, respectively, a wooden, an aluminium or a plastic window frame or of an ordinary light bulb or a long-life light bulb or the milk carton as opposed to the milk bottle throughout the entire product life cycle ? Such comparisons are made, for example, in the context of ecolabelling or of debates elicited in society about the environmentunfriendliness of particular products. The results of these product comparisons have frequently been the subject of debate. This is due to the fact that various assumptions have to be made in assessing the environmental performance of a product. For instance, the results depend on how the boundaries of the object of study are defined. Moreover, the results will vary according to the technical qualities of the two products to be compared. For example, comparing a milk bottle with a milk carton requires assumptions about the technical qualities of both types of products. Finally, a lack of information on specific environmental aspects forces one to assess on the basis of incomplete data.

Thus, the value of LCA in product comparison is very much dependent on the acceptance of the data used, the system boundaries and the methodological aspects of

data interpretation, classification and

evaluation. In order to minimize the degree of subjectivity in assessing the environmental performance of products, attempts are being made to

21 establish an internationally accepted methodology. At the international level, SETAC (Society of Environmental Toxicology and Chemistry) is the leading forum for the development of such an accepted methodology.

THE USE OF LIFE CYCLE ANALYSIS I N 'ECO-DESIGN' The LCA approach ha5 not generated a great deal of experience in the systematic improvement of products. It does, however, play a role in

' environment-oriented p r o d u c t development i n companies', commonly known as 'ecodesign'

. Environment-oriented product development can

be described as: designing and developing a product in such a way that environmental criteria a r e given equal weight to other criteria.

This

method seeks to limit, or if possible prevent, deleterious effects on the environment throughout the product's life cycle.

A number of demonstration projects have already been conducted in the

Netherlands in the field of environment-oriented product development, especially in the context of programmes such as Ecodesign and Milion. The designs have included an environment-friendly office chair, a reusable plant tray for flower auctions and a new package for dried coffee creamer. There has also been a growth in international demand for environmentally aware product design and development. This was also evident from the first European 'Design for the Environment' Conference which was held in Nunspeet, the Netherlands between 21-23 September 1992 (National Reuse of Waste Research Programme, 1992).

To date, the demonstration projects have been instituted mainly in cooperation with interested individual companies. The major problem in the implementation of these demonstration projects has been a lack of

22 environmental information. This could be a lack of information about the environmental properties of substances and materials that might be used,

for instance. Nor was there always adequate information

regarding the application of materials in products, the use of products or the disposal of the waste produced by them.

In view of this lack of information, it proved difficult in practice to use an extensive LCA. Moreover, resource limitations and time constraints led to the application of a simplified, 'streamlined' LCA. This implies that only the major environmental bottlenecks in the product chain were identified and improvements to the product were concentrated on these. The selection of these improvement options is still largely based on an ad-hoc approach. Improvement options are not systematically compared.

As a result,

environment-oriented product development initially

developed separately from the LCA method. This is gradually changing, however. On the basis of the experience already gained with environment-oriented product development there a r e a number of follow-up steps that could be taken (Cramer ( e d . ) , 1993). The first step would be to extend the attention to environment-oriented product development within the company as a whole. Up to now the projects have concentrated mainly on the design process in a company, which only involves one department.

A second advance would be to intensify the linkage between process and

product improvement. In the context of waste prevention and emissions, companies still concentrate mainly on process improvement; in this respect, the product is generally ignored.

23 On the other hand, with environment-oriented product development the production process is generally unaffected.

A third step would be to stimulate product improvement throughout the

entire chain o r column of companies involved in the manufacture of a certain product. This requires intensive cooperation between the various suppliers and customers in a given chain. The basis for such collaboration is the effective exchange of information between producers and within a product chain.

In response to the three problems raised above a third type of application has been initiated: the application of integrated chain management within companies.

THE USE OF LIFE CYCLE ANALYSIS IN 'INTEGRATED CHAIN MANAGEMENT' Integrated chain management has become a central concept in Dutch environmental policies. It is not a familiar concept abroad. In other countries, for example, the terms 'lifecycle management' o r 'productstewardship' a r e used in much the same way as the term 'integrated chain management'. Integrated chain management aims to ensure that substance cycles in product chains a r e managed in an environmentally, socially and economically responsible manner.

To realize such a 'sustainable

substance cycle' the relevant product must generate the least possible emissions and consume the least possible amount of energy in all phases of that product's life cycle (from extraction of the raw materials, the manufacture of the material and the product, via use by the consumer,

24 up to the disposal of the product in the waste s t a g e ) . This is why 'integrated chain management' transcends the individual company level and includes the whole product chain from cradle to grave. To encourage the adoption of integrated chain management in industry, in association with three companies TNO has developed a concrete methodology for i t s practical application. The participating companies were: AKZO Chemicals, EPON ( t h e Electricity Production Company for East and North Netherlands) and Van den Bergh Nederland (Cramer et a l . , 1993). In principle, this methodology does not differ fundamentally from that

.

of 'ecodesign' In practice, however, the present approaches diverge. The 'ecodesign' approach is to generate and select improvement options in a rather ad-hoc way, while 'integrated chain management' attempts to do this in a very structured way. Central to the method TNO and the three companies have developed is the identification and comparison of various options for bringing about environmental improvements both in the company itself and throughout the rest of the product chain. In this way, the company taking the initiative for chain management can act as a catalyst for change throughout the entire product chain.

The first step in the methodology for implementing integrated chain management is to select one major environmental bottleneck to be improved. This identification of environmental bottlenecks is based on a simplified, 'screening' life cycle analysis. The next step is a structured comparison of various improvement options on the basis of an ecological assessment.

25 To provide an indication of the extent to which a certain option constitutes an improvement from an environmental perspective, the "concept of environmental merit'lis introduced. "Environmental merit" is the difference in the environmental impact before and after the implementation of a given improvement option (including both the primary and secondary environmental impacts of the improvement option). After comparing the potential improvement options on the grounds of a purely ecological assessment, the social, technological and economic feasibility of the options and their suitability for the specific company a r e assessed. The option finally adopted will be determined by weighing up the ecological assessment and the social, technological and economic feasibility and the company-specific feasibility. The resulting step-by-step plan for implementing integrated chain management in individual companies has been tested in the participating companies. Although the approach followed should be further developed and evaluated, the experiences of the companies involved have been positive.

THE USE OF LIFE CYCLE ANALYSIS IN INFORMATION EXCHANGE BETWEEN PRODUCERS I N A PRODUCT CHAIN In order to bring about actual changes in products and production processes the information exchange between producers in a product chain is crucial. To date no structural system for such an exchange of information exists. In this context, the introduction of 'environmental product profiles' ( E P P ) is being investigated within the framework of

.

the Economic Commission for Europe ( E C E ) An environmental product profile is defined as an objective set of relevant environmental

information relating to a product and aspects of its life cycle, especially for producers and professional users (Weterings et al., 1993). The question, however, is which type of information should be exchanged among producers. To answer this question three case studies were carried out by TNO and TAUW Infra Consult in close cooperation with manufacturers. Three (groups of) products were selected: printer ribbons, roofing plates and carpets. The aim of the experiments was to test which type of information exchange was considered useful and advisable. The information presented was based on a 'screening' life cycle analysis. The quantitative data were presented by means of environmental indicators, such as the consumption of raw materials, energy consumption, greenhouse gas emissions, emissions of gases contributing to acidification, etcetera. In order to compare different forms of presentation, two versions with different levels of data aggregation have been developed: -

.

a long version (approx 10 to 20 pages) in which the environmental data consist of a classification of the (potential) environmental effects per step in the product chain and an evaluation of the most important environmental effects;

-

a short version (approx. 5 to 10 pages) in which the environmental data are limited to the evaluation of the most important environmental effects.

In response to these two sets of data those interviewed criticized the way in which environmental data were presented by means of environmental indicators. The amount of oil, gas and coal used, and the volume of several categories of emissions and waste products were quantified per product unit. Although, in general, quantitative data

27 were regarded as useful, most respondents felt the way in which the data w e r e presented was meaningless. They lacked the expertise to understand the quantitative indicators without a lengthy explanation of the reasoning behind the methodology and about the reliability of the resulting data. A few respondents even preferred one grade for all environmental aspects together. Based on the experiments it was concluded that authorities should take a cautious step-by-step approach in implementing E P P s. The content and presentation of environmental product profiles should be further developed

in

organisations

close

cooperation with

manufacturers

and

their

.

CONCLUSIONS

The above examples show the importance of life cycle analysis for various applications. Some bottlenecks in the use of life cycle analysis come to the fore as well. Due to the complexity of life cycle assessment ( L C A ) (including life cycle analysis) an extensive L C A is very time-

consuming. Moreover, an internationally accepted methodology of LCA i s still in development. In practice, therefore, simplified, so-called screening L C A ' s a r e often used. While the approaches used in various applications have been developed separately, there now seems to be a demand for closer attuning of these various approaches. This is a hopeful sign. Ultimately, coherence is needed in the methodologies for assessing and improving the environmental performance of products. This growing consensus will

28 stimulate both government and industry to put environment-oriented product policy into practice.

REFERENCES Cramer, J . et a l . , Theorie en praktijk van integraal ketenbeheer (Theory and practice of integrated chain management), NOVEM/RIVM, TNO- Apeldoorn, 1993.

Cramer, J. (ed. )

. , Productgericht

milieubeheer (Product-oriented

environmental management), Advisory Council for Research on Nature and Environment ( R M N O ) , publication nr. 78, Rijswijk, 1993.

Heijungs, R . et al., Environmental life cycle assessment of products, Guide and Backgrounds, NOVEM/RIVM, Centrum voor Milieukunde, Leiden, 1992.

National Reuse of Waste Research Programme, First NOH European conference; 'Design for the environment',

21-23 September 1992,

Nunspeet, the Netherlands, Utrecht , 1992.

TAUW Infra Consult, Environmental indicators; An evaluation of the pilot projects, NOVEM/RIVM, TAUW Infra Consult, Deventer, 1992.

Weterings, R . et al., The exchange of environmental product profiles between professional users : three case studies in the Netherlands, Discussion paper to the ECE-Seminar on low-waste technology and environmentally sound products, Warsaw, Poland, 24-28 May 1993, TNOApeldoorn, 1993.

SECTION 2: Environmental Aspects


Environmentol Aspects of Consttuction with Wmte Moterials JJJM Goumons, H A von &r SImt and l71.G. Aalbers (Edtom) a1994 Elsevier Science B. K All rights reserved.

31

Chemical Processes Controlling the Mobility of Waste Material Contaminants in Soils

L.G. Wesselink', P.M. Dekker' & Th. G. Aalbers' 1) National Institute of Public Health and Environmental Protection, P.O. Box I 3720 BA

Bilthoven, the Netherlands.

ABSTRACT

Effects of solid waste materials on the chemistry of underlying soils are investigated experimentally and through modelling of fundamental soil chemical processes.

INTRODUCTION

Solid waste materials are increasingly re-used in construction works [ 11. Release of contaminants from these waste materials may affect the chemistry of underlying soils and groundwaters. Metal ions are known to bind to soil organic matter and (hydr)oxides [ 2 ] , which strongly reduces their mobility in soils. Current knowledge of the fundamental mechanisms underlying these binding processes has been compiled in the ECOSAT model [3, 41. ECOSAT combines chemical speciation calculations with surface complexation- and transport models. Here, we report laboratory column experiments in which effects of leachates from steel- and phosphorous slag (P-slag) on four sandy soils were studied. The ECOSAT model will be applied to these experiments to identify and quantify processes that control contaminant mobility in soils under waste materials. To assess the potential hazards of waste materials to soils and groundwaters, knowledge of these processes is indispensable 11 I.

32 MATERIALS AND METHODS

Column studies

Steel- and phosphorous slag (P-slag) were percolated in large columns, up-flow with synthetic rain water @H ~ 4 . 5 )The . columns (30 cm diameter) held 90 kg of slag, and a flow rate of 0.2 US (l/kg) per day was maintained. Subsequently, slag effluents were percolated up-flow through four different columns holding 1 kg of soil, also at a flow rate of 0.2 L/S per day. The chemical composition of percolates at L/S= 0.1, 0.5, 1-5, 7.5, 10, 12.5 and 15 was analyzed. General characteristics of the soils are given in Table 1. Table 1. Soil characteristics

a is surface soil, b is sub soil, ox refers to oxalate extractable Fe aid Al

Model calculations

ECOSAT [3,4] calculates chemical equilibria involving speciation in solution, mineral

dissolution/precipitation and sorption on organic matter and hydroxide surfaces. In addition, transport (convective and dispersive) of dissolved species is calculated. Proton and metal binding to humic substances can be described by several variable or non-variable charge modules within ECOSAT. In this study, metal and proton binding was modelled using the multicomponent Langmuir-Freundlich equation (1). which considers the natural heterogeneity in binding properties of humic ligands [3, 51:

33 where O,., is the fraction of total available surface groups

(a,,,) covered with metal or proton

i, Ki the metal or proton surface complexation constant and m (O<m 95 % R.H. A total number of 140 batches of 12 cubes were prepared. 2.2 Material properties The physical homogeneity of the samples was checked by measuring the apparent density and the vacuum porosity. From seven out of 14 production dates one batch was selected at random, of which 4 cubes were tested following RILEM CPC-I 1.3 [3]. Based on an analysis of variance one batch proved slightly different for both density and vacuum porosity. The average apparent density proved to be 1968 kg/m3 with a standard deviation of 7.9 kg/m3. The one batch deviates less than 0.7 % in density from the others. The average vacuum porosity amounts to 22.2 % VJV with a standard deviation of 0.2 % VJV. The deviation of the one batch is less than 2.7 % from the overall average. This leads to the conclusion that except for a small difference in one batch the cubes can be considered homogeneous with respect to the physical properties apparent density and vacuum porosity. The compressive strength was measured after 7, 28, 90 and 182 days. The results are: 7 days: 48.1 * 1.7 MPa; 28 days: 54.4 * 3.5 MPa; 90 days: 60.7 * 0.9 h4Pa and 182 days: 64.0 1.6 MPa. This level of compressive strength indicates that no problems with the durability are to

65 be expected. The permeability of the specimen was tested by a water penetration test, which led to a value of 4.9 * 10 - I 2 m/s. 2.3 Chemical composition To verify the homogeneity of the specimen between cubes and within one cube out of 7 production dates a single cube was selected at random and analysed after size reduction to less than 125 pm and complete homogenization. A subsample was taken for analysis by ICP, Atomic Absorption Spectrometry and Ion Chromatography. One cube was selected at random and cut in equally sized slices, which were size reduced to below 125 pm, homogenized and analysed with the same techniques. The samples were brought in solution by bomb destruction for Cu, Li, Mo, S and Cd using a HNO3 ,HF,HC104 mixture. For Ca, Mg, K, Na, Ba, Sr, Zn, Pb, Co and Si a fusion with lithium metaborate was applied. 2.4 Availability for leaching To be able to define a driving force for release by diffusion the availability for leaching is determined using a method described in NEN 7341 (formerly NVN 2508[4]), which is based on leaching a fine ground sample under pH control at pH =7 using a liquid to solid ratio (L/S) of 50 Vkg and subsequently at pH=4 using again L/S=50. The extracts are combined and analysed using the same methods as for the analysis of solid samples. 2.5 Tank leaching test (common procedure)

The common procedure used in the intercomparison is a tank leaching test similar to the NEN 7345 (formerly NVN 5432 [5]), which in its general principle resembles the ANS16.1 procedure [6]. This method allows distinction of release mechanisms, such as wash-off effects, dissolution and the main process diffusion controlled release. In addition, physical restriction (tortuosity) and chemical retention of individual constituents can be calculated, when the release of an inert constituent (no retention in the matrix) is measured. Often Na, K or CI can be used for that purpose. A short description of the method is given below. The procedures deviates from the NEN procedure as the procedure has been shortend to 16 days to limit the occurrence of possible depletion of mobile constituents from the 4 cm cubes [7]. Procedure: After rinsing the tank or vessel with acid and washing with water the specimen is placed in the tank on a support. The vessel is filled with water using 5 times the volume of the speciment to be tested. The specimen must be submersed completely. The leachate is removed and replaced by fresh leachant after 2 , 8 , 2 4 , 4 8 , 72, 102, 168, and 384 hours (16 days). The proposed renewal time series follows from the formula: tn = n2 . t l using t l = 0.083days (2 hours) and n= I , 2, 3, 5, 6, 7, 9 and 14. The leachate is filtered and after measurement of pH and conductivity acidified pH=2. Part of the sample in kept unacidified for analysis of e.g. sulfate, bromide, chloride. To demonstrate the reproducibility of the leaching procedure the leaching test was carried out in one laboratory on 10 cubes randomly selected from the different batches. To demonstrate the consistency of the shorter procedure (16 days) in comparison with the full procedure (64 days) the test was also carried out on specimen of lOxlOxl0 cm. To be able to identify possible changes in leachability with time due to further curing of the specimen the test was also carried out three month and seven month after the first test.

66 2.6 Calculations From the leachate analysis data the release (ms/m2) in each time interval is calculated. Based on the assumption that this release is entirely based on diffusion an effective diffusion coefficient is calculated from:

D,i = z (Ei)2/ (4. Uavaii.p)2.(dti -

in m2/s

In which De,i is the effective diffusion coefficient for a component calculated for fraction I; E; is the measured release of the component in fraction i in mg/m2 ; Uavail.is the availability for leaching according to NEN 7341 in mg/kg dry matter; p is the density of the product in kg/m3 ;ti is the time of liquid renewal of fraction I in s and ti.l is the liquid renewal time of fraction I1. The effective diffusion coefficient is usually expressed as pD. = - log D,. By averaging the thus obtained effective diffusion coefficients (De in m%) for an interval of several points, in which the first and last cycles may be omitted due to resp. wash-off effects or depletion, an average D, is obtained, which can subsequently be used to calculate release for other geometries and other time intervals. 2.7 Other test methods applied

Apart from the common method other leaching tests have been: Tank leach test as described but in stead of using a closed vessel air was bubbled through the solution causing an almost neutral pH in the leachate. Tank leach test as described but in stead of using a closed vessel carbon dioxide was bubbled through the solution resulting in a pH between 5 and 6 in the leachate. The German standard DIN 38414 S4 [8], the new proposed CEN procedure for waste [9], the Swiss TVA procedure [lo], the US - EPtox and TCLP method [ll], a modified availability test with pH control at pH =12.5, a pH static procedure [2,12] and the AFNOR method for stabilized waste [ 131. 2.8 Standard leachate A standard leachate has been prepared by extracting a 1 : 1 mixture of MSWI fly ash ( metals: Pb, Cu , Cd and Zn) and coal fly ash (oxyanions: Mo, B, V) at liquid to solid ratio (LS) = 10 using pH control at pH = 4.This leachate needs to be diluted 10 times before use as a standard leachate. The aim of the leachate is to provide a common solution to be analysed by all participants, which will allow conclusions on the degree of agreement between analytical methods used. Therefore the concentration level of constituents is chosen such that with the currently applied methods measurement should be sufficiently accurate.

3. RESULTS AND DISCUSSION 3.1 Material homogeneity The data obtained for the chemical composition of 10 randomly sampled cubes and the results obtained on 8 separately analysed slices from one cube to are given in table I. The following elements were analysed: Ba, Br, Ca, Cd, CI, K, Li, Mo, Na, Pb, S, Si, Sr and Zn. In the table the average and standard deviation and relative standard deviation (RSD) for both datasets are given. The data indicate that the relative standard deviation is less than 6% for several elements both in the individual cubes as well as within one cube. The high relative standard deviation for Mo is entirely due to the limited analytical sensitivity for this element. For Sr

67

and Zn in the individual cubes a RSD slightly higher than 6 YOis observed. For Ba and Pb in the slices of one cube a RSD of respectively 7 and 9% is observed. This higher variability is not due to statistically rejectable outliers. Based on an analysis of variance of the two datasets it can be concluded that Na, Pb and Si do not fUllfill the nulhypothesis at 95% confidence. In the case of Si this can be attributed to the very low RSD in the slices from one block. If the same more realistic RSD as for the separate blocks is applied the condition is hllfilled. In case of Na the difference is just significant, but not critical. In case of Pb the difference is significant, which may be attributed to known heterogeneity of MSWI ash samples. The occurrence of minute metallic particles may cause such effects [ 141. The results of the analysis of individual cubes from different batches as well as the analysis of subsamples taken from one cube indicate that the cubes are sufficiently homogeneous to Table I. Verification of homogeneity of test specimen based on chemical composition between cubes and within one cube. 10 Cubes

Br Ba Ca Cd K Li Mo Na Pb S Si Sr Zn

One Cube

Mean

SD

RSD

55.5 244.0 130325 28.3 5544 17.1 7.5 4581 692 6890 27998 1 324 1826

2.43 4.38 58.7 13.58 5.57 257 6676 5.12 132646 29.9 1.23 4.34 5.09 6109 282 0.85 4.97 17.9 2.28 30.37 5.6 188 4.11 4871 5.83 763 40 4.46 7291 307 3.65 284946 10207 6.69 330 22 6.38 1902 117

Mean

SD

RSD

3.81 2.24 18 7.06 5.20 690 1 5.02 1S O 5.26 321 0.92 5.11 1.26 22.52 302 6.20 70 9.13 5.34 389 1.67 4750 16 4.75 112 5.87

F

P

1.18 1.78 1.07 1.49 1 29 1.16 3.25 2 58 2.98 1.60 4.62 1.91 1.09

0.42 0.19 0.45 0.26 0.34 0.40 0.05 0.07 0.05 0.23 0.02 0.18 0.46

Fcrit 3.31 2.30 2.30 2.30 2.30 2.30 3.31 2.30 2.30 2.30 3.3 1 3.31 3.31

warrant the leaching intercomparison studies. From other work the role of total composition of elements has been shown to be of limited importance for the leaching behaviour of constituents and Pb in particular, which would imply that the somewhat larger variability of Pb may not be reflected in the leaching results [ 151. 3.2 Availability In table I1 the data obtained for the availability test on fine ground materials is given. In addition to the availabilities for individual elements in mdkg used as driving force in the calculation of the effective diffusion coefficients for the elements, the acid consumption in the test is reported. The two step extractions required about 5.95 mequiv of acid/g to control the pH at pH=7 and about 3 mequiv of acid/g for pH control at pH=4.

68

Table 11. Availability (mglkg) and acid consumption (mmoVg) Ba 1 102.9 2 94.6 3 111.6

Na 1 3797 2 3828 3 4005

Br

Ca

Cd

CI

K

Mo

Li

50 51

114200 116400 122500

22.9 14.6

8450 9164

5382 4874 5148

2.2 1.6 2.4

11.4 11.6

Pb

S

Si

Sr

Zn

Acid

71 72.7 61.5

6630 6850 7020

5315 4483

270 272

1249 1178 1304

7.1 6.5 6.2

The sum is 113 mequiv of acid. The three series of availability tests carried out in May 1993(1), September 1993 (2) and January 1994 (3) point at a significant reduction in acid consumption, which is tentatively attributed to carbonation. The plastic wrappings, in which the samples are stored, are not sufficiently airtight to prevent uptake of carbondioxide. Relative to the composition the availability for leaching amounts to about 34 % for Ba, 90 % for Br, Ca and CI, 100 YOfor K and S, 75 % for Cd, 30 % for Mo, 62 YOfor Li, 80% for Na, 10 % for Pb, 2 % for Si, 70 % for Sr and 60% for Zn. The reproducibility of the availability test is good for elements that can be analysed with sufficient analytical accuracy at the concentration levels encountered in the availability test. 3.3 Standard leachate The composition of the standard

standard deviations as indicated in table 111. In general the relative standard deviation is close to or within the desired analytical precision of 5 %, except for V and Mo with respectively 13 and 32 % RSD. This is caused by the analytical limitations of the methods used at the concentration levels in the leachate. The

Figure 1. Na in Standard Leachate

h

9

69 67 6 5 . . 63

N

_ . _ - - - _2 _ - - - . * - . :, : * ; . : * ! ;

3 -

61

3.= z

579 ; 5 55 53 ~

51;

' t :

, -

;: ~

8

'

t

- - - - - - - - -

4 9 - " " ' ~ " " ~ " " ' ~ ~

69 3.4 Tank leaching data

TableIII. Average composition and standard deviation of the standard leachate (mg/l).

3.4.I Effective dijjuusion coefjcierit Mean Stdev RSD N As was shown in several studies [17,18,19] the leaching of constituents Ba 0.0476 0.003 6.3 from stabilized waste is not related to 4 Ca 227 7.0 3.1 the chemical composition. So in 4 Cd 0.835 0.042 5.0 addition to establishing the homo10 0.542 0.010 1.8 cu 10 geneity in terms of chemical comF 5.65 0.39 6.8 8 position the reproducibility of leaching 0.0055 0.0018 32.0 Mo 10 of 10 randomly selected samples was 55.8 2.1 3.8 12 Na tested to ensure a usehl inter0.275 0.0136 5.0 Pb comparison. To assess the difference 4 52.8 S 12 1 . 5 2.8 in sample size on the release three 0.0062 0.0008 13.4 V 10 cubes of lOxlOxl0 cm were tested in 28.2 Zn parallel. Since the release is related to 1.2 4.4 12 the surface area, the diffusion coefficients should be the same, which has been tested statistically. the results are Figure 2. pDe versus given in table IV. The agreement relative analytical SD. between the effective diffusion coefficients, expressed as pDe = - log 18 I 1 I D, , between the smaller and larger cubes is generally good with the exception of S, Ca and to a lesser extent CI. The release of Ca from the larger cubes appears to be slightly higher than from the smaller cubes. With an increase in pD, the standard deviation generally goes up as well due to the fact that the concentration levels associated with higher pD, 's are 12 also lower and therefor closer to detection limits. In figure 2 this is 11 illustrated. The elements Na, K , Br and to a lesser extent CI can be 10' ' ' ' ' ' ' ' ' regarded as inert i.e. non-reactive with 0 10 20 30 40 50 60 70 80 90 100 the productmatrix and as such can be Rel. analytical SD (%) used to calculate the tortuosity or physical restrictivity [7,15]. Their DD,'~are verv close. Constituents such as Cd and Pb show high pD, 's (= low mobility) caused by a strong interaction with the productmatrix. The difference between the pD for inert constituents and reactive components can be expressed in a chemical retention value. This value is a knction of pH, redox condition, complexing constituents in the pore solution and sorption reactions on the walls of the pores.

i

1;

1

'

1

-

70

Table IV. Effective diffusion coefficients, standard deviations and relative standard deviations for 10 randomly selected 4 x 4 ~ 4cm cubes and 3 cubes of lOxlOxl0 cm. 10 Cubes Mean

CI Ba Ca Cd Br K Li Mo Na Pb S Si Sr Zn

11.69 13.43 13.80 16.09 11.36 11.14 12.22 13.66 11.24 15.51 15.06 14.85 13.10 17.32

3 Cubes

SD 0.04 0.08 0.04 0.06 0.03 0.02 0.04 0.08 0.02 0.13 0.04 0.05 0.05 0.26

RSD 7.98 16.26 9.46 13.64 7.58 4.66 8.64 17.14 5.45 25.33 9.46 11.06 9.87 9.87

Mean 11.57 13.33 13.62 15.78 11.21 11.08 12.17 13.99 11.18 15.21 14.61 14.24 12.93 16.38

SD

RSD

F

0.06 13.76 5.28 0.03 6.90 3.46 0.06 12.73 4.27 0.03 1.15 7.11 0.02 3.50 2.28 0.02 3.50 1.30 0.01 2.64 8.43 0.11 22.88 2.61 0.02 3.94 1.46 0.21 37.82 9.03 0.06 12.21 13.35 0.04 8 13 8.97 0.03 7.54 1.28 0.07 7.54 1.28

P

Fcrit

0.03 0.24 0.05 0.36 0.34 0.51 0.11 0.3 1 0.47 0.01 0.00 0.01 0.33 0.33

3.01 19.38 3.01 3.01 19.38 19.38 19.38 19.38 19.38 3.01 3.01 3.01 3.01 3.01

Of these pH is a very prominent Figure 3. Mean pDoand 95% release controling parameter as will be shown later. The relative confidence interval for Na. standard deviation ranges from 3 to 37 %. In the latter case the measurements were at or close to the detection limits of the analytical methods employed. In judging these numbers it should be remembered that these values are not directly measured, but derived from other measurements adding to the overall uncertainty of the final answer. In addition, the release derived from this leach parameter is proportional to the square root of the effective dihsion coefficient, which implies that the error is not propagated linearly in the final answer. The standard deviation in the release data as derived from the effective diffusion coefficient, the availability and the size of the specimen is discussed below. 3.4.2 Intercomparison of lank leach data.

At the time of writing of this paper only part of the dataprocessing was carried out. Therefor only data for Na are given here. For the pD, of Na the results of 18 participants in the intercomparison have been treated statistically using I S 0 5725[ 161. The repeatability and the

71

reproducibility standard deviation of the pD, for Na amount to resp. 0.071 and 0.095 (pD = 3.47 .10 - I 2 m2/s). In figure 3 the individual data units) with a mean value of 11.46 (D=,N~ obtained by the participants are given with the 95 % confidence interval. 3.4.3 Tortuosity or physical restriction Based on the mobility data for inert constituents (here Na) the tortuosity can be calculated. The results are given in table V. The tortuosity data for the small and the larger cubes are only slightly different. The tortuosity for the samples aged for another 4 month show tortuosities significantly higher than the earlier data. This is attributed to the hrther curing of the product. The samples

Table V. Tortuosity data

Series

Period

T

SD

10cubes

May93

212

18

3 cubes

May93

187

12

Aged

Sept93

379

30

exposed to leaching under a carbondioxide Air Sept 93 100 4 flush fall slightly below the aged data. It is surprising to note that the exposure to air c02 Sept93 328 40 during leaching apparently leads to a reduction of the tortuosity. This effect is not only noted for Na but also for K and Br. The reason for this observation is at present unclear

3.4.4 Release estiniates The final answer of a leaching test on monolithic specimen is a release expressed in mglm’ . The uncertainty in release estimates based on the calculated effective difision coefficients is given in table VI. The reproducibility in terms of release is satifactory for the intercomparison. The cumulative release patterns for Ca, S, Mo and Zn under different experimental conditions - after aging, exposure to air and to carbondioxide during leaching - are given in figure 4. The difference between the early measurements (1 month cure) and measurements after 5 month curing, is an overall decrease in release due to ongoing hydration of cement resulting in a denser pore structure. The release of Mo is not significantly influenced by the different conditions of leaching. In the case of Zn the release is directly related to the pH dependence of leaching. This aspect will be addressed in more detail below. Under the low pH conditions imposed by COz all of the Zn available for leaching can be leached in a relatively short period.

3.4.5 Leachingproperties as afrinction of aging and exposure to air and C02 The question has been raised to what extent the leaching properties of cement-based specimen of the type studied in this work will change appreciably as a result of aging (or rather hrther curing) Another aspect of leaching solid specimen has been the issue of leaching in a closed vessel, exposure to the air or exposure to carbondioxide In the latter two cases carbonation of the specimen occurs, which may alter the leaching behaviour of the specimen To assess this aspect, which is accompanied by a drop in pH of the leachant, pH static experiments were carried out in the pH range from 4 to 12 5 The difference in leachability between the cubes

t

100000 i

A '

100

'

" " " "

'

" " " "

10

1

"

100

200

50'

'

' " " -

'

' " " -

'

"

500

Total

_

Available ~

~

_

~

~

~

10

9

a e 9 0.1

[

0.05'

1

A

A

BI '

'

" " " "

10

0.1'

'

" " " "

100

500

1

'

'

" ' -

'

" " " "

10

100

"

500

Time (hours) Figure 4. Release of Ca, S, Mo and Zn from cement-stabilized MSWI fly ash measured in a closed vessel after l(square) and 5 month (plus) curing, exposed to the air (triangle) and CO after 5 month (dot) curing.

cured for about 4 month and the first series of measurements after 1 month curing in a closed vessel is reflected in a higher pD, for Na, K, CI and Br, which points at a increase in physical restriction (tortuosity) due to ongoing hydration resulting in a denser structure of the cementitious matrix. A final series of measurements after about 9 month curing points at a stabilization of the curing process, because about the same pD, for Na is obtained as in September 1993. The same trend is observed for CI, which also shows a stabilization of the pD, after 4 to 5 month of curing (figure 5 ) . The mobility of Ba and Ca is more significantly

73

reduced, which is most likely related to the behaviour of sulfate, as it behaves quite different in the aged series. In stead of diffusion controlled release sulfate shows a marked surface wash-off effect in the aged samples. This is probably the result of carbonation, which decomposes the monosulfate phase in the cement matrix. The cubes were stored wrapped in plastic, which also may have led to some surface carbonation. In the test with forced exposure to air (air bubbling through the solution) the mobility of Ba and Ca decrease hrther (pD. higher). Zn mobility is also decreased. In the test with forced exposure to carbondioxide (COZ bubbling through the solution) the mobility of Ca is significantly increased and that of Zn is more than 4 orders of magnitude higher. This effect is caused by the leachability of Zn as a function of pH (figure 6) as obtained from a pH static leaching test on finely ground cube samples. This figure confirms that from a leachate pH around 10 to a leachate pH between 5 and 6 about 4 orders of magnitude difference in leachability exists. From other studies incite (Zn(0H)Z ) was found to be the solubility controlling phase[ 121. Here the same mineral phase appears to be solubility controlling. In case of Mo the difference between the test conditions is limited, which is in accordance with the pH static data shown in figure 6. With the forced carbondioxide exposure a slightly higher mobility is noted compared to the data obtained in a closed vessel and with air exposure. The pH stat data agree qualitatively with other studies [20]. The forced exposure to carbondioxide, which is supposed to represent accelerated carbonation and aging, leads to unrealistic release data for z" some metals as sorption reactions are usually too slow to follow the rapid change brought about by excessive CO2 exposure. The pD, values and Na release data obtained by 13 participants are given in figure 5 and compared with the data obtained in the verification study. In figure 5 the pD. values for Na are plotted as a function of time showing the change in tortuosity with time due to the ongoing curing process and the agreement between these data and the results

Table VI. Release (mglm2), standard deviation and relative standard deviation for cubes after 28 days of curing. 10 Cubes ( 4 x 4 ~ 4cm)

Mean

Stdev

RSD ~

Br Ba Ca Cd CI K Li

409 1 I0 79956 1.17 98707 80858 49.60 2.01 51047 6.93 1087 1122 426 14.90

MO

Na Pb S Si Sr Zn

10 2.39 7.64 6.95 3541 4.43 0.09 8.11 3076 3.12 1723 2.13 2.01 4.05 0.16 7.94 1335 2.62 0.93 13.40 47 4.34 61 5.46 20 4.63 3.00 20.12

Figure 5. Change in tortuosity upon curing 11.90 9

11.70

11.50

11.30

*

A

11.10

0

2

4

6

8

Curing time (month)

10

74 500

0.5

.

100

h

d

OD

E

v

10

4 : : A

-8 0.1 % 3 +l

I

I

A

*

t

1

0

e

0.1

e 0.01 A

0.01

0.w1

Mo ~

0.005 3

4

"

5

'

6

'

7

'

8

'

9

'

1011

'

0.m1

1213

3

4

5

6

7

8

9 1 0 1 1 1 2 1 3

PH Figure 6. Leachability of Mo and Zn from crushed cement-stahilized MSWI fly ash as measured in a pH controlled test.

Table VI. Effective diffusion coefficients derived from measurements on different sized cubes, aged products and products exposed to air and COz (pD, = - log D, , D, in m2/s). Blocks( 10) 4x4x4cm May-93

CI Ba

Ca Br K MO Na Pb S Zn

11.69 13.43 13.80 11.36 11.14 13.66 11.24 15.51 15.06 17.32

Blocks(3) 10x10x1Ocm May-93

Aged blocks Sep-93

Air pH=7 Sep-93

c02 pH=5 Sep-93

11.73 14.80 14.54 11.37 11.35 13.48 11.49 15.28 15.03 17.99

11.66 16.60 16.44 10.45 10.99 13.57 10.91 15.23 14.80 18.18

12.19 13.59 13.12 10.99 11.36 13.21 11.43 15.24 14.19 13.16

11.57 13.33 13.62 11.21 11.08 13.99 11.18 15.21 14.61 16.38

obtained by participating laboratories in Europe 3.5 Potential uses of the tank leaching test This type of test is a usehl characterization test to identify the leaching controlling parameters and conditions for a given material or class of materials[7, 15, 17 - 191. Then shorter procedures should be developed as compliance tests to assess basically the same parameters

75

however with less accuracy due to the limited number of data points used to quantify the parameters. Options for developing such shorter procedures should aim at minimizing initial wash-off effects, ensure timely wetting of the entire product, make use of the square-root of time dependence of diffusion controlled release and optimize the liquid to surface area ratio in the test to facilitate chemical analysis. Based on the type of leach parameters derived from this test predictions of release at longer time scales than those corresponding with the actual test duration can be made. Based on the pH static information supplied other leaching conditions in terms of pH can be largely explained and most likely modelled after some firther studies into this issue. In addition, the leach parameters obtained can be used for management purposes to improve product quality and performance[7, 211. 4. CONCLUSIONS The tank leaching test studied in the framework of this intercomparison is a good characterisation method for the leaching behaviour of monolithic materials as it provides knowledge on release controlling parameters and allows prediction of release at longer time scales by the leaching parameters derived form the test results. The homogeneity of the specimen prepared for the intercomparison prove to be sufficient between batches as well as within one specimen. The leaching data obtained in one laboratory on randomly selected specimen prove to be sufficiently reproducible in terms of release for most elements studied. In a few cases the concentrations to be measured are close to the analytical detection limit leading to a higher relative standard deviation for those elements. Based on the mobility data for Na and CI , which reflect the tortuosity of the matrix, it can be concluded that the product has changed in leaching properties in the first few months. It appears to be stabilizing in its properties after about half a year. Upon aging the cement-based product is changing in its leaching properties. This is an aspect that can not be avoided for any type of cement-based product. By measuring the release parameters in one laboratory in three time intervals covering the period of analysis by the other participants the results can be placed in the proper perspective. Leaching under different pH conditions was studied, which results in differences in release, which can be largely explained by the results of pH stat experiments carried out on crushed material. Based on this longer test shorter procedures with a close correlation with this test can be derived, which may largely provide the same basic information. Standardization of such a short compliance method will start in the framework of CEN TC 292. It is recommended that the characterization method is also standardized by CEN TC 292.

Acknowledgenienl This work is carried out in the framework of the EEC Measurements and Testing programme (BCR) 93/94. Participants are: University of Aberdeen, GB (Prof.Dr. F.P. Glasser); POLDENINSAVALOR, FR (Dr. J. Mehu): RIVM, NL ( Drs. G.A. Rood); ENEA ,IT( Drs. S. Balzamo): VKI, DK (Dr. 0. Hjelmar); K K , DE (Dr. J. Vehlow ); WRc, GB (N. Blakey, K.Lewin); SGI, SE (J. Hartlen); VTT, FI (M. Wahlstrom); VITO, BE ( Ir. B. Leathem); Institute Quimic de Sarria, ES (Dr. J. Obiols): Junta de Residus, ES (Mrs H. Sala); INASMET, ES (G. Ortiz); Umwelt Bundesamt, DE (P. Henschel); UNINOVA, PT (Dr. A. Steiger Gargao); ISDS , IT (L. Musmeci); WTC, Canada (J. Stegemann).

76 5. REFERENCES 1. Waste Materials in Construction: Proceedings of the International Conference on Environmental Implications of Construction with Waste Materials,Eds. J.J.J.M. Goumans, H.A. van der Sloot, Th.G. Aalbers, Elsevier Science Publishers, Amsterdam, 1991. 2. H.A. van der Sloot. Leaching behavior of waste and stabilized waste materials; characterization for environmentalassessment purposes. Waste Management and Research, 8, 1990,215-228. 3. RILEM CPC-I 1.3. Methods for the determinationof apparent density and vacuum porosity.1984. 4. NEN 7341 (formerly NVN 2508). Determination of leaching characteristics of inorganic components from granular (wastes) materials. "I, Delft. 1993. 5. NEN 7345 (formerly Draft NVN5432). Determination of the release of inorganic constituents Delft. 1993. from construction materials and stabilized waste products. "I, 6. ANS. 16.1 Measurement of the leachability of solidified low-level radioactive wastes by a short-term test procedure. American Nuclear Society, Illinois 60525 USA 1986. 7. G.J de Groot and H.A van der Sloot. Proc. Sec. Int. Symp. Stabilizatiodsolidification of Hazardous, Radioactive and Mixed wastes. Williamsburg, Virginia, May, 29 to June 1, 1990. 8. DIN 38414 S4: Geman standard procedure for water, wastewater and sediment testing - group S (sludge and sediment); determination of leachability (S4). Institut fiir Normung, Berlin, 1984. 9. CEN TC 292 document: Proposed leaching test for granular solid waste. H.A van der Sloot, 0. Hjelmar, Th.G. Aalbers, M. Wahlstrom and A,-M. Fallman, February, 1993. 10 Bericht zum Entwurf fur eine technische Verordenung iiber Abfalle (TVA), 1988. Departement Federal de I'Interieur. Switzerland. 11 Toxicity Characteristic Leaching Procedure(TCLP). Federal Register Vol 5 1 No 114, Friday, June 13, 1986, 21685-21693 (proposed rules). Federal Register, Vol No 261, March 29, 1990 (final version). EPA Toxicity Test Procedure (EP-tox), Appendix 11, Federal register, Vol45(98), 1980, 33127 - 33128. Govemment Printing Ofice, Washington D.C. 12 R.N.J.Comans, H.A.van der Sloot, P.Bonouvrie. Proc. Municipal Waste Combustion. VIP 32. Air & Waste Management Association Pittsburg, Pennsylvania. 1993. 667 -679. 13 J. Mehu, Y.Perrodin, B. Sarrazin and J. Veron. Reference I . page293 - 300. 14 C.W. Versluijs, I.H. Anthonissen and E.A.Valcntijn. Mammcet '85. Report 738504008. RIVM, June 1990. 15 S.E.Sawell, A.J.Chandler, T.T.Eighniy, J.Hartlen, O.Hjelmar, D.Kosson, H.A. van der Sloot, J.Vehlow. The International Ash Working Group: Treatise on MSW Incinerator Residues. This conference Special Session. 16 IS0 5725. Accuracy (trueness and precision) of measurement methods and results. part 2. International Organization for Standardization, 1990. 17 P.L. C6te. Thesis : Contaminant leaching from cement-based waste forms under acidic conditions. MacMaster University, Hamilton, Canada, 1986. 18 D.S.Kosson, T.T.Kosson, H.A. van der Sloot.,"USEPA Program for Evaluation of Treatment and Utilization of Municipal Waste Combustor Rcsidues", Cooperative agreement CR 8 18178-01O.USEPA/RREL, Cincinnatti, September 1993. 19 M. Hinsenfeld. Reference 1: page 33 1-340. 20 G.J de Groot, H.A van der Sloot and J. Wijkstra. In: ASTM STP 1033, P.L. Cote and T.M. Gilliam, Eds, ASTM, Philadelphia, 1989, pp 170 - 183. 21 H.A van der Sloot, G.L. van der Wegen and E. Vega. Beoordeling van immobilisaten. Een voorstel voor criteria en testmethoden. CUR report 93-6. Civieltechnisch Centrum Uitvcering Research en Regelgeving. Gouda. 1993.

EnvironmentalAspects of Construction with Waste Materials J J J M Goumans, H A . van der SIoot and 7b.G. Aalbers (Editors) el994 Elsevier Science B. V. All rights reserved.

77

Immobilisation Potential of Cementious Materials F.P. Glasser Department of Chemistry, University of Aberdeen, Old Aberdeen, Scotland. Abstract The immobilisation potential of lime and Portland cement matrices is two-fold. They afford physical immobilisation by converting liquids, sludges and particulates to solids. They also afford a chemical immobilisation potential, sorbing and precipitating otherwise soluble species. Both the physical and chemical potentials are difficult to quantify. The chemical immobilisation potential is perhaps easiest to measure and model by laboratory simulations. Progress in this area, of characterizing mechanisms of insolubilisation, is described using the Cr-Mo-U triad as examples. Remaining problems necessary to predict the performance of cement-conditioned wastes are discussed. 1. INTRODUCTlON Lime and Portland cement are relatively inexpensive manufactured products having consistent properties. Cement and Ca(OH)2 may also be mixed with each other and with a variety of other reactive wastes including slags, coal-combustion fly ash etc., to form solid matrices. These have been used successfidly to immobilize a range of waste materials. Conner reviews commercial technologies (1). Physical containment is most important for mobile liquids, dusts, sludges and solutions. Because cements are tolerant of wet wastes and can, within limits, neutralize acids and tolerate salts, wastes can frequently be dispersed throughout a cementitious matrix. The matrix affords both physical resistance to leaching and a definite chemical immobilization potential. Characterizing these potentials requires special methodologies. The porositypermeability relations of cementitious matrices are not well understood; most reports have been restricted to formulations intended for load-bearing constructional applications. Most of the intrinsic porosity of well-made cement matrices is less than Ipm effective radius, so the matrix has only limited permeability. However, extrinsic porosity is often introduced at grain-paste boundaries and the amount of such porosity increases rapidly with increased water content (2). This, in turn, affects permeation properties. The mix water used in formulating cementitious matrices is partially combined in the cementitious solids. Normally an excess of water, beyond that required for complete hydration of the cement, is needed to achieve the necesary plasticity or fluidity for The chemically mixing: also, to achieve economic loadings of wet wastes. uncombined water is held in pores, from whence it can be extracted by pore fluid expression (3). Analyses of the expressed pore fluid provides a unique method of determining how much of the added waste species remains soluble. The pore fluid comprises the most leachable portion, and its analysis provides an immediate quantification of the source term for leaching. The solids of cement have high surface area and provide potential for sorption and a source of reactive species for precipitation and hence exert a strong modifjmg influence on pore water composition.

78 2. PHYSICAL IMMOBILISATION Several methods are available to determine pore structures in hardened cement paste. Mercury intrusion can be used to determine pore sizes in the range 0.005-5pm (approximately), with neutron scattering used for finer pores. However the bulk diffusional and leaching properties are determined by the larger pores, within the range of mercury intrusion, as well as by pore interconnectivity. A special type of porosity arises at the interface between particles and cement paste. Fig. 1 illustrates schematically the different ranges of porosity. Interface porosity characteristically arises when grains are physically unequal in size. The standard for comparison is that of the cement, lime, fly ash etc. particles, typically 5-50pm, with larger particles, especially >50-IOOpm, giving rise to intefacial porosity. The larger pores become partly filled with crystals, notably Ca(OH)2 and ettringite, a hydrated calcium sulfoaluminate. The remaining space is occcupied by a permeating aqueous phase. The picture is representative of the state of hydration achieved within a few weeks or

-

20 % Intruded Volume

Slag Cement blend, mcist cured at 18°C

/d

10

0.1 Pore entry diameter

Fig. 1. Mercury intrusion porosimetry scan of a typical slag-cement blend cured for 30d and 2 years. Pore entry diameter in pm. Slow hydration of slag converts much of the open porosity to closed porosity and the pore size distribution shifts to finer pores.

0.01

Fig. 2. Microstructure of a cement containing particulate material. The main part of the Figure is on a micrometer scale. A large particle occupies the lower lefthand corner. Porous regions, ( I ) , exist in partly hydrated paste, but a process zone of enhanced porosity occurs, (2), in the vicinity of the particle. The inset shows on a nanometer scale the structure of the paste. A large part of the intrinsic nanoporosity, (3), is associated with the gel constituent of the paste.

79 months. The presence of residual cement or blending agent indicates that the system still has the capacity for formation of more hydrate. Some of this additional hydrate goes into blocking pores, although interfacial porosity, shown as region 2 in Fig. I , Fig. 2, showing mercury intrusion data for a typical remains little affected. constructional cement, indicates how the porosity continues to decrease with cure. It should be recalled that mercury intrusion only measures uccrssihle porosity: upon continued hydration, pore blocking contributes to the decrease in accessible porosity. However the actual permeation properties achieved may represent a compromise between achieving good waste loadings and realizing low permeability. The permeation properties of cements intended for waste conditioning have received less study. Table 1 summarizes some of the anticipated similarities and differences between constructional mixes and conditioned wastes. A particular concern is that high waste loadings will degrade the microstructure which, in turn, will adversely affect the permeation properties. The intrinsic permeation properties achieved may thus represent a compromise between achieving good waste loadings and realizing low permeability. The formulations which are used in waste treatment do not generally require high strengths. Nevertheless, most cementitious matrices acceptable for conditioning will gain strength and become susceptible to cracking, which increases the effective surface area available for leaching. Cracking may arise from purely mechanical causes, e.g settlement, shrinkage, but it may also arise as a consequence of inherent dimensional instability, from chemical reactions with waste components or those in the disposal environment. To act as a conduit or channel for leachants, cracks have to be relatively large, greater than 1-2pm. Therefore, if cracking cannot be prevented, it is better to have a dense network of microcracks rather than a lower density of relatively wider cracks. However, at present, little theoretical or practical guidance be given on the prevention or occurrence of cracking and, where cracking does occur, on crack density.

Table 1 Physical Properties of Some Cement Formulations Property

Waste Treatment

Constructional Materials

water:solid ratio

as high as possible to minimise cost

generally as low as practicable

intrinsic porosity

apt to be high

low, except in air-entrained materials

interfacial porosity

variable, depends on waste

always present in normal mortars and concretes

microstructure

influenced by presence of soluble component

relatively constant (see Fig. 1).

permeability

highly variable

'ordinary' materials; 10-8 to 10-10 m / s ; 'special' materials, 10-10 to 10-12 m / s

80

3. CHEMICAL FIXATION 3.1 General principles Cements provide a strongly alkaline internal environment. Ca(OH)2 and calcium silicate hydrogel (shorthand, C-S-H) are available to buffer the pH to about 12.4 at 18°C. In the short term, any alkali in the cement or waste tends to raise the pH above 12.4 because counterions - other than OH- - are relatively insoluble: chloride and nitrate are the main exceptions. Hence the pH of a lime- or cement-conditioned matrix is likely to be within the range 12.4-14 and is well-buffered by the cement solids.

10

-

F

1

:

Pb

Zn

Cd

~~

0.001 -

pH range in alkaline cements I

I

I+

1

Fig. 3 . pH control of the solubilities of a few selected heavy metals. The examples shown are for amphoteric elements. The characteristic internal pH of Ca(OH)2, Portland and blended Portland cements is shown Many metals are relatively insoluble in alkaline aqueous environments. However, there are many examples of amphoteric elements, so-called because they are soluble at low and high pHs. In strongly basic solution they form soluble anionic complexes, e.g. (At(OH)4-: tin and chromium (111) are also examples). Fig. 3, taken after reference (4) is a guide to these relations. The thermodynamics of metal speciation are well known and it might at first sight seem that the chemical conditioning action of cement would not be too effective for amphoteric species. However, these considerations are too simplistic because they fail to include the often specific and very strong interactions between cement components and waste species. These interactions depress solubilities, perhaps by orders of magnitude. However, the conditioning action arises from a number of mechanisms; examples will be given . The cement components vary in composition and crystallinity. Some, like the gel binding phase - a calcium silicate hydrate - are largely non-crystalline but have a very high specific surface, leading to a sorptive potential. The more crystalline hydrates favour crystallochemical substitution and, in the case of layer structures, intercalation. When a waste stream is mixed with water, a complex series of reactions ensue. Assuming for simplicity an initially soluble species, the general sequence is as shown in Fig. 4.

81

I initial Waste Concentration :',

.= ._ n %

Pcn

-

I

initially

';Relatively ,-

Amorphous':, Precipitates.!,, Sorption, e t c j :'

Crys:allization.

Fig. 4. Decline in solubility of waste species in a cement matrix as a hnction of time. Not all species undergo all the reactions shown, but the declie in solubility with time is characteristically encountered The first stage of reaction, usually achieved within the first few minutes of mixing, is the precipitation of relatively insoluble precipitates of oxides, hydrous oxides or precipitates containing other readily-soluble anions hrnished by cement, e.g. sulfate, which precipitates barium. These precipitates are generally amorphous, so are difficult to detect directly. As the time scale of reaction is extended to weeks or These include (i) crystallization of months, a series of slower reactions occur. previously-amorphous precipitates with concomitant reduction in solubility, (ii) reaction between waste species and cement components, leading to fixation by ion exchange, sorption, etc., as a result of which waste components are bound in dilute form into matrix components and finally, (iii) reaction of initially formed precipitates with cement components to yield new phases. For example, a cement component A may react with waste component X giving a compound AmXn or AmXn zH20. Reactions in this latter category are driven by the approach to equilibrium. Since AG is thereby decreased, and AG -RTCnK where K has the dimensions of a solubility product, the overall result is a decrease in solubility. Of course, not all three classes of reaction will necessarily occur for any particular species. These considerations highlight the need for mechanistic studies. These can be pursued at different levels. Table 2 outlines briefly some of these. Single speciessingle cement component studies provide the most satisfactory way of isolating for hrther study the insolubilizing reactions. But the data obtained from simple systems may be too naive: for example, the insolubility of BaSOq has been noted. Cement systems also contain much OH and Ba(OH)2 is relatively soluble. In strongly alkaline environments will B a s 0 4 redissolve? In order to answer questions of this sort, it is almost always necessary to move to stage 2, in which the possiblity of more complex interactions can be investigated. Once this has been done, it may be possible to extrapolate the results into the future. Finally, level 3 studies are necessary to ensure

82

Table 2. Methods of Studying Fixation of Wastes in Cement

Simulate Conditions

Remarks and Notes

Selected single waste component and cement component

Results relatively easy to control, interpret and extrapolate but neglect complex interactions. Not readily accepted into action programmes, e.g. compliance with legislation.

Selected single waste component in "real", chemically complex cements and blends

More difficult to interpret results in a fundamental sense, but likely to include complex interactions and provide acceptable basis for decision making.

'Real,' mixed waste streams with chemically-complex cements and blends

Fundamental mechanisms almost impossible to interpret but results necessary to demonstrate compliance. Difficulty remains of extrapolating present performance into the future.

compliance with standards, although they do not themselves provide a mechanistic basis for understanding the basis of containment or of extrapolating into the future the performance of cemented waste forms. In general, therefore, a combination of approaches is necessary to ensure that a broadly correct perspective towards research and practice is maintained. Experimental techniques have been greatly improved whereby specific immobilization mechanisms can be identified and, if needed, isolated for firther study. Computer-based computational routines will enable fiture performance to be assessed, given site-specific information and an adequate database. 3.2 Case studies: chromium Chromium is widespread in industrial and domestic waste streams. Its toxicity is mainly associated with the upper, Cr(VI), oxidation state. The other common state, Cr(III), is known to be better immobilized in cement than Cr(V1). However, the source of the immobilisation potential is uncertain: Kindness et al. ( 5 ) have reviewed the literature and determined the source of the immobilisation potential. Cr(VI) substitutes in part for sulfate in ettringite, 3CaS04 At203 32H20. Its substitution for sulfate in other phases, e.g. in the AFm type phases, is less. However even in ettringite, where substitution is most favourable, relatively high aqueous CrO 2concentrations are required to sustain significant replacement of SO42- by CrO4 . Thus the potential for chromate immobilisation is poor. However, Cr(V1) is readily reduced to Cr(II1) by contact with metals, e.g. with Fe, or by ferrous salts. Many natural disposal environments are also likely to be reducing in nature; the reducing conditions are generated by the presence of organic matter, and bioactivity which produces CH4, C02, etc. Therefore Cr(VI), if present in waste, can be reduced to Cr(II1) and, in the majority of disposal situations, it is unlikely to reoxidise with the result that the target species for immobilisation is Cr(II1). In simulate experiments, Cr(OH)3 is rapidly precipitated in alkaline solutions. Cr(II1) is amphoteric, so precipitation may be incomplete. Moreover, the initial

4-

83 precipitate is often amorphous, or nearly so, and could be expected to have anomalously high solubility relative to crystalline Cr(OH)3. Experiment shows that the amorphous precipitate crystallizes with a few days at -18°C. But Cr(OH)3 is unstable in the cement environment. It gradually reacts with the aluminate phases, where it substitutes for A t in octahedral sites. The open, layered structures of AFm phases are kinetically most accessible to these exchanges. Kindness, et al. ( 5 ) have reported the synthesis of CaO-Cr203-H20 phases which are structural analogues of the aluminates. The denser hydrogarnet structure, based on 3Ca0 At203 6H20, is kinetically relatively inert, but synthetic experiments disclose it to be a very effective host for Cr(II1). Synthesis of various Cr-containing host phases and measurement of their corresponding Cr solubilities has shown that they are very effective hosts for the immobilisation of chromium. Since the solid solutions require time to form, pore fluid Cr(II1) concentrations tend to decrease with cure duration until an equilibrium level is reached. Theory and experiment are in good agreement that the stable solubility threshold in pore fluid is about 0.2-0.5ppm Cr(II1). Thus the potential for resolubilization, which might be expected from the amphoteric character of Cr(III), is suppressed at normal cement pH's by other factors. Further work does require to be done on the long-term behaviour of cemented Cr containing wastes. In the disposal environment ground water components, including carbonate, chloride and sulfate, may react with the aluminate phases. Comprehensive documentation about the long-term fate of Cr awaits further study of these reactions. 3.3 Case studies; molybdenum Compared to Cr, the chemistry of Mo in cements is less complex. It has only one common oxidation state, Mo(V1). With oxygen, it forms very stable M 0 0 4 ~ groups. The effective ionic size of M 0 4 groups increases in the order SO4 < CrO4 < MoO4, so that substitution of SO4 by Moo4 in calcium aluminosulfates, e.g. in ettringite, is even less favourable than for CrO4. Instead, Mo precipitates as CaMoO4, a phase isostructural with the naturally-occumng mineral powellite. Anhydrous phases of the structurally related zircon-fergusonite-scheelitefamily, to which powellite belongs, are often observed to precipitate directly from aqueous solutions across a broad range of pH's. The high lattice energies of these phases stabilize the anhydrous form; apparently, hydration energies are insufficient to form hydrates. Kindness et al. (6) have synthesized CaMoO4 and determined its solubility. Values are shown in Table 3, and the synthetic models predict quite successfully the Mo content of pore fluids made by spiking "real" cements with Mo.

Table 3. Solubility of Mo in Cement Matrices (water:ordinary Portland Cement 0.4,18"C) Aqueous Concentration after (davs) 5 10 15

20 30

Concentration. porn Mo in mix water

500 200 100 75 65 60

1ooo 500 250 125 80 60

2ooo 1000

400 200 100 60

84 3.4. Case Studies: uranium Stabilisation and immobilisation of uranium-containing

mine tailings and process residues arising from a range of sources, including phosphate processing residues, present problems. Most of the mineral residues are, however, compatible with cementitious formulations. Relatively little data exist on immobilisation mechanisms. Moroni has characterised some of the reaction products (7). Ca(OH)2 reacts readily with U(VI) solutions: the nature of the products obtained depends on the Ca/U ratio of the system. At high U loadings, becquerelite CaO 6UO3 l l H 2 0 , forms. However, such high loadings are unlikely to be encountered in practice and in any event, becquerelite appears not to be compatible with Ca(OH)2 or C-S-H gel. Nevertheless, becquerelite is much less soluble than schoepite, U 0 3 2H20, a normal weathering product of uranium under oxidising conditions. At 5 5 T , the U solubili of a becquerelite precipitate had, after repeated dispersion, decreased to between 1 0 8and 10-6M(.IC-1by 400d. Examination of the system CaO-U03-Si02-H20 is still far from complete. Present indications are that the phases likely to be formed in real cement compositions are uranophane, CaO *2UO3 2Si02 6H20, and a phase structurally related to CaU04. This synthetic phase is apparently a hydrous version of probable formula CaU04x(OH)2x. Formation of these phases, together with sorption of anionic U(V1) species on C-S-H gel, appears likely to limit U solubilities to 10-7 to 10-8hUt. Several other incompletely characterised phases occur in synthetic mixtures, but their occurrence is unlikely to affect the broad picture: at very low U concentrations, 12), increase steeply over two orders of magnitude between pH 12 and 10, and show a gradual further increase when the pH decreases towards a value of 4. The highest Ca-concentrations at each liquid/solid (L/S) ratio approach the "available" concentration, measured using the Dutch availability test [7]. Below pH 10, the concentrations increase also with decreasing L/S ratio, in a nearly proportional manner, whereas Ca-leaching at strongly alkaline pH is

106 independent of L/S ratio.

3.3. Modelling Belevi et al. [8] have suggested that the major reactions in bottom ash involving Ca are:

CaO(s)

+

H,O

#

Ca2+ +

20H

(hydrolysis of lime in unquenched bottom ash)

(solubility of portlandite in hydrolysedkpenched bottom ash). The authors postulate that hydrolysis of lime starts immediately after the quench tank and progresses during storage of the fresh bottom ash. The bottom ash samples used for the present study have been quenched and, hence, are likely to contain portlandite. Figure 1 shows the Ca-concentrations modelled with MINTEQA2 for the conditions of our experiments, assuming equilibrium with portlandite. It is evident that, at the "natural" pH of the samples (i.e. pH 10.3-10.4), the leachates are not in equilibrium with portlandite. Only at pH 1 3 (with added base in the pH-stat) do the Ca-concentrations approach the solubility line of portlandite. Belevi et al. [8] and Zevenbergen & Comans [2] have also calculated that the leachates of their quenched bottom ash samples are undersaturated with respect to this mineral. In our previous modelling study of MSWI bottom ash [3], we have not been able to model Ca-solubility between pH 10 and 12. The Ca-mineral ettringite (Ca6AI,(SO,),(OH),,~26H,O)has been shown to exist in alkaline waste materials containing sufficient Ca, Al, and SO, [9].Ettringite is a well known mineral that plays an important role in cement chemistry [e.g. 101. A solubility product for this mineral was recently published by Atkins et al. [ 6 ]and was added to the MINTEQA2 database for the purpose of this study. Caconcentrations modelled assuming equilibrium with ettringite are included in Fig. I , The concentrations measured in the leachates between pH 10 and 12 follow the same slope and are similar to the values modelled on the basis of ettringite solubility. W e postulate, therefore, that it is ettringite that controls Ca-leaching between pH 10 and 12 and, hence, at the "natural" pH of the bottom ash samples used for this study. Very recently, ettringite has indeed been identified by XRD analysis of a fresh bottom ash sample from the same incinerator as sample AVI-1 [2].

107

100000

AVI4,US=lO \

C

g m

AVI-1, U S 5

10000 A

AVI-I, U S = 2

0

AVIP.US=lO

A

AVIZ,US=2

_ _ _ _ _ ETTRlNGlTE CI\LCITE

1

2

4

6

8

10

12

14

GYPSUM PORTLANDITE

PH Figuie 1 Dissolved Ca-concentrations in leachates from the two bottom ash samples, as a function of pH and liquidkolid ratio, and MINTEQA2 predictions assuming equilibrium with different Ca-minerals.

In addition to ettringite, two other minerals containing Ca, Al or SO, may coexist in equilibrium with these bottom ash leachates at a pH of about 10: gypsum (CaSO4*2H,O) and gibbsite (AI(OH),) [3]. It is interesting to note that MINTEQAZ calculations using these three minerals as coexisting phases, in equilibrium with the leachates, predict a leachate pH of 10.14. This value is very close to the "natural" pH of bottom ash samples AVI-I and AVI-2 (10.2-10.3). In a very recent review of leaching data of about 400 MSWI bottom ash samples, it is shown that more than half of the samples have a "natural" pH of about 10 [ I l l . We hypothesize that this pH value of fresh bottom ash results from the coexistence of ettringite, gypsum, and gibbsite in the bottom ash matrix. When the pH of the bottom ash samples is lowered to values of below pH 10, the leachates become undersaturated with respect to ettringite, and Ca-concentrations increase only slightly with decreasing pH. At L/S values of 10 Lkg, the solutions are calculated to be in equilibrium with gypsum (CaS0,*2H20). At lower L/S ratios, the leachates appear to be oversaturated with respect to this mineral. Gypsum has frequently been identified by XRD analysis of fossil fuel combustion residues [9]and MSWI bottom ash [ 1,2]. As gypsum seems to control Ca-leaching at low pH, this mineral may be the phase that controls Ca-availability when measured using the Dutch availability test [see e.g. 71.

3.4. Cahnrtion piwesses

The leaching experiments shown in Fig. 1 were performed in experimental vessels which were open to the atmosphere. Hence, carbonation of the bottom ash suspensions is likely to

108

occur, especially at high pH. When CO, is absorbed by the leachates, calcium carbonate is likely to precipitate according to the reaction:

Ca2+

+

CO,(g)

+

H,O

*

CaCO,(s)

+

2H’

Fig. 1 includes a line indicating the Ca-concentrations modelled assuming equilibrium with calcite (CaCO,) and independently measured total inorganic carbonate concentrations [3]. It is obvious that Ca-concentrations in the 24-hour leachates are not in equilibrium with calcite. However, fresh bottom ash from the same incinerator as sample AVI-I, exposed to the atmosphere for 100 days in an aqueous environment, releases Ca in concentrations close to those in equilibrium with calcite and the partial pressure of CO, in the atmosphere (P = 10-3,5atm.)[2]. The pH in those experiments had decreased to 8.0, which is close to the pH of calcite in equilibrium with the atmosphere (8.4). At this point it is important to emphasize that, for reliable modelling of Ca-solubility, it is mandatory to measure total dissolved carbonate. These measurements are not only needed to enable modelling the solubility of carbonate minerals, but also because dissolved carbonate strongly affects Ca-speciation at alkaline pH, because of the stability of the dissolved CaCO: complex (see also discussion in [2]).

3.5. Implications for contaminant leaching The Ca-chemistry of bottom ash can exert a strong influence on the leaching of potential contaminants. We have previously shown that the leaching of particularly the heavy metals Cd, Cu, Pb, Zn is probably controlled by (hydr)oxide or carbonate minerals [3]. The solubility and, hence, the leaching of those phases is strongly dependent on leachate pH. The solubilityminimum for these heavy metals lies between pH 8 and 9. The carbonation process, which changes the pH of the fresh bottom ash (controlled by ettringite/gypsum/gibbsite) from 10.2 to the value controlled by calcite in equilibrium with the atmosphere, i.e. 8.4, may, therefore, reduce heavy metal leaching. A further decrease of pH, e.g. by prolonged contact with acid rain or groundwater may, however, lead to a strong increase in heavy metal leaching. The acid neutralizing capacity of Ca-minerals in bottom ash constitutes, therefore, a very important factor controlling the period of time during which the system can maintain a pH of 8. Calcium minerals may also limit contaminant leaching through direct binding of the elements. Cadmium, and to a lesser extent other heavy metals, possess a strong affinity for the surface of calcite [I21 and may be sorbed on this mineral by coprecipitation or solidsolution formation during the carbonation of bottom ash. Ettringite has been shown to have a strong affinity for oxyanions of As, Se [I31 and possibly Sb and Mo. We are currently investigating these and other binding processes of contaminants to single solid phases in MSWI bottom ash.

109 4.

CONCLUSIONS

The geochemical speciation code MINTEQA2 has proven to be very useful in modelling the dissolved Ca concentration in leachates collected from carefully controlled batch laboratory experiments with fresh bottom ash, covering a range of liquidkolid ratios and pH. and gypsum (CaS04*2Hz0) We have shown that ettringite (Ca6AI,(S04),(OH),,-26H,0) control Ca-leaching from fresh bottom ash at pH 10-12, and pH < 10, respectively. It is hypothesized that the coexistence of the minerals ettringite, gypsum, and gibbsite (AI(OH),) in fresh bottom ash controls the pH at a value of about 10.2. In contact with the atmosphere, absorption of CO, by the alkaline leachates will lead to carbonation of bottom ash and the formation of calcite. In equilibrium with the atmosphere, this mineral controls the pH at approximately 8.4. In view of the solubility-minimum of the (hydr)oxide and carbonate phases that are likely to control heavy metal leaching, the carbonation process may have a favourable effect on the leaching of these contaminants. Laboratory experiments with single solid (Ca-)phases, such as ettringite and calcite, are needed to investigate their potential to bind metallic and non-metallic contaminants and limit leaching from bottom ash.

5,

REFERENCES

Kirby, C.S. A geochemical analysis of municipal solid waste ash. Ph.D. thesis, Department of Geological Sciences, Virginia Polytechnic Institute and State University (1 993). 2. Zevenbergen, C. & Comans, R.N.J. Geochemical factors controlling the mobilization of major elements during weathering of MSWI bottom ash. These proceedings. 3. Comans, R.N.J., van der Sloot, H.A. & Bonouvrie, P.A. Geochemical reactions controlling the solubility of major and trace elements during leaching of municipal solid waste incinerator residues. In: Kilgroe, J. (ed.) Proceedings 1993 Municipal Waste Combustion Conference, Williamsburg, VA. Air and Waste Management Association, Pittsburg, PA, 1993, pp. 667-679. 4. Schramke, J.A. Neutralization of alkaline coal fly ash leachates by CO,(g). Applied Geochemistry, 7 (1992) 48 1-492. 5 . Comans, R.N.J., Van Der Sloot, H.A., Hoede, D. & Bonouvrie, P. Chemical processes at the redox/pH interface during the application of steel slag in the aquatic environment. In: Goumans, J.J.J.M., van der Sloot, H.A. & Aalbers, Th.G. (eds.) Waste Materials in Construction. Elsevier, Amsterdam, 1991, pp. 243-254. 6. Atkins, M., Macphee, D., Kindness, A. & Glasser, F.P. Solubility properties of ternary and quaternary compounds in the CaO-AI,O,-SO,-H,O system. Cement and Concrete Research, 21 (1991) 991-998. 7. Comans, R.N.J., Van Der Sloot, H.A. & Bonouvrie, P.A. Speciatie van contaminanten tijdens uitloging van AVI-bodemas (in Dutch with English abstract). ECN-C--93-090 (1993). 8. Belevi, H., Stampfli, D.M. & Baccini, P. Chemical behaviour of municipal solid waste incinerator bottom ash in monofills. Waste Materials & Research, 10 (1992) 153-167. 1.

110 9.

10.

11.

12.

13.

Mattigod, S.V., Rai, D., Eary, L.E. & Ainsworth, C.C. Geochemical factors controlling the mobilization of inorganic constituents from fossil fuel combustion residues: I. Review of the major elements. Journal of Environmental Quality, 19 (1990) 188-201. Odler, I. and Abdul-Maula, S. Possibilities of quantitative determination of the AFt (ettringite) and AFm (monosulphate) phases in hydrated cement pastes. Cement and Concrete Research, 14 (1984) 133-141. Chandler, A.J., Eighmy, T.T., Hartlen, J., Hjelmar, O., Kosson, D.S., Sawell, S.E., Van Der Sloot, H.A. & Velow, J. Treatise on Municipal Solid Waste Incinerator Residues (in preparation, 1994). Comans, R.N.J. & Middelburg, J.J. Sorption of trace metals on calcite: applicability of the surface precipitation model. Geochim. Cosmochim. Acta, 51 (1987) 2587-2591, van der Hoek, E.E., Bonouvrie, P.A. & Comans, R.N.J. Sorption of As and Se on mineral components of fly ash: relevance for leaching processes. Applied Geochem. (1994, in press).

Environmental Aspects of Conshuction with Waste Materials JJJM Goumans, H A . van der Sloot and l3.G. Aalbers (Editors) @1994Elsevier Science B.V. AN rights reserved.

111

Particle Petrogenesis and Speciation of Elements in MSW Incineration Bottom Ashes T.T. Eighmf, J.D. Eusden, Jr.", K Marsellab,J. Hoganb, D. Domingo", J.E. Krzanowski', and D. Stampfli' "Environmental Research Group, Department of Civil Engineering, A1 15 Kingsbury Hall, University of New Hampshire, Durham, N.H. 03824, U.S.A. bGeology Department, Bates College, Lewiston, Maine 04240, U.S.A. 'Mechanical Engineering Department, Kingsbury Hall, University of New Hampshire, Durham, N.H. 03824, U.S.A. Abstract The speciation of elements in municipal solids waste incineration bottom ash is important with respect to its impact on leaching behavior and to its treatment for utilization or disposal. We used a variety of techniques to identify the speciation of major, minor and trace elements in both intact bottom ash particles as well as bottom ash powders. Petrography and scanning electron microscopy/x-ray microanalysis (SEM/XRM) were used to classify intact particles and identify ash particle petrogenic sequences. Two distinct features were seen. Particles are comprised of about 15% of materials present in the MSW waste feed to the incinerator. The remaining portion of the particle (85%) is melt structure. A typical particle contains waste glass (10%) waste soil minerals such as pyroxenes, SiO, (quartz), and feldspars (2%), waste metals and metal alloys (2%). and waste organics (1%). Particles are also comprised of slag or melt products, derived from the MSW feed material, that include opaque glass (25%), isotropic glass (20%). schlieren (lo%), and spinel-group minerals (magnetite, hercynite, chromite) (10%) and melilite group minerals such as C%Al,SiO, (gehlenite) and MgCazSi,07 (akermanite) (20%) which precipitated out of the melt as it cooled. The paragenic sequence is similar to that described for melelite-bearing, igneous rock systems. The system can best be described petrogenically using the CaO-MgO-Al,O,-SiO,-N~O-FeO(CMASNF) system. The melt structure was formed at about 1,200"C. Thermodynamically incompatible phases are present in the ash, making it reactive to aging (oxidation, hydrolysis), weathering, and diagenesis. Increasing the silicon content of the ash could result in the formation of more geochemically stable phases. The residue was ground into powders less than 300 p n in size. Magnetic and density separations were performed to segregate powders for further analysis. The residue is comprised of approximate equal fractions of magnetic, high density; nonmagnetic, low density; and nonmagnetic, high density material. Isodynamic separation of the nonmagnetic fraction was also effective in separating minerals. SEM/XRM of powders fractions in thin section was particularly

112

effective in identifying major minerals in identifiable mineral structures as well as minerals associated with "hot spots" of minor and trace elements. These minerals include many pyroxenes, quartz, feldspars, and melilite-group minerals as well as many spinels. Lead appears to largely be incorporated in complex silicate melt structures. X-ray powder diffraction (XRPD) confirmed the presence of minerals seen by petrography and SEM/XRM. X-ray photoelectron spectroscopy (XPS) of powder surfaces also documented the presence of many of these minerals. A number of oxides and carbonates were also seen with XPS, reflecting the role of O,(g) and CO,(g) in altering the speciation of the particle exterior surface. X P S is particularly well suited for identifying phases associated with leaching at this surface. Solid phases controlling leaching, as determined with the geochemical thermodynamic code MINTEQA2, are not always the same as ones observed with the above mentioned methods. The role of mineral respeciation and diagenesis in controlling leaching is highlighted. The use of such models in predicting leaching behavior is discussed. 1.0 INTRODUCTION

Municipal solid waste incineration is a viable management strategy for treating combustible municipal solid waste that cannot be recycled. Organic material is oxidized, The volume of material is reduced while exothermic energy is recovered. Less volatile inorganic contaminants in the waste feed remain in the bottom ash while more volatile inorganic contaminants are captured in air pollution control devices. The residues from municipal solid waste incineration have been generally characterized with respect to composition and to speciation of some elements (Eighmy et al., 1993). Methods frequently employed involve petrography (Project EKESA, 1992; Vehlow et al., 1992), X-ray powder diffraction (DiPietro et al., 1990; Gardner, 1991; Kirby & Rimstidt, 1993; Ontiveros, 1988; Stampfli, 1992), Fourier transform infrared spectroscopy (Henry et al., 1983), scanning electron microscopy/) 10. The equilibrium calculations summarized in table 1 indicate, however, that the solutions from the closed and N2purged batch experiments are strongly undersaturated with respect to this mineral. These calculations were performed with the same speciation code and solubility product as was used by Comans and Meima [12]. There is reason to believe that the total-CQ concentrations that were measured in the closed- and N2-purged batches (4 and 4.5 mmoles/L, respectively, using total alkalinity titrations) in the present study may be too high. Especially in the batch which

189

has been purged with nitrogen for 100 days, we would expect total-CO, to be very low. These high carbonate concentrations lower the free Ca” activity at high pH by the formation of strong complexes with the metal ion in solution and, hence, decrease the Ion Activity Product of ettringite. MINTEQAZ calculations with dissolved carbonate < lo5 M indicate that the solution from the N,-purged batch is only one order of magnitude underaturated with respect to ettringite. In view of the fact that ettringite has been identified by XRD and considering the uncertainty in its solubility product, it seems reasonable to assume that the data points around pH 11 in Fig.5 are controlled by ettringite solubility. The presence of ettringite is known to limit the SO4 concentration in solution in contact with alkaline fly ash [13,14]. It is, therefore, likely that this mineral controls SO4solubility at the beginning of the waterlogged and N,-purged experiments. The computed SI values suggest that the SO4 concentration in the air-purged batch is controlled by gypsum. The air and N,-purged extracts from the weathered sample are highly undersaturated with respect to the listed sulfate containing minerals. In these extracts the total available sulfate fraction is presumably insufficient to reach saturation. At a lower pH, however, which is found in the waterlogged batch, the solution is slightly undersaturated with respect to basaluminite (Al.,(OH),,,SO.,). This mineral may control the SO, concentrations in this batch. Basaluminite is a naturally occuring mineral in acid soils that is probably formed by reaction of sulfate with clay minerals [15]. Silicon concentrations are relatively high under the waterlogged and N,-purged conditions in the batches with the fresh ash sample, so that aluminosilicates are stable in addition to the aluminum-hydroxides. It appears from our observations by means of high-resolution electron microscopy that more hydrated and less ordered amorphous aluminosilicate phases begin to form under these conditions. At high Mg concentrations, brucite andlor dolomite and, posssibly, sepiolite are the expected stable Mg-phases. Supersaturation with respect to the latter minerals may indicate that their formation is relatively slow. In the air-purged batch dolomite rather than brucite seems to control the Mg concentration. Analcime seems to remain a metastable mineral in both ash samples, even after the high Na and pH values are lowered by leaching. Halloysite seems to be the stable aluminosilicate mineral at lower pH in both the fresh and weathered ash sample. It is important to note here that the predicted silicate minerals represent mineral assemblages commonly found in alkaline soils and soils of volcanic origin [16-211. In the present study, the lower detection limit of x-ray diffraction (approx. 3-5%) appeared to be too high to reveal any of the silicates possibly formed in this relatively short span of time. The measured iron concentrations, which were all below detection limit in the batch experiments after 100 days, allow no reliable estimation of the Saturation Indices of relevant iron containing minerals to be made.

190 Ca concentration lmg/ll 10000

t

closed. weathered

't

N2, weathered

'

air, weathered

a

closed. fresh

0

N2. fresh

A

air, fresh

- calcite, air

11 7

8

,

10

9

11

12

PH

Figure 5 . Ca concentrations in the solution from the batch experiments with the fresh and weathered ash sample and MINTEQA2 predictions assuming equilibrium with calcite. 3.6. Weathering sequences There is some evidence that the rate of crystallization with respect to amorphous aluminosilicates is inhibited (and probably deviations in stoichiometry) when there is no alternate wetting and drying [22,23]. These phenomena may be of particular relevance in the batch experiments with the fresh sample, resulting in increasing solubility values of silicate minerals. Caution with estimations on mineral solubility and formation on the L-A A.' of themodynariiic equiliorium modelling during experimental bottom ash leaching should be taken. In spt' of tbese shortcomings, relevant information can be obtained about the direction and sequence of secondary mineral formation under different conditions from our experimental data and from known natural weathering sequences observed in tuffs and lavas. Hypothetical weathering products as a result of hydration, hydrolysis, oxidation/reduction and carbonation in relation to some specific environments are summarized in Table 2.

191

Table 2. Hypothetical weathering products of MSWI bottom ash in relation to some specific environments. Environment

Dominant processes

I

Mobility

Waterloerred alkaline reducing low water intiltration rate

hydrolysis of prtlandite formation of ettringite hydration L hydrolysis of glasses formation o f zeolites redoxprocesses

high

QE!! alkaline to neutral oxidizing-reducing high water intiltration rate

carbonation hydration L hydrolysis of glasses formation of 2:l clays redoxprocesses

high : moderate : low :

low

: :

Si, Al, Na, K Ca, Mg, (Fe), SO,

Mineralogy

ettringite Ca-zeolites sepiolite analcime hmcite ~______

Ca, Mg, SO,, Na, K Si. Fe Al

calcite dolomite hasaluminite 2:l clays halloysite gypsum analcime

In the storage pile the initial weathering reactions, including carbonation, hydration and hydrolysis, may progress rapidly due to the prevailing hydrothermal conditions. The subsequent weathering reactions are determined by predominating conditions during disposal and utilization. When bottom ash is waterlogged, gas exchange between ash and air is drastically curtailed. Oxygen and atmospheric CO, can enter the bottom ash environment only by molecular diffusion. The pH of waterlogged, initially fresh, bottom ash is controlled by portlandite. In this alkaline environment the pH is sufficiently high to cause solution of aluminum and precipitation of magnesium and sulfate. Although the formation of zeolites has as yet not been substantiated with high resolution AEM, these conditions provide an ideal setting for formation of zeolites. Migration of atmospheric CO, into the bottom ash environment and microbial respiration producing CO, may cause a gradually decreasing of pH. Carbonate minerals will ultimately control the equilibrium pH of the pore solution in a well drained, unsaturated, bottom ash environment. Under these conditions the solubility of aluminium is relatively low and hence may give rise to the formation of 2:l clay minerals. Indeed, the distinct and extensive neoformation of illite from weathered bottom ash in an open disposal environment has recently been documented [1,2]. It has been long noted that altered (aluminosilicate) layers formed on glasses play a significant role in the retention of trace elements during leaching [24]. In view of the environmental significance, further evaluation of mechanisms of clay mineral formation during MSWI bottom ash is warranted. It must be emphasized that microbiologically mediated oxidation-reduction reactions are probably important as well in controlling element mobility in bottom ash environments [25]. However, very little information is available with respect to these types of reactions during weathering of bottom ash. Low (negative) redoxpotentials were recorded in percolates from waterlogged bottom ash after six months of incubation in large field lysimeters [26]. In a more oxidizing environment, microbiological action was likely to be responsible for the observed translocation of iron in a bottom ash profile, resulting in the formation of an iron pan on the ash-soil interface [ 11.

192

In the present study anaerobic conditions have not been attained in the waterlogged and N2 purged batches, presumably due to slow reaction kinetics. 4. CONCLUSIONS MSWI bottom ash consists primeraly of an assemblage of metastable phases and minerals. Upon weathering these metastable solids will transform into naturally occurring secondary minerals. The experimental observations and the calculations reported here allow the following conclusions to be drawn with respect to the leaching behaviour of major elements during weathering of MSWI bottom ash. The initial stage of weathering is dominated by an extreme solution alkalinity and by instantaneous dissolution of those elements (e.g. Na, K, and C1) that are assiociated with soluble salts. The rate and sequences of consecutive weathering reactions controlling the concentrations of Si, Al, Ca, Mg, S04, and possibly Fe, in the pore solution, is dictated to a large extent by the rate of atmospheric COz entry (andlor production of C02 by microbial respiration). Two factors which are of importance but not considered in this paper are the rate of atmospheric 0, entry and the hydrodynamic conditions. The predicted secondary minerals, which may form on the longer term, represent mineral assemblages commonly found in alkaline soils and soils of volcanic origin. We emphasized that the combination of microanalyses of the solid phase and the geochemical modelling of the processes in solution, followed in this paper, constitutes a powerful approach in revealing the major element chemistry ans secondairy mineral formation in waste materials such as MSWI bottom ash. Knowledge of these processes is mandatory in assessing the long term environmental impacts of these waste materials.

5. REFERENCES Zevenbergen, C., Bradley, J.P., Vander Wood, T., Brown, R.S., Van Reeuwijk, L.P., and Schuiling, R.D. Weathering as a process to control the release of toxic constituents from MSW bottom ash. In: Geology and Confinement of Toxic Waste, Proc. of the Int. Symp. Geoconfine '93, Montpellier, France, 591-595, 1993. Zevenbergen, C., Bradley, J.P., and Van Reeuwijk, L.P. Mobility of heavy metals during leaching of municipal solid waste ash. In: Microbeam Analysis, 2, Proc. of the 27th Annual MAS Meeting, Los Angeles, 1993. Dipietro, J.V., Collins, M., Guay, M., and Eighmy, T.T. Evaluation of pH and oxidation-reduction potential on leachability of municipal solid waste incinerator residues. Proc. Int. Conf. Municipal Waste Combustion, Hollywood, Florida, April 11-14, 2B, pp. 21-43, 1989. Comans, R.N.J., Van der Sloot, H.A., and Bonouvrie, P.A. Geochemical reactions controlling the solubility of major and trace elements during leaching of municipal solid waste incinerator residues. Proc. Int. Conf. Municipal Waste Combustion, March 30- April 2, Williamsburg, VA, J. Kilgroe, ed., AWMA, Pittsburg, PA, 1993.

193

5

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Schnieder, J., Kossl, H., and Pfrang-Stotz, G. Vergleichende Untersuchungen an MV-Schlacken unterschiedlicher Rost- und Reuerungssysteme. VDI Bildungswerk. Seminar Slackenaubereitung, -verwertung und -entsorgung, December 6-7, Dusseldorf, 1993. NVN 5432. Determination of the maximum leachable quantity and the emission of potentially hazardous components from construction materials and stabilized waste products of mainly inorganic character. NNI, October 1992. Felmy, A.R., Girvin, D,C., and Jenne, E.A. MINTEQ--A computer program for calculating acqueous geochemical equilibria, EPA-600/3-84-032, U.S. Environmental Protection Agency, Athens, 1984. Allison, J.D., Brown, D.S., and Novo-Gradac, K.J. MINTEQA2IPRODEFA2, A Geochemical Assessment Model for Environmental Systems: Version 3.0 User’s Manual, EPA/600/3-91/021, U.S. Environmental Protection Agency, Athens, 1991. Bradley, J.P., and Brownlee, D.E. Cometary particles: Thin sectioning and electron beam analysis. Science, 231, 1542-1544, 1989. Atkins, M., Macphee, D., Kindness, A., and Glasser, F.P. Solubility properties of ternary and quarternary compounds in the Ca0-A1,0,-S03-H,0 system. Cement and Concrete Research, 2 1, 99 1-998, 1991. Schramke, J.A. Neutralization of alkaline coal fly ash leachates by C02(g). Applied geochemistry, 7, 481-492, 1992. Comans, R.N.J. and Meima, J.A. Modelling Ca-solubility in MSWI bottom ash leachates. These Proceedings. Simons, H.S., and Jeffery, J.W. An x-ray study of pulverised fuel ash. J. Appl. Chem., 10, 328-336, 1960. Mattigod, S.V. Chemical composition of acqueous extracts of fly ash: ionic speciation as a controlling factor. Environmental Letters, 4, 485-490, 1983. Adams, F. and Z. Rawajfih. Basaluminite and Alunite: Possible cause of sulfate retention by acid soils. Soil Sci. SOC.Am. J., vol. 41,686-692, 1977. Boekschoten, G.J., Buurman, P., and Van Reeuwijk, L.P. Zeolites and palygorskite as weathering products of pillow lava in Curacao. Geologie en Mijnbouw 0016-7746, pp.409-415, 1983. Hay, R.L. Zeolites and zeolitic reactions in sedimentary rocks. Geol. Soc. Amer. Spec. Paper 85, 1966. Baldar, N.A., and Whittig, L.D. Occurence and synthesis of soil zeolites. Soil Sci. Soc. Amer. Proc. 32, pp. 235-238, 1968. Wada, K. Minerals and mineral formation in soils derived from volcanic ash in the tropics. Sci. Geol., Mem., 85, 69-78, 1990. Wada, K., and Kakuto, Y. Embronic halloysites in Ecuadorian soils derived from volcanic ash. Soil Sci. Soc. Amer. J . , 49, (1985), 1309-1319. Tazaki, K., Observations of primitive clay precursors during microcline weathering. Conrrib. Mineral. Petr., 92, (1986), 86-88. Magonthier, M.C., Petit, J.C., and Dran, J.C. Rhyolitic glasses as natural analogues of nuclear waste glasses: behaviour of an Icelandic glass upon natural acqueous corrosion. Applied Geochemistry, Suppl. Issue No. 1,pp. 83-93, 1992.

194 23 Brinkman, R. Clay transformations: aspects of equilibrium and kinetics. In: Soil Chemistry. B. Physico-chemical models. Bolt, G.H. (ed.) Elseviers Science Publishers BV, 1983. 24 Petit, J.C., Dran, J.C., and Trotignon, L. Mechanism of heavy element retention in hydrated layers formed on leached silicate glasses. Mat. Res. Symp. Proc. Vol. 127, 33-40, 1989. 25 Belevi, H., Stampfpli, and Baccini, P. Chemical behaviour of municipal solid waste incinerator bottom ash in monofills. Waste management 8~ Research, 10, 153-167, 1992. 26 Van der Sloot, H.A., and Hoede, D. AVI-bodemas als aanvulmateriaal: migratie van contaminanten uit AVI-bodemas in een isolerende kleilaag en evaluatie van het lange termijn gedrag. ECN-C-91-0441, 1991.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, HA. van der SImt and Th.G.Aalbers (Editors) el994 Elsevier Science B.V. AN rights reserved.

I95

LEACHING BEHAVIOUR OF BUILDING MATERIALS WITH BYPRODUCTS UNDER PRACTICAL CONDITIONS. P.J.C.Bloem, F.L.M.Lamers and L.Tamboer KEMA Nederland B.V.; P.O. Box, 6800 ET Arnhem, The Netherlands ABSTRACT

From sand-lime bricks in which 20 wt% of a mixture of fly ash and S(pray) D(ry) (Absorption) P(roduct) was processed, the leachability was determined by means of a standard diffusion test. Besides a test wall has been built up to determine the leachability under practical conditions. This experiment was started at June 1991 and some provisional results are presented and discussed. The leached quantities from the standard diffusion test meet the U1 values of the draft Dutch Standard involved. Further the amounts of dissolved species in the collected rainwater from the test wall are low up to now. 1. INTRODUCTION

At the end of the eighties all the Dutch coal-fired power stations have been provided with flue-gas desulphurization (FGD) units, producing about 250,000 tonnes/year at the moment. There was some concern, however, that not all the produced FGDgypsum could be applied in that field in the near future. Therefore alternative processes were examined to prevent an excess of FGD-gypsum. The Spray Dry Absorption (SDA) Process might be a good option. This process yields an endproduct (SDA Product) with handling properties similar to those of fly ash; it is primarily composed of calcium-sulphite and -sulphate and an excess of calciumhydroxide and calciumchloride. Application of SDA Products, as a mixture with fly ash, in sand-lime bricks was studied both on laboratory and factory scale. Therefore samples (bricks) were pressed and autoclaved in which sand was partially substituted by a mixture of fly ash and a SDA Product. A big-scale experiment was performed on a sand-lime brick yard (KZI Loevestein). The aim of this was twofold; first to get information about the processing and properties of the bricks with byproducts if the preparation was conducted on production scale. On the other hand it is necessary to determine the leaching behaviour of building materials with byproducts from coal-fired powerplants. First of all a standard test was performed in the laboratory, namely the diffusion test. Some aspects from practise, however, could be hardly simulated by tests performed on laboratory scale, like the changes of the temperature and variations on dry and wet periods. Therefore a test wall has been built up to examine the leaching behaviour of the bricks just-mentioned. The start of this experiment was June 1991.

196

In this paper the provisional leaching results, both from the diffusion test and the test under practical conditions, will be mentioned and discussed.

-

2. SAND-LIME BRICKS WITH (FLY ASH SDA PRODUCT) MIXTURE 2.1. Raw Materials

The conventional raw materials for the production of sand-lime bricks are sand and lime. The chemical compositions of the fly ashes and SDA Products are mentioned in table 1 and 2. Table 1 Chemical composition of fly ash (wt%)

A B C

90,

AI,O,

Fe,O,

CaO

MgO

Na,O

K20

TiO,

SO,

54.9 64.7 51.0

30.2 20.2 24.2

6.0 5.1 7.7

3.2 1.6 2.6

1.0 0.7 1.0

0.32 0.32 0.40

1.49 0.82

1.7 1.1 1.1

0.32 0.22

1.05

LO1

0.91 3.9 0.35 6.9

Table 2 Chemical composition of SDA Product (wt?/b)

1 2

CaS03,0.5H,0

CaS0,.2H20

Ca(OH),

CaCO,

71.8 50.2

3.0 10.0

40 mm) migration of the components take place by means of diffusion. The so called column test and cascade test are designed for measuring the leaching properties of granular products. The results give information on leaching properties within five years and on the long term (> 50 years) respectively. The determination of the leaching properties of the sand-lime bricks was performed by the diffusion test. It consists of submerging a brick in an aqueous solution of pH =4. Further some examinations are being performed in practice. Therefore a test wall has been built up and some provisions have been made onto the wall to collect the rainwater coming from the surface of this wall. The amounts collected were registered automatically and at particular times these aqueous solutions were analyzed. The results of both the diffusion test and the test under practical conditions are compared with the draft Dutch Standard values (Bouwstoffenbesluit). 3.2. Diff usiontest

First of all the measurements of the delivery of potentially harmful components from sand-lime bricks with fly ash and SDA Product were performed by means of the Dutch Standard NVN 7345. According to this a brick is immersed into an acidified aqueous solution (pH 4).

198

After 1/4, 1, 2, 4, 8, 16, 32 and 64 days the liquid is refreshed and then the supernatant analyzed with some components mentioned in the draft Building Materials Act (Bouwstoffenbesluit). The cumulative diffusion is the total amount of a component in all the supernatants determined. The values were corrected for the geometric surface of the brick and expressed as mg.m-’ (cumulative diffusion). It was assumed that the leachability was controlled by diffusion. These cumulative results were compared with the standard values of the draft Building Materials Act. 3.3. Leaching test under practical conditions

A test wall has been set up by means of a part of the produced sand-lime bricks. The wall was divided into four sections; each section consists of one type of the sand-lime bricks (figure 1). So four types of these bricks were subjected to this experiment under practical conditions, namely I, VII, Vlll and XII. The leaching behaviour of these sections is being determined by first collecting the water coming from each section at set times and then analyzing them. Therefore the sections of the wall provided with plastic gutters, sloping down and connected to a vessel.To prevent direct capture of rainwater and contaminations (leaves) a shelf has been placed above the gutters. After removal from the collecting vessels the aqueous solutions has been analyzed with respect to some components mentioned in the draft Building Materials Act.

Fig. 1

Testwall consisting of four sections

199

0

1

mmn mm

AS

BO

Cd

Cr

cu

Mo

Ni

Pb

Se

v

Zn

SO,

Rip.

mmP

m a

AS

Ba

Cd

Cr

cu

Ma

Ni

Pb

Se

v

Zn

o m mmm m!x

As

BQ

Cd

Cr

cu

Mo

Ni

Pb

Zn

Se

SO,

o x mmx m m

AS

BO

Cd

Cr

cu

Mo

Ni

Fig.2 Leaching results from diffusion test o f sand-lime expressed as o fraction of the

U1 limits

Pb

Se

v

Zn

SO'

bricks with fly ash and SDA product

200

From these results the "cumulative diffusion" per unit area of a section was calculated and compared with the already mentioned values of the draft Building Materials Act.

4. RESULTS AND DISCUSSION 4.1. Diffusiontest

The results of the standard diffusiontest of the twelve types of sand-lime bricks are given in fig. 2. They are presented as a fraction with respect to the U1 values of the draft Building Materials Act.If the quantity of a component measured in the supernatant is lower than the detection limit 50% of this limit was introduced into the calculation of the cumulative diffusion. This is an compromise between an optimistic estimation and the "worst case". From these results it may be concluded that all the cumulative diffusion values are far lower than the U1 values mentioned in the draft Building Materials Act except selenium.With regard to the element last-mentioned the quantity dissolved was always lower than the detection limit. 4.2. Test under practical conditions

It was supposed that 10% of the rainwater has been in contact with the wall. This agrees with about totally 180 litres of water during the whole period examined up till now with respect to one section. The amount of water collected is about 33 I. So it may be that the assumption of 10% rainwater being in contact with the wall is too high. Other factors contributing to this figure are evaporation and absorption of water into the bricks. With respect to each period the amounts of collected water of the four sections are of similar order; besides the correlation between these values and the quantities of rainwater that has fallen during these periods is reasonable. The "cumulative diffusion" expressed as the ratio of the U1 values are given in fig. 3-7. After the first periods higher concentrations of some components were found in the collected water. In March '92 higher quantities of some elements were measured. The collected water of November '92 showed increased amounts of elements, whereas in the collected water of January '93 the concentrations of arsenic, barium, cadmium and chromium were comparatively high.

20 1

Fig.3

The r o t i o of cumulative leaching of arsenic and barium from the test wall and the U1 limits

Cd

. -

A m

I

1994""

Fig.4

1992

1993

The ratio of cumulative leaching of codmlum and chromium from the test wall and the U 1 limits

1994

202 (9

lo-')

6.0

r

bl0-21 cu

'.O

r

Mo

Ni

V

Fig 6 The ratio o f cumulatlve leaching o f nickel and vanadium from the test wall and the U 1 limits

203 (.10-~)

c

Zn

a 1

o

m

o m A m

Fig.7

The ratio of cumulative leaching of zinc from the t e s t wall and the U I l i m i t s

This effect may be caused by the (partial) absorption of the rainwater into the pores of the bricks, followed by a period of dryness. During these periods various salts together with the components measured were transported to the surface of the wall. Then during heavy or prolonged rainfall the salts were rinsed from the wall and collected in the vessel. To get more information about the absorption of rainwater followed by migration of the salts the period of rainfall and dryness should be exactly known. Further it is important to determine the humidity of the sections during the whole testperiod. The component concentrations found in rainwater were negligible with respect to the amounts determined in the collected aqueous solutions (RIVM/KNMI; 1991). Fig. 3-7 show that the total quality of the greater part of the components determined till May '93 are much lower than the U1 limit values of the draft Building Materials Act; only the cadmiumconcentration is somewhat higher.

204 It should be noticed that the experiment has not yet been finished, so the results presented are provisional. To examine the effects of evaporation and absorption of the rainwater in the bricks it is decided to build another testwall consisting bricks with a higher poresize and porevolume.The periods of rainfall and dryness will be exactly registered automatically. Further the humidity and dryness of the bricks themselves will be measured.

5. CONCLUSIONS The results of the diffusion test show that the leaching behaviour of all types of sand-lime bricks with 20 wt% of fly ash and SDA Product meet the U1 values of the draft Building Materials Act (Bouwstoffenbesluit). Since limited quantities of fly ash and SDA Product were processed into the sandlime bricks it may be expected that these bricks meet the S1 values of the abovementioned "Bouwstoffenbesluit"too. The results of the collected water from the testwall show that the differences of the leachability between the various types of sand-lime bricks are up to now rather low. Evaporation and absorption of rainwater into the bricks strongly influenced the leaching behaviour. Sometimes the leachability of sand-lime bricks with byproducts is even lower than for conventional bricks (arsenic, vanadium). To examine the effects of evaporation and absorption of rainwater in more detail another testwall consisting of bricks with a higher porosity is being built up.

6. ACKNOWLEDGEMENT

Thanks are due to the Amer Power Station (Geertruidenberg) and Flakt (Sweden) for providing the fly ash and SDA-Product respectively. This study is undertaken by order of the Dutch Electricity Production Sector.

Environmental Aspects of Consmction with Waste Materials J.J.J.M. Goumans, H A . van der Sloot and Th.G.Aalbers (Editors) Q1994 Elsevier Science B. K AN rights resewed.

205

FGD GYPSUM DEFINITIONS AND LEGISLATION IN THE EUROPEAN COMMUNITIES, IN THE OECD AND IN GERMANY Franz Wirsching, Rolf Huller, Rainer Olejnik Eurogypsum Environmental Group, 3, rue Alfred Roll, F-75017 Pans 17

Abstract The production of FGD gypsum in a FGD plant has been explained in detail in this paper. This shows that FGD gypsum is produced in a FGD plant as a product with specification and quality standards. The operations which may lead to the recovery of FGD gypum are carried out in the FGD plant itself It has therefore been conclusively proved, both technologically and scientifically, that FGD gypsum is a product. Furthermore, it has been shown that, as a product, FGD gypsum is not included in the European Waste Catalogue, is not included in the OECD lists and is not included in the German Waste Catalogue. 1. INTRODUCTION

In recent years there has been a rapid growth in the area of the law relating to the protection of the environment. Essentially, there are 2 organizations which have taken an active part:

-

EC European Communities (12 Member States, see Table 1)

Table 1 Member States of the EC (State August 1992) Belgium, Denmark, France, Germany, Greece, Ireland, Italy, Luxemburg, Netherland, Portugal, Spain, United Kingdom

-

OECD Organisation for Economic Cooperation and Development (24 Member States, see Table 2)

Table 2 Member States of the OECD (State August 1992) Australia, Austria, Belgium, Canada, Denmark, Finland, France, Germany, Greece, Ireland, Island, Italy, Japan, Luxembourg, Netherland, New Zealand, Norway, Portugal, Spain, Sweden, Switzerland, Turkey, United Kingdom, United States In addition to the European States, the following are also Member States of the OECD: Australia, Canada, Japan, New Zealand, United States of America

206

The gypsum industry is also affected by the preparation of the environmental law in one essential point: namely its FGD gypsum product (Flue Gas Desulphurisation Gypsum) It has been found in this connection that the facts relating to FGD gypsum must be considered on a broad basis. The expression "FGD gypsum" was often used for all kinds of residues from FGD plants and led to false conclusions which caused incorrect listing of the FGD gypsum product in the waste catalogue. The fact that FGD gypsum is produced in power stations as a product using operations for recovering the material was completely overlooked. This product from power stations is directly used in the gypsum industry without any further treatment, and is identical with natural gypsum. This paper gives a definition of FGD gypsum, and the recovery operations carried out in power stations to produce FGD gypsum as a product are described and discussed. All the European political and industrial organisations and institutions, e.g. Eurogypsum,, the Working Community of the European Gypsum Industry, ECOBA European association for use of the by-products of coal-fired power stations, EURELECTRIC European grouping of the electricity supply industry, the OECD and the EC, are now agreed in their understanding that FGD gypsum is a product. There are also comments on the EC Waste catalogue and the OECD Waste List. Definitions and translations of important keywords are also given in the three languages, English, French and German. 2 DEFINITION OF FGD GYPSUM

FGD gypsum is defined as follows: Gypsum from flue gas desulphurisation plants (FGD gypsum, desulfogypsum) is moist, finely divided, crystalline, high purity calcium sulfate dihydrate - CaS0i2H20. It is specifically produced in a flue gas desulphurisation process incorporating after lime(stone) scrubbing, a refining process involving oxidation followed by gypsum separation, washing and dewatering. 3 . PRODUCTION OF FGD GYPSUM IN COAL POWER STATIONS

FGD gypsum is produced in power stations as a product with a specification and quality standards. To fulfil these requirements, the flue gas desulphurisation plant (FGD plant) must be designed, built and operated so that FGD gypsum is produced as a product. The individual steps for producing FGD gypsum are shown on the following flow diagram, Fig. 1.

207

Figure 1. Typical flow diagram of a wet flue gas desulphurisation process based on limestone with gypsum as the product. FGD gypsum is produced in 4 stages: Stage No. 1: Desulphurisation In the scrubber, the dedusted flue gas is sprayed with a limestone suspension in counterflow. During this operation the limestone CaC03 combines with the sulphur dioxide SO2 and produces calcium sulphite CaS03%H20. This chemical reaction is represented by the following chemical equation: SO2 + CaCO3 + %H20 -+ CaS01%H20 + CO2 The legal requirements of the desulphurisation system are fulfilled by eliminating the sulphur dioxide SO2 from the flue gas. The calcium sulphite CaS03'%H20 thus obtained appears as calcium sulphite sludge in the quencher of the scrubber. In some power stations this sludge is still drawn off from the quencher and deposited in large ponds near the power station. However, further reaction steps are needed if the calcium sulphite is going to be worked up into FGD gypsum. These operations for recovering the material are described hereafter as stages 2, 3 and 4. Stage No. 2: Forced Oxidation When converting the calcium sulphite into calcium sulphate dihydrate, the calcium sulphite CaSO,'%H20 is oxidized in the quencher with atmospheric oxygen 02. This chemical reaction is represented by the following chemical equation: 2CaS03.1/J120+02+3H20 + 2CaS0;2H20 The calcium sulphite reacts spontaneously with atmospheric oxygen to form first calcium bisulphite and then calcium sulphate dihydrate. The calcium sulphite must be completely oxidised to calcium sulphate dihydrate. This oxidation is carried out in FGD plants by blowing air into the aqueous sulphite slurry in the quencher. During this procedure the gypsum crystals grow by permanent circulation to the required average size of 30 - 70 microns. This 2nd stage is the first operation for recovering the material.

208

Stage No. 3: Gypsum Separation The calcium sulphate dihydrate crystals produced in the quencher slurry have to be separated and refined to remove solid impurities. This is carried out using a hydrocyclone.

Figure 2. Method of operation of a hydrocyclone The hydrocyclone can be classified as a mechanical separation device in which sedimentation takes place in a centrihgal field. In practise, it is a good on-stream classifier for the 5 - 100 micron particle size range. The coarser calcium sulphate dihydrate particles are separated with the underflow and are fed into the fourth stage of the operation. The smaller particles are separated with the overflow and are recycled to the quencher to grow larger. Stage No. 4: Gypsum Washing and Dewatering During this stage of the recovery operations the calcium sulphate dihydrate crystal suspension from the hydrocyclon underflow is filtered into filter cake and filtrate by a filter or centrifuge. The filter cake consisting of moist calcium sulphate dihydrate crystals, is further refined by washing with clear water (of drinking quality) to remove water-soluble substances, especially chloride, sodium and magnesium ions. The dewatered filter cake contains less than 10 % moisture by weight. This moist, finely divided, crystalline, high purity calcium sulphate dihydrate is the "FGD gypsum" product.

209

Figure 3 shows a washing and dewatering station in a flue gas desulphurisation plant. This fourth stage is the last operation for recovering the material. The FGD gypsum obtained is suitable for general use in the same way as natural gypsum.

Figure 3. Washing and dewatering station in a flue gas desulphurisation plant Figure4 shows a typical flow diagram of a flue gas desulphurisation plant for producing FGD gypsum. The four stages of FGD gypsum production are marked with circles No. 1 - 4, showing the desulphurisation (1) and the three recovery operations (2, 3 and 4) of the refining process. It is clear that such a desulphurisation plant producing salelable gypsum will be more expensive - approximately twice as expensive as a FGD plant producing calcium sulphite sludge.

4.

Figure 4. Flow diagram of a flue gas desulphurisation plant for producing FGD gypsum with the 4 operation stages. The specification and quality standards for the FGD gypsum product are shown in Table 3.

210

Table 3 Quality Requirements for FGD Gypsum Property

Requirement

free moisture

:10

M.-YOby weight

Calcium sulfate dihydrate CaS04.2H20

'95*

M.-% by weight on dry basis

Magnesium oxide MgO water soluble

:0,l


Chloride CI-

:0,Ol

M.-Yoby weight on dry basis

Sodium oxide Na20

:0,06


Sulphur dioxide SO2

:0,25


pH value

5 to 9

Colour

white**

Odour

neutral

Toxicity

non toxic***

* ** ***

Reduced purities consistant with acceptable environmental impacts and product performance are allowable, e.g. for the cement industry comparable with natural gypsum conforming to national requirements over the product life cycle

Table 3 shows that the FGD gypsum product is characterized by its: low moisture content of less than 10 % moisture by weight high purity of more than 95 % of calcium sulphate dihydrate very low content of water-soluble substances, such as magnesium at less than 0,l %, chloride at less than 0,Ol % (< 100 ppm) and sodium at less than 0,06 % high level of oxidation, with less than 0,5 % calcium sulphite (or 0,25 % SO*) neutral pH value white colour, comparable with natural gypsum neutral ordour, comparable with natural gypsum absence of toxic substances. FGD gypsum can also be supplied in the form of dry powder or dry lumps to suit different market requirements. Drying and compacting can be carried out at the power station or at a gypsum plant.

21 1

4. FGD GYPSUM IN THE EC LEGISLATION

The legal provisions for wastes in the EC are laid down by the Council Directive of EC, dated 18th March, 1991 (91/156/EEC). These so-called general waste provisions of the EC provide for the drawing-up of a European WASTE Catalogue (EWC). In this Council Directive, WASTE is defined as follows: "WASTE" shall mean any substance or object in the categories set out in Annex I which the holder discards or intends or is required to discard. FGD wastes come under Category Q 9 of Annex I with the following wording Q 9 Residues from pollution abatement processes (e.g. scrubber sludges, baghouse dusts, spent filters, etc.) The FGD gypsum product, as described, cannot be and is not included in the European Waste Catalogue (EWC). All other inorganic residues from thermal processes which are considered as waste are listed under the item 10 of the EWC, as follows (State 20. December 1993). 10 Inorganic waste from thermal processes, Nos. 10 01 00 - 10 01 13

The wastes from FGD plants of power stations are listed under the following items 10 01 05, 10 01 06, 10 01 07 and 10 01 08: 10 01 05

calcium based reaction wastes from flue gas desulphurisation in solid form

10 01 06

other solid wastes from gas treatment

10 01 07

calcium based reaction wastes from flue gas desulphurisation in sludge form

10 01 08

other sludges from gas treatment

As mentioned above calcium based reaction wastes are residues which are not refined by recovery operations. According to the EC definition FGD gypsum is a product, because the following requirements are satisfied: product with specification and quality standards product produced for a specific purpose (used in the same way as natural gypsum e.g. by the building products industry) product with positive economical and ecological value the product use is regulated by delivery contracts FGD gypsum also fulfills the criteria for a product with respect to quantity. At present about 3 million tonnes of FGD gypsum are being produced annually in the Federal Republic of Germany, purchased and used by the building products industry. More than 6 million tonnedyear will be produced and used in Europe in the near future.

212 5 FGD GYPSUM IN THE DIRECTIVES OF THE OECD

The Council decision by the OECD on the Control of Transfrontier Movements of Wastes Destined for Recovery Operations (C(92)39) controls the transfrontier movements of wastes. The following conditions shall apply to transfrontier movements subject to this decision:

-

-

The wastes shall be destined for recovery operations within a facility which, under applicable domestic law, is operating or is authorized to operate in the importing country. The transfrontier movements shall be carried out under terms of applicable international transport agreements. Any transit of wastes through a nonmember country shall be subject to all applicable international and national laws and regulations.

The Organization for Economic Cooperation and Development, in the Council Session on 30 March 1992, essentially adopted the stipulations of the Basel Convention, enriching them by a three-level waste monitoring system: 1. "Green" list "Waste with no hazardous contamination" Wastes destined for recovery operations which are subject to normal controls (,,green tier"); 2. "Amber" Control System and list "Waste contaminated with material, which prevents the recovery in an environmentally sound manner". Wastes destined for recovery operations which are subject to enhanced control including written contracts, specific consent, additional provisions relating to re-export to a third country, provisions relating to recognized traders, and tracking documents (,,amber tier") ; 3. "Red" list "Waste contaminated with or containing hazardous materials" Wastes requiring written consent before transfrontier movement (,,red tier") Initially FGD gypsum was listed on the OECD green list. However, because FGD gypsum complies with the provisions of the OECD for a product, EUROGYPSUM requested the OECD to delete FGD gypsum from the green list, and the OECD have complied with EUROGYPSUM's request. FGD gypsum is thus recognized as a product by the OECD. Therefore, FGD gypsum is not included in the any of OECD green lists. All other inorganic residues from thermal processes, but also gypsum or gypsum containing residues which are considered as waste, are listed in the Green List or in the Amber List, as follows (State 23. July 1993).

213 Green List GG 010

Partially refined calcium sulphate produced from flue gas desulphurisation (FGD)

GG 020

Waste gypsum wallboard or plasterboard arising from the demolition of buildings

Amber List

AB 140

Gypsum arising from chemical industry processes

AB 150

Unrefined calcium sulphite and calcium sulphate from flue gas desulphurisation (FGD)

According to the OECD definition, the following requirements of the OECD are satisfied: FGD gypsum, a product and a secondary raw material, is directly used in the gypsum industry, without any additional recovery operations. Its economic value is comparable with that of natural gypsum, but is also dependent on the freight costs for transportation from power station to gypsum factory. FGD gypsum can be transported by truck, railway or ship without any special provisions. 6 . FGD GYPSUM M GERMAN LEGISLATION

In Germany, differentiation is made between Ruckstande (residues), Sekundarrohstoff (secondary raw material) and Abfall (waste). If residues are properly and harmlessly put to an intended use in accordance with the German Federal Emission Protection Law $ 5 , $9 1, No. 3, they are designated as a product. Only when residues can no longer be utilized and have to be disposed of, are they considered as waste. (State 22. June 1992, 5. Novelle) According to German law FGD gypsum is first designated as a residue. But because it complies with a specification and with quality standards of the Gypsum Industry and because it is properly and harmlessly put to an intended use, the German law therefore considers FGD gypsum to be a secondary raw material. This legal provision has been adopted by other countries. FGD gypsum is also recognized as a product in, for example, the United Kingdom, France, Belgium, Netherlands, Denmark and Austria. It is the intention that in the future the national waste catalogues (e.g. german AbfBestV; Abfall-Bestimmungs-Verordnung) will be brought into line with the European Waste Catalogue and with the OECD lists.

214 7. DEFINITIONSAND TRANSLATIONS OF KEYWORDS RELATING TO FGD GYPSUM

However, some questions still remain unanswered in spite of all the efforts to recognize FGD gypsum as a product and to bring the term "Waste" and the legal provisions governing waste into line in the EC, in the OECD, and nationally. An important and decisive key to answering these questions lies on the exact definition and the correct translation of keywords relating to FGD gypsum. For example: Definitions There is as yet still no uniform definition of the term "Waste" in the EC, in the OECD and on a national basis. Definition of WASTE in the EC (Council Directive 91/156/EEC): Waste shall mean any substances or object in the categories set out in ANNEX I which the holder discards or intends or is required to discard. ANNEX I: Categories of waste Q 9 Residues from pollution abatement processes (e.g. scrubber sludges, baghouse dusts, spent filters, etc.)

Definition of WASTE in Bale Convention for the OECD On the control of the transboundary movements of wastes and hazardous wastes and their disposal Article 2 Definitions Wastes are substances or objects, which are disposed of, or are intended to be disposed of, or are required to be disposed of, by the provisions of national law. Definition of WASTE in Germany (State 22. June 1992, 5. Novelle) Residues ($ 3 (1)) are movable things (substances and objects) in the sense of byproducts from energy processing or from the production, processing and manufacturing or other treatment of substances and products in installations that are regulated by the German Federal Emission Protection Law. Two subdivisions: Secondary raw materials ( 5 3 (2)) are residues submitted to recovery operations as defined in the waste disposal law. Waste (6 3 (3)) are residues for which utilisation as secondary raw materials is not allowed. It can be seen from this that the definitions of "Waste" in the EC, in the OECD and in the national laws are far from consistent. The terms

-

residue secondary raw material by-product

have not yet even been defined.

215

Translations There are, for example, some official translations from English into French and into German, and these also demonstrate how difficult it is to translate the English expressions, which have been defined in the conference, correspondingly and appropriately into French and into German Example 1

Council Directive 18. March 1991 91/156 /EEC (Page 1)

english:

Whereas common terminology and a A n i t i o n of waste are needed in order to improve the efficiency of waste management in the Community II est necessaire de disposer d'une terminologie commune et d'une definition des dechets Fur eine offizielle Abfallbewertung in der Gemeinschaf? sind eine gemeinsame Terminologie und eine Definition der Abfalle erforderlich.

french: german: Example 2

Council Directive 18. March 1991 91/156 /EEC ANNEX I Categories of Waste Q 9

english:

Residues from pollution abatement processes (e.g. scrubber sludges, baghouse dust, spent filters, etc.) Residues de procedes antipollution (par exemple boues de lavage de gaz, poussieres de filtres a air, filtres uses etc.) Riickstande von Verfahren zur Bekamphng der Verunreinigung (2.B. Gaswaschschlamm, Lufifilterriickstande, verbrauchte Filter usw.)

french: german: Example 3

Council Directive 18. March 1991 91/156/EEC ANNEX I1 B R4

english: french: german:

Recycling/reclamation of other inorganic materials Recyclage ou recuperation d'autres matieres inorganiques VenvertungRuckgewinnung anderer anorganischer Stoffe

Example 4

Council Directive 18. March 1991 9 1/ 1 56/EEC ANNEX I1 B

english: french: german:

Operations which may lead to recovery Operations Debouchant sur une possibilite de valorisation Venvertungsverfahren

216

From these few examples it is clear that, in spite of the agreement already reached, there is still much detailed work to be done in the fbture to reach an international understanding in the field of products and wastes. In particular, there must be clear scientific and technical conformity in definitions and translations. It is also necessary to make an exact delimitation between the term WASTE and the term PRODUCT. No such a delimitation has yet been made. 8. SUMMARY AND CONCLUSION

The production of FGD gypsum in a FGD plant has been explained in detail in this paper. This shows that FGD gypsum is produced in a FGD plant as a product with specification and quality standards. The operations which may lead to the recovery of FGD gypum are carried out in the FGD plant itself It has therefore been conclusively proved, both technologically and scientifically, that FGD gypsum is a product. Furthermore, it has been shown that, as a product, FGD gypsum is not included in the European Waste Catalogue, is not included in the OECD lists and is not included in the German Waste Catalogue. These regulations are of great importance, particularly for Europe and Germany. At present a about 3 million tonnes of FGD gypsum are being produced annually in Germany and used as a secondary raw material as well as natural gypsum, and there will be more than 6 million tonnedyear in Europe in the near future. If this FGD gypsum used in Europe and Germany were to be defined internationally as WASTE, this valuable product would become "Abfall" (WASTE) when translated into German. However, the label "WASTE" projects a decidedly negative image everywhere, and the future use of FGD gypsum in Europe would be endangered. FGD gypsum is a product which is identical with natural gypsum and therefore useable in the same way. Elimination of the term "WASTE" (Abfall) for FGD gypsum is essential to ensure its future use as a valuable product.

Environmental Aspects of Consmtction with Waste Materials J J J M Goumans, H A . van der SIoot and l3.G. Aalbers (Editors) 91994 Elsevier Science B.V. All rights reserved

217

In-situ Utilization of Waste Bentonite Slurry Noburu Uchiyama and Sumio Horiuchi Underground Engineering Department, Institute of Technology, Shimizu Corporation, 4-17, Etchujima 3-chome, Koto-ku, Tokyo 135, JAPAN

Abstract The increase in waste bentonite slurry, being discharged through substructural constructions, has become a serious problem because of its negative environmental effects and the decrease in the capacity of disposal sites. This paper describes two methods to utilize the waste slurry: in-situ slurry solidification and cast in place slurry-cement material. Therein the effectiveness of sodium carbonate with respect to viscosity decrease of the mixtures, and higher compressive strength of the solidified slurry are confirmed through laboratory tests and field application. Also, the additions of a retarder and a dispersant make long-distance transportation possible by preventing segregation. This procedure will help in the development of low-cost recycling systems involving collection, processing, transport and utilization.

1. INTRODUCTION The increase in waste bentonite slurry, being discharged through substructural constructions, has become a serious problem because of its negative environmental effects and the decrease in the capacity of disposal sites in Japan. The waste slurry, originally bentonite slurry, is important to prevent trench collapse and water leakage for construction of cast in place piles or walls. Although bentonite is originally an inorganic mineral, properties of bentonite slurry is damaged with cement contamination, and is disposed of by reclamation or sea disposal as an industrial waste material. The reasons for the extended use of the slurry method which causes the waste slurry, are that the driven pile methods can not be used in cities because of their noise and vibrations; and substructural constructions in soft ground are increasing rapidly. Waste slurry amounts to 14,000 ton a year in Japan, but only the 10% has been utilized. The utilization of waste slurry is not promoted due to the following reasons : (1) Slurry state makes its transport and treatment difficult, (2) cost of stabilization exceeds the cost of disposal, and (3) supply and demand of slurries are unbalanced. For increase of the waste slurry utilization, two methods are reported in this paper. One is the in-situ slurry solidification .The other is the use for a cast in place slurry-cement material. In-situ slurry solidification is the method that uses bentonite slurry as the main component, and decreases the discharged waste slurry. Fig.1 shows the conventional procedures, Ground is excavated down to a given depth, filling trench with bentonite slurry

218

(Step 1). Steel as a member of the earth retaining wall, is then installed in the trench, and then vinyl chloride tubing is attached to deliver air (Step 2). While air is blown into the trench to mix the slurry, an additive and mortar are thrown in. The materials can be well mixed for 30 minutes of mixing to develop enough strength for the wall (Step 3). As a result of this application, more than 70% of the waste bentonite slurry can be utilized. In the conventional method, the addition of water glass as a solidifying additive makes the mixture excessively viscous during air-blowing. This high viscosity prevents homogeneous mixing, and splashes the mixture during air blowing. Difficulties for the viscosity control have made this method unpopular.

Excavating

(1) Trench excavation

(2) Installation of steel

(3) Air blowing and materials mixing

Fig. 1. Procedures of conventional in-situ slurry solidification

The first approach of this paper is for the alternative additive. In our past research, it was c o n f i e d that the use of sodium carbonate is effective on strength development of cement-soil mixture without viscosity increase. So, the effectiveness of sodium carbonate was examined the laboratory and field tests. The second approach is for improvement of waste slurry. Fig2 schematically shows the circumstances of waste slurry. The mixture of the waste slurry and cement would be usable for filling, however it is difficult to stock the waste slurry in the same construction site. A new idea consists of a treatment center, where the waste slurry is improved for the use as a cast in place slurry-cement material. The key points to be solved are the prevention of material segregation and the retardation of its viscosity increase that allow long-distance and long-time transportation from the center plant; and the variation of the waste slurry gathered from many construction sites. To achieve these, the effectiveness of a retarder and a dispersant to improve waste slurry is also investigated using eight waste slurries from a waste sluny treatment plant. In this paper, new effective usages of the waste slurry are proposed based on the laboratory and field studies.

219

.

Wastes dealer collection treatment

;' Ouestions

Problems system cost balance

legal regulation properties

treatment plant

-

waste slurry's flow at present waste slurry's

-----) flow proposed

Fig.2. Processing and utilization of waste slurry 2. STUDIES ON EFFECTIVENESS OF SODIUM CARBONATE

2.1.

Laboratory tests

2.1.1. Materials In laboratory tests, 300 mesh bentonite from Gunma prefecture in Japan and three kinds of cement were used. For solidifying agents, water glass, a highly viscous liquid, and sodium carbonate, a white powder, were used. 2.1.2. Test procedure To confirm the influence of the mixing methods, a Hobert-type soil-mixer with two stirring speeds and a hand-mixer were used. Bentonite slumes were mixed with water glass or sodium carbonate for 10 minutes. Next, cement paste with a water/cement ratio of 50% was added to the slurry and mixed together for another 10 minutes. Afterwards, the mixtures were poured into molds and cured in 20 degree water. The unconfined compressive strength (qu) was then measured in accordance with ASTM(D2166-91). 2.1.3. Results (1) Effect of mixing methods Tables 1 and 2 show the effects of mixing methods on qu. In the case of water glass, qu of the high speed mixing and the low speed mixing were 65% and 40%, respectively, the hand-mixer. But in the case of sodium carbonate, qu of the low speed mixing was 68% of that made by the hand-mixer. That means, the use of sodium carbonate decreases the influence of mixing method on qu compared to water glass. (2) Strength changes in compositions Table 3 shows the effect of additives on strength development. The results indicate that

220

the amount of sodium carbonate needed is only 1/3-1/4 of water glass to obtain the same qu. Because the qu developed with sodium carbonate is higher than water glass, especially within the first 14 days, the construction of the vicinal block can be started earlier. Table 1. Unconfined compressive strength using three mixing methods : qu (MPa) Bentonite content : 80 kg/m’, High early strength cement : 200 kg/m’, Water glass : 10 kg/m3. Mixing method

1 day

3 days

7 days

14days 21 days 28 days 70days ~

hand-mixer high-speed soil-mixer low-speed soil-mixer

0.11 0.04 0.03

0.21 0.09 0.05

0.45 0.19 0.12

0.83 0.35 0.20

0.87 0.48 0.29

0.99 0.64 0.40

1.24 0.94 0.60

Table 2. Unconfined compressive strength using two mixing methods : qu (MPa) Bentonite content : 80 kg/m3, Ordinary Portland cement : 200 kg/m3, Sodium carbonate : 4 kg/m3. Mixing method

1 day

3 days

7 days

0.06 0.04

0,15 0.07

0.19 0.13

hand-mixer low-speed soil-mixer

14 days 21 days 28 days 70 days 0.27 0.19

0.31 0.16

0.33 0.26

0.39 0.27

Table 3 Unconfined compressive strength of some compositions : qu (MPa) Cement :Portland blast-furnace slag cement Bentonite content : 60 kg/m3 Solidifying materials cement content water glass sodium carbonate (kg/m3) (kg/m3) (kg/m3)

200 200 200

0 0 0

4 10 20

Curing time 7days

0.16 0.25 0.38

14days

28days

0.36 0.49 0.63

0.56 0.66 0.70

22 1

2.2. Field studies of in-situ slurry solidification 2.2.1 Test procedure The new method using sodium carbonate was applied to a retaining and cut-off wall of a subway construction site in Tokyo. This wall was composed of seven blocks, and the total size was 0.6m thick, 18m wide and 38m deep. Strength required for the slurry wall were 0.98MPa in 28-day qu and O.05MPa in 24-hour qu. During the field mixing, powdery sodium carbonate was poured into the trench, followed by mortar addition. Each mixing time was planned for 30 minutes. 2.2.2. Results Table 4 gives the compositions of the materials in all seven blocks along with the original design. From the observation of the material splashing, it was confirmed that viscosity increasing with time was independent of the volumes of the additive or mortar, and viscosity of the new method after 120 minutes mixing was less than that using water glass. Table 4 Compositions of the solidified material Cement : Portland blast-furnace slag cement Block No.

slurry bentonite cement sodium compressive strength (MPa) density content * carbonate curing time (g/cm3)(kg/cm3) (kdm’) (%) 7days 14days 28days 70days _ _ _ _ _ _ _ _ _ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ~ ~ ~ ~ ~ ~ ~ Design

1.06

60

225

5.0

1 2 3 4

1.12 1.07 1.06 1.09 1.07 1.10

91 65 57 48 15 57

225 250 260 312 300 270

5.0 5.0 7.5 7.5 8.5 5.0

5 6

0.98 0.23 0.33 0.31 0.49 0.26 0.66

0.53 0.73 0.57 1.05 0.59 1.31

0.97 1.13 0.85 1.61 0.98 1.78

1.54 1.17 1.28 2.07 1.30 2.28

* measured by methylene blue adsorption. Table 4 also shows the qu of the molded samples of the mixtures. All of them exceed the 28-day requirement. Because of the wide variety of the bentonite contents, it was important to know this value prior to the determination of cement content. In Fig.3, the changes in qu of the No. 1 wall are plotted. As the depth increased, qu increases. The average qu at a 35m depth is approximately 1.8MPa, 140% of that at ground level. The distributions of dry density and water content show simple linearly relationship. Because there was no segregation in the molded samples, the tendencies in Fig.3 appear to result from the consolidation of the materials.

or-

222

........... .,.......................................

- 10 ............ .......... >! ............. p .....j ............ .................... .......... ;...

h

-6g-20

EI;"

@.!

j

............. j ..........

.........

_i

........... _/. ........... ............. (...........

3o

I

.......

-4n 1

.

j I ... ,....... . .~..................

...... ..; ....

.o

2 .o

3.0

Compressive

1.3

1.4

1.5

Wet density (g/cm3)

strength (MPa)

100

110 120 130 140 Water content (70)

Fig.3. Properties of boring specimens

3. STUDIES FOR UTILIZATION THROUGH TREATMENT CENTER

3.1.

Materials Waste slurry samples were periodically taken out from the first reservoir in a waste dealer for more than a year. Almost all waste slurry discharged around the Tokyo area is brought to the center. Three retarders and two dispersants were used in the tests. Table 5 shows the main constituents of the agents. Table 5 Composition of agents symbol retarder (A) retarder (B) retarder (C) dispersant (a) dispersant (b)

main constituents sugar hydrooxycarboxylate phosphate sulfonate+carboxylate carboxylate

3.2. T:st procedure First, the physical and chemical properties of the waste slurry were examined before the mixing tests. Each slurry sample was mixed with 50-150 kg/m3 of Portland blast-furnace slag cement, and the strength development of the hardened mixtures was measured. Retarders and dispersants were added to the waste slurries and then the cement was mixed. The PA flow test with ASTM(C939-87), the bleeding test with ASTM(C940-89) and the q u test were conducted on the mixtures.

223

3.3. Results (1) Properties of waste slurry The properties of the waste slurry samples are given in Table 6. There is a wide variety of water content and slurry density; 330-840% and 1.07-1.17 Vm3, respectively. The bentonite content, which is one of the major factors for cement solidification as speculated from Table 4, is low and varies widely. The most significant problem is the high bleeding ratio. Large part of this bleeding water would be segregated after cement mixing, and it makes the direct utilization difficult. Chemical compositions are given in Table 7. CaO contents, which show the cement contamination in the waste bentonite slurries, are higher than the original bentonite slurry. Table 6 Properties of waste slurry Date slurry of density samples (g/cm’)

‘92.3 ‘92.4 ‘92.5 ‘92.9 ‘92.10 ‘92.11 ‘92.12 ‘93.2

1.175 1.132 1.117 1.170 1.165 1.104 1.108 1.072

specific gravity

water bentonite sand content content * content (kg/m3) (%)

( ~ d

326 429 517 327 335 545 708 838

2.723 2.727 2.748 2.769 2.897

22 23 24 36 37 25 15 17

funnel pH viscosity

bleeding (%)

(set)

28

6.0 6.5 3.5 2.7 1.0

25.4 22.6 22.4 21.8 20.9

8.0 10.0 10.5 10.0 10.5

11 11 22 29

35

* measured by methylene blue adsorption. Table 7 Chemical compositions of waste slurry and bentonite slurry

No.

SiO,

&32’

‘92.10 ‘93.2 Bentonite

50.67 48.06 70.80

14.70 14.61 13.05

CaO

Fe2co3

9.35 10.33 2.49

5.7 1 5.87 1.97

(2) Cement solidification of waste slurry Fig. 4 shows the correlation of the slurry density and after 28-day qu. Using the broken lines, qu can be estimated from the slurry density for each cement content. Strength required for backfilling would be more than 0.2MPa in qu. The waste slurries could, therefore, be utilized with 150 kg/m3 cement addition. The strength of a hardened slurry could be controlled by the cement content.

224

1.05

1.10 1.15 Slurry wet density (g/cm3)

1.20

Fig.4. Relation of slurry density to qu

(3) Effectiveness of agents Table 8 gives the components of mixtures, bleeding ratio and qu. Figs. 5 and 6 show the changes in PA flow with time. Table 8 Compositions of mixtures and compressive strength Cement :Portland blast-furnace slag cement 100 kg/m’ waste slurry

‘92.10 ‘92.10 ‘92.10

dispersant sym. content (%)*l a a a

0.5 0.5 0.5

retarder sym. content (%)*2

A A

1.2 2.4

bleeding (%)

1.5 2.0 2.5

compressive strength (MPa) curing time 7days 14days 28days 70days 0.19 0.06 0.03

0.33 0.15 0.09

0.49 0.24 0.18

0.64 0.33 0.27

.......................................................................................................................................................

‘92.11 ‘92.11 ‘92.11

a a a

0.5 0.5 0.5

A B C

2.4 2.4 2.4

6.0 6.5 5.0

0.07 0.03 0.01

0.14 0.10 0.04

0.25 0.17 0.08

0.29 0.20 0.13

’92.11 ‘92.11 ‘92.11

b b b

0.5 0.5 0.5

A B C

2.4 2.4 2.4

4.5 7.0 3.5

0.07 0.03 0.01

0.15 0.08 0.04

0.24 0.14 0.09

0.29 0.16 0.13

* 1. ratio to slurry volume *2. ratio to cement weight

225 As shown in Fig.5, cement mixture of '92.10sample shows a good fluidity even after 6 hours by using 2.4% retarder and 0.5% dispersant, contrasting to an excessive increase in viscosity after 3 hours of mixing without retarder. The retarder addition resulted 28-day qu decrease to 40% , however it might be easily recovered by cement increase. According to Fig.6, PA flow changes for '92.1 I sample, dispersant(a) is more effective on viscosity than (b) without in the bleeding ratio. It was also found that the appearance of qu is determined by a retarder and is not affected by a dispersant. From the Figs.5 and 6, appropriate use of the additives makes the long-distance transportation possible, and will lead to the increase of the waste slurry utilization. 2

0 . .. ... .

8

0

; . ; . : .. : .. : . . . : . .. . .... .... ... ... . .. . .. .. ..

1

I

I

I

I

I

I

2

3

4

5

6

7

8

Passing time (hours) Waste slurry : '92.10 Dispersant (a) : 0.5%

F i g 5 Effects of retarder addition on PA flow

14

13

p

12

g

11

2

10

+Retarder (C)

h

v

6:

.. ...

OO

. .. .,.. .. ,.

,. .. ..

.

.

.

....

.

...

-

+Retarder(B) uRetarder (C)

....... ........... ......... .. .. .. .... ... ,.

d.. .

... .

,

9

U Retarder (A)

Retarder @) ............................

~

,. .. ..

...

:

.......................

.....

.

;

i......

.

-

..

. . . . .

..

. .

,

..

,

..

,

..

,

..

..

1

2

3

4

5

6

7

Passing time (hours) Waste slurry : '92.11 Dispersant (a) : 0.5%

8

O O

1

2

3

4

5

6

Passing time (hours) Waste slurry : '92.11 Dispersant (b) : 0.5%

Fig.6. Effects of dispersant addition on PA flow

7

8

226

4. CONCLUSIONS The superiority of sodium carbonate as a solidifying additive during slurry solidification was verified with respect to viscosity of the mixture and qu of the solidified materials. The mixture with sodium carbonate was less influenced by mixing methods than that with a conventional additive; furthermore, sodium carbonate of only 1/3-1/4 by volume of a conventional additive, was needed to obtain the same qu value. As for application in the field, material splashing decreased, and handling of the

additive became so easy that the operational environment was improved. Waste sluny gathered from many work sites could be used as back filling materials by mixing 150kg/m3 portland blast-furnace slag cement. Adding a retarder and a dispersant to the mixture at the same time made long transportation of the slurry-cement mixture possible without segregetion of the materials.

REFERENCES 1 SHoriuchi, The effects of additives to the strength of soil-cement, Proc. 13th Japan Nat.

Conf. on soil mechanics and foundation engineering, 1393- 1394, 1978. 2 N.Uchiyama and S.Horiuchi, A new in-situ slurry solidification method using inorganic carbonate, Pro. 47th Ann.Conf. of the Japan society of civil engineers, 986-987, 1992. 3 N.Uchiyama, S.Horiuchi and M.Tuyusaki, A recycling method of waste bentonite slurry, Proc. 28th Japan Nat. Conf. on soil mechanics and foundation engineering, 2599-2600, 1993. 4 N.Uchiyama, SHoriuchi, Y.Nakabayasi and M.Matui, The application of a new in-situ solidification method", Proc. 48th Ann. Conf. of the Japan society of civil engineers, 642-643,1993.

Environmental Aspects of Construction with Waste Materials J.J.J.M. Goumans, H A . van der Slmt and 7’h.G.Aalbers (Editors) 91994 Elsevier Science B, K All rights reserved.

227

The use of M.W.I. fly ash in asphalt for road construction J.B.M. Hudales Vulstof Combinatie Nederland B.V., P.O. Box 259, 2100 AG Heemstede, The Netherlands

Abstract In The Netherlands several years of experience with the application of M.W.I. fly ash in filler for asphalt for road construction have been obtained. This application is accepted, not only from a technical, but also from an environmental point of view. 1. INTRODUCTION In The Netherlands asphalt fillers are produced on the basis of limestone, calciumhydrate and several industrial waste materials like coal fly ash and M.W.I. fly ash. Limestone and calciumhydrate are specifically gained and worked up for the filler industry in an energy devouring process. From the point of view of protection of nature as well as for conservation of precious natural raw materials it is justified and recommendable to make use of secondary raw materials for the production of fillers on a large scale, although the use of primary raw materials will not be excluded completely. Since the early 1980’s efforts have been undertaken to find useful applications of the waste materials like the bottom ash and fly ash. In an overcrowded country like The Netherlands landfill is never a good solution. In the case of the fly ash we now have about ten years of experience with its application as a raw material in filler for road construction. In The Netherlands about 60,000 tons of fly ash were produced as a result of the incineration of municipal waste in 1993. Although this is only a fraction of the amount of bottom ash produced during the same process, it is much harder to find useful applications for it. Until now the only application is in asphalt filler, which consumes about 40 % of the amount of fly ash produced. For the near future a total amount of 150,000 ton of fly ash is foreseen, of which with a lot of effort only 50 % may be reused depending of course on the demand for asphalt.

228

2. TECHNICAL REQUIREMENTS

Filler is an aggregate for asphalt: in fact, it completes the particle size distribution of the gravel and sand fraction and fills up the pore volume between the sand grains. In priciple, chemically inert it is in asphalt, but it has a positive effect on the viscosity of the binder so that demixing of the asphalt mixture is prevented and the asphalt becomes more stable. Many fillers contain hydrate which is added in the form of slaked lime to enhance the attachment between bitumen and aggregate. This is especially needed in drain asphalt, where the bitumen must achieve the cohesion between the coarse aggregate particles at much smaller contact areas than in the case of dense asphalt because of the lack of a part of the sand and fine gravel fraction. All the fillers have to satisfy many technical requirements to be allowed in road construction, for which purpose they are certified. These requirements are listed in Table 1. They have to be tested according to the dutch draft standards Ontwerp NEN 3975 up to and including 3984 which were jointly published in the booklet "S.V.C.; Normen en Proefvoorschriften" in 1992 [I]. The four filler types only differ in their bitumen binding capacity according to which they are nominated, and air void, except for the class 50 filler and the class 50 filler with hydroxide which differ in the obligatory hydroxide content and therefore in the water solubility. Furthermore, two properties have been added to the list in Table 1 to facilitate the determination of a certain filler. These are the particle density which is also needed for the calculation of the air void and the solubility in hydrochloric acid, both of which are included in the range of draft standards listed above. M.W.I. fly ashes are at the moment only applied in the class 40 and 50 fillers only, but investigations are being carried out for application in small amounts in a class 50 filler with hydroxide which is specially developed for drain asphalt. The properties of the M.W.I. fly ash makes it impossible to use it in class 30 filler. These properties which limit the application to 35 % of the filler, differ from one plant to another, but the ashes used fit in very well in cooperation with the other raw materials. For filler production grinding of the fly ash is necessary to meet the final filler requirement for the particle size distribution (Table 1). Mean values of the relevant properties of several M.W.I. fly ashes used by V.C.N.in 1993 are listed in Table 2.

Table 1 Specifications of the dutch filler types Property

Class 30

Unit

min.

Particle size: Remainder on sieve 2 mm 90 pm 63 pm

5

0 15 25

28

38

% (m/m) % (m/m) % (m/m)

Bitumen binding capacity Air void

%

(vm

28

Loss on heating at 150°C

% (m/m)

Solubility in water

% (m/m)

Susceptibility to stripping

% (m/m)

Swelling

% (v/V)

-

Hydroxide content

max.

% (m/m)

Class 40 min.

max.

5

0 15 25

40

50

-

36 1.5 10

10

3

Class 50 min.

10

3

-

max.

5

5

0 15 25

52

62

52

62

44

10

min.

0 15 25

-

1.5

-

max.

Class 50 with hydroxide

-

44

1.5

1.5

-

10

3

-

-

-

25

10

15 10

3

Reprinted from: 2e Ontwerp NEN 3975 [l] N N \o

230

Table 2 Mean values of fly ashes from two arbitrary dutch M.W.I.’s in 1993 Property Particle size: Remainder on sieve

90 pm 63 pm

Unit

M.W.I. 1

M.W.I. 2

% (m/m) % (m/m)

38.7 f 7.3 48.2 f 7.7

44.2 f 10.4 59.7 f 7.1

53.4 f 5.1

52.3 f 2.8

% (V/V) 46.8 f 3.0

50.2 f 3.1

Bitumen binding capacity Air void Particle density

kg/m3 2586

f 34

2620

f 14

Solubility in water

% (m/m)

20.5 f 3.5

16.8 f 1.7

Solubility in hydrochloric acid

% (m/m)

62.6 f 5.8

67.3 f 2.1

3. ENVIRONMENT There are no sanctioned environmental requirements for fillers, as the dutch Building Materials Decree (B.M.D.) has not yet been accepted; a draft of this decree was published in 1991 [2]. It falls under the responsibility of the filler producers to keep an eye on the environmental aspects of the fillers they produce. M.W.I. fly ash falls under the Toxic Waste Law, unless it is for 100 % used as a secondary raw material, as does the filler industry. By order of the Road and Hydraulic Engineering Division of the dutch Ministry of Transport, Public Works and Water Management TAUW Infra Consult investigated the composition and leaching behaviour according to the dutch leaching test NVN 5432, of asphalt tablets produced with standard fillers some of which containing M.W.I. fly ash [3]. Although a clear difference was measured in the chemical composition of the fillers, this difference was found again only in a limited extent in the composition of the asphalt tablets because of the small amounts of filler in asphalt. Tank leaching tests according to NVN 5432 showed no difference in the leaching of metals between the asphalt tablets with the different fillers. No more a difference in leaching was found between asphalt tablets with differing pore structures like dense asphalt concrete, porous asphalt and poro-elastic alphalt concrete. To check if a filler with M.W.I. fly ash satisfies the above mentioned draft decree filler producer V.C.N.had fillers with standard to high contents of M.W.I. fly ash and asphalt tablets containing these fillers investigated by

23 1

the Netherlands Energy Research Foundation E.C.N. [4].This investigation has shown that the composition of the asphaltic concrete falls within the composition limits set by the government in S1 FORM GIVEN BUILDING MATERIALS of the draft B.M.D. These values also fall within the limits of S l NON FORM GIVEN BUILDING MATERIALS, which means that if the asphaltic concrete is ground down after use it cannot be designated as chemical waste. The leachability of brokedweathered asphaltic concrete is at that stage decisive for the additional work-up. The availability of the metals in the product asphaltic concrete in itself agrees reasonably well with or is lower than that of the separate materials used. The decrease is caused by the bitumen which, due to its hydrophobic nature, has an effect on the degree of contact with water. The possibility exists that after ageing (weathering) of the bitumen the availability will increase; this has to be investigated further. The tank leaching test shows that the leaching of the products easily lies within the U1 limit for FORM GIVEN BUILDING MATERIALS of the current draft B.M.D. (Table 3). The composition can be optimized on the basis of other requirements so that no problems are expected here. Critical components are lead, cadmium and zinc. These three, of which lead and cadmium approach U1 within a factor of 3, originate from the M.W.I. fly ash. One has to keep in mind that in case of the lower M.W.I. fly ash contents this material had to be replaced by other components like coal fly ash, which explains the irregularities in Table 3. The slope in the tank leaching test for the elements antimony, vanadium and zinc is quite sharp (0.67), which may indicate solubilisation. This solubilisation effect is clearly different from the diffusion behaviour of the other elements. On the basis of these results a calculation has been performed on a theoretical filler with 35 % of M.W.I. fly ash, which is considered to be the technical limit. This calculation showed that no problems are to be expected for such a filler according to the draft B.M.D. regarding composition (FORM GIVEN and NON FORM GIVEN BUILDING MATERIALS) and leaching behaviour .

232

Table 3 Measured cumulative release after 64 days mg/m2

M.W.I. fly ash content in filler (% m/m) 5 7.5 10 20

Metals 578 Sodium < 1.1 Copper 24 Zinc Molybdenum < 0.13 Cadmium < 0.16 Tin Antimony < 0.06 25 Lead Inorganic compounds Cyanide Fluoride Chloride 497 Bromide Sulphate 1105 Reprinted from [4]

788 < 1.1 24 0.27

8) was preserved. 4.3 Dependency of S, and SRon concentration level and type of material

Before a final result of the precision parameters can be calculated, a possible dependency of the type of material and/or concentration level on the result has to be determined. In Figure 3 the precision is plotted as a function of the concentration level. Figure 3 shows generally higher

312 60 50 --

-

s

40

-

~~

Y

0

0

E

30 - -

4oj

20

Na --

.I I cu

Na

1

AWH MCBA A AVSH x VACS

I

x KZFH 0

CU

TAS '

T

Ba

T

100

10

I

KBAA

1000

10000

Concentration level (relative to DTL) Figure 3. Relation between precision parameters S, and SRand concentration level S, and SK values at low concentration levels. This effect should be eliminated after the correction of the variance of the chemical analysis (see section 4.1) if it is caused by the analysis. To examine this effect further, the same type of graph is shown in Figure 4 for two elements that have been measured in more than one material, Na and Sod. The precision is expressed as a percentage of the availability and also as an absolute value in mg/kg. Plotted this way it, becomes clear that the standard deviation of the r and R values, expressed in mg/kg, apparently 50 SO4

40 h

m

i

Y

g, 30

I

C

e

4

20 a

vi 10

0 1

10 100 1000 10000 Concentration level (relative to DTL)

1

10 100 1000 10000 Concentration level (relative to DTL)

Figure 4. Relation between precision expressed as percentage (left) and as mgkg (right) and the concentration level for Na and SO4.

313 25 1

25

I -g 20

15

cn"

10 5

0 AWH

MCBA AVSH

VACS

KZFH

Materials

KBAA

A W H MCBA AVSH

VACS

KZFH

KBAA

Materials

Figure 5 The precision, S, and SR,as a function of the type of material cannot decrease further with decreasing concentration at low concentration levels, and therefore approaches a constant value. This results in an increase of the precision parameters at low concentrations when expressed as a percentage of the availability. Taking into account the above, Figure 4 also show that for Na and SO., no significant influence exists of the type of material on the precision values. This is further illustrated by Figure 5 , in which the mean values of S, and SR of all elements for each material are shown. The only material for which possibly some higher values are found is KBAA. However, the number of elements (As and V) for this material to support this difference is rather small. 4.4 Mean values of the precision

It can be deduced from the above that the precision can be obtained by calculation of the average of the data in Table 5. Only the data for the elements marked with * are not used in the final calculation of de mean S, en SRfor the following reasons: - Low concentration levels for Na in the samples MCBA en KBAA (6-8 times DTL) - Cu en Pb inhomogeneity in sample AVSH - Low concentration levels of Cu in sample VACS These values correspond with the higher values at a low concentration level shown in Figure 3, except for Cu in AVSH. The resulting mean values for the repeatability S, and the reproducibility SR,corrected for the chemical analysis variances, are respectively: S, = 5.2% S, = 8.6%

5. CONCLUSIONS

The precision of the standard leaching tests can be determined by the method in NEN-IS0 5725. For the availability test (NEN 7341) it was shown that a mean value of the S, and SR parameters can be used, independent of the type of material tested. Also, the influence of the different elements on the precision parameters is rather small when the concentration level is

314 higher than about 20 times the detection limit. Therefore, the reported mean S, and SR values can be regarded valid for all measured elements. It cannot be excluded however, that some other elements have a different precision. The same procedure used for the availability test will also be used for the validation of the other 3 Dutch standard leaching tests. 6. ACKNOWLEDGEMENT This work is hnded by the Netherlands agency for energy and environment (NOVEM) and the Netherlands Ministry of Public Health, Physical Planning and Environment (VROM) 7. REFERENCES 1. NEN 7340. Leaching characteristics ofbuilding and solid waste materials - Leaching tests General Instruction. Draft 1993; Netherlands Normalisation Institute; the Netherlands 2 . NEN 7341. Leaching characteristics of building and solid waste materials - Leaching tests Determination of the availability of inorganic components for leaching. Draft 1993 (previously part of NVN 2508); Netherlands Normalisation Institute; the Netherlands 3. NEN 7343. Leaching characteristics of building and solid waste materials - Leaching tests Determination of the leaching of inorganic components from granular materials with the column test. Draft 1993 (previously part of NVN 2508); Netherlands Normalisation Institute; the Netherlands 4. NEN 7345. Leaching characteristics of building and solid waste materials - Leaching tests Determination of the leaching behaviour of inorganic components from building materials, monolithic waste and stabilised waste materials. Draft 1993 (previously draft NVN 5432); Netherlands Normalisation Institute; the Netherlands 5. NEN 7349. Leaching characteristics ofbuilding and solid waste materials - Leaching tests Determination of the leaching of inorganic components from granular materials with the cascade test. Draft 1993 (previously part of NVN 2508); Netherlands Normalisation Institute; the Netherlands 6. NEN-IS0 5725. Accuracy (trueness and precision) of measurements methods and results Part 2: A basic method for the determination of repeatability and reproducibility of a standard measurement method. Draft 1990. 7. A N S . 16.1. Measurements of the leachability of solidified low-level radioactive wastes by a short-term test procedure. American Nuclear Society, Illinois 60525 USA.

Environmental Aspects of Consmetion with Waste Materials 1JJ.M. Goumans, H A . vm der S l w t and 771.G.Aalbers (Editors) @I994 Elsevier Science B. T*: All rights reserved.

315

The Laconia, New Hampshire Bottom Ash Paving Project C. N. Musselman('), M. P.KiUeen('), D. Crimi0, S. H a d 3 ) , X. Zhang"), D. L. Gress"), and T. T. Eighmf3)

(')CMA Engineers, Portsmouth, NH, 03801, USA (*)WheelabratorEnvironmental Systems, Hampton, NH, 03842, USA (3)EnvironmentalResearch Group, University of New Hampshire, Durham, NH, 03824, USA

SUMMARY In May, 1993, a 600 meter section of US Route 3, a two lane secondary highway in Laconia, NH,was reconstructed utilizing screened and aged grate ash as a 50% aggregate substitute in base course asphalt paving. A two year monitoring program is underway to assess potential surface water and groundwater quality impacts and the physical performance of the roadway. This paper reports on bottom ash asphalt mix formulations, asphalt plant operating challenges and air testing results, the apparent effect of excluding siftings on bottom ash total composition, and the effect of ash aging on total availability leaching. The initial results of monolith leaching tests designed to further the understanding of fundamental leaching behavior are also reported.

1.0 INTRODUCTION

In the late 1970's and early 1980's, a number of demonstrations were undertaken in the United States to assess the feasibility of utilizing municipal solid waste combustion bottom ash as an aggregate substitute in asphalt paving applications. While those demonstrations were largely successful from a physical performance standpoint, progress in furthering ash utilization in the United States has been hindered by regulatory uncertainty and, in some cases, local controversy. Research and demonstration efforts are now again proceeding and are focusing mostly on utilization techniques which entail encapsulation of the bottom ash in asphalt paving or concrete construction materials. In May, 1993, a 600 meter section of US Route 3 in the City of Laconia, New Hampshire was reconstructed using, in part, grate ash aggregate in a binder course asphalt pavement(1). US Route 3 in this area is a two lane secondary roadway having an average daily traffic which varies seasonally from about 5,000 to 20,000 vehicles per day. Of the 600 m of reconstruction, 350 m was reconstructed as a control section using natural aggregate both in the 5 cm binder course and the 2.5 cm wearing course. The 260 m test section was constructed using a 50% bottom ash/50% natural aggregate blend in the 5 cm binder course pavement. A 2.5 cm wearing surface of 100% natural aggregate was applied over the bottom ash asphalt binder course such that, in this demonstration, the bottom ash asphalt is not exposed to traffic or the environment.

316

317

A plan view of this section of US Route 3 is presented as Figure 1, showing the test demonstration and control sections(2). The binder course pavement for the first 30 m on either side of the transition point between the two pavements was constructed to a 10 cm depth to allow the installation of strain gauges; moisture, resistance and temperature probes; and traffic counters. The wearing course remained at a 2.5 cm thickness through this 60 m transition section. The land use in the control section is commercial, including a resort/conference center, several smaller motels, a restaurant, and retail businesses. In the test section, abutting properties were largely undeveloped. Paugus Bay, a part of the Lake Winnipesaukee system, is in close proximity to the test section. Over a two year research period, the demonstration roadway, including the control and test sections, are being monitored through comprehensive sampling and analysis of both upgradient and downgradient groundwater monitoring wells on each of the roadway sections. Also indicated on the plan are the locations of surface water monitoring stations, roadway runoff collection manholes, and suction lysimeters which were installed 1.5 to 3 meters beneath the pavement surface. These are also included in the comprehensive sampling program. A cross section of the test section pavement is presented as Figure 2. This figure shows the bottom ash binder course with the natural aggregate wearing course above. Below the bottom ash asphalt is a layer of about 8 cm of recycled asphalt consisting of recompacted "cold planings" from the original asphalt surface. The bottom ash asphalt is thus surrounded by relatively impervious natural aggregate materials above and below. The roadway construction entailed utilization of conventional asphalt paving and compaction equipment and procedures. The bottom ash asphalt compacted well to specified densities with some additional non-vibratory compactive effort, and the pavement has performed well through nine months of use. I , , . ,, . 5 l l O cm binder'bourse (507: Grate Ashy I

//

I

0.6-1 2

m

'u -

I 1.5.3

m

I Fiaure 2

-

Pavement Cross Section

318

The environmental and physical performance monitoring data is in the process of being gathered and evaluated and is intended to be reported in future papers. The following sections provide a description of a variety of environmental and civil engineering topics which may be of interest both to those planning further demonstrations and full scale utilization of bottom ash in asphalt paving and to those involved in research in fundamental leaching behavior of encapsulated materials used in construction.

2. BOlTOM ASH ASPHALT MIX FORMULATION Initial efforts to formulate an effective bottom ash asphalt mix design were based on conventional Marshall mix testing procedures. The top line in the graph in Figure 3 presents the relationship between percent bottom ash and optimum percent asphalt content based on the Marshall test procedures(3). Based on these test results, a mix of bottom ash with 9% asphalt cement was manufactured, and a test patch was paved within the footprint of the lined landfill in Franklin, NH. The resultant mix flowed easily and would probably have exhibited rutting failure. Following the first test patch paving experience, additional laboratory work was undertaken utilizing gyratory test methods (GTM), a process which essentially kneads the sample rather than impacting it as in the Marshall mix test. The resulting mix designs using the GTM test were dramatically different, predicting a 7 percent optimum asphalt cement content for a 50% bottom ash/50% natural aggregate blend. A second test paving was completed successfully with this blend, and the same mix was subsequently used in the reconstruction of US Route 3. I

I

% BOTTOM ASH

Fiaure 3 - Optimum Asphalt Content

319

Figure 3 indicates that the optimum asphalt content is about 5 percent for these aggregates when 100% natural aggregate is utilized, using either the Marshall or GTM methods. The two percent additional asphalt required when utilizing a 50% bottom ash blend represents that portion of the asphalt cement which is absorbed by the bottom ash particles. As indicated in Figure 3, asphalt blends with decreased bottom ash percentages would reasonably be expected to require less additional asphalt cement. The additional asphalt cement required is an economic factor which will need to be considered in full scale applications, to be offset by the savings represented by the use of bottom ash aggregate and the costs of bottom ash storage and handling. The use of additional asphalt cement has an environmental benefit in that there is greater assurance that internal pores and vesicles in the ash aggregate are coated with asphalt.

3. ASPHALT PLANT OPERATING CHALLENGES

Although the roadway construction itself presented no significant challenges, the operation of the asphalt plant did present challenges during the manufacture of bottom ash asphalt. The asphalt plant utilized was equipped with a rotating cylindrical drum dryer for drying the aggregate and an air pollution control system consisting of a fabric filter/baghouse. The plant is normally operated at a rate of about 180,000 k g h . During the manufacture of the grate ash asphalt, the plant throughput rate was decreased to 127,000 kg/hr because of the relatively high moisture content in the ash. This helped to avoid extinguishing the flame of the No. 6 fuel oil fired gun used to dry the aggregate. The aged grate ash, after five months of aging, was determined to have a moisture content of 23 percent while the natural aggregate had a moisture content of two percent. The paving demonstration was completed in early spring when the bottom ash moisture content was near its highest level due to spring snowmelt and rainfall conditions. Using a bottom ash asphalt blend of less than 50%, and/or utilizing bottom ash at a lesser moisture content, would allow the asphalt plant to operate at, or close to, its normal operating capacity. The second operating challenge experienced at the asphalt plant pertained to the generation and transport of fines in the aggregate drum dryer. The fines transport system at this asphalt plant was found to be an operating constraint due to the quantity and light weight of the fines produced during ash aggregate drying in comparison to normal natural aggregate operating experiences. A vacuum truck was required to be connected to the plant’s ductwork to periodically withdraw fines. The mix manufactured for the demonstration had about 6% passing the #200 sieve, which was acceptable for the binder course paving. It should be noted that the additional fines did not result in significant increases in particulate air emissions as described below. The fines generated can be reduced in future work by decreasing the bottom ash percentage to a level which does not create material handling constraints, if required. Stack testing was completed at the asphalt plant during the manufacture of both natural and bottom ash aggregate asphalt. The results are presented in Table 4(4).

320

The length of the sampling runs were limited to the amount of time required to manufacture the needed quantity of ash asphalt, and therefore were shorter than the three 90 minute replications which might otherwise be desired for a full air test. The observed opacity was within specified New Hampshire standards for asphalt plants. Particulate levels were somewhat higher when bottom ash asphalt was being processed, but the particulate concentrations for both bottom ash and natural aggregate were within the New Hampshire asphalt plant standard of 91.8 mg/Rm3. The facility was capable of controlling particulate air emissions despite the build-up of fines on the plant side of the baghouse. Emissions tests for multiple metals showed all metals at low levels regardless of aggregate source. Six metals were slightly higher for the natural aggregate runs (cadmium, lead, arsenic, mercury, chromium, and nickel) and four were slightly higher for the bottom ash aggregate runs (beryllium, copper, selenium, and zinc).

-

Table 1 Asphalt Plant Air Testing Results

Number of Sampling Runs Length of Sampling Runs (Minutes) Opacity (NHStandard: 12; Figs. 4 and 5) or, possibly, ettringite (Figs. 4 and 5 ) . Mullite may be important at neutral pH, but only when there is no iron oxide at the fly ash surface (Figs. 4 and 5 ) . 100

-$

-4-

-

g

-E

50

-e

-+

0

2

4

6 8 10 12 14

PH Fig. 4: Sorption of As on different matrix minerals as a function of pH.

2

4

6 8 10 12 14

PH Fig. 5: Sorption of Se on different matrix minerals as a function of pH.

473

It was shown above that sorption on iron oxide is important in controlling the leaching of As and Se. In a subsequent study [41] an attempt was made to model this process in the fly ash. Leaching experiments were followed by selective extractions of iron oxides from the leached fly ash, in order to obtain model parameters. Both a crystalline and an amorphous iron oxide extraction were performed, because only crystalline iron oxides (hematite and magnetite) are present in dry unweathered fly ash, while amorphous iron oxide can arise as a secondary precipitate during leaching of the fly ash [lo]. Amorphous iron oxide proved to be more important than crystalline iron in controlling the leaching of As and Se [41]. A simplified surface complexation model [41] was applied to the leaching and extraction data (Figs. 6 and 7). In Figs. 6 and 7 it is shown that it is possible to describe the leaching of As and Se (pH c 10) from acidic fly ash by using a simplified surface complexation model for the sorption on amorphous iron oxide. Se leaching above pH 10 is probably controlled by another (still unknown) mineral [41]. 7

0 0

a

6

2 0

0 -

5 4

3 2

4

6

8

10 12

14

PH

Fig. 6: Apparent overall equilibrium constant (KA) of As during leaching of fly ash (0) and of As model experiments ([37, 381 lines 1,2 and 3) on amorphous iron oxide.

2

4

6

8

10

12

14

PH

Fig. 7: Apperant overall equilibrium constant (K,) of Se during leaching of fly ash (0) and of Se model experiments ([38,42] lines 1.2 and 3) on amorphous iron oxide.

As the reversibility of the sorption processes is important for the actual release, we also studied the reversibility of the sorption processes of arsenate and selenite on the different minerals. There is a difference between the sorption of arsenate and selenite on mullite, portlandite and hematite [40,43] in that arsenate sorption was in general less reversible, especially on hematite (Fig. 8). This may explain the lower availability of As relative to Se leaching.

5. Conclusions The leaching of As and Se from coal fly ash can be described by sorption processes. In this study we have identified a number of relevant sorption reactions. We found that

474

E'

arsenate and selenite are the most important redox species in fly ash leachates. The leaching of arsenate and selenite from alkaline fly ash is likely to be controlled by sorption on a Ca-phase. Possible sorbents are portlandite and/or ettringite. The leaching 0 8 .S 0 40 from acidic fly ash is controlled by sorption 0 0 P on iron oxide. Selective extractions have f P 20 . shown that amorphous iron oxide is the most important sorbent during leaching of acidic 0 fly ash. It is possible to model the leaching of 0 10 20 30 As and Se from acidic fly ash using a time (days) simplified surface complexation reaction for Fig. 8: Desorption of As and Se from amorphous iron oxide. It is important to know hematite at pH 12 o.3. Prior to the reversibility of the sorption reactions in desorption, As and Se were adsorbed for order to be able to quantify the actual release weeks at the pH values indicated in the Of these oxyanions from fly ash. The sorption reversibility of arsenate on the studied legend. sorbents is different from that of selenite. Especially on iron oxide, arsenate is sorbed much less reversibly. This property can explain the lower availability of As relative to Se, for leaching from fly ash. The results of this study can be used to reveal also the leaching behaviour from other combustion residues, because of the fundamental approach and the systematic leaching behaviour of combustion residues in general.

T

loo

L

6. References 1. Carlson, C.L. and Adriano D.C. (1993) Environmental impacts of coal combustion residues. J. Environ. Qual. 22, 227-247. 2. Theis, T.L. and Gamer, K.H. (1990) Environmental assessment of ash disposal, C.R.C. Crii. Rev. Environ. Conirol. 20, 21-24

3. van der Sloot, H.A. (1988) Leaching procedures for waste materials and waste products. Hazardous Waste: Deieciion conirol, Treatment, (Ed) Abbou, R., Elsevier Science Publishers B.V., Amsterdam, 637-649. 4. Eary, L.E., Rai, D., Mattigod, S.V. and Ainsworth C.C.(1990) Geochemical factors controlling the mobilization of inorganic constituents from fossil fuel combustion residues: 11. Review of the minor elements. J . Environ. Qual. 19, 202-214. 5. de Groot, G.J., Wijkstra, J., Hoede, D. and van der Sloot, H.A.(1989) Leaching characteristics of selected elements from coal fly ash as a function of acidity of the contact solution and the liquidsolid ratio. In Environmental aspects of stabilization and solidiJicaiion of hazardous and radioactive wastes (eds. P.L. CBtC and T.M. Gilliam) ASTM STP 1033 pp. 170-183, American Society for Testing and Materials, Philadelphia. 6. van der Sloot, H.A. (1991) Systematic leaching behaviour of trace elements from construction materials and waste materials. In Wasre materials in construciion, Proceedings

of ihe iniernaiional conference

on

environmenial implicaiions of

475 construction with waste materials, Maastricht (eds) Goumans, J.J.J.M., van der Sloot,

H.A., Aalbers, Th, G. Elsevier, Amsterdam, 19-37 Comans, R.N.J., van der Sloot, H.A., Hoede, D. and Bonouvrie, P.A. (1991) Chemical processes at a redox/pH interface arising from the use of steel slag in the aquatic environment. In Waste materials in construction, Proceedings of the international conference on environmental implications of construction with waste materials,

Maastricht (eds) Goumans, J.J.J.M., van der Sloot, H.A., Aalbers, Th, G. Elsevier, Amsterdam, 243-255 Schramke, J.A.( 1992) Neutralization of alkaline coal fly ash leachates by C02(g) Applied Geochem. 7 , 481 -492. Sakata, M. (1987) Movement and neutralisation of alkaline leachate at coal ash disposal sites, Environ. Sci Technol. 21, 771-777. 10. Warren, C.J. and Dudas, M.J. (1984) Weathering Processes in relation to leachate properties of alkaline fly ash , J. Environ. Qual. 13, 530-538. 1 I . Zevenbergen, C., Bradly, J.P. Van der Wood, T., Brown, R.S., Van Reeuwijk, L.P., and Schuiling R.D. (1993) Weathering as a process to control the release of toxic constituents from MSW bottem ash. In Geology and Confinment of toxic waste, Proc. of the Int. Symp. Geoconfine '93, Montpellier, France, 591 -595. 12. Warren, C.J. and Dudas, M.J.(1985) Formation of secondary minerals in artificially weathered fly ash. 1. Environ. Qual. 14, 405-410. 13. Fruchter, J.S., Rai, D. and Zachara, J.M.( 1990) Identification of solubility-controlling solid phases in a large fly ash field lysimeter. Environ. Sci. Technol. 24, 1173-1179. 14. Comans R.N.J., van der Sloot, H.A., and Bonouvrie, P.A. (1993) Geochemical reactions controlling the solubility of major and trace elements during the leaching of municipal solid waste incinerator residues. In VIP-32 Municipal Waste Combustion Proceedings of an international specialty conference, Williamsburg, Virginia, 667-680. 15. Salomons, W. and Forstner, U.: Metals in the hydrocycle. Berlin, Springer verlag, ( I 984). 16. Belzile, N. and Tessier, A.( 1990) Interactions between arsenic and iron oxyhydroxides in lacustrine sediments. Geochim. Cosmochim. Acta 54, 103-109. 17. Manz, O.E., Faber, J.H., Takagati, H. (1989) Worldwide production of fly ash and utilization in concrete. In third CanmetlACI international conference on j i y ash, silica fume, slag & natural pozzolans in concrete, supplementary papers, Trondheim. 18. Mattigod, S.V., Rai, D., Eary, L.E. and Ainsworth C.C.(1990) Geochemical factors controlling the mobilization of inorganic constituents from fossil fuel combustion residues: I. Review of the mayor elements. J. Environ. Qual. 19, 188-201. 19. van der Sloot, H.A., Weyers, E.G., Hoede, D., Wijkstra, J. (1985) Physical and chemical characterization of pulverized-coal ash with respect to cement-based applications, ECN-I 78, Netherlands Energy Research Foundation, Petten. 20. Natusch, D.F.S. and Taylor, D.R.(1980) Environmental effects of western coal combustion. Part IV. Chemical and physical characteristics of coal fly ash. U.S. Environmental Protection Agency Rept. EPA 60013-80-094. 21. Helmuth, R. (1987) Fly ash in cement and concrete, Portland Cement association, Skokie, Illinois. 22. Tauber, C ( 1 987) Spurenelementen in flugaschen: Kohle-Kraftwerk-Umwelt, Verlag TUV Reinland.

416 23. Personal Communication R. Meij, KEMA, Arnhem, The Netherlands. 24. van der Sloot, H.A., Zonderhuis, J. and Meij, R. (1983) Spoorelementen in steenkool en steenkoolas. Energiespectrum 7 , 3 18-325. 25. McCarty, G.J., Manz, O.E., Johansen, D.M. and Steinwand, S.J. (1988) X-Ray Diffraction Analysis of fly ash. In Advances in X-ray Analysis. 31 (eds) Barrett, C.S., Gilfrich, R.J., Russ, J.C., Richardson, Jr, J.W. and Predecki, P.K. Plenum Publishing Corporation, 331 -342. 26. Meij, R. (1989) Tracking trace elements at a coal-fired plant equipped with a wet fluegas desulphurisation facility. Kema Scientific & Technical Reports 7 ,267-339. 27. Dudas, M.J. and Warren, C.J.(1987) Submicroscopic model of fly ash particles. Geoderma 40, 101-1 14. 28. Buffle, J. (1988) Complexation reactions in aquatic systems: An analytical approach, Ellis Horwood Limited. Chichester, England. Joint group of 29. Gesamp ( 1 986) (IMO/FAO/UNESCO/WMO/WHO/IAEA/UN/UNEP experts on the scientific aspects of marine pollution) Review of potentially harmful substances- arsenic, mercury and selenium, Rep. Stud. GESAMP 28. 30. Cutter, G.A. (1992) Kinetic control on metalloid speciation in seawater. Marine Chem. 40, 65-80. 31. Parfitt, R.L.(1978) Anion adsorption by soils and soil materials. Adv. Agron 30, 1-50. 32. Maher, W.A. (1984) Mode of occurrence and speciation of arsenic in some pelagic and estuarine sediments. Chemical Geology, 47, 333-345. 33. Neal, R.H., Sposito, G., Holtclav., K.M. and Trana, S.J. (1987) Selenite adsorption on alluvial soils: I. Soil composition and pH effects. Soil Sci. SOC.Am. J . 51, 1161-1 165 34. Goldberg, S., and Glaubig, R.A.(1988a) Anion sorption on a calcareous, montmorillonitic soil-selenium. Soil. Sci. SOC.Am. J . 52, 954-958. 35. Goldberg, S., and Glaubig, R.A.(1988b) Anion sorption on a calcareous, montmorillonitic soil-arsenic. Soil. Sci. SOC.Am. J . 52, 1297-1300. 36. Masscheleyn, P.H., Delaune, R.D. and Patrick, Jr, W.H. (1991) Arsenic and selenium chemistry as affected by sediment redox potential and pH. J. Environ. Qual. 20, 522527. 37. Pierce, M.L. and Moore, C.B.(1982) Adsorption of arsenite and arsenate on amorphous iron hydroxide. Water Res. 16, 1247-1253. 38. Hayes, K.M., Papelins, C. and Leckie, 5.0.(1987) Modeling ionic strength effects on anion adsorption at hydrous oxide/solution interfaces. J . Colloid Interface Sci. 125, 7 17-726. 39. van der Hoek, E.E., van Elteren, J.T. and Comans, R.N.J. (to be published) Determination of As, Sb, and Se species during leaching from fly ash. 40. van der Hoek, E.E., Bonouvrie, P.A. and Comans, R.N.J. (submitted) Sorption of As and Se on mineral components of fly ash: relevance for leaching processes. 41. van der Hoek, E.E. and Comans, R.N.J. (submitted) Sorption of As and Se on iron oxide in acidic fly ash as a model for the leaching process. 42. Balistrieri, L.S. and Chao, T.T. (1990) Adsorption of Selenium by amorphous iron oxyhydroxide and manganse dioxide. Geochim. Cosmochim. Acta 54, 739-75 1 43. van der Hoek, E.E., Boots, B. J. and Comans, R.N.J. (to be published) Sorption reversibility of arsenate, selenite and molybdate on hematite and amorphous iron (hydr)oxide.

Environmental Aspects of Construction with Waste Materials J.J.J.M. Goumans, H A . van der SIoot and Th.G. Aalbers (Editors) 01994 Elsevier Science B.V: All rights resewed.

411

Measurement of redox potential during standardized column tests J. Keijzer and A.J. Orbons IWACO B.V., P.O. Box 8520, 3009 AM ROTTERDAM, The Netherlands

Abstract A method for continuous measurement of the Eh during the column test as described in the Dutch standard NEN 7343 has been developed. This method has been used on a variety of waste materials such as MSW bottom ash and fly ash, phosphorous slag, lavalite and various kinds of (contaminated) soil. The reproducibility of the method was satisfactory (* 50 mV). The observed redox changes during the column test give an indication of the redox capacity of waste materials and provide important information about (microbiologically mediated) leaching processes within the column. By taking into account redox potential this column test method enables a more accurate prediction of the actual leaching behaviour of reducing waste materials in field situations. 1. INTRODUCTION

The first Dutch standard describing leaching tests N V N 2508 [l] does not take into account the redox potential. Nowadays it is widely accepted that redox behaviour is an important factor influencing leaching of contaminants from waste materials [3, 41. The importance of measuring the redox potential is also recognized in the column test described by the recently published Dutch standard NEN 7343 [2]. However, a method to determine this parameter is not described in this document. The experimental setting for this column test is a waterlogged system, in which the uptake of atmospheric O2 (and COJ by the material is very limited. Therefore, if reducing materials are placed in the column, they may impose reducing conditions on the system, depending on their actual reducing capacities. This paper reports on monitoring data with respect to the redox behaviour during the column test leaching of different waste materials and soils, using a newly developed continuous method for measuring redox potential. Redox potential in waste material environments is largely a function of only a limited number of redox reactions. The most common reactions are those of nitrates, manganese (IV 11), iron (111 < - > 11) and sulphates [ 5 ] . The redox conditions during column test leaching are controlled by the actual redox capacity of the sample being investigated. Decay (oxidation) of organic matter and microbiological activity are also factors influencing this parameter, and subsequently redox potential [6]. The redox potential in leachate samples can change very fast when exposed to air [3]. For this reason it is necessary to

478 measure redox potential in-situ in order to get a reliable description of redox changes occurring in the column. In the method newly developed the redox potential of the leachate is measured directly after leaving the column, without being exposed to air. 2. EXPERIMENTAL

All column tests were performed on a variety of waste materials using the apparatus shown in figure 1. In accordance with NEN 7343 demineralized water acidified with HNO, was used as influent. The oxidant NO< might have some influence on materials with low reducing capacity. With the continuous flow applied L/S=10 was reached after three weeks. Contact of the sample with atmospheric air is virtually absent under these circumstances, and the material investigated will control the value of the redox potential in the column. A flowcell (k 3 ml; zero headspace) with a built-in electrode was placed directly after the column (length 3060 cm, internal diameter 5 cm). Redox potential of the leachate was continuously measured with a platinum electrode to a calomel electrode (+244 mV vs. S.H.E.). Data were recorded digitally. Electrodes were validated using a buffer solution containing 0.1 M (NH,),Fe(SO,), and 0.1 M (NH,)Fe(SO,), in 0.1 N H2S04 (Eh +430 Figure 1: Apparatus used for mV) to correct for drift, caused mainly by leaching and redox test measurements sulphide uptake of the platinum surface [7]. 3. RESULTS The reproducibility of the experimental procedure proved to be satisfactory. Variations between duplicate measurements on waste materials were limited to 50 mV (in ranges +/100-300 mV). The redox potential of waste materials measured during the column test was reasonably constant. In most cases variations did not exceed 100 mV over the time period of three weeks. In figure 2 the variation of the Eh during the column test for four waste materials is given as an example. In figure 3, Eh/pH positions measured during the column test for these waste materials are shown. Figure 4 shows Eh/pH positions for four types of soils. The variation in redox potential during the column test was substantially larger, as shown in figure 5.

479

A

B

-E

c

9Qo-

D

300

100 -100 3 9w-

Figure 2. Redox potentials measured during column tests of demolition waste (A), phosphorous slag (B), MSW fly ash (C) and MSW bottom ash (D)

Figure 3. Eh/pH positions measured during column test leaching of waste materials. The solid line represents the redox potential as function of pH in demiwater.

480

"

-m400-

Figure 4. Eh/pH positions measured during column test leaching of four types of soils. The solid line represents the redox potential as function of pH in demiwater.

Figure 5. Redox potentials measured during column tests on different soils with 5.9 wt% (A), 7.5 wt% (B), 7.0 wt% ( C ) and 4.1 wt% organic matter (D)

48 1

Figure 6. Eh measured during elongated column tests on phosphorous slag (A), MSW fly ash (B) and MSW bottom ash (C)

5. CONCLUSIONS Using a continuous method to measure Eh during the column test, different waste materials investigated could be categorized as creating either a stable negative redox potential (reducing) or a positive redox potential in the column. Eh during the column test (L/S 10, 3 weeks) was fairly stable with these wastes (k 100 mV). Four soils investigated were harder to categorize. Reducing capacity in soils is associated with organic matter, and the soil sample used in this study containing less than 2.5% organic matter showed virtually no reducing capacity. The variations in Eh during column tests on soils were larger than for the (inorganic) waste materials. The results reported can help to understand leaching processes in the column, and may provide an extra tool to extrapolate laboratory results to actual leaching in field situations. 6. REFERENCES

1 NVN 2508. Dutch Standardization Institute NNI, 1988. 2 NEN 7343. Dutch Standardization Institute NNI, 1993, 3 H.A. van der Sloot, D. Hoede and P. Bonouvrie. Invloed van redoxcondities op het uitlooggedrag van reststoffen. Taakstellend Plan Uitloging, Activiteit V6, ECN, Petten 1993. 4 C. Amrhein, P.A. Mosher and D.A. Brown. Soil Science Vo1.155, No.4, April 1993, pp. 249-255. 5 D.J. Greenland and M.H. Hayes. The chemistry of soil processes. Wiley & Sons, New York 1981. 6 C. Zevenbergen, W.F. Hoppe. Leaching tests and the influence of oxidation-reduction processes. In: Waste materials in construction, J.J.J. M. Goumans, H.A. van der Sloot and Th.G. Aalbers Eds., Elsevier, Amsterdam 1991, pp. 369-370 7 T.S. Light. Anal. Chem. 44, 1972, pp. 1038-1039. 8 R. Bartlett and B. James. Soil SCi. SOC.Am. J. 44, 1980, pp. 721-724.

482 4. DISCUSSION

From figure 3 it appears that the waste materials investigated can be divided in two different categories according to their redox behaviour in the column. Phosphorous slag, MSW bottom ash, MSW fly ash and to a lesser extent coal fly ash create (slightly) reducing conditions during the experiment, indicating that these materials have enough reducing capacity to create a negative redox potential in the column. This is in accordance with the findings of van der Sloot et a1.[3] about the reducing capacities of these materials. Lavalite, demolition waste, asphalt and blaster grit show a distinctly higher Eh. All waste materials showed a reasonably constant Eh (* 100 mV) during the column test. In order to investigate the duration of this Eh stability column tests were elongated up to 4 months (L/S=50). Figure 6 shows the Eh measured during elongated tests on phosphorous slag, MSW bottom ash and MSW fly ash, wastes with a relatively strong reducing capacity. All wastes show the same type of curve: Eh slowly rises from negative values (reducing conditions) to values of 0 to +50 mV, while pH slightly falls. Apparently the actual reducing capacity of the wastes diminishes in time. This can be explained by the leaching of the available reducing agents, which lowers the reducing capacity of the waste. The soils investigated are much harder to categorize than the waste materials, as can be seen from figure 4. The soil with low organic matter content ( < 2.5%) has virtually no reducing capacity, which suggests that the redox behaviour of soils is associated with organic matter. The progress of Eh during the column test of soils is quite different from the waste materials discussed previously. Eh is always positive at the beginning of the experiment. The rapid initial decrease of Eh in soil A is probably due to the release of (mobile) reducing substances, accompanied by oxygen depletion. Eventually oxidizing agents are mobilized (a process with comparatively slow kinetics), and the buffering capacity is restored. Microbiologically mediated processes could account for the decrease of Eh at high L/S ratios [8]. In measuring redox behaviour during column tests on soil, special care should be taken to avoid artifacts caused by pretreatment of the sample. If a soil sample is dried and rewetted, a sharp initial decrease in Eh (up to 800 mV) was observed. This sharp dip in Eh is caused by an explosion of microbiological activity induced by the previous drying, and can be avoided by storing soil samples with preservation of their original moisture content [8]. The importance of measuring redox potentials during the column test is twofold. Monitoring of Eh can provide an explanation for seemingly anomalous results, such as a sudden release of arsenic (whose solubility is particularly sensitive to sudden changes in redox conditions). Eh measurement provides an additional tool to help understand processes taking place within the column. Most of all, insight in redox behaviour is essential to help predict actual leaching in field situations. In the case of reducing wastes that are stored in an oxidizing environment a modification of the column test is required to assess redox behaviour in order to predict the actual leaching under field conditions. However an additional test (for example determination of chemical oxygen demand) is needed to quantify the reducing capacity of the waste material.

Environmental Aspects of Construction with Waste Materials J J . M . Goumans, H A . van der Sloot and Th.G.Aalbers (Editors) a1994 Elsevier Science B. V. AN rights reserved.

483

THE INFLUENCE OF REDUCING PROPERTIES ON LEACHING OF ELEMENTS FROM WASTE MATERIALS AND CONSTRUCTION MATERIALS. H.A. van der Sloot , D. Hoede, R.N.J. Comans. ECN, P.O. Box 1 , 1755 ZG Petten, the Netherlands

Abstract In testing waste materials and construction materials for their leaching properties none of the existing regulatory tests take reducing properties of materials or application of materials in a reducing environment into account. This omission can lead to mismanagement of wastes because results of leaching tests of short duration fail to show the potential leachability of initially reducing materials after oxidation in a certain utilization or disposal scenario. Nor do they reflect the behaviour of oxidized materials, when brought in a reducing environment. It is clear that a range of constituents feature highly different leachability under oxidized versus reducing conditions. Typical examples of potentially critical situations are discussed. A procedure to identify whether a waste or a construction material possesses reducing properties is presented, as well as a method to assess the reducing capacity of materials, which can be used to determine how long a material may stay reducing or will be able to impose reducing properties on its environment. Implementation of the assessment of reducing properties of materials in decisionmaking on waste handling, utilization and disposal is discussed. 1. INTRODUCTION

The application of secundary materials in construction usually takes place under oxic conditions due to the permanent contact with the atmosphere. Some materials, such as slags from industrial processes, possess reducing properties as a result of the prevalent oxygen starved conditions in the furnace. This material property is not addressed in the evaluation of materials with current regulatory test procedures (TCLP or EP tox[l], DIN 38414 S4[2], Afnor X-3 1-210[3], Swiss TVA[4], NEN 7300 series[5,6]). When the material imposes reducing conditions on the leachate that will have consequences for the release of several constituents. The question arises whether the release measured in a test properly reflects the actual release that may occur under the conditions of the application. A few situations can be identified in which reducing properties may play a major role - reducing materials exposed to the atmosphere. - oxidized materials exposed to reducing conditions imposed by its surroundings (e.g. material in contact with reducing soil or sediment) - materials with latent biological activity (e.g. material rich in organic degradable matter) turning anoxic with time.

484

For a proper assessment of release in these specific circumstances additional information is needed. First it is crucial to identie whether reducing conditions will play a role in the application aimed for. To be able to address that issue it is necessary to know whether a material has reducing properties. Once that has been established the reducing capacity needs to be determined to be able to assess how long a material will feature reducing properties and impose reducing conditions on its environment. Finally the consequences for the leaching behaviour of several constituents under oxic and anoxic conditions needs te be addressed to allow an evaluation of the critical nature of the occurrence of changes in redox conditions with time on release of constituents of concern. As examples studies on steelslag [7], blast furnace slag, phosphorus slag, lead slag will be discussed, that have revealed the common characteristics of these materials due to the release of reduced sulphur species, which are the main carriers of reducing capacity affecting the surrounding. Studies on Municipal Solid Waste Incinerator bottom ash has shown the relevance of developing reducing conditions upon degradation of residual organic matter on the leaching behaviour of Cu. The oxidation of stabilized waste containing reducing substances to retain constituents of concern and stabilized reducing wastes are discussed in light of the management of such wastes.

ZEXPERIMENTAL 2.1 Identification of reducing properties of niaterirrls. The procedure that is applied to identi@ whether materials exhibit reducing properties consists of a comparison of the redox potential (Eh in mV) measured in the leachate obtained after extraction for 24 hours at a liquid to solid ratio (LS) of 1 in a closed vessel and the redox potential of normal oxygenated water at the final pH of the leachate. When the Ee value of the leachate, exposed for 24 hours to the waste or a crushed waste product, proves to be lower than that of the demineralized water at the same pH by more than 50 mV, then the material can be considered to exhibit reducing properties and the reducing capacity has to be determined as described below. 2.2 Deterntination of reducing potential For the determination of the reducing capacity of a material a cerium titration is applied [8,9]. The procedure for the determination of the reducing capacity of extracts consists of an extraction at liquid to solid ratio (LS) is 1 for 24 hours with 0.1 N Ce4' solution in 1 M HzS04. The reduced fraction of the Ce added is back-titrated with Fe2'- solution. The amount of Ce converted to Ce3' is calculated as mMol Oz/g of material. The procedure for the determination of the reducing capacity of solid materials is based on the same principle at a LS of 10 at for 2 hours only. The data need to be corrected for the moisture content, as drying samples prior to the determination may affect the reducing capacity. The carbon content of the material can contribute to the measured reducing capacity. In slags of melting processes the carbon content is usually not relevant, which means no additional corrections are needed. In combustion residues a fraction of unburnt material is common. In case the carbon content of the sample is not marginal (> l%), a correction is needed. The correction is a function of the carbon content and the specific surface area. When the specific surface area is smaller than 50

485

m2/g and the carbon content is below 5 %, the contribution of carbon is marginal and can be omitted. In many combustion residues this condition is fulfilled. The detection limit of the reducing capacity measurement is 0.02 mMol 0 2 /g (or 0.6 mg 0 2 /g). 2.3 Redox stntic test. A redox static setup has been developed using hydrogen as the redox controlling constituent [lo]. Based on the experience gained it has been possible to maintain the redox ofthe leaching medium at a stongly reducing condition. Other forms of redox control are based on applying reducing substances (e.g. sulfides, hydrochinon, hydrazine). Only in systems where sulfur species are the redox controlling species addition of a mixture of sulfur species rather than sulfide only is a suitable option. 2.4 Suljiur specintion In many cases it is important to know the distribution of the individual sulfur species as they have different chemical properties with respect to their interaction with other constituents. The following constituents are relevant: sulfate, sulfite, thiosulfate, polysulfides and sulfide. For a given redox potential a specific ratio of the sulfur species may be found. The measurement of the individual species requires sophisticated separation techniques. In this work HPLC was applied [ 111.

3. RESULTS AND DISCUSSION

-B ? .

3.1 Materials with reducing properties

15

1

B

'W

Industrial slags, such as phosphate slag, c blast furnace slag, steel slag and metal Q I2 -0d slags from several metal processing plants G 9 (e.g. Pb slag, Zn slag) exhibit reducing 5 v properties. The data in figure 1 show the m relation between the availability of S and 2 6 $ the total S content for blast furnace slag (circles), phosphate slag (triangles) and 3 steel slag (squares). There is no direct 9 correlation between S content or 0 availability and the the reducing capacity 500 1M)I) 1500 IMO 25W according to the method described before. Available S (mg/kg) The relatively high reducing capacity of Figure 1. Relation between available S, steelslag is caused by the high Fe I1 content of steel slag. S-species are total S and the reducing capacity of slags. important for imposing reducing conditions. Much more so than reduced Fe or Mn species, which are only released from slags in relatively low dissolved concentrations. A substantial fraction of S in fresh slags can be considered to be speciated as sulfides. In the case of slags, a low redox potential is usually associated with a high pH. In figure 2 the change in EH - pH condition upon exposure to air is indicated.

-

Y

486 1000 It leads to a combined oxidation/ neutralization. In contact with biologically 800 active environments with CO2 - production 600 and not directly in contact with the air, the v lower curve reflects the changes with time. 3 400 * In the case of application of industrial slags c Q 200 as hydraulic binder or subbase in road n construction, the importance of placing such x o 0 a construction at least 0.5 m above -200 groundwater level on a sandy soil (good aeration) is illustrated in figure 3. The -400 oxidation of reduced S-species, the 2 3 4 5 6 7 8 9 10111213 neutralization of leached alkalinity and the PH formation of calcite prevents uncontrolled spreading of reducing sulhr species. Thus Figure 2. Changes in redox behaviour of preventing adverse effects on the reducing slags in different applications. environment. In addition, release of reduced Fe- and Mn- species (FeII and MnII) will lead to formation of hydrated Fe(II1) and manganese oxide phases upon oxidation, which act as a sorption barrier for several metals and oxyanions. h

$

3.2 Dimerenee in leaching behaviour under oxidized and under reducing conditions

ROAD CONSTRUCTION

3.2.I M S W bottom ash

The leachability of Cu from MSWI bottom ash can be used as Subbase with an hydraulic slag mi an illustration of the magnitude of the effect of reducing conditions on metal release. Under oxidized conditions Cu is complexed with Dissolved Organic Carbon leading so: so: so: CaCO,$ to release of about 1 mg/kg at neutral pH. Upon heating the ash $ 4 4 Groundwater to 550 C for 6 hours the release is substantially reduced (almost two Figure 3. Oxidationheutralization reactions occurring ii A orders of magnitude). verification of the effect of the construction of a roadbase with reducing materials. reducing conditions on Cu release using a recently developed " Redox stat"[ 101 based on H-2 purging has shown a reduction in leachability of at least an order of magnitude. It is clear that the occurrence or absence of reducing conditions has a drastic effect on metal release and can not be neglected.

487

3.2.2 Availability tinder oxidized and reducing conditiotis. The availability has been measured for a reducing material and three oxidised materials under oxidized and reducing conditions. In the case of the oxidized materials the reducing conditions were enforced by using a Sspecies mixture as derived from blast-furnace slag leaching. From the availability data a clear difference amounting up to a factor of several thousands for some metals is noted between oxidized and reducing conditions. The difference for anionic species is less pronounced.

50

f

I

I

10

v

XI

40

I

6

0. I

0.01

3

4

5

6

7

8

9 1 0 1 1 1 2 1 3

PH Figure 4. Influence of reduction and removal of DOC on Cu leachability from MSWI bottom ash.

3.3. Sulphur speciation under reducing conditions.

In an experiment blast furnace slag was placed in a layer at the bottom of a large cilindrical vessel, which was subsequently filled with degassed water. The vessel was closed at the top to prevent uptake of 02 from the air. The S-speciation was followed at different levels in the cilinder at different contact times. The ratio of S-species relative to total S are given in figure 5 as a function of pH. In the bottom of the cilinder the solution turned yellow, indicative of the presence of significant concentrations of polysulfides. Thiosulfates are the most abundant S-species in BFS extracts, whereas polysulfides can amout to 10 % of the total S. Both polysulfides and

Table I. Availability data (in mg/kg) under oxidized and reducing conditions. Material

Cu

Mo

Zn

As

V

0.1

0.3 7.5 1.6 2.4

1.2 2.2 4.7 0.3

0.8 11.5 0.3 22.3

166.9 46.8 3.6 1.3

85 107 615 9420 65

11) but upon aging, the pH can decrease to 8 - 9. Another key factor in facilitated transport is the stability of the colloid particles: are the colloidal suspensions stable or are the colloids readily precipitated, adsorbed etc. The recovery of added particles in the experiments varies between 0 to 2% for Fe and 0 to 25% for humics. It is therefore concluded that the nature of the particles is very important.

516

Also the separation procedure, which was not always optimal has an important effect on the measured values. Furthermore, the initial presence of carriers in the material itself is of major importance. For a good understanding of facilitated transport, characterization of these material-borne carriers is necessary. The results of this investigation show that, in addition to standard leaching tests, specific tests for the quantification of colloid-bound emissions may be necessary to accurately evaluate the quality of secondary raw materials. ---n----ro, l

.o 0,80 P c

-

.-C

I

0,60

0

-m I

D

0,40

s

an

0,zo

0,oo 3

4

5

6

7

8

9

1

0

1

1

12

11

12

.-C 0,

r

C

p

-z

0,60

m

c

0

0,40

~

c

3

0

n

g 0,zo C (u

2

0,oo 3 4

5

6

7

8

9

10

PH

Figure 3 Fraction of bound copper (3A) or arsenic (3B) by ferrihydrite (HFO); 2 to 20 ppm HFO. 600 pgfl Cu, 150 pgfl As. Model constants derived from [El.

517 Acknowledgement This research was carried out in the framework of the target orientated research program on leaching characterization of construction and waste materials, under a contract with NOVEM (Netherlands Organization for Energy and the Environment).

6 . References 1 J.F. McCarthy & J.M. Zachara: Subsurface Transport of Contaminants, Environ. Sci. Techn., 23 (1986) 496.

2 D. Perret et al.: Submicron Particles in the Rhine River - I, 11. Wat. Res., 28 (1994) 91. 3 T A W Infra Consult B.V. (1992): Role of Facilitated Transport in the Dispersion of Poorly Soluble Components. Phase 1, Literature Search (original title: Rol van drager gebonden transport bij de verspreiding van relatief slecht in water oplosbare componenten. Fase 1, Literatuur onderzoek) . 4 T A W Infra Consult B.V. (1993): Role of Facilitated Transport in the Dispersion of Poorly Soluble Components. Phase 2, Preliminary Laboratory Experiments (original title: Rol van facilitated transport bij de verspreiding van relatief slecht in water oplosbare componenten. Fase 2, orienterend laboratorium onderzoek). 5 M.A. Schlautman & J.M. Morgan: Effects of Aqueous Chemistry on the Binding of Polycyclic Aromatic Hydrocarbons by Dissolved Humic Materials. Environ. Sci. Techn., 27 (1993) 961.

6 De Wit, J.C.M. et al: Analysis of Ion Binding on Humic Substances and the Determination of Intrinsic Affinity Distributions. An. Chim. Acta, 232 (1990) 189. 7 J. Kragten, Atlas of Metal-Ligand Equilibra in Aqueous Solution, Ellis Horwood Limited, Chichester, Sussex, England, 1978, ISBN 85312-84-6.

8 T. Hiemstra & W.H. van Riemsdijk (1990): Adsorption Modelling of Cations and Anions at the Solid/Solution Interface of Metal(hydr)oxides: A New Mechanistic Multisite Approach. I: Model Description. 11: Evalution of Intrinsic Constants. Dep. of Soil Science and Plant Nutrition, Agricultural University, Wageningen, The Netherlands. 9 G.J. van Rossum and B.H. te Winkel, to be published. 10 D.A. Dzombak and F.M.M. Morel, Surface Complexation Modelling - Hydrous Ferric Oxide, John Wiley & Sons, 1990, ISBN 0-471-63731-9.


Environmental Aspects of Construction with Waste Materials J..I..I,M. Goumans, H A . van der Sloot and 7h.G.Aalbers (Editors) @I994 Elsevier Science B. K All rights resewed.

519

Immobilization of heavy metal ions by the alkali activated slag cementitious materials J. Malolepszy and J . Deja Academy of Mining and Metallurgy, Cracow, Poland

Abstract The granulated blast furnace slags or nonferrous slags are the main component of the alkali activated slag cementitious materials. The calcium silicate hydrates (C-S-H type) of low basicity, hydrogarnets and sodium zeolites form as the alkali activated slag hydration products. Their structure and properties indicate that they can play an essential role in the immobilization of some elements. The microstructures of alkali activated slag pastes shows a higher gel pores content as compared with OPC pastes and simultaneously, significantly lower capillary pores fraction. The properties of alkali activated slag pastes in the presence of Zn, Cd, Cr and Pb ions were studied. The leaching and tank procedure were used to evaluate the level of immobilization of particular elements in the paste.

1. INTRODUCTION The problem of heavy metals immobilization becomes more and more significant with l Several technologies will develop only when increasing contamination of ~ t u r a environment. the heavy metals containing by-products are sufficiently and safely well separated. In many research centers the studies are carried out to solve this problem. The cementitious materials play an important role in the heavy metals immobilization. They can be used not only in the construction of waste dumps and concrete shields but also as immobilizing agents forming a matrix incorporating the heavy metals in a physical or chemical way. Cements are particularly useful in the wet wastes processing; it is important in view of the fact that the wastes occur predominantly as slurries (e.g. galvanic wastes containing Cr+6). The efficiency of the heavy metals immobilization is strongly related to the hardened paste microstructure, particularly to the pore size distribution and porosity. It is commonly known that the large pores of diameters > lOOnm influence decisively the paste tightness and permeability. The microstructure and properties of hardened paste depend on the C-S-H phase content and properties [6]. These features, in turn, are often related to the presence of pozzolanic admixtures. Such materials as silica fume, natural pozzolans and granulated blast furnace slags give the hydration products as a result of pozzolanic reaction thus influencing the porosity of paste. The admixtures listed above bring about the gel pores fraction increase and capillary pores decrease [5, 71. The advantageous changes accompanying the occurrence of

5 20

pozzolans give, as a consequence, the significant decrease of permeability attributed to the hardened cement matrix in concrete [8]. The pH values in the pastes are very high (about 12) because of the basic Ca(OH), formation. The heavy metal salts are neutralized at the presence of Ca(OH), and, as a result, the heavy metals hydroxides of very low solubility precipitate. The calcium zincates or chromates can also form [9]. Therefore the immobilization of heavy metals in the hardened cement matrix is the consequence of the significant C-S-H phase content and high pH value. The properties of alkali activated slag concretes have been studied in our laboratory for many years [lo-131. lt have been found that the alkali activated slag matrix would produce the idealized conditions for immobilization of heavy metals. The slag hydration products consist mainly of the gel-like C-S-H phase, zeolites and hydrogarnets [12, 141. The pastes are very compact. The pores of diameters less than lOnm predominate; these pores do not take a part in the filtration of water throughout the paste [12, 151. The high pH values resulting from the presence of alkaline activators, ensure the neutralizing properties of pastes. Such phases as sodium zeolites and hydrogarnets can incorporate the heavy metals to the structure [ 161. The alkali activated slag cementitious materials have been also applied in heavy metals immobilization by the other author as it is reported in some works [ 17,181. The results of the studies on the C P 6 , Zn 12, Pb+* and Cd+*immobilization in the alkali activated slag mortars will be presented hereby.

2. EXPERIMENTAL

2.1. Materials The granulated blast furnace slag, standard sand (strength determination), alkaline activators and compounds of heavy metals such as Zn(NO,),, Pb(N03),, CdCI, and Na,CrO, have been used. The blast furnace slag was ground to the specific surface 3500cm2/g as measured by Blaine method. The chemical composition of slag is given in Table I . Table 1 Chemical composition of slag Component CaO SiO, '41203

MgO Fe20s

so3

+

Na,O K,O residuum

wt (%) 41.10 38.10 9.60 8.40 0.40 1.10 1.20 0.10

521

In Poland this slag is used in the metallurgical cement production. The sodium carbonate and water glass have been used as alkaline activators. The mortar was prepared at water to cementitious material ratio equal to 0.36. The proportion between slag and sand was 1:3. The heavy metals compounds were dissolved in water. The mortars denoted as A-I were prepared using the sodium carbonate and alkaline activator whereas those denoted as J-S were activated by water glass. The samples denoted as 1 and J were prepared as a control alkali-activated slag pastes without heavy metal compounds addition. The mortars were mixed in the standard laboratory mixer, cast into the moulds for IS0 40 X40 X 160mm bars and shaken on a laboratory shaker. The samples were domoulded after 24 hours. The mortars prepared with water glass as an activator were stored for 28 days at 20°C, 100%RH.The mortars activated by sodium carbonate were subjected to the steam curing at 85°C for 4 hours and subsequently stored at 20"C, IOO%RH. The characteristics of mortar specimens are shown in Table 2. The total concentration of Zn, Cd, Cr and Pb ions in the mortars is presented in Table 3. Table 2 Characteristics of Mortar Specimen Type of mortar

Density (glcm') A

Na,CO, activation

B C D E F G H I J

K L Water glass activation

M N 0 P R S

Compressive strength (N/mm*) 3 days

28 days

2.31 2.38 2.37 2.34 2.37 2.38 2.36 2.31 2.37

34.0 25.4 35.4 39.1 45.0 39.2 37.4 31.5 33.8

36.2 28.9 38.5 38.4 46.0 40.4 38.4 39.0 38.6

2.38 2.36 2.28 2.31 2.35 2.38 2.38 2.36 2.37

74.5 48.3 48.4 40.2 28.0 69.0 57.2 68.0 50.9

82.2 52.1 52.1 41.7 29.0 74.4 72.5 70.5 62.4

522

Table 3 Concentration of Zn, Cd, Cr and Pb ions in the mortars Type of activator

Na2C03

Water glass

Ions concentration (mg/kg) Martar

Zn

Mor-

tar

Cd

Mortar

Cr

Mortar

Pb

A B I

787 397 7

C D I

1384 2767 40%) and the formation of reusable by-products (fly ash, bottom ash and gypsum) compared with conventional waste incineration plants. A research program was defined to investigate the technical feasibility of cocombustion of coal and waste wood in Dutch power plants. The main objectives of the project were: demonstrate the co-combustion of powdered coal and waste wood determine the consequences for the emissions, such as NO,, SO,, heavy metals and dioxines

544

determine the influence on the by-product quality, such as heavy metal content. The paper will give an overview of the project with in-depth discussion of the influence of co-combustion of wood on the quality of the by-products.

2. WASTE WOOD CHARACTERIZATION

The particle size of fine and coarse waste wood and reference wood has been determined by sieve analysis. The results are given in Table 1. The Drayton coal used has been milled to a particle size of 90% < 60 pm. Table 1 Sieve analysis of fine and coarse waste wood and reference wood sieve width (mm)

fine waste wood % within range

reference wood % within range

sieve width (mm)

< 0.50

62

57.9

< 0.21

6.4

0.50 - 0.85

27.9

40.6

0.21 - 0.50

9.6

0.85 - 1.00

4.1

1.25

13.7

1.00 - 1.25

3.4

0.1 1

1.25 - 1.60

1.7

0.13

> 1.60

0.9

- 1.00 1.00 - 3.00 3.00 - 4.00 4.00- 5.00 5.00 - 8.00 0.50

> 8.00

coarse waste wood % within range

13.0 53.8 2.5 0.45 0.55

Waste wood and coal have been analyzed with respect to combustion parameters and heavy metals. The results are presented in Table 2. Drayton coal can be regarded as representative for the average values with respect to physical (ash, volatile, LHV) and chemical parameters (macro and trace elements) of the total mix of coal types fired in Dutch power plants.

545

Table 2 Analyses of Drayton coal and the fine and coarse fraction of waste wood (as received) parameter

unit

fine waste wood

coarse waste wood

Drayton coal

total water

6.0

bounded water

5.02

6.31

2.10

ash

2.13

1.87

9.63

volatile matter

75.20

75.18

34.55

LHV

17.10

18.63

29.08

C

48.61

17.28

75.1

N

0.44

1.53

S

0.02

0.81

H

6.33

4.94

0

36.4

6.1

As

9.5

10.9

Cd

1.13

0.07

Cr

10.9

25

cu

37.6

23

Hg

0.07

0.23

Pb

980

14.0

Sb

9.1

< 1

Sn

2.2

< 2

Zn

870

19.8

797

426.5

546 3. REACTIVITY MEASUREMENTS

Waste wood has to be reduced in size to ensure complete burn-out in the boiler. The energy necessary for size reduction increases rapidly below a certain point. Therefore the maximal allowable size has to be determined.

1m7,J

supply of coal

Furnace furnace length: 1.5 m rnax. temperature: 1600 "C capacity: 30 g l h

Collector

Figure 1. Drop tube furnace set-up.

The experiments are performed in a so-called drop tube furnace, see Figure 1, in which wood particles fall through a heated tube filled with air. The residence time can be varied within the range representative for coal-fired boilers in power plants. The ash is collected and the amount of carbon can be determined. From the results it appeared that waste wood has to be reduced in size to below 1 mm.

4. PILOT PLANT EXPERIMENTS

KEMA has a 1 MW,, powder coal-fired test installation at its disposal. Figure 2 shows a simplified flow-diagram of the installation.

547

natural gas

r-1,

flue-gas cooler

P; -

pulverized

low. pressure cooling system

/’

primary air

//

’

combustion chamber

ash disposal

cooling system

3

‘test zone HT-pipes

6

to ash disposal system

Figure 2. Simplified flow-diagram of the powder coal-fired test installation.

Experiments have been performed in which 2.5-8% (calorific value based) waste wood has been co-combusted with Drayton coal. Operational parameters, furnace temperatures, emissions and by-product compositions have been measured. 4.1 Emission measurements

During the experiments the concentration of NO,, SO,, C,H, CO, CO, dust, Hg, Cd, Pb, and Zn in the flue gas has been determined. The results are shown in Table 3. The measurements have been conducted in the flue gas ducting behind the bag filter. The oxygen concentrations measured varied between 4.7 and 8.7% suggesting excess air levels of at least 20%. However it appeared that air had leaked into the bag filter house. The actual excess air levels were much lower than those calculated from the measured flue gas values. Dioxin concentrations have been measured in duplicate during run 1 and 3. Only one measurement gave a concentration of 0.01 ng TEQ/m3, the three others were below this detection limit.

548 Table 3 Analytical results of emission measurements during co-combustion waste wood experiments

SO, (mg/m3)'

0,(% v/v)

co,

(% v/v)'

run 1

run 2

run 3

run 4

run 5

0

2.7

5.6

8.0

6.0

1.2

1.3

2.2

6.2

0.8

16.4

2.9

< 2.5

< 2.8

< 3.1

8.5

30

36

63

87

24

53

62

100

93

121

74

78

115

117

40

260

179

173

39

CaCO, (s) and the second one is the oxidation of unburned carbon with atmospheric 0, and further acid-base reaction with free calcium oxide: C (s) t 0, (g)

+

CaO(s) ===> CaCO, (s)

Granulometric data: Particle distribution, particle mean diameter and calculated specific surface are given in Table 1.

Table 1 Granulometric data for fly ashes Fly Ash

Percentage of particles with diameter greater than

Mean diameter

Specific surface

TO

60

20

6

32.19

2400

T10

43

5

0

13.48

4020

T20

35

0.7

0

9.96

4640

T30

30

0

0

8.49

4900

T40

25

0

0

6.73

5410

T60

23

0

0

5.93

5959

Granulometric data indicated that for short-grinding periods (10-20 minutes) nearly all of coarsest fly ash particles (greater than 45 pm) were crushed; additionally, hollow fly ash particles (cenospheres) are easily crushed and they can release smaller spheres (pherospheres). When grinding time increases finest particles (diameter less than 45 pm also were crushed as indicates the decreasing of percentage of particles with diameter smaller than 10 pm. However, effectiveness of grinding is reducing as the particle size is being smaller. So, we can observe that the decreasing of mean diameter is not linear because the loss of effectiveness of grinding. Crushing produced particles with irregular shape as was observed by

575

electronic microscopy; these new particles were covered with fine needless and flakes which were originated in the grinding process.

3.2 Applications in mortar production Test Workability: It is extensively accepted that partial substitution of Portland cement by fly ashes enhances workability of mortars, concretes and pastes [5,6,7] and in the same way it is found that the role of fly ashes is related with their fineness, shape morphology of particles, vitreous character and, even, chemical composition. Obviously, when fly ashes are ground, two of their properties are dramatically modified: fineness and shape morphology. Crushing fly ash by grinding yields samples with larger fineness than "as received" fly ash (see granulometric data) which would contribute to enhance workability. On the other hand, crushing original particles, mainly spherical or spheroidal, increases the percentage of irregular particles (mainly flake, needle or splinter shape, sometimes semispherical or semispheroidal morphology) and, so, their lubricant effect in Portland cement mixtures is limited. The behaviour of fresh mortars containing ground fly ashes has been studied using a flow table and following already reported procedure [5]. Flow table spread values (FTS) have been measured (see experimental section) for mortars containing 30 % of fly ash replacing Portland cement and varying water con tent. Figure 2 shows the results obtained for "only Portland cement" mortars (PC) and mortars containing original fly ash (TO) and ground fly ashes (T1O T60). We can observe that mortars containing ground fly ashes yielded FTS values greater that corresponding PC ones.

On the other hand, significant differences among fly ash series are observed: so, workability of mortar containing short-time grinding sample (T10) is similar than mortar containing "as received" (TO) fly ash ones. For higher grinding-time fly ashes a clear decreasing of FTS values is found. Flexural and compressive strengths: The fineness of fly ashes, specially that of its glassy phase is found as a crucial parameter in strength development of concretes and mortars containing fly ashes, and direct correlations between fineness of fly ashes and strength development have been reported [8].

576

_c

+

-

--sC

+ + -

PC TO T10

145 135

T20 T30

-+-

T40

-4-

T60

125 115 105 I 200

I I

205

I

I

210 215 water (mL)

I

220

225

Figure 2. Flow table spread (ITS) values for prepared mortars. Grinding process of fly ash increases its fineness, and possibly, enhances reactivity towards lime. So, pozzolanic reaction rate will be different depending on the grinding time, and strength development may be influenced. Mortars containing 30% ground fly ashes (T10-T60) replacing Portland cement have been prepared and their early age strengths compared with "only Portland cement" mortars and mortars containing ''as received" fly ash (TO). Compressive and flexural strength developments of specimens cured at 20" C are showed in Figures 3 and 4 respectively. We can observe that for compressive strength value (RJ of fly ash containing mortars always are lower than "only Portland cement" ones. However, a significant difference is observed among fly ash series; so, we note that R, values increase from TO to T60 and differences among them are greater for 28-days test. Similar tendency is obtained for flexural strength development (RJ. In this case, 28-day R, values for mortars containing from T20 to T60 ground fly ashes are equal or greater than "only Portland cement'' ones. Both facts indicate that, even at early ages, there is an important influence of fineness on strength development, probably due to pozzolanic reaction rate is favored when fly ash particle size is mechanically reduced.

571

50

PC

45

+

TO

40

*

Ti0

-+-

T20

_c

+

T30

+

T40

-A-

T60

Rc(MPa)

35 30 25

20 15

0

7

14 t(day)

21

28

Figure 3. Compressive strength development for prepared mortars.

a

R f ( MPa) PC

+ TO

7 6 5

4

*

T10

*

T20

--x-

T30

-4-

T40

&

T60

3 0

7

14 t(day)

21

28

Figure 4. Flexural strength development for prepared mortars

578

4. CONCLUSIONS 1. 2. 3. 4. 5.

6. 7.

Grinding fly ashes produced the formation of litle amounts of calcium carbonate. The rest of components remained unchanged. Fineness of ground fly ashes depends on grinding-time, and it is easy to obtain samples with mean diameter less than 10pm. Grinding process crush fly ashes particles, yielding new particles with irregular morphology. In general workability of mortars containing fly ashes is reduced when ground fly ash are used, but, for short grinding time samples, FTS values are not specially affected. In all cases, mortars containing ground fly ashes showed better workability than only "Portland cement" mortars. Compressive and flexural strengths of mortars containing fly ashes are improved when ground samples are used, and in general, they increase when grinding time is increased Flexural strength for mortars containing finest fly ashes, are equal or greater, at 28-day age, than "only Portland cement" specimen at the same age

5. REFERENCES 1 2 3 4

5 6

7 8

W.B. Butler, M.C. Mearing, MRS Symposia Proceedings: Fly Ash and Coal Conversion By-products; Characterization, Utilization and Disposal 11, 65 (1986) pp.11 E. Peris Mora, J. Pay& J. Monz6. Materiales de Construccih 41 (1991) 29. R. Hardtl, Studies in Environmental Science 48, Waste Materials in Construction Proceedings: Environmental Implications of Construction with waste materials, Maastricht (1991) 399. E. Anakura, H. Fujinawa, T. Nishida, Y. Fukada. Jpn. Kokai Tokkyo Koho,41,137,1991 E. Peris-Mora, J. Paya and J. Monzo, Cement and Concrete Research, 23 (1993) 917. E.E. Berry and V.M. Malhotra, Fly Ash for Use in Concrete: A Critical Review, ACI Journal, March-April, American Concrete Institute (1980). U. Costa and F. Massazza, I1 Cement0 (1986) 397. Fly Ash in Concrete: Properties and Performance, Riley Report 7, Ed. K. Wesche, London, Chapter 3 (1991) 62, and references therein.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, H A . van der SIoot and Th.G. Aalbers (Editon) 91994 Elsevier Science B.V. AN rights resewed.

579

Development of cementitious products using industrial process wastes as sources of reactive sulfate and alumina G. Belz a, J. Beretka b, R. Cioffi C, L. Santoro d, N. Sherman b and G.L. Valenti e aENEL Direzione Studi e Ricerche, Centro Ricerca di Brindisi, Via Dalmazia 21/C, 72100 Brindisi, ITALY. bCSIRO Division of Building, Construction and Engineering, P.O. Box 56, Highett, Victoria, AUSTRALIA. CUniversita degli Studi di Napoli "Federico 11", Dipartimento di Ingegneria dei Materiali e della Produzione, Piazzale Tecchio, 80125 Napoli, ITALY. dUniversitA degli Studi di Napoli "Federico 11", Dipartimento di Chimica, Via Mezzocannone 4,80134 Napoli, ITALY. Wniversita degli Studi della Basilicata, Dipartimento di Ingegneria e Fisica dell'Ambiente, Via della Tecnica 3,85100 Potenza, ITALY. Abstract Two series of mixtures containing up to 90% waste materials have been tested to assess their potentialities for the manufacture of ettringite-based building materials. One series of mixtures is useful for the manufacture of preformed building elements by hydrothermal reaction between a chemical gypsum and reactive oxides or hydroxides of calcium and aluminium. Curing temperatures in the range 55-85OC have proved to give adequate mechanical properties. The other series of mixtures has been used to produce a clinker by firing at about 1200OC. The resulting binder contains calcium sulfoaluminate and sulfosilicate as well as anhydrite. Upon hydration it gives mechanical strengths well above those of ordinary portland cements. The wastes used in the present work are phosphogypsum, fly ash and blastfurnace slag. 1. INTRODUCTION Calcium sulfoaluminate hydrates 4CaO.A12036@,.12H20 (monosulfate) and 6CaO.Al203.3S03.32H20 (ettringite) are compounds characterized by good binding properties and water resistance. Hence systems able to generate them upon hydration behave as cementitious products [l-131. Such systems belong to two different categories: (a) blended compositions containing calcium sulfate and sources

580 of reactive lime and alumina, and (b) hydraulic binders based on anhydrous calcium sulfoaluminate, 4Ca0.3A1203SO3, which can be obtained by high-temperature synthesis of raw mixes containing the required oxides. The mixtures in the first category generally require elevated curing temperatures and are suitable for the manufacture of preformed building elements [14-171. The source of sulfate can well be hemihydrate instead of gypsum, in order to exploit the contribution to the hardening given by the hydration of plaster of Paris. Moreover a further increase of early strength can be achieved if portland cement is incorporated in the mixes. The hydraulic binders based on calcium sulfoaluminate rapidly generate ettringite by hydration at room temperature and are therefore termed rapid-hardening cements [18-241. These binders are important inasmuch as they can be produced at temperatures considerably lower (1100-1300°C) than those required by ordinary portland cements. Most importantly, both categories of cementitious products can utilise large amounts of industrial wastes as sources of reactive sulfate and alumina. 2. EXPERIMENTAL

2.1 Materials

Except for analytical grade CaC03 the materials used for the experiments and their principal chemical components are indicated in Table 1. The composition of the systems investigated is shown in Tables 2 and 3 . Table 1 Principal chemical components of materials used (wt%) Material

CaO

SiO2

A1203

Fe2O3

MgO

SO3

H20

Bauxite Blast furnace slag Clay Fly ash Hydrated lime Natural gypsum Phosphogypsum Portland cement n.a. = not analysed

0.02 41.13 1.30 4.80 72.80 32.60 32.60 63.80

4.70 33.17 46.80 56.80 n.a. 3.33 0.05 22.22

51.50 14.15 34.50 25.50 n.a. 0.35 0.23 4.52

15.30 1.57 1.33 4.20 n.a. 0.22 0.02 3.60

0.04 7.00 0.12 1.50 0.71 0.06 0.22 1.72

n.a. 2.58 0.10 0.40 ma. 43.40 49.00 2.43

25.40 0.15 14.69 0.40 24.39 20.70 20.50

--

Table 2 refers to six blended compositions (BL) containing calcined phosphogypsum, fly ash or blast-furnace slag, portland cement and/or hydrated lime. Six additional compositions containing calcined natural gypsum instead of phosphogypsum and the same amounts of the other components were prepared and used as reference terms. Calcined natural gypsum was prepared by heating in a laboratory oven at 140-145°C for 16 hours, followed by conditioning for 1 day at 21OC

58 1

and 67% R.H., in order to obtain complete conversion to hemihydrate. Phosphogypsum was calcined in a kettle and conditioned as above. Table 2 Blended compositions (wt%) System Calcined Fly ash p hosphog ypsum BL-1 28.5 43.0 BL-2 26.0 43.3 BL-3 30.0 50.0 BL-4 28.3 47.2 BL-5 18.5 -BL-6 20.0 --

Portland cement

--

17.4 10.0 10.0 20.0 10.0

Hydrated lime 28.5 13.3 10.0 14.5

-1.0

Blast furnace slag

---__

61.5 69.0

Table 3 Calcium sulfoaluminate-based compositions (wt%) Material Bauxite Blast furnace slag CaC03 Clay Fly ash Phosphogypsum

FA

BS

CL

22.14

23.30 17.24 25.23

18.97

-34.72

--

Total

---

--

35.40 12.01

--

9.60 33.54

34.23

33.62

100.00

100.00

100.00

Table 3 refers to three calcium sulfoaluminate-based compositions, labelled FA, BS and CL, according to whether fly ash, blast furnace slag or clay, respectively, was used in the raw mix. The compositions indicated in Table 3 were calculated to give a fired product containing C4A3SI C2S and CS in the weight ratio of 1.5:l:l (cement chemistry notation: C=CaO, A=Al2O3, S=SO3, S=SiO2 and H=H20, is used). 2.2 Procedures Blended compositions were pre-cured for 16 and/or 24 hours at 55,70 and 85OC, then allowed to dry at 21OC and 67% R.H.. For hydration studies small (2g) samples were mixed with water (water/solid ratio w/s=0.5) and, at the end of the curing period, ground in acetone to stop the reaction, dried with ether, stored in a dessicator, then analysed by differential thermal analysis (DTA) and X-ray diffraction (XRD). Measurements of compressive strength were made after 1, 7 and 28 days of post-curing at 21OC and 67% R.H. on paste specimens (25 mm cubes). Calcium sulfoaluminate-based compositions were prepared by blending the previously sieved ( d 5 0 pm) raw materials, then firing in an electric kiln for 8 h at

582

1220OC. After firing, the sintered products were crushed, ball-milled and sieved to pass a 53 pm screen. These compositions were paste hydrated (w/s = 0.4) and cured at room temperature and 100% R.H. from 1 to 90 days. Small samples and cubed specimens, as described before, were submitted to DTA/XRD and compressive strength tests, respectively. XRD was also used for studying the mineralogical composition of fired products. 3. RESULTS AND DISCUSSION 3.1. Blended compositions

In these systems, at any pre-curing temperature, the main hydration product is ettringite. No calcium monosulfate forms. Typical thermograms are shown in Fig. 1, relative to specimens of composition BL-1 pre-cured 16 hours at 55,70 and 85OC. The presence of neoformed ettringite as well as unconverted gypsum and hydrated lime is revealed by the endotherms at about 120, 160 and 47OoC, respectively. Furthermore, at 70 and 85OC, the formation of calcium silicate hydrate is evidentiated by a shoulder on the rising slope of the ettringite peak.

Figure 1. Thermograms of specimens of composition BL-1 pre-cured 16 hours at 55, 70 and 85OC.

583

The compressive strengths for all the blended compositions pre-cured 24 hours at 55, 70 and 85OC are shown in Figures 2 and 3, which are referred to 1 and 28 day

m

Q

z

i

E" g

i

.-

3

I

I--

20.0

0.0 50

I

I

I

1

60

70

80

90

1 0

Temperature, "C

Figure 2. Compressive strengths, at 1 day post-curing, of blended compositions precured 24 hours at 55,70 and 85OC. 28 days

2

EL- 5

-

40.0

EL- 2

z

i

p

BL- 6 EL- 4 EL- 3

30.0-

f? c

u)

2!

'B In

20.0-

8

10.0-

ii

0.0 50

EL- 1

60

70

80

90

1 0

Temperature, "C

Figure 3. Compressive strengths, at 28 day post-curing, of blended compositions precured 24 hours at 55,70 and 85OC.

5 84

The results show that a great increase of compressive strength is obtained when precuring temperature is raised from 55 to 70°C. The effect of further increasing the precuring temperature to 85°C is much less favourable. Comparing Figures 2 and 3 shows that, at 55"C, the increase of post-curing time from 1 to 28 days has a positive effect on the development of compressive strength. On the other hand, at 70 and 85"C, the systems develop within 1 day most of their attainable strength. As far as the effect of composition is concerned, the most relevant observation is that mechanical strength increases with portland cement content. Additional data, not reported here, have shown that replacing phosphogypsum with natural gypsum has no relevant effect on the mechanical properties of the blended compositions. 3.2. Calcium sulfoaluminate-based compositions

The mineralogical compositions of the fired materials fired varied only slightly for the three systems listed in Table 3. Fig. 4 shows a typical XRD trace for system CL.

30

40

"28.C O k a

Figure 4. XRD diagram for the composition CL fired at 1220°C.

585

Although the composition of the systems was designed to contain C4A3SI C2S and C S, all the fired materials consisted mainly of C4A3S, C5S2S (2C2S.CS ) and C S. C2S did not form in the firing conditions tested as a major phase. Traces were only present in the system CL. Furthermore, traces of C3A were also present in all

the three systems. When hydrated, the three calcium sulfoaluminate-based compositions generate ettringite and hydrated alumina gel, according to the following reaction:

Fig.5 shows the thermogram of the specimen of composition FA hydrated for 28 days. Thermal dehydration of the two products, ettringite and hydrated alumina gel, is evidentiated by the two endotherms at about 120 and 250°C, respectively.

I

I

I

I

I

200

400

600

800

1000

T e m p e r a t u r e , 'C

Figure 5.Thermogram of the specimen of the composition FA hydrated for 28 days.

5 86

The compressive strengths of the hydrated specimens of the three compositions tested are shown in Fig.6. It can be seen that all the compositions, particularly FA and CL, develop very good early (Id) strength. Increasing the curing time up to 90 days makes the strength increase further to values ranging between 60 and 90 MPa.

h I

80.0

0

I

I

I

I

25

50

75

100

Time, days

Figure 6. Compressive strengths of hydrated specimens of the compositions FA, BS and CL.

4. CONCLUSIONS

This study has shown that systems containing up to about 90% waste materials are of interest in the field of building materials manufacture. Blended compositions containing wastes such as phosphogypsum, blast furnace slag and fly ash, are suitable for the manufacture of preformed building elements. For all the blended compositions and under the most favourable curing conditions, it is possible to achieve compressive strengths higher than 20 MPa with a maximum of 44 m a . Phosphogypsum, blast furnace slag and fly ash can also be employed in raw mixes for the synthesis of calcium sulfoaluminate-based cements at about 1200°C. Compressive strengths ranging between 35 and 50 MPa at 1day, 58 and 76 MPa at 28 days, 61 and 90 MPa at 90 days, have been obtained. These values are higher than those achievable by ordinary portland cements.

587

Part of this investigation was carried out with natural gypsum instead of phosphogypsum and no relevant differences were found. The extension to other chemical gypsums, in particular desulphogypsum which is usually generated together with fly ash within coal-fired power plants, seems worthy of consideration and is being carried out. 5. REFERENCES 1 2 3

4 5 6 7 8 9 10 11 12 13 14 15 16 17

T.Azuma, Kkhimaru, T.Murakami and K.Tateno, Calcium aluminate monosulfate hydrate, Ger. Offen. No. 2 551 310 (1976). T.Azuma and Kkhimaru, Calcium aluminate sulfate-based inorganic hardened product, Japan Kokai No. 76 62 826 (1976). P.K.Mehta, World Cement Technol., May (1980) 166. K.Ikeda, Proc. 7th. Int. Congr. ChemCement, Paris (1980) 31, Vol. 2, Theme 111. GSudoh, T.Ohta and H.Harada, Proc. 7th. Int. Congr. Chem.Cement, Paris (1980) 152, Vol. 3, Theme V. Deng Tun-An, Ge Men Win, Su Mu-Zen & Li Xiu-Ying, Proc. 7th Int. Congr. Chem. Cement, Paris (1980) 381, Vol. 3, Theme V. L.Santoro, G.L.Valenti and G.Volpicelli, Thermochimica Acta, 74 (1984) 35. G.L.Valenti, LSantoro and G.Volpicelli, Thermochimica Acta, 78 (1984) 101. L.Santoro, R.Garofano and G.L.Valenti, Proc. 8th Int. Congr. Chem. Cement, Rio de Janeiro, (1986) 389, Vol. IV. L.Santoro, 1.Aletta and G.L.Valenti, Thermochimica Acta, 98 (1986) 71. L.Santoro, R.Garofano and G.L.Valenti, Thermochimica Acta, 116 (1987) 145. J.Beretka, L.Santoro and G.L.Valenti, Proc. 4th Int. Conf. on Durability of Building Materials and Components, Singapore, (1987) 64, Vol. I. G.L.Valenti, R.Cioffi, L.Santoro and S.Ranchetti, Cement and Concrete Research, 18 (1988) 91. G.L. Valenti, L.Santoro and J. Beretka, Proc. 2nd Int. Symp. on Phosphogypsum, Miami, 2 (1988) 167. J.Beretka, R.Cioffi, LSantoro and G.L.Valenti, Proc. 3rd Int. Symp. on Phosphogypsum, Orlando, (1990) 417. J.Beretka, R.Cioffi, LSantoro and G.L.Valenti, Proc. 3rd NCB Int. Seminar on Cement and Building Materials, New Delhi, 3 (1991) 110. RCioffi, M. Marroccoli, L.Santoro and G.L.Valenti, J. Therm. Analysis, 38 (1992) 761.

W.Kurdowski, C.M.George and F.P.Sorrentino, Proc. 8th Int. Congr. Chem. Cement, Rio de Janeiro, (1986) 292, Vol. I. 19 G.A.Mudbhatka1, P.S.Parmeswaran, A.S.Heble, B.V.B.Pat and A.K.Chatterjee, Proc. 8th Int. Congr. Chem. Cement, Rio de Janeiro, (1986) 364, Vol. 4. 20 G.L.Valenti, L.Santoro and R.Garofano, Thermochimica Acta, 113 (1987) 269. 18

588

21 22 23 24

A.K.Chatterjee, Proc. 9th Int. Congr. Chem. Cement, New Delhi, (1992) 177, VOl. 1. Su Muzhen, W.Kurdowski, and F.P.Sorrentino, Proc. 9th Int. Congr. Chem. Cement, New Delhi, (1992)317, Vol. 1. J. Beretka, L. Santoro, N. Sherman and G.L.Valenti, Proc. 9th Int. Congr. Chem. Cement, New Delhi, (1992) 195, Vol. 3. J. Beretka, B. de Vito, L. Santoro, N. Sherman and G.L.Valenti, Cement and Concrete Research, 23 (1993) 1205.

Environmental Aspects of Constnrcfion wifh Waste Materials JJJ.M. Goumans, H A . van der Sloot and Th.G. Aalbers (Editors) G.1994 Elsevier Science B.V. AN rights reserved.

589

Potentials for utilisation of PFBC ash J. Rogbeck and P. Elander Swedish Geotechnical Institute, S-581 93 Linkoping, Sweden Abstract Pressurised Fluidised Bed Combustion (PFBC) is a coal combustion technique commercialised during the last ten years. Development of PFBC has been carried out for more than 20 years and has resulted in a combustion technique with low emissions to the atmosphere, producing ashes with favourable properties concerning utilisation. Two types of ash are produced, fly ash and spent bed material. For utilisation, a mix of the two ashes and water has been found to be of the greatest interest. In this paper, laboratory investigations and field tests carried out to clarify significant properties of PFBC ash mixtures in different utilisation objects are presented. It is concluded that the ash has excellent potentials for utilisation regarding mechanical properties as well as environmental effects. The paper is based on research kindly supported by ABB Carbon AB, EFO Coal & Oil AB, Sweden and Stockholm Energy AB.

1. THE PFBC TECHNIQUE Pressurised Fluidised Bed Combustion (PFBC) is a coal combustion technique which has been commercially developed by ABB Carbon AB. The development of PFBC has been carried out for more than 20 years and has resulted in a combustion technique with low emissions to the atmosphere and solid residues with favourable properties concerning utilisation. The PFBC technology uses a combined cycle, involving generation of electricity by a gas turbine and a steam turbine. This ensures high efficiency, giving something like 15 % lower fuel consumption than with conventional technologies. Combustion takes place in the fluidised bed at elevated pressure, 5-12 bar depending on load. The combustion temperature is about 820O to 880° C. This means that the nitrogen oxide emissions can be kept down, since thermal NO, is only formed at higher temperatu-res. Prior to combustion, the coal is crushed to a maximum size of about 5 mm and is then mixed with a sorbent (limestone or dolomite). During combustion, the sorbent will capture released sulphur to form calcium sulphate. Residues from a PFBC plant are created in three streams; as granular bed material, as fly ash captured by the cyclones and as filter catch from the final back end filter. The ratio between spent bed material and fly ash varies, but is normally between 50/50 and 30/70, with fly ash dominating. The amounts of ash from the back end filter are very small, less than 1 to 2 %, and are normally added to the fly ash from the cyclones. Regarding the grain size distribution, the fly ash can be characterised as sandy silt and the bed material as coarse sand.

590

2. MECHANICAL PROPERTIES The results from laboratory investigations and field tests presented in this paper are mainly based on a comprehensive study carried out in 1988 on ashes from the pilot plant at ABB Carbon in Finsping (I). The results have then been complemented with recent tests on ashes from the commercial Vartan PFBC plant in Stockholm. The bed material in the tests is mainly based on limestone as sorbent, althoug dolomite ashes have also been investigated. At an early stage in the investigations it was found that, even if spent bed material and fly ash can be used separately, a mix of them is of the greatest interest. If these ashes are mixed with water and vibro compacted, a concrete-like material with high bearing capacity and compressive strength is obtained. The results presented below refer accordingly to mixes of the ashes. Although the mixing ratio between bed material and fly ash has been varied in the investigations, the most common ratio has been 50/50 or 30/70 with fly ash dominating. In the tests, bed material and fly ash have almost always been mixed in a dry state before adding water. The amount of water varies, depending on whether the intention is to obtain a wetted mixture or a slurry. The samples are then vibro compacted. Curing normally takes place under high humidity (RH about 90 %) at a temperature near +20° C. Some test series have been cured under other conditions, such as under water or at a high (+50° C) or low ( - 1 8 O C) temperature. Curing times up to one year have been investigated. An important factor when estimating the potential for utilisation of fine grained combustion residues is their strength properties. For ashes, the strength is usually determined (at least in Sweden) as the unconfined compressive strength. This is normally assessed from samples with varying curing times so that a time strength relation can be achieved. The growth of compressive strength concerning PFBC ash mixes is relatively fast and values of over 5 MPa are achieved within a few days. The final strength is normally between 20 and 45 MPa, even if values over 50 MPa have been measured. Figure 1 presents examples of the development of strength of ash mixtures. In this case, has the ratio been 30 weight-% bed material and 70 weight-% fly ash (Polish coal, limestone as sorbent). Other results have shown that when dolomite is used as sorbent, the compression strength may decrease (2). Maximum measured values so far for dolomite based bed material vary between 15 and 25 MPa. However, the test series in this case are too small to be statistically significant.

Strength properties 100

Compression strength (MPa)

10

1

"I'

1

10

100

1000

Curing time (Days)

Figure 1. Examples of the development of strength of PFBC ash mixtures (70 %fly ash and 30 % bed material). Polish coal, limestone as sorbent.

591

To clarify the long term durability of the compression strength, one test series based on limestone as sorbent was cured for 28 days and then placed in pressurised cell permeameters. Water under high pressure (170 Wa) was forced through the samples for up to 8 months. The unconfined compression strength was then determined. The results indicated no decrease in strength compared with samples cured in the normal way. However, it should be observed that the high strength properties are very dependent on curing the mixture can be cured above freezing temperature until the hardening process is completed or at least has progressed for a certain time. In some laboratory and even full scale tests, the ash mixture has been exposed to temperatures below 0 C from the beginning or only after a few days of curing, which has resulted in almost no increase in strength. Results from freeze-thaw tests also show that the ash mixtures are sensitive if the curing time is too short before freezing. As a result of the concrete-like material obtained, the permeability of the ash mixtures is very low. Test results show that the permeability after 28 days curing is less than 1 0 1 0 d s . Se Figure 2.

Permeability 1OE-09

Permeability (m/s)

1OE-10

1OE-1 1 .___

I OE-12

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100

Time (days) -50/50 bed ashhyclone ash *30/70 bed ash/cyclone ash --Swedish clay

Figure 2.

Permeability ofPFBC ash mixtures (Polish coal, limestone as sorbent, curing time 28 days).

In addition to the above mentioned parameters, a large number of laboratory tests have been carried out, for example to clarify the properties of synthetic aggregates produced from PFBC residues. These tests included compacting characteristics, degradation of aggregates, Swedish flakiness index and Swedish impact value. In general, the results have shown that after curing and crushing, PFBC ash mixtures are well suited for use as synthetic aggregates in fills and road building. 3. LEACHING CHARACTERISTICS

Like coal ash, PFBC ash mostly consists of a mixture of amorphous glass and crystalline phases and some unburnt material. The main components of the ash are compounds of silicon (Si), calcium (Ca), aluminium (Al) and iron (Fe). The desulphurisation process in a PFBC results in capture of sulphur as (CaSO,), while calcium surplus is obtained as calcium carbonate (CaCO,). The chemical composition of the ashes may vary to a certain extent, depending on the type of coal burned and the type of sorbent used (limestone or dolomite). If dolomite is used as

592

sorbent, the ash will also contain a certain amount of magnesium. In the 1988 study, a 50/50 mix of fly ash and bed material was analysed. The content of different trace elements in the mixture was generally less than 200 mgkg and for most of the elements less than 30 mgkg. In general, the environmental consequences of utilisation of residues are associated mainly with the release of contaminants, in particular trace elements, with percolating water. The possible release of contaminants from PFBC ashes were evaluated by means of leaching tests according to the Swedish ENA-method. This test is a serial batch test with four of leachings at the L/Sratio 4 (accumulated L/S-ratio 16) and with 24 h agitation by horizontal oscillation. Leaching at the L/S-ratio 1 is also determined. To achieve this build-up in L/S ratio concentration is used in the same procedure as above, but the material is renewed instead of the leachant. The particle size of materials used in ENA-tests should be BAGA

14270 > BAGA

6500 > BAGA

34402 > BAGA 6286 > BAGA

5650

448 > BAGA

MWI 1 of Table 7 uses the so-called semi-dry lime injection technique. After having removed the fly ash using an electrostatic precipitator a slurry of water, Ca(OH), and active carbon is injected into the flue gas. The resulting dry reaction product (mainly Ca(OH),, CaCI, and spent active carbon) is trapped using a fabric filter.

Finally it should be noted that the limits for the quality of waste water to be drained off varies considerably in the Netherlands. Some new MWI (not listed in Table 7) are not allowed to drain of waste water containing substantial amounts of SO[ and CI'. These new installation will be equipped with wet scrubbers in conjunction with a spray dry adsorber. In the Netherlands APC-residues are disposed of by means of landfilling. The criteria for landfilling are equal to those for MWI fly ash. As with fly ash the leachability is to be validated using the column test (NEN 7343) at US = 1. In Table 8 the leaching limits (U, and U,) are listed, together with the measured leaching behaviour of Dutch MSW APC residues. Based on Table 8 most APC residues should be disposed of at C,-conditions.

644 Table 8

10,OO 25,OO

Leaching behaviour of Dutch APC residues.

40,OO 280,OO

4,325 77,455 C2

5-13

0,072 11,373 2,473 C3

33,072 C3 8,607

N.M. 2,088

1,055 C2 5,005 C2

0,005 0,731

3-13 3140

203746

13490

FUTURE DEVELOPMENTS The data presented in this paper have been gathered as part of an inventory study on the state of the art for upgrading techniques for the quality improvement of MWIresidues. The results of this inventory are presented elsewhere in this book of abstracts of WASCON '94. Briefly, the following options seem viable: Bottom ash: 1) tighter acceptance criteria for the waste feed 2) separation of grate-siftings and/or boiler ash from bottom ash 3)washing of bottom ash, possibly in conjunction with 4) induced aging of the bottom ash Fly ash: 5) immobilization using an inorganic binder 6) melting aiming at a produce with an added value (La:energy, economy) 7) artificial gravel production APC-residue 8) immobilization using an inorganic binder Currently research programmes in order to evaluate all these options have been launched by (members of) the Waste Processing Association.

6.

ACKNOWLEDGEMENT This paper is based on the results of an inventory study of existing data on MWI residues supported by the National Research Programme for the Recycling of Waste substances (NOH), project number 353320/1910. NOH is administered by the Netherlands Agency for Energy and the Environment (Novem) and the National Institute of Public Health and Environmental Protection (RIVM). The data on the chemical composition of MSW fly ash were a kind gift of dr. J.B.M. Hudales (Vulstof Combinatie Nederland B.V.).

7.

Environmentol Aspects of Construction with Woste Motenoh J.J.J.M. Goumons, H A . von der Sloot and Th.G.Aolbers (Editors) a1994 Elsevier Science B.V. All rights reserved.

645

UPGRADING TECHNIQUES FOR THE QUALITY IMPROVEMENT OF MUNICIPAL WASTE INCINERATION RESIDUES

F.J.M. Lamersa and J.G.P. Bornb aKEMA Netherlands BV, P.O. Box 9035, 6800 ET Arnhem, The Netherlands %VAV (Waste Processing Association), P.O. Box 19300, 3501 DH Utrecht, The Netherlands Abstract An inventory was made on the state of the art for upgrading of Municipal Waste Incineration (MWI) residues by primary methods and post treatment systems. The main goal for upgrading of MWI residues is the reduction of the leaching rate of the particular residue and a secondary goal is the improvement of the utilization quality. Based on leaching rate changes, technical and economical criteria, the most viable systems seem to be: primary measures and washing / aging for MWI bottom ashes; vitrification and immobilization for MWI fly ashes and immobilization for MWI flue gas cleaning (fgc) residues. 1. INTRODUCTION

Nowadays in the Netherlands, about 750,000 tons of residues from the incineration of municipal waste (MWI residues) are generated yearly. It is expected that this number will be doubled in the next ten years. The MWI residues consist of bottom ash, fly ash, flue gas cleaning (fgc) residues and spent carbon. Because of new legislation in the Netherlands, restrains on the utilization and disposal of MWI residues are upcoming; these restrains are related to the leaching rate of the MWI residues. In the near future, quality improvements of MWI residues will therefore become necessary, considering the growing supply of MWI residues and the tightening of environmental demands. In anticipation of the necessary quality improvements, a literature study has been performed on the state of the art for the effective upgrading of MWI residues [I]. The upgrading methods were evaluated on the following criteria: stage of development, technical feasibility, environmental improvements, utilization potential of the upgraded product and costs. The results of the study are presented in this paper.

646 2. MWI BOlTOM ASH 2.1. General remarks At the moment, the main part of the MWI bottom ashes is utilized as embankment materials for roadbuilding. As a consequence of the enforcement of the Building Materials Decree (BMD), environmental restrictions will arise. The leaching rates of molybdenum and copper will likely exceed the limits of the future BMD. Figure 1 and 2 show that for a large part of the MWI bottom ashes, the N2 leaching requirements for utilization will probably not be met [2,3]. The goal for upgrading of MWI bottom ashes is to meet the N2 requirements of the BMD consistently. Both primary and post treatment techniques are available for the upgrading of the A survey of upgrading methods is shown in environmental quality of MWI slags [4,5]. table 1. In the following sections, several primary measures and post treatment techniques are shortly discussed. frequency

frequency

1 2 1 - 7 -

~-

Boundary N2

I 2

3

4

5

6

r

8

g i o i i

leached amount, mglkg

Fig. l a Frequency distribution of the copper leaching rate of MWI bottom ashes

"

0.30.6 I 2

3 4

5

6

7

8

9 10 11

leached amount, mglkg

Fig. l b Ibid., molybdenum leaching rate

2.2. Upgrading of MWI bottom ashes by primary measures

Acceptance criteria It is significant, that the molybdenum leaching rate of MWI bottom ashes is dependant of the MWI where the bottom ash is generated. It is assumed that in the MWl's with high molybdenum leaching rates, a certain amount of molybdenum containing waste is accepted. If this turns out to be true, the molybdenumleaching rate can be significantly reduced through tightening of the acceptance criteria for municipal waste. Research into this aspect is being performed.

647

Table 1 Upgrading measures for MWI bottom ashes Primary methods

- Tightening of acceptance criteria for municipal

Acceptance

waste ~~

Post treatment methods

~

~

~~~

0, - NO, measures lay out of the incinerator residence time in the burning zone windsift at the end of the burning zone

Measures during the burning process

-

Separation in plant

- separation of bottom ash and boiler ash - separation of bottom ash and grate siftings

Separation measures

- conventional upgrading (separation at 40 mm, ferro separation)

- non ferro separation - separation of the fine fraction ( c 2 mm) Washing

/ aging

Immobilization Thermal treatment

- sintering - vitrification

Measures during the burning process A combination of oxygen dosage under the grate and nitrogen dosage above the burning zone, appears to influence the copper leaching potential significantly.Through the oxygen dosage, the temperature in the grate bed is increased, leading to an optimal burn out, better sintering and reduction of leaching (up to 10 times for Cu) [6]. The nitrogen is necessary, to prevent too high temperatures rises. For new MWl's, this measure could be considered. Optimum burn out and sintering can also be reached through an optimal incinerator design and through a maximum residence time of the slag in the burning zone [5]. A so called "burn out beam" [7], that can be easily constructed, operates like a sort of windsifter at the end of the burn out zone; because fine organic particles are blown back into the burning zone, the loss on ignition of the bottom ash can be reduced significantly. It is expected that this measure will work optimal for an MWI with low contents of grate sifting. Separation measures In the literature, the positive effect of the separation of boiler ashes from bottom ashes on the leaching behaviour is stated [El. Strange enough, in the Dutch practice, the bottom ashes of the MWl's where this measure was performed, did not show significantly better leaching behaviour than others. In any case, the N2 limits were not met. The separation of grate siftings from the bottom ashes can lead to lower copper leaching [8],probably because the content of digestible carbon, that can act as a complexing agent, is diminished significantly.

648 2.3. Upgrading of MWI bottom ashes by secundary measures

Separation measures The intensive conventional upgrading of MWI bottom ashes (separation and crushing of grains > 40 mm, intensive iron separation), will lead to a technically good bottom ash with a low iron content and a low content of unburnt organic parts. This kind of post treatment does not lead to a bottom ash that meets with the leaching limits of the Building Materials Decree. Non ferro separation from bottom ashes leads to an optimized slag quality for cement stabilized slag foundations (expansion reactions are prevented). The leaching behaviour is not improved, since only coarse non ferro’s are removed [9]. About the hypothesis, that the separation of fine particles diminishes the leaching from the bottom ash [lo] the literature is controversial. We feel that on the following grounds this measure should be rejected: 1) technically it is difficult to operate sieves with an opening < 4mm, if the material is not dried; 2) the bottom ashes contain 30 50% of fine fraction, that should be dumped as a waste material after the separation. Washing / aging Washing of the bottom ashes can lead to a substantial reduction in the leaching of both copper and molybdenum [l 11. The suitable washing of bottom ashes directly after their generation appears to lead to a product that meets with the N2 limits of the Building Materials Decree. An aging period prior to washing of the bottom ashes even seems to improve the leaching characteristics.A drawback of washing is the amount of fine sludge that will be generated. The aging of slags leads to a reduction of copper leaching. The influence on molybdenum is unclear [ 121. Immobilization Immobilizationof bottom ashes is not practized, except in situations where the slag is dumped together with MWI fly ashes and / or fgc neutralization sludges. Thermal treatment Sintering and vitrification of bottom ashes lead to a product with a strongly improved leaching behaviour. Those techniques are so energy intensive and so expensive, that it is generally recommended not to use them. 2.4. Conclusions

To realize sufficient quality improvement in MWI bottom ashes to meet with the N2 limits of the Building Materials Decree, in an economically interestingway, the following techniques can probably be used, sometimes in combination. primary measures - acceptance criteria (Mo) - measures during the burning process (02/N2) - separation of grate sifting and boiler ash from bottom ash post treatment - washing - aging

649 3. MWI FLY ASH

3.1. General remarks Utilization of (part of) the MWI fly ash At the moment, about 25,000 tons of Dutch MWI fly ash are utilized as a raw material for asphalt fillers. Although this utilization is sound according to the building materials decree, (the leaching of asphalt with this filler, meets with the V1 limits), there is discussion about the continuation of the use of MWI fly ash as an asphalt filler. The rest of the MWI fly ash is disposed. Environmental quality of M WI fly ash Based on its very high leaching rate of inorganic hazardous components, MWI fly ash is classified as a chemical waste material, that has to be disposed in the strictest disposal regime (C2), at high costs. Aside from the leaching rate of MWI fly ash, its content of dioxins is regarded as a problem by some parts of the society. Disposal The disposal regimes in the Netherlands are called C2, C3 and C4. C2 is the strictest and C4 the mildest regime. The leaching of inorganic hazardous components from waste materials is decisive for their classification. Starting from 1996, it is forbidden to dispose MWI fly ash in an untreated form. Upgrading measures Taking into account the growing quantities of MWI fly ash that will be generated yearly in the future, upgrading measures are sought that offer an environmentally and economically feasible alternative for disposal at C2 level. The goal for these upgrading measures is at least disposal at a milder regime and if possible, utilization as a building material. In table 2, the known upgrading measures are listed [4, I]. They are shortly discussed. 3.2. Wet cleaning

Washing + disposal By washing the MWI fly ash with neutral water, the leachable chloride content is removed. By washing with slightly acid water, some heavy metals are removed [4]. Judging from the literature, washing of MWI fly ash does not lead to sufficient upgrading to reach the C4 level. Washing is promoted exclusively, to upgrade the disposal regime of MWI flyashes. Washing results in mass increase of the MWI fly ash (by the water that is taken up) and in an increased quantity of FGC neutralizing sludges. Washing, pelletizing, refeed in the MWI In one specific washing process [13], the wet MWI fly ash is dried through filterpressing, after that the moist ash is mixed with cement and pelletized; the pellets are fed back into the MWI. The results of the leaching tests of the MWI bottom ash with

650

Table 2 Upgrading measures for MWI fly ashes Wet cleaning

-

Removal of dioxins

- reducing conditions, 400 - 500C - oxidizing conditions, 600 - 700C

immobilization

-

washing t disposal washing, peiietizing, refeed in the MWi microbioloaicai cieanina

immobiiization with inorganic binders

- combination with fgc neutralizing sludge - low T artificial gravel production (through pozzolanic reaction)

- chemical fixation

-

immobilization with organic binders

Sintering techniques

- sintering techniques - aiinite cement

Vitrification techniques

-

melting

- melting under reducing conditions - plasma techniques

pellets, are comparable with the leaching results of normal MWI bottom ash. It is still unclear wether these "combined" bottom ashes meet with the limits of the Building Materials Decree. Microbiological cleaning In the past years a study has been performed into the possibilities to use microbiologicalcleaning for MWI fly ashes. The results of the study indicated that there was only minimum upgrading of the leaching behaviour of the fly ash; furthermore a large quantity of sludge was generated, that has to be dumped at a C2 disposal. 3.3. Removal of dioxines

By heating the MWI fly ash at 300 - 400C (under reducing conditions) or 600 - 700C (oxidizing), dioxins can be destroyed. During the oxidizing process, also mercury is removed. The processes for removal of dioxins cannot lower the leaching rate of MWI fly ash. They can possibly be used as a pretreatment technique for cold immobilization. 3.4. Immobilization

Immobilization with an inorganic binder In foreign countries, immobilization of MWI fly ash with inorganic binders (such as The portlandcement, blastfurnace slag and waterglass) is practiced commercially [14]. purpose of the immobilization is the environmentally safe disposal of MWI fly ashes. The immobilized MWI fly ash is physically encapsulated and chemically stabilized. The immobilized and stabilized MWI fly ash is allways disposed. For the Dutch situation, the MWI fly ash can probably be upgraded to a C4 level disposal, if the correct recepture

65 1

is used. There is no certainty that products can be made that meet with the limits of the Building Materials Decree and with the technical demands for utilization. The actual level of upgrading is dependant on the dose and the type of the immobilization binder. Possibly, high dosages of binder have to be utilized, which will also realize in large volume increases, which can be considered as a drawback. An advantage of immobilization is the low price level. With very limited information on the actual leaching behaviour of immobilized products, we still assume that in the majority of cases, diposal costs have to be added to the immobilizing costs. Immobilization of MWI fly ash combined with FGC neutralizing sludges FGC neutralizingsludges from MWl’s have a surplus in sulfide; this can be used for the stabilization of MWI fly ash. Often an inorganic binder has to be added. In Germany, Switzerland and Austria, this combined immobilization is practiced at some disposal sites, for the purpose of environmentally safe dumping [15]. From the literature, we conclude that is difficult to reach the C4 level, if not sufficient quantities of binder are used. Low T artificial gravel Low T artificial gravel production has been tested for gravel that contains about 35% of MWI fly ash. Concrete that contains this type of gravel, meets with the strictest limit of the Building Materials Decree. Economically it is more interesting to produce a gravel that contains more than 75% of MWI fly ash. Regretfully that option has not been tested. Immobilization with organic binders The immobilization with organic binders (the utilization in asphalt fillers is not meant here) is based on an optimal physical encapsulation of the MWI fly ash. No chemical stabilization occurs. The costs are so much higher than for immobilization with an inorganic binder that this is no real option for MWI fly ash. 3.5. Sintering

Sintering techniques Sintering of MWI fly ash probably will not lead to a product that can meet the N2 or the V2 limits of the Building Materials Decree. In the past, some efforts have been done to utilize MWI fly ash in sintered gravel; they were not continued, as the gravel with MWI fly ash (25%) showed an unacceptable leaching rate. Alinite cement Alinite cement is a special cement that is produced from MWI fly ash and dry flue gas cleaning residues. Although laboratory tests showed a favorable leaching behaviour, there are still doubts about the leaching rate of the product at an industrial scale. Additionally it is felt that the marketing possibilities for alinite cement in the Netherlands are very small. The cost price is high compared to immobilization.

652 3.6. Vitrification techniques

Melting techniques The final product that results from the treatment of MWI fly ash in a melting furnace, is a granulate that has a very low leaching rate (it meets the N1 limits of the Building Materials Decree). The hazardous inorganic components are partly removed and partly immobilized in the granulate. The dioxins are completely destroyed [16]. Melting techniques + reduction The difference with "oxidizing" melting techniques is the possibility to separate all hazardous inorganic components. The reduced metal phase can possibly be sold [16, 171. Plasma techniques The granulates from plasma techniques and melting techniques are comparable. A general remark about all electric vitrificationtechniques is that they have a very high energy consumption (ca 1MWh/ton for melting techniques and 2MWhlton for plasma

techniques). The costs are uncertain because in the available literature, investment costs are often unclear; the reported costs of melting vary between NLG 250 and 1,000.=. Because of the high energy consumption and the high costs, these techniques should only be considered when a high grade market for the granulate is available and certain. 3.7. Conclusions

In the study, the following was concluded: To realize sufficient quality improvement in MWI fly ashes to meet with the C4 limits for disposal or with the limits of the Building Materials Decree, in an economically interesting way, the following techniques can be used, in order of decreasing priority: - immobilizationwith an inorganic binder (probably C4) - melting techniques and melting techniques t reduction, if the market for the granulate is available (N1 utilization, destruction of dioxins) - low temperature artificial gravel production - joint immobilizationwith neutralizing sludges 4. MWI FLUE GAS CLEANING NEUTRALIZING SLUDGES

4.1. General remarks

In the past few years, wet flue gas cleaning has been installated at several Dutch MWl's. There is only limited information about the quality of FGC neutralizing sludges in the Netherlands; because of that only tentative remarks can be made. It appears that the FGC sludges have a varying quality. Based on the the leaching rate, FGC neutralizing sludges are C2 waste materials and sometimes C3 waste materials. FGC neutralizing sludges are disposed at high costs. Upgrading must lead to a milder disposal regime. Upgrading measures are summarized in table 3 [17].

653 Table 3 Upgrading measures for MWI FGC residues

-

Immobilization

immobilization with inorganic binders - combination with MWI fly ash - low T artificial gravel production (through pouolanic reaction)

Vitrification techniques

- melting - melting under reducing conditions

4.2. Immobilization

Immobilization with inorganic binders Immobilization can possibly result in a product that meets the limits of the C4 disposal class. Immobilization with sulfur is also considered. Because of the high contents of chlorides, sulfates and alkalies in the FGC neutralizing sludge, immobilizationwill be even more difficult than for MWI fly ashes. The costs will therefore be higher. Combined immobilization with MWI fly ash In Germany, Switzerland and Austria, this combined immobilization is practiced at some disposal sites, for the purpose of environmentally safe dumping, often with addition of cement. As stated earlier, we conclude that it is difficult to reach the C4 level, if not sufficient quantities of binder are used. Low T artificial gravel production Theoretically, possibilities exist for the preparation of artificial gravel. 4.3. Vitrification MWI FGC neutralizing sludges could possibly be treated in a vitrification plant, together with MWI fly ash. Because of high chloride and alkalies emissions, this option is not recommended. 4.4. Conclusions

For MWI FGC neutralizing sludges, the main option for upgrading is immobilization. Immobilization with an inorganic binder is preferred, but combined immobilization is also possible. 5. EVALUATION

In this article, an overview was given of the present state of the art on upgrading measures for MWI residues. No reference was made to new municipal waste processing methods such as pyrolysis. A selection was made of techniques that could possibly be used in the future. The evaluation was based on literature data. Further

654

practical R&D is necessary to be able make a founded choice for the future upgrading approach. 6. ACKNOWLEDGEMENT

The financial support (contract number 35332011910) of the National Research Program for the Recycling of Waste Substances, which is jointly managed by the Netherlands Agency for Energy and the Environment and by the National Institute of Public Health and Environmental Protection, is gratefully acknowledged. 7. REFERENCES

1 KEMA, (in Dutch) Upgrading methods for MWI residues, NOH publ. 93028, 1993. 2 W A V , Internal data technical/environmental quality of MWI residues, 1993. 3 W A V , (in Dutch) Residual materials from municipal waste incineration, NOH publ. 93029, 1993. 4 M. Faulstich and D.Zachaus. Ruckstande aus der Mullverbrennung, EF Verlag Berlin (1992) 1. 5 D.O. Reimann, Mull und Abfall 9/92, (1992) 609. 6 F. Rampp et al., VDI Seminar "Schlacke, Aufbereitung, Verwertung und Entsorgung", Presentation nr 13, 1993. 7 D.O. Reimann, VDI Seminar "Schlacke, Aufbereitung, Verwertung und Entsorgung", Presentation nr 9, 1993. 8 J. Vehlow, Ruckstande aus der Mullverbrennung, EF Verlag Berlin (1992) 161. 9 Feniks recycling Maatschappij, (in Dutch), Expansion of MWI slags, reports 91.009/n/5 and T&A N/092/me/wdw/5 10 J.A. Stegemann and J. Schneider, Proc. WASCON conf, Maastricht, nov 1991, Elseviers studies in environmental science 48, (1991) 135. 11 TAUW, Research into the possibilities of upgrading of MWI bottom ashes by washing processes, TAUW report 51161.50, 1989. 12 U. Lahl, Ruckstande aus der Mullverbrennung, EF Verlag Berlin (1992) 609. 13 J. Vehlow et al., Mullverbrennung und Umwelt 3, EF Verlag Berlin (1989) 687. 14 CSO, (in Dutch) The "state of the art" of immobilisation, report nr 090.90, 1990. 15 H . 4 . Ponto and J. Demmich, Ruckstande aus der Mullverbrennung, EF Verlag 16 M. Faulstich and P. Kocher, VDI Seminar "Schlacke, Aufbereitung, Verwertung und Entsorgung", Presentation nr 17, 1993. 17 F.J.M. Lamers et al., Proc. WASCON conf, Maastricht, nov 1991, Elseviers studies in environmental science 48, (1991) 513. 18 J. Demmich, Report VGB Congress 09.02.1993, Essen, nr VGB - TB 703.

Environmental Aspecfs of Conshuction wilh WmfeMaterials JJJ.M. Goumans, H A van der SIoot and lI1.G. Aalbers (Editors) @I994 Elsevier Science B.V. AN rights resewed.

655

Re-use of colliery spoils in construction materials using Fluidized Bed Combustion J . J.M Heynen", H.N.J . A. Bolkb, G.J. Senden' and P.J. Tummers"

YWACO B.V., Consultants for Water and Environment, P.O. Box 525, 5201 AM 's-Hertogenbosch, The Netherlands 'Heijmans Milieutechniek B.V., P.O.Box 377, 5240 AJ Rosmalen, The Netherlands "NOVEM, Netherlands Agency for Energy and the Environment, P.O. Box 17, 6130 AA Sittard, The Netherlands "COMAN B.V. Consulting Engineers, P.O. Box 198, 6400 AD Heerlen Abstract This article describes a plan to upgrade colliery spoils to construction materials. The plan is based on the idea that the mineral composition of which colliery spoils are made of are similar to the composition of construction materials. However, colliery spoils also contain carbon and sulfides whilst construction materials mostly do not. By thermal treatment, i.e. burning out the carbon and oxidation of sulfides, the mineral part can be upgraded into a form, suitable for production of construction materials. An optimized Fluidized Bed Combustion (FBC) technology in combination with treatment of coarser particles in a shaft-furnace, is regarded the most suitable method for this purpose. An integrated processing facility based on proven technologies will be able to upgrade colliery spoils into (1) basic minerals to be used for the production of construction materials (a high valued re-use), simultaneously recovering the remaining energy-content, i.e. (2) electricity and (3) heat. The facility itself can very likely be a basis or crystallization point for innovative building material industry, thus causing an economic stimulus for the region. Furthermore, the removal of colliery spoil deposits will prevent groundwater contamination caused by percolate which may contain sulphuric acid resulting from the oxidation of sulfides. A feasibility check for this project has been carried out for FBC capacities up to 200 MW-fuel, aimed at the removal of an uncovered colliery spoil deposit of about 30 million tonnes in Liinburg, the southernmost province of The Netherlands. Production of ceramic limestone as an end-product was found to be a very interesting option.

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1. INTRODUCTION In Limburg, the most southern province of the Netherlands, large scale coal mining activities were carried out until 1975, leaving considerable amounts of colliery spoils in the direct environments of the former collieries. Most of these colliery spoil heaps have been covered and integrated in the landscape, but some 36 million tonnes are still uncovered and not integrated, thus forming an obstacle in the landscape. More important, the groundwater quality is threatened by these uncovered heaps. Colliery spoils and minestone contain a considerable amount of pyrite (ironsulfides) which can be oxidized to sulphuric acid. Moreover, the oxidation can be accelerated by thiobacilli bacteria, especially at lower pH values. As a result of this biological catalyzation, the oxidation process can be speeded up, at pH-values below 2.5, by lo5 lo6 times [I]. As long as the colliery spoils contain enough lime, the sulphuric acid will be buffered. However, when the lime buffer is exhausted, pH values in the percolate will drop (and boost accelerated biological oxidation) and form a threat for the groundwater quality as a result of acidification of the percolate[2-3]. In order to prevent groundwater pollution in the future, the best solution is to remove the colliery spoil heaps. An appropriate approach to accomplish this aim is to upgrade the colliery spoils by thermal treatment towards basic materials for production of construction materials, thus accomplishing a total, high valued re-use of colliery spoils and recovery of the remaining energy content. The basic ideas of this approach can, in principle, be used in any region where colliery spoil and/or low-grade coal deposits are available. In this perspective Novem, the Netherlands Agency for Energy and the Environment, and Mauran B.V. investigated a plan for a relatively small upgrading unit (50 MW-fuel) in the municipality of Kerkrade, Limburg. This moment this approach, based on upgrading by thermal treatment, is being further developed and implemented by Heijinans Milieutechniek B.V., aimed at a location in the municipality of Brunssum, The Netherlands, at a scale of about 150 MW-fuel. A feasibility check is being finalized and more detailed cost calculations and engineering are planned for 1994. 2. PRINCIPLES OF THE COLLIERY SPOIL UPGRADING FACILITY (CSUF). 2.1. General It is known that by using the proper upgrading technologies, colliery spoils can be used as a basic material for the production of high-valued construction materials [4]. As colliery spoils can still contain a relatively large amount of coal (especially older, lowefficient washed minestone can contain up to 40 % coal), energy recovery is also an interesting feature. In the Netherlands, the development of a Colliery Spoil Upgrading Facility (CSUF) was initiated[5]. This facility will be an integrated colliery spoil processing plant producing: construction materials; electricity; heat (which can be used in greenhouses and/or municipal heating systems).

The CSUF is based on a combined Fluidized BedlShaft Combustion reactor in which the

657 colliery spoils are burnt-out to a sufficient high extent. As a result of the carefully chosen burning conditions the combustion products are suitable for producing high-valued construction materials, whereas the produced electricity and heat are useful by-products. 2.2 Fluidized Bed Combustion Fluidized Bed Combustion (FBC) is a proven technology especially suitable for the combustion of smaller particles containing a relative low caloric value. Coarser particles > 20 mm can be burnt in a shaft furnace [6]. For completeness the FBC technology will be briefly explained. Simplified, a FBC-furnace can be described as a cylindrical vessel with a porous bottom plate. The combustion air is blown through this bottom plate with a such velocity that the particles in the furnace will be lifted and be whirled: they get in a so-called "fluidized" condition. When fluidized the solids behave almost like a liquid. Because of this, process conditions like temperature, heat exchange, residential time etc. can be well controlled. Furthermore additives (such as limestone for SOz emission reduction) can be added easily. In figure 1 a principle scheme for a FBC furnace is drawn. This is a so-called "slow" or "bubbling" fluidized bed. There are several other types (e.g. the "fast" or recirculating fluidized bed) which will not be further discussed here. Further details on FBC-technology are available in literature [6].

A

I

Dust

Air distributor plate

Figure 1. Principle scheme of a Fluidized bed system.

2.3. The Colliery Spoil Upgrading Facility (CSUFJ The CSUF in the Netherlands is planned to be situated in the municipality of Brunssum on the site of a colliery spoil deposit of about 30 million tomes. These colliery spoils will be fed into a pre-treatment unit (drying, breaking, sieving, grinding) from which the fines (0-6 mm) will be fed into the FBC-unit. The coarser particles (20-45 mm) will be fed into the shaft-furnace. This will result in two types of mineral product: calcinated clay, applicable as a raw material for production of construction materials and broken burnt-out minestone, for direct use as gravel and tillers. Simultaneously, a minestone washery plant has just been taken into operation on this colliery spoil deposit as well. By use of gravitational separation techniques, this washery

658

.

plant separates the colliery spoils into: washed minestone (usable as filling material); low-grade coal; washery sludge. The low-grade coal and the washery sludge can very well be used as an additional feed for the FBC, thus acting as a replacement for a caloric equivalent of unwashed colliery spoils. If done so, the CSUF can be operated complementary to the washery-plant, thus increasing the possibilities for re-use of the colliery spoils. A flow-sheet the CSUF has been drawn in figure 2.

Colliery Spoils 0-300 mm

I I1

CSUF

I Pretreatment

I

I

I I

I I

I

i

I

: I

I

I

I I

I

I

--

I I

Washery-plant

washery sludge

I shaft-furnace

I

I

V

Fluidized Bed Combustion (FBC)

- -- - - - - -

I

I 1

lowgrade coal

Dossible FBC-feed

I gravel I

washed minestone

cerainic limestone production

Figure 2. Flow-sheet of the Colliery Spoil Upgrading Facility (CSUF). At the time of writing, a feasibility check was carried out by Heijmans Milieutechniek B.V., COMAN B.V. and IWACO B.V. under supervision of LIOF (Limburg regional economic development institute) and NOVEM. In the next chapters a brief overview of this feasibility check will be given.

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3. FEED OF THE COLLIERY SPOIL UPGRADING FACILITY In table 1 properties of the feed of the CSUF are given: Table 1 Approximate composition of feed of the CSUF Ash content (%-weight) Untreated colliery spoils Low-grade coal Washery sludge

Combustion value (MJ/kg)

90

4.25 18 12

40

60

These values have been used for the feasibility check, however, they need to be further investigated for verification. 4. PRODUCTS AND APPLICATIONS The feasibility of the CSUF depends largely on possibilities to actually sell the products that are made. In table 2 some potential products are given. Table 2 Potential Droducts of the CSUF ~

Product

Application

broken burnt-out minestone

- bulk-fill material

- aggregate material

Market potential in The Netherlands (tonneslyear) 40,000,000 8,000,000

Estimated revenue (Dfl. per tonne) 5 to 6 7 to 8

1,200,000 (gravel) 1,700,000 (split)

13 17 to 26

9,000,000

13 to 26

25,000 to

15 to 30

for road-bases - supplementary

calcinated clay

materials for asphaltic concrete (warm production) - supplementary materials for cementous concrete brick industry

50,000 500,000*

ceramic limestone construction industry 80 to 100 (via end-production using dcinated clay) *: based on 20% of the market volume of ordinary limestone and 75% replacement of primary raw materials by calcinated clay; ceramic limestone is a new product with improved properties.

660

Remarks on table 2 the mentioned market volume of 8 million tonnes for aggregate materials for roadbases is a very competitive market, where also many demolition debris products are used; in the estimate for the market potential for supplementary materials for cementous concrete (9 million tonneslyear) a maximum use of demolition debris granulates is already assumed. in the estimate for the market potential for supplementary materials for asphaltic concrete (3 million tonnedyear) maximum recycling of secondary asphaltic concrete is already taken into account. Regarding the applications of broken burnt-out minestone, applications like supplementary materials for cementous and/or asphaltic concrete seems to be most interesting because of the higher revenues to be obtained. With regard to applications for calcinated clay, ceramic limestone is an especially interesting material because it can be directly produced from calcinated clay (as estimated by TNO [7]). For ordinary production, natural clay has to be calcinated whereafter ceramic limestone bricks can be produced by pressing, by use of an autoclave. The FBC, however, produces calcinated clay as a ready-to-use product, not needing further pretreatment. This overall process of FBC-combustion (in which calcination is integrated) followed by autoclave production of limestone bricks seems to be a very attractive option which is planned for further detailed investigation in 1994. 5. ENVIRONMENTAL ASPECTS OF THE CSUF

The operation of the CSUF will lead to positive effects on the environment: a likely long term groundwater pollution source can be eliminated; by using upgraded colliery spoils as a basis for the production of construction materials, primary raw material resources (sand, clay, gravel etc.) can be preserved and the amount andlor size of landscape destroying sandlclaylgravel exploitations can be reduced; burnt-out minestone can be produced without uncontrolled emissions (e.g. SOz) to the air; large obstacles in the landscape (the colliery spoil heaps) will be removed. -

With respect to the environmental effects of the upgrading process itself, the following precautions will be taken: reduction of emissions to the air by process-integrated measures; lime supplied in the reactor-feed will cause a significant SO,-emission reduction (85 to 90%); NO,emission reduction can be reached by staged combustion at low temperatures (down to 200 mg/m3) and dust emissions can be reduced by a dust filter (to 20 mg/m3). These measures together will assure low emission concentrations. minimization of the needed amounts for process and cooling water, since the Dutch governinent’s policy is to restrict further use of groundwater; at the planned location, no surface water is available.

66 1

The potential leachability of the CSUF-products has been looked at. Based on available information on the composition and a few cascade leaching tests of locally available colliery spoils, it is deducted that the composition and leachability of the (at low temperatures, 850 "C) burnt-out CSUF-products will be similar to natural clay soils and thus will fully comply with the Dutch Construction Materials Act. This however should be confirmed by tests at the actual CSUF-products. In the Netherlands an Environmental Impact Assessment (EIA) is compulsory and will be dealt with by the authorities together with the demand for legally required permits. By carefully balancing the complementary environmental effects and costs of extra emission reducing measures, the authorities will have to impose well-considered requirements (described in the permits to be given). Eventually, the EIA should balance the positive and negative environmental effects and compare several variants with each other and with the so-called zero variant: when nothing at all will be done. At this moment (January 1994) the actual Environmental Impact Assessment has not yet been carried out. The preliminary inventory has been made and discussions with governmental authorities confirmed that no major constrains are to be expected.

6. ECONOMIC ASPECTS OF THE CSUF 6.1 Financial calculations Based on literature [8-91, expertise and experience with similar projects, preliminary economic calculations for a CSUF have been made based on the location in Brunssum. Financial data were calculated over FBC capacities in the range of 50 to 200 MW fuel. Because most of these figures are regarded as confidential, at present, they will not entirely be described in this paper. However, a brief overview of the assumptions will be given below as well as the resulting Costs of Mineral Product (COMP).

Assumptions have been made on investment costs regarding:

- fuel preparation: excavating, transport, breaking, sieving, drying and grinding; - FBC-unit; - shaft-furnace; - civil works, infrastructure.

Annual costs comprises: - capital costs: calculated from annuities of investment costs at an interest rate of 8 % and

a life-time of 20 years. Also governmental investment premiums were taken into -

account, ranging from 0 to 50% energy costs of fuel-preparation; maintenance: 2 to 8% of respective investment costs personnel (a total of approx. 80 persons); miscellaneous; risk and profits. Further, electricity revenues are calculated assuming:

- 54 MW electric power at 200 MW (FBC) fuel capacity;

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- 13.5 MW electric power at 50 MW (FBC) fuel capacity; - 8000 production hours per year; - electricity prices (supply to local electricity distributing company) ranging from Dfl 0.06 to 0.12 per kWh; Dfl O.O84/kWh is considered as a basic minimum price to be obtained. - potential revenues from produced heat are until now not taken into account. After calculating the annual costs and subtracting the electricity-revenues the Costs of Mineral Product (COMP) remain. Several variants in the above mentioned ranges including variants where colliery spoil is partly replaced by washery sludge and/or washed low grade coal (at zero prices) have been calculated. In table 3 a brief overview of some variants for a CSUF with a capacity of 150 MW-fuel (40.5 MW electric) is given. In the 150 MW,,, -variant the total amount of CSUF-product will be about 1,4 million tonnes of product/year. In the case of replacement of colliery spoils with washery sludge and washed-out low grade coal (both approx. 80,000 tonnedyear) from the on site present washing facility, the total product amount will be about 700,000 tonnedyear. Table 3 Overview of Costs of Mineral Product in some selected variants at 150 MW-fuel Costs of mineral ~roduct(Dflhonne. total average) Input: Colliery spoil only (1,564,000 t/a)

Electricity price (Dfl/kWh)

0.06 to 0.12

Output: calcinated clay (915,000 tla) and burnt-out minestone (493,000 t/a)

Input: Colliery spoils (695,000 t/a) plus washery sludge and lowgrade coal (80,000 t/a each) Output: calcinated clay (487,000 tla) and burnt-out minestone (219,000 t/a)

No investment premi u i n

40 % investment premium

No investment premium

40 % investment premium

30 to 17

22 to 8

45 to 17

30 to 3

Remarks on table 3 Replacement of a caloric equivalent of colliery spoils with washery sludge and low grade coal results in higher COMP at lower electricity prices. Because of the higher caloric content of the washery product less total feed is needed. This results in a lower amount of product over which the total remaining costs are divided. At lower electricity prices this is not sufficiently coinpensated by lower investment costs in handling equipment.

6.2 Econoniic feasibility The facility is feasible if the revenues obtained from products to be sold equal the COMP. If broken burnt-out minestone and calcinated clay are the only products (described

663 in chapter 4) from the CSUF, the revenues of the products can be estimated at about Dfl. 13 to 26/tonne. In this perspective, the option for producing ceramic limestone is very interesting from a financial point of view. The revenues for ceramic limestone can be estimated at Dfl. 80 to 100/tonne. However, costs of the autoclave end-production process still have to be added to the COMP. Because the produced calcinated clay does not need further pre-treatment and the CSUF produces heat, which can be used for the autoclave-process, it is estimated this option could be economic feasible. This should, however, be further investigated. In particular, the market potential of this new product and technical details should be further analyzed. However, by granting an investment premium and/or higher electricity prices, the regional government can encourage an elegant way to remove the remaining colliery spoil deposits. In that way a future threat for groundwater quality will be removed and the economic development of the region will be stimulated. 7. CONCLUSIONS A Colliery Spoil Upgrading Facility (CSUF) offers a realistic opportunity for a highvalued 100% re-use of colliery spoils and/or low grade coal. Furthermore, in this way an obstacle in the landscape can be removed and future groundwater quality deterioration can now be prevented at probably lower costs than curing will require after acidification of the deposit’s percolate. A CSUF is especially interesting for regions with large colliery spoil and/or low grade coal deposits and where a need for building materials is present. Once realized it will probably form a regional stimulus for economic development and innovative construction material industry. Economic feasibility mostly depends on: revenues: dependent of the size and accessibility of the market and kinds of construction materials; revenues are also dependable on possibilities to sell or use the surplus of electricity and heat. investment and exploitation costs; environmental requirements. These parameters will undoubtedly differ for each considered region, and should be investigated in an at the target region aimed feasibility study.

In the investigated case of the Brunssum location of the CSUF, the option for production of ceramic limestone appears very interesting: the CSUF-product will be a ready-to-use basic material for this purpose and the in the CSUF recovered energy can find a direct application in this end-production. This idea should be further investigated. Local government supports (investment premiums and/or higher electricity prices) could tip the feasibility balance into a clearly positive scale. Such support will stimulate economic development and employment (directly approximately 80 men, excl. ceramic limestone end-production) and can very well stimulate further development of innovative ceramic industry.

664 8. REFERENCES 1 B.B. Jrargensen, The microbial sulphur cycle, Microbial Geochemistry (Ed. W.E.

Krumbein), pp. 91-124, Blackwell Sc. Publ., Oxford, 1983. 2 I. Twardowska and J. Szczepariska, Transformations of pore solutions in coal mining wastes, Proc. 3rd. int. Symposium on the Reclamation, Treatment and Utilization of Coal Mining Wastes, Glasgow UK (Ed. A.K.M. Rainbow), pp. 177-185, Balkema publ., Rotterdam, 1990. 3 M. Kerth, Untersuchungen zur Pyritverwitterung in einer Steinkohlenbergehalde des Ruhrgebietes, N. Jb. Geol. Palaont., 1988 (lo), pp. 592-604, Stuttgart. 4 J. Leonhard and Th. Schieder, Utilization of Washery Waste as Secondary Raw Materials in Civil Engineering and other Industries/Verwendung und Verwertung von Aufbereitungsabgangen als Sekundarrohstoff in der Bauindustrie und anderen Industriezweigen (in English and German), Aufbereitungstechnik, No. 3 1, pp. 89-97, 1990.

5 J.J.M. Heynen, G.J. Senden and P.J. Tummers, Re-use of Mining Wastes in Construction Materials via Fluid Bed Combustion and combined Energy-Utilization, Proc. 4th. int. Symposium on the Reclamation, Treatment and Utilization of Coal Mining Wastes, Krak6w Poland, (Ed. K.M. Skariyriska), pp. 681-688, Dept. Soil Mech. and Earth Str.,Un. Agr. Krak6w, 1993. 6 R.H. Perry and D. Green (Eds), Perry’s Chemical Engineers’ Handbook, 50th int. ed., pp. 20-47 to 20-48 and 20-58 to 20-75, McGraw-Hill Book Co, Singapore, 1984. 7 R. van der Stel and A.H. de Vries, Verkennend onderzoek naar de mogelijkheden om gecalcineerde kleiachtige inassa’s te verharden in een autoclaaf, TPD-KK-RPT-93-124, TNO-report, Eindhoven, 1993.

8 Northeastern Power Company, Resource Recovery Facility Kline Township Pennsylvania, Reading Energy Company, Philadelphia USA (information sheet). 9 J. Bailey, Colliery Spoil as a feedstock in Fluidized-Bed Combustion, Minerals and the Environment, London, V01.2. P. 49.

Environmental Aspects of Construction with Waste Materials JJJM Goumans, H A . van der Slmt and Th.G. Aalbers (Editors) el994 Elsevier Science B.V. All rights resewed.

665

Recovery of raw materials from reclaimed asphalt pavement E. Mulder'), C. de Groot'), C. Joke$) and J. van der Zwan4) *)

TNO Environmental and Energy Research, P.O. Box 342, 7300 AH Apeldoorn, The Netherlands

')

Rasenberg Wegenbouw B.V., Breda, The Netherlands

3,

Wegenbouwmaatschappij J. Heijmans B. V., Rosmalen, The Netherlands

4,

Dutch Ministry of Transport and Public Works, Road and Hydraulic Engineering Division, Delft, The Netherlands

Abstract A research programme is being carried out to find a way to re-use all the constituents of bituminous asphaltic concrete, as well as the mineral fractions of tar-containing asphaltic concrete. From the results of a feasibility study it may be concluded that this is technically feasible. The most critical process step is the extraction of the asphalt. A twostage counter-current extraction with toluene as a solvent seems to be convenient to obtain mineral fractions (gravel and sand) containing only 0.1 % asphalt and a filler containing ! asphalt. Recovery of the solvent from the mineral fractions can best be done about 1.5% by means of drying.

1.

Introduction

In The Netherlands a large part of reclaimed asphalt pavement is re-used. Mostly the crushed asphalt granulate is added to a mixture of primary raw materials during the preparation of new asphaltic concrete [l]. However, the supply of reclaimed asphalt is higher than the capacity of this high grade "re-use'' option. For this reason, more and more reclaimed asphalt is being used as a low grade foundation material in road construction, or is being dumped. A special category of asphaltic concrete is formed by the tar containing asphaltic concretes. Reclaimed pavement of this category cannot be re-used by means of "in-plant" mixing because of the emission of polycyclic aromatic hydrocarbons (PAH's) at the prevailing temperature. From an environmental point of view, PAHcontaining reclaimed asphalt should be removed from the chain. To overcome the above mentioned problems, two road construction firms, i.e. Rasenberg Wegenbouw B.V. and Wegenbouwmaatschappij J. Heijmans B.V., started a research programme to fmd a way to re-use all the constituents of bituminous asphaltic

666 concrete, as well as the mineral constituents of tar containing asphaltic concrete. This research is being carried out by TNO Environmental and Energy Research and is being guided by the Road and Hydraulic Engineering Division of the Dutch Ministry of Transport and Public Works. The research consists of three phases, the first of which, a feasibility study, has already been completed [2]. Based on this work, the road construction firms have applied for a patent for the process. The second phase, aiming a further technical development of some major unit-operations, is now in progress. The third phase will be an optimisation of the defined process on a pilot-plant scale. In this paper in chapter 2 a description will be given of preliminary investigations that have been done, according to some important parameters. Then the results of this parameter study are evaluated in chapter 3. In chapter 4 the results are translated in a design of the different process steps. The paper will end with some conclusions.

2.

Parameter study

The intention of the research programme was to develop a process to recover all raw materials from reclaimed asphalt pavement. These raw materials are gravel (the coarse aggregate > 2 mm, 55%), sand (mineral aggregate between 63 pm and 2 mm, 35%), filler (fine mineral filler material < 63 pm, 5%) and asphalt 5 % . In the first instance, a raw process design was made, consisting of the following steps: - extraction of the bituminous (or tar containing) asphalt by means of an organic solvent; - separation of the coarse mineral fractions (gravel and sand) and recovery of the adhering solvent; - separation of the filler from the loaded solvent and recovery of the filler as a dry powder; - separation of the asphalt from the solvent. In order to be able to make a more detailed process design, a number of parameters had to be investigated. These parameters were the type of solvent (for the extraction of the asphalt), the extraction conditions and the way of recovering solvent from the mineral fractions. The study of these parameters is described in the following sections.

Type of solvent This study was started with a literature search. A number of solvents were found to be able to dissolve bituminous (or tar containing) asphalt. The solvents were divided into three categories: halogenated solvents, aromatic solvents and aliphatic solvents. From each category one solvent was chosen (based on characteristics such as toxicity, inflammability, boiling point, cost etc.). The following three solvents were chosen: dichloromethane, toluene and heptane. Knowing that part of the bitumen and tar components do not dissolve very easily in the a-polar solvent heptane, 10%methanol was added to the heptane.

667 After this pre-selection, a laboratory research was carried out, in which two types of asphalt granulates (bituminous and tar-containing, respectively) were mixed up with the three types of solvent in a liquid to solid ratio (L/S ratio) of 1 I/kg. The mixture was rolled in a flask on a roller table for 30 minutes. The following conclusions were made: - From the 3 solvents the heptane/methanol mixture showed the poorest ability to dissolve both bituminous and tar containing asphalt from the granulates. - As far as bituminous asphalt was concerned, dichloromethane and toluene were equally good, but toluene happened to be better than dichloromethane for tar containing asphalt. - So, from a technical point of view, the best choice was toluene. However, also other selection criteria have been taken into account. For that reason in the experiments as described in the following sections both dichloromethane and toluene were used as solvents. The final choice between dichloromethane and toluene was made after that also these experiments had been carried out.

Extraction conditions The extraction of asphalt from reclaimed asphalt concrete granulates is affected by several parameters. The effect of the following parameters was investigated: the way of agitation, the agitation time, the number of extraction steps, and the L/S ratio. It was clear from the beginning that the mixture of asphalt granulates and solvent had to be agitated. Investigations with a so called Soxhlet extraction apparatus had shown that, if the granulates were not agitated, the extraction time would be up to about 5 hours. The next step was to put the flask with the mixture on a roller table (as described before). This decreased the extraction time to about 2 times halve an hour (in two subsequent steps). It seemed that a more intensive agitation would further decrease the extraction rime. Stirring was not thought to be a real option because of erosion, caused by the heavy coarse mineral fraction. Then a small cask was supplied with obstructions to make the granulates tumble over each other, when the cask was rolled on the roller table. This decreased the extraction time to 2 times 20 minutes. A counter-current extraction always has a higher efficiency than a co-current extraction. To simulate a counter-current extraction the mixture of asphalt granulates and solvent was decanted after an agitation time of 20 minutes and a settlement time of 15 minutes. New solvent was then added to the half-extracted asphalt granulates and the mixture was agitated for another 20 minutes. After these two extraction steps, the coarse mineral fractions (gravel and sand) appeared to be clean enough (appr. 0.1 % asphalt). As far as the L/S ratio is concerned, a ratio as low as possible is, of course, the most profitable. However, the ratio has to be high enough to guarantee a good liquid to solid contact and to have enough capacity to dissolve the asphalt. Investigations were done with L/S ratio’s of 0.5 and 1 I/kg. The L/S ratio of 1 llkg yielded much cleaner products than 0.5, so for following investigations an L/S ratio of 1 l/kg was chosen. The extraction conditions that were found suitable for the extraction of asphalt (both bituminous and tar containing asphalt) from reclaimed asphalt concrete granulate are summarised in table 1.

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Table 1: Optimum extraction conditions Condition / parameter

Optimum / quantity obstructions

Way of solvent recovery Two different ways of recovering the solvent from the coarse mineral fraction have been investigated. One way is a kind of washing (or suppression) of the solvent by means of adding subsequently another solvent and water. A second way is drying (evaporation of the solvent). To obtain a good starting-material for the solvent recovery experiments, the following activities were carried out: - a mixture of 2 kg of reclaimed asphalt concrete granulates and 2 1 solvent were agitated for 20 minutes in the cask with obstructions as described before; - after settlement and decantation of the loaded solvent new solvent was added and the mixture was agitated for a further 20 minutes; - now the mixture was sieved over a 90 pm sieve to separate the solvent, asphalt and filler inclusive, leaving the clean but wet mineral fractions (gravel and sand). In the wash route, the last step has to be a washing with water. It is not a problem to have wet mineral aggregate fractions as a product. Nevertheless, washing at once with water is not possible because of the insolubility of the used solvents (toluene and dichloromethane) in water. For this reason, a second solvent was chosen that had to be able to dissolve toluene and dichloromethane on the one hand and to dissolve itself in water. Methanol was found to be such a solvent. The wet mineral fractions from the preliminary experiment, carried out with dichloromethane, was mixed with methanol (in an L/S ratio of 1 Vkg) and was agitated for 20 minutes. The agitation time may have been too long, but it had to be ensured that all dichloromethane was suppressed by methanol, also in the pores. After agitation and settlement the methanol was decanted and the mineral fraction was mixed up with water. After the mixture had been rolled for 20 minutes, the coarse aggregate (gravel) was separated by means of sieving over a 2 mm sieve. Then the fine aggregate (sand) was de-watered by means of filtration. In this way it appeared to be possible to obtain wet, but clean and solvent-free mineral fractions (remaining asphalt content < 0.1%). The results of these investigations are summarised in the next chapter. In the dry route, the most important assessment criterium was the solvent content in the product. To prevent asphalt molecules remaining in the aggregate fractions after evaporation of the solvent, the aggregate fractions were washed with new solvent once more. After agitation, settlement and decantation of the solvent, the solids were dried at the boiling point of the solvent. The evaporated solvent was condensated again to be

669

recycled. The dry mineral fractions could simply be sieved into a coarse and fine fraction. Also, in this case, the remaining asphalt content was approximately 0.1 %. In both cases the filler was separated from the loaded solvent by means of filtration. It was then mixed with new solvent and intensively agitated by means of stirring. (Here, erosion was not expected to be a problem.) After filtration, the filler was dried also, like the other mineral fractions in the drying route. The remaining asphalt content appeared to be still rather high, about 1.5%.

3.

Evaluation

From a technical point of view, toluene seemed to be the most appropriate solvent, but dichloromethane has better characteristics as to inflammability and boiling point. After a severe discussion, politics turned the scales. In future, the production of halogenated solvents will be decreased because of EC legislation, so the choice was made for toluene as a solvent. Starting from an extraction under optimum conditions as summarised in table 1, two different ways were investigated to recover the solvent from the mineral fractions (as was described in the previous chapter), the wash route and the dry route. Four experiments were carried out to compare the results: 1 Subsequent washing with methanol and water of the mineral fractions from bituminous asphalt concrete, extracted with dichloromethane. 2 Drying at a temperature of 40 "C of the mineral fractions from bituminous asphalt concrete, extracted with dichloromethane. 3 Drying at a temperature of 110 "C of the mineral fractions from bituminous asphalt concrete again, extracted with toluene. 4 Drying at a temperature of 110 "C of the mineral fractions from tar containing asphalt concrete, extracted with toluene. The results of these four experiments, expressed in terms of remaining asphalt content, are given in table 2.

extraction step

1

7

After second extraction step

After solvent recovery (coarse)

After solvent recovery (filler)

1.0 %

0.1 %

< 0.1 %

1.4 %

1.0 %

0.1 %

0.1 %

1.4 %

0.5 %

0.1 %

< 0.1 %

1.7 %

0.7 %

0.1 %

0.2 %

1.1 %

The choice between the two recovery routes was made on the basis of the results of experiments 1 and 2. Table 2 shows that the wash route probably gives a slightly better

670

result. However, from an economic point of view, the dry route is preferred. The wash route leads to much higher investment costs because of washing and distillation columns. The dry route "only" needs a drying apparatus. If the 0.1 % asphalt content in the mineral fractions is acceptable, an additional washing step of the coarse mineral fractions is not necessary. The second extraction step already yields a product with an asphalt content of only 0.1%. The results of experiments 2 and 3 show that the difference between dichloromethane and toluene can be assessed. Table 2 shows that in the first extraction step toluene is able to extract slightly more asphalt than dichloromethane. This also holds for the final coarse mineral product. The filler, however, still contains more asphalt in the experiment with toluene. Overall, the two solvents do not differ very much, so the choice was made on other bases than technical ones (as has been described before). The results of experiments 3 and 4 show that both bituminous and tar containing asphalt concrete can be extracted with toluene as a solvent. In the mineral fraction (more specifically the sand fraction) of the tar-containing asphalt concrete some more asphalt remained. It is not quite clear what the reason is for this. The recovered mineral fractions gravel and sand contained only 0.1% of asphalt, whilst the filler still contained approximately 1.5%. The PAH-contents of the three mineral fractions, recovered from the tar containing asphalt concrete were measured. The total PAH-content was found to be 3.9, 0.8 and 0.2 mglkg for filler, sand and gravel respectively. When assessed visually all three mineral fractions seemed to be re-usable. The filler was a loose, dry powder. Nevertheless, the quality of the products (technically as well as environmentally) has to be proved in the next phase of the research. From the results of the feasibility study it may be concluded that the process for the recovery of the original raw materials from reclaimed asphalt pavement is technically feasible.

4.

Process Design

Based on the results of the investigations, carried out during the first phase of the research programme, and the choices that had been made, the next step was to obtain an insight into the equipment that will have to be used in the next phase. The aim is to work in phase 2 on a pilot-plant scale with a capacity of about 100 kg/h. The design of the pilot-plant equipment should, preferably, also be usable for the equipment in practice. First of all, the implications of working with toluene as a solvent were mapped out. Especially the flammability of toluene makes that safety measures will have to be taken. Some of the implications and measures are listed below: - To prevent the origin of explosive gas mixtures in the process equipment, the whole installation has to be operated under nitrogen atmosphere.

67 1 The whole system therefore has to be leak proof and possible leakage has to be detected. All in- and output of solid materials (asphalt concrete granulate, gravel, sand and filler) has to be operated by means of locks. Because of the poor conductivity of toluene, the liquid will charge when transport velocities become higher than 7 d s e c because of static electricity. This has to be avoided and, if this is not possible, buffer tanks will have to be implemented to enable the toluene to relax. All process parts have to be coupled and the whole installation has to be earthened. In designing the process and the different process steps, the most difficult step is the extraction of the asphalt from the asphalt concrete granulates. No commercial apparatus seems to be convenient for this, especially because of the stickiness of the asphalt, coming into contact with toluene. The tentative conclusion was that the extraction apparatus had to be specifically designed and verified by means of experiments. The other process steps consist mainly of unit operations that do exist, namely separation and washing of the mineral fractions (gravel, sand and filler), distillation (asphalt from solvent) and drying (of the mineral fractions again). The overall, but simplified process scheme is shown in figure 1. Tentatively the choice has been made to firstly separate the gravel from the sand fraction and then dry it (instead of drying the gravel and sand fractions together and then separating them) because of the expectation that drying the gravel will be much easier than drying the sand. So, the chosen sequence might lead to a more profitable overall process.

*

Sand

igure 1: Simplified process scheme

612

5.

Conclusions

The following, tentative conclusions can be drawn from the research that has been carried out:

*

From the results of the feasibility study it may be concluded that the process for the recovery of the original raw materials (gravel, sand and filler) from reclaimed asphalt pavement is technically feasible.

*

The extraction conditions that were found suitable for this extraction of asphalt (both bituminous and tar containing asphalt) are: - a liquid to solid ratio of 1 Ilkg; - a two-stage counter-current extraction (with agitation); - with an extraction time of two times 20 minutes.

*

After extraction, the mineral fractions, gravel, sand and filler respectively, contained < 0.1, 0.1 and 1.5%asphalt.

*

For the recovery of the solvent from the mineral fractions drying is a better option than washing (subsequently with another solvent and water).

*

From a technical and political point of view, toluene has been chosen as the most appropriate solvent, notwithstanding its flammability. This choice implicates operation under nitrogen atmosphere.

*

The most critical process step is the extraction of the asphalt. For this a new technology is needed. For the remaining process steps use can be made of existing unit operations.

6.

References

[l]

H. Helfrich, Re-use of reclaimed asphalt in-plant (in German), Strassen- und Tiefbau (1990), vol. 44, no. 9, pp. 41-44.

[2]

E. Mulder, Recovery of raw materials from reclaimed asphalt pavement, phase 1 : feasibility study (in Dutch), TNO-report ref.no. 93-032, Apeldoorn, February 1993.

Environmental Aspects of Constmction with Waste Materials JJJM Goumans, H A . van &r Sloot and Th.G. Aalbers (Edton) 019p4 Ekevier Science B. V. AN rights reserved.

613

Applications for coal-use residues: an international overview L. B. Clarke IEA Coal Research, Gemini House, 10-18 Putney Hill, London, SW15 6AA, England Abstract The utilisation of coal produces large quantities of residues. Worldwide production of coal-ash is estimated to exceed 550 Mt/y. In addition to fly ash and bottom ash from pulverised coal combustion, that comprise the bulk of these residues, there are now a whole range of by-products produced by the many technologies developed for flue gas desulphurisation (FGD). Alternative methods of utilising coal, for example in fluidised bed combustion (FBC) and integrated gasification combined cycle (IGCC) systems, produce residues with other, distinctive, properties. Many utilisation options have been demonstrated for coal-use residues, including applications in building materials, for civil engineering uses, in industrial materials and in agriculture. Various commercial applications are well documented and have been carried out for many years. Research into new applications for residues is in progress at many countries around the world. Applications range from high-volume uses that require minimal processing, to low-volume, but highly specialised applications. 1. INTRODUCTION

Coal utilisation produces large quantities of residues. In addition to fly ash and bottom ash from pulverised coal combustion, which comprise the bulk of coal-use residues, there are many different by-products produced by technologies developed to control air pollution. Coal utilisation technologies such as fluidised bed combustion and gasification systems also produce a range of distinctive by-products. The general heading coal-use residues includes the following materials: fly ash, collected in particulate control devices bottom ash and slags, discharged from the boiler residues from atmospheric or pressurised fluidised bed combustion (FBC), which may contain spent sorbents from in-bed desulphurisation residues from wet-lime FGD processes, discharged either as mixture of calcium sulphite and sulphate or, after additional processing, as gypsum

674 residues from dry and semi-dry FGD processes, which consist either of a mixture of fly ash and spent sorbents or a separate by-product stream containing mainly calcium sulphite/sulphate gasification residues, including those from integrated gasification combined cycle (IGCC) systems, discharged as glassy slags or fluidised bed residues (similar to FBC residues) Most residues produced from the utilisation of coal may be described as nonhazardous. In many countries landfill provides a simple way of disposing of a large proportion of the coal-use residues produced. However, dumping is likely to become more strictly controlled and more expensive. In many countries there is now a greater emphasis on the utilisation of by-product materials, with disposal only permitted if utilisation is not possible (Clarke, 1994). 2. ASH PRODUCTION AND USE

Many uses have been developed for coal ash and other residues (Figure 1).In some countries applications have been found for a large proportion of the residues produced. Table 1 lists recent coal ash production and utilisation figures for some major coal using countries.

fly ash

absorbent, plant propagation media, fertiliser, soil amendment

agriculture

building

I I I

residues FBc

residues gasifier

FGD residues

t-

I

'

I

cement, concrete, concrete filler, foamed concrete, mortar

t H 1

artificial aggregate, artificial reef, asphalt filler, backfill, foundations, land reclamation, mine fill, paving, soil stabilisation

civil engineering

artificial sand and aggregates, ceramics, decorative material, filter media, gas cleaning, industrialfiller, liming agent alumina, silica, ceramics, trace elements, integrated materials recovery

materials recovery I

I coalprep. ........

i

residues

Figure 1

j

artificial aggregate, bricks, building blocks, tiles, wallboards and panels

.

4

waste treatment

Utilisation of coal-use residues

I

grout, waste disposal, waste stabilisation, waste solidification

675 Table 1 Coal ash production and use, kt/y a. OECD countries ~~

Country Australia Austria Belgium Canada Denmark Finland France Germany Italy Japan Netherlands Spain Sweden UK USA

Fly ash

7050 375 930 3280 840 640 2290 20460 1250 3480 815 7865 300 9950 51300

Coarse ash Total ash

850 25 160 1100 140 70 420 10910 130 445 85 1530 190 2590 19350

7900 400 1090 4380 980 710 2710 31370 1380 3925 900 9395 490 12540 70650

Utilisation %Used

800 100 795 1290 880 180 1550 17870 1270 1920 940 1570 100 6120 21800

10 25 73 29 90 25 57 57 92 49 >lo0 17 20 49 31

Year

1990 1989 1990 1989 1990 1988 1989 1989 1989 1989 1991 1991 1988 1989 1991

Data includes ash from hard and brown coals. Data for Finland and Sweden also includes peat ash.

b. Other countries

Country China Czech & Slovak Reps Hungary India Poland Romania South Africa Former USSR

Fly ash

Coarse ash Total ash

55000 13800 3880 36000 26300 7000

7500 4300 940 4000 3200 20000

90000

35000

62500 18100 4820 40000 29500 27000 13000 125000

Utilisation O/oUsed

16200 1400 600 6750 4500 700 580 11500

26 8 12 17 1s 3 4 9

Year

1989 1989 1989 1991 1989 1989 1987 1989

676

- Other uses 1% -Asphalt filler, 9% Artificial aggregates, 18%

Netherlands

grlculture and fisheries, 3% adbase and asphalt filler, 7% Artificlal aggregates 3% Concrete, 6%

1

L Building materials. 9%

Japan Blocks, 64%

-Other uses, 2% -Grouting. 4% Structural fills 18%

United Kingdom ement and concrete products. 39% Structural fills. 15%

Other uses, 21%

Blasting grit and roofing granules, 10% Roadbase and sub-base. 8 Snow and ice control, 4%

A L Grouting. 1%

USA

Figure 2

Source: Vliegasunie, Japan Coal Ash Ass.. NatPowerlPowerGen. ACAAI

Utilisation of coal ash (fly ash, bottom ash, boiler slags) by sector

677

In several European countries and Japan, the cement and concrete industries use a high proportion of the residues produced. Figure 2 shows coal ash utilisation by industrial sector for the Netherlands, Japan, the United Kingdom, and the USA. The UK is unusual in the large proportion of ash utilised in the building block industry, and also the relatively poorly developed use of fly ash in the cement industry compared with other European countries. It is also noticeable that those countries with stringent environmental legislation utilise larger quantities of residues compared with countries where disposal is either cheap or poorly regulated. The USA produces a much larger amount of ash compared with other O E C D countries (about 70 Mt/y). Whilst the total per cent utilisation is lower than many other countries (about 31%), the actual quantity of ash and other residues used is enormous (about 22 Mt/y). In the USA applications which involve little or no processing are important, and structural fill and road construction applications account for almost 25% of the total ash used. Countries where power stations are situated far from the centres of population (for example Australia, Canada, and the USA) generally utilise less of the residues produced because it is currently uneconomic to transport the ash to market. Table 1 also lists production and utilisation figures for some other countries. Many eastern European countries, the states of the former USSR, and those countries which are undergoing rapid industrialisation, such as China and India, are producing huge quantities of ash. Widespread industrial restructuring in many central and eastern European nations and the states within the former USSR has resulted in a reduction in demand for coal in these countries. As a consequence the quantity of fly ash produced is currently static or falling. In countries such as China and India the rate of ash production will probably continue to increase over the course of the decade. 3. APPLICATIONS FOR RESIDUES

The following sections provide a n overview of the most important applications for residues. Most applications centre on fly ash, the most voluminous by-product from coal utilisation. A more comprehensive review of applications for coal-use residues is provided in a report by IEA Coal Research (Clarke, 1992). 3.1. Concrete Fly ash has been used widely in concrete and in pre-cast concrete products for many years. In addition to acting as an inexpensive filler or extender, the use of fly ash yields certain benefits as a result of its pozzolanic activity, rounded particle shape, and reduced demand for water. The following technical advantages have been noted when using fly ash as part of the design mix for concretes:

greater cementitious activity, reducing permeability reduced heat of hydration superior surface finish and workability improved chemical resistance, especially against sulphates and chlorides

678

Fly ash may be added to a concrete mix either as a separate material, or as a blended component with Portland cement. If fly ash is incorporated as a separate material, then the optimum proportions may be predetermined for the design mix in order to meet the specific requirements of concrete (for example, improved chemical resistance). Pre-blended mixtures of Portland cement and fly ash eliminates the need for additional handling and mixing, resulting in improved batch consistency. However, pre-blending also removes the ability to select the optimum mix for a given situation. Many fly ash-concrete mixes have been described in the literature and it is clear that the best mixes are designed for specific applications based on inherent conditions and trial mixes. International specifications for fly ash used in concrete vary considerably from country to country (Clarke, 1992). 3.2. Cement Fly ash may be used in cement in a variety of ways. Up to about 8% of the cement clinker can consist of fly ash if it is used as a raw material during the production stage. The ash can be of a relatively low quality, and if it contains a high carbon content, may be used as part of the fuel in the manufacturing process. It has also been suggested that glassy IGCC slags could be suitable, after sizing and grading, as a substitute for natural ahminosilicates in the manufacture of Portland cement clinker (Clarke, 1991). Fly ash can also be used as a replacement for cement in the production of Portland fly ash cement; a mixture of Portland clinker, gypsum anhydrite, and up to 30% fly ash. Bijen and others (1991) note that in principle the effects of this fly ash addition on concrete properties should be similar to those of fly ash added as a partial Portland cement replacement. However, treatment of the fly ash during the manufacturing processes (such as screening and grinding) and adjustment of the quantity of gypsum anhydrite allows production of cement with strength and other characteristics similar to Portland cement. Figure 3 illustrates various methods for the production of Portland fly ash cement. In many European countries (notably Belgium, Denmark, Germany, the Netherlands, Norway, and Sweden) the production of ordinary Portland cement is now being wholly or gradually replaced by the production of Portland fly ash cement (Bijen and others, 1091). The cement industry is a large consumer of gypsum. Portland cement contains gypsum, used as a retarding agent. The quantity of gypsum incorporated varies depending on the application, but may be up to 5 wt%. Gypsum granules are ground together with cement clinker. Gypsum usually needs to be agglomerated prior to use in cement (Clarke, 1993).

3.3. Aerated and foamed concretes Fly ash may be used as a raw material for the production of autoclaved aerated concrete, a lightweight material used to manufacture building blocks for residential, commercial, and industrial use. Fly ash is used to replace ground quartz sand or ground quartz sand and binders. Given an appropriate fly ash it is possible to replace up to 30% of the lime/cement binder without greatly altering the properties of the concrete. Fly ash is being used in autoclaved aerated concrete blocks produced by Celcon, Durox, Thermalite, YTONG, and other European manufacturers. In the UK,

619

Open circuit grindinglmixing processes

A

p*

@+ .-

a

5=

..............................

'

mill

finemill

...........................

:

+-

;

Closed circuit grinding processes

B

sifter

I

b .c Y

f

c m v)

I:

2.

+
900'C

I 1

I I I I I

--

Figure 4

Manufacture of artificial aggregates using coal-use residues

683

The production of synthetic aggregates using FBC residues has been demonstrated in several countries. Production methods tend to use mixes of fly ash and FBC residue, either pelletised or briquetted. The manufacture of aggregates from FBC residues produces a more consistent by-product. Synthetic aggregates can be manufactured from IGCC residues, either by fusing or bonding ash into pellets, or by ballooning slag particles (Clarke, 1991, 1992). 3.7. Fill, foundations, and soil stabilisation Coal residues have been used as fill material in road construction, bridge repair, mining, void filling and as a general landfill. Fly ash has three main advantages over conventional fill materials:

it is lightweight, suitable for applications on ground of poor load-bearing capacity it has self-hardening properties, reducing settlement within the fill, and decreasing horizontal pressures on infilled structures liquid fly ash-based grouts can be hydraulically placed enabling complete infilling of voids, tunnels, and disused tanks Fly ash has been used for a number of years as a road construction material. It has been used as fill, sub-base, and as a road base material. Both cement and lime have been employed to stabilise the fly ash. Several types of slag have also been used in road construction. Bottom ash from pulverised coal-fired power stations has been used widely as a sub-base material, and has a number of beneficial properties:

9

it can be handled and compacted easily sub-base construction may take place in most weather conditions it provides protection for the subgrade against cold or wet weather and damage during construction works it is not susceptible to frost heave bottom ash is a granular, free-draining material

Fly ash, mixed with lime or cement, can be used to stabilise soils. Pozzolanic reactions between fly ash, lime, and water yield products which bind soil particles together. Residues possessing self-hardening properties can be used to stabilise soils without additional additives. FBC residues with a high lime content may be especially suited to acid waste neutralisation or mine soil rehabilitation. Fixated sludges from wet scrubber systems have been successfully used as a subbase for road construction. The material is cementitious and forms a monolithic layer which may be suitable for a variety of other civil engineering applications, such as structural fill. F G D gypsum could also be used for similar applications, but its solubility and thixotropic properties require stabilisation with other materials (such as fly ash) and therefore discourage its use as this adds to the cost. In Germany, FGD gypsum from lignite-fired power stations is mixed with lignite fly ash which contains a high concentration of lime. The fixated product, known as stabilisate, is used to backfill lignite surface mines (Demmich and others, 1991). This application provides a method of utilising gypsum which does not meet the required specifications of the

684

wallboard industry and is also useful for disposing of surplus gypsum in times of overproduction. 3.8. Waste stabilisation Immobilisation of toxic wastes has been carried out successfully using stabilisation and solidification. Fly ash has been used in these processes, together with water and bonding and activating agents such as lime, lime and gypsum, or Portland cement. Tests have also been carried out using FBC residues, which do not require the addition of lime or Portland cement because of their high lime content. Most processes aim to produce a hardened mass with a low leachability. The majority of applications have been used to stabilise inorganic wastes. Physico-chemical bonding occurs and additives may be used to make specific ions insoluble. Organic wastes, such as oil sludges, have also been successfully stabilised. 3.9. Miscellaneous uses Some coal-use residues may be used in agricultural applications as fertilisers or soil amendments, However, application of residues containing ash to agricultural land is not permitted in some countries, such as the Netherlands. Gypsum is a useful conditioning agent on saline and sodic soils and is typically applied at rates of 57 t/ha (CRE, 1992). It is also reported that gypsum addition enhances the production of root nodules, which promote the conversion of nitrogen to nitrogenous compounds (Steffan and Golden, 1991). FGD gypsum could potentially supply this market, providing the moisture content of the residue is reduced to prevent problems during use. The calcium content of the gypsum may be especially useful as a plant food for peanut farming and a utility in Florida, USA, is supplying FGD gypsum for this purpose (McIntyre, 1991). Residues from FBC systems and some F G D residues (for example furnace injection residues) could be added to soils to control acidity. The neutralising capacity of these residues is usually much lower than that of pure limestone. Other miscellaneous applications include substitute abrasives, mineral wool, specialist ceramics, and materials recovery. These uses are reviewed elsewhere, together with more esoteric applications (Clarke, 1992). A variety of processes have been developed for the recovery of materials from coal residues, including alumina, titanium, trace elements, and ceramic materials. Most recovery processes, although feasible, are currently uneconomic compared with processing natural ores. Research has recently centred on integrated materials recovery, in which streams such as alumina and/or magnetite are extracted together with silica or aluminosilicates which can be used as fillers or raw materials in various industries. 4. CONSTRAINTS ON UTILISATION

The potential for use of coal-use residue depends on their physical and chemical properties, and the extent to which they might vary. In addition to technical requirements the following factors also influence utilisation potential:

685

competition with other natural or traditional materials attitudes of potential users subsidies and incentives equating supply with demand transport and storage of resources The success of each application will depend on local requirements, and must be based on detailed market assessments. Natural prejudices against a new product must be overcome, even if the new material is technically superior or more cost effective. Problems also exist in certifying new products which do not use conventional raw materials. It is important that such barriers are removed to allow the effective re-use of materials rather than disposal. High-volume, low-technology applications such as road and embankment fill have in the past dominated the market for coal-combustion by-products. The commercial potential of such applications depends largely on local demand, which allows transport and storage costs to be kept to a minimum. Governmental action and incentives have served to promote the market for coaluse residues Japan, Germany, and the Netherlands. The following measures have been identified: restrictions on disposal of materials, thus promoting production and availability of a usable by-product research and development initiatives to find new applications for residues funding of studies to assess and ensure by-product quality financial support for demonstration projects More unusual applications may be needed in future if the viability of current applications decreases, or the market becomes over-supplied. Discontinuous applications (such as road construction) usefully dispose of large quantities of waste, but need to be balanced with continuous applications (for example building materials) in order to optimise supply and demand, and thus minimise environmental impact by reducing disposal. 5. CONCLUSIONS

Legislation concerning disposal of coal-use residues varies from country to country. Nevertheless most residues may be described as non-hazardous under current legislation. In the past disposal has been the main option for dealing with residues. There is now a greater emphasis on recycling and reuse. In some countries dumping of residues is now only permitted if utilisation is not possible. As the cost of landfill escalates, greater utilisation of residues becomes a more feasible alternative to disposal, provided environmental criteria are satisfied. The most promising applications for most residues are in the building and construction industries. Fly ash and bottom ash have been used in these industries for many years. FGD gypsum is now widely used in the wallboard industries and in

686

cement manufacture. Favourable uses have been developed for other residues, but at present few of these applications have reached commercial status. More unusual uses for coal-use residues may be needed in future if the viability of current applications decreases, or the market becomes over-supplied. 6. REFERENCES Bijen J, Skalny J P, Vazquez E (1991) Other uses of fly ash. In: Fly Ash in Concrete, Properties and Performance, RILEM report 7, Technical committee 67-FAB (Use of fly ash in building), K Wesche (ed). London, UK, E & FN Spon/Chapman and Hall, p160-178 (1991) Clarke L B (1992) Applications for coal-use residues: Handbook. IEACR/SO, IEA Coal Research, London, UK, 406p (May 1992) Clarke L B (1993) Management of FGD residues. IEACR/62, IEA Coal Research, London, UK, 82p (Oct 1993) Clarke L B (1994) Legislation for the management of coal-use residues. Report for IEA Coal Research, London, UK (Apr 1994) CRE Coal Research Establishment (1992) Disposal and utilisation of flue gas desulphurisation (FGD) residues. EUR report EUR-14071-EN, Commission of the European Communities, Luxembourg, vp (1991) Demmich J, Weinflog E, Roeser G, Ghoreishi F (1991) German experience of FGD by-product disposal and utilisation. Paper presented at: The 1991 SO, control symposium, 3-6 Dec 1991, Washington, DC, USA, p397-419 (Dec 1991) EPRI (1992) Mobile demonstration plant produces fly ash-based cellular concrete. ECS Update, 27 (Fall/Winter), Electric Power Research Institute, Palo Alto, CA, USA, p6-8 (1992) Hamm H (1991) Overcoming the desulphurisation gypsum problem in Germany from the technical, economic and marketing points of view. Paper presented at: XIX EUROGYPSUM congress, Interlaken, Switzerland, 16-20 Sep 1991 Kappe J, Moonen L, Ellison W (1991) Growth in by-product gypsum yield, use for floor screeds. In: Proceedings of the second international conference on FGD and chemical gypsum, Toronto, Canada, 12-15 May 1991. Mississauga, Ontario, Canada, Ortech, p30.1-30.10 (1991) McIntyre W W (1991) The St Johns River Power Park experience with by-product gypsum production and sales. In: Proceedings of the second international conference on FGD and chemical gypsum, Toronto, Canada, 12-15 May 1991. Mississauga, Ontario, Canada, Ortech, p12.1-12.11 (1991) Pytlik E C, Saxena J (1991) Autoclaved cellular concrete: A unique fly ash based building material. In: Eighth annual international Pittsburgh coal conference, Pittsburgh, PA, USA, 14-18 Oct 1991. Greensburg, PA, USA, Pittsburgh coal conference, pS75-581 (1991) Steffan P, Golden D (1991) FGD gypsum utilisation: survey of current practices and assessment of market potential. In: Proceedings of the second international conference on FGD and chemical gypsum, Toronto, Canada, 12-15 May 1991. Mississauga, Ontario, Canada, Ortech, p4.1-4.18 (1991)

-

Environmental Aspects of Conshuction with Waste Materials JJJM Goumans, H A . van der SIoot and Th.G.AaIbers (Editors) 01994 EIsevier Science B.V. All rights reserved.

687

Specifications and the use of wastes in construction in the United Kingdom R J Collins and C J Atkinson Building Research Establishment, Watford WD2 7JR, United Kingdom British Crown copyright 1994. Published by permission of the Controller of HMSO

Abstract Recycling and the reuse of wastes is expected to play an increasing part in the UK construction industry but this must be achieved within acceptable standards of performance, including health and safety. This paper reviews the present position in the UK with regard to current Standards, specifications and other guidelines, and introduces some current initiatives in Government policy, research and the development of European standards, with particular reference to the supply of aggregates and the reuse and recycling of demolition materials. 1. INTRODUCTION

A comprehensive statement of UK environmental strategy is given in the Government White Paper ""his Common Inheritance" [l] in which commitments are made to encourage the best use of valuable raw materials, minimisation of waste, and recycling of waste, as part of a duty of care for the world in which we live. "he largest producers of waste are the minerals and construction industries and thus in terms of tonnage have the greatest potential to make an impact on the construction industry. Such wastes are thus given greatest coverage in this paper, however consideration is also given to concerns on wider issues of waste utilisation and waste minimisation. 2. MINERALS PLANNING RESEARCH

Aggregate requirements are expected to increase and long term projections indicate that over the next 20 years the construction industry in the UK may need as much as 7,000 million tonnes (Mt). Already by-products and waste materials account for 10% of aggregates and bulk construction materials in the UK [21, however it is Government policy to increase this level of usage where this furthers aims of materials conservation and environmental protection.

688

The UK Department of the Environment (DOE)in its Geological and Minerals Planning Research Programme has recently commissioned several research studies to follow up these issues and make recommendations for consideration by Government. Some of the findings are now being used in the revision of Government minerals planning guidance to the local authorities and aggregates industry on what needs to be done to ensure an adequate and steady supply of minerals at the best balance of social, environmental and economic costs, compatible with the objectives of sustainable development. The initial project in this series was a new survey of the current situation in the UK with regard to the occurrence and utilisation of secondary aggregates and recycled construction materials. The report, by Arup Economics and Planning, which was published in mid-1991 [21, makes a number of recommendations on how an increased utilisation of wastes could be promoted. There is also a concern that the most efficient use of all aggregates materials, including waste and recycled ones is inhibited by standards and specifications and this is the subject of a second project carried out and published by the Building Research Establishment [3]. This has found that wastage through overspecification occurs quite frequently, major causes being the avoidance of any risk, however small, and the economic pressure of fiercely competitive fee bidding. Waste materials in particular tend to be marginalised by these factors. A follow-up report explores in more detail the accommodation of waste materials within British Standards and other UK specifications [41. The present paper discusses the recommendations of these reports in relation to the latest developments including current progress in the development of specifications, particularly within the context of European harmonisation. 3. ENVIRONMENTALIMPACT

Historically the UK has had an excellent supply of high quality aggregates but increasingly, traditional sources have been unable to keep up with demand. The reasons for this are many and varied but include resource depletion, loss of land through development and tighter planning controls due to growing awareness of the environmental impacts of raw materials extraction. New consents to develop quarries now normally require an environmental impact assessment (EIA) to be carried out. The EIA should consider all aspects of the environment likely to be significantly affected by the development including population, fauna, flora, soil, water, air, climate, resources, architecture, archaeological heritage, landscape and transport infra-structure [5]. Alternatives to the development also have to be considered together with ways of alleviating the worst environmental impacts. Tighter planning controls are not the only manifestation of environmental concerns and architects and designers are increasingly demanding information about the environmental impacts of the products they specify. There is now an EC

689

ecolabelling scheme [6] which although developed for consumer goods is also applicable to building products. The EC regulation on ecolabelling is designed to promote the use, design and production of products which have a reduced environmental impact a t all stages in their life cycle. The application of the EC regulation on ecolabelling to building products is discussed in BRE papers by Atkinson et al. [7-81. BRE’s work has shown that for many building materials the environmental impacts associated with raw materials extraction are very significant. BRE has also developed a number of environmental assessment methods for buildings which are known collectively as BREEAM (Building Research Establishment Environmental Assessment Method) [91. Some companies require eco-audits of their suppliers in order to promote a “green“ image or in some cases to ensure compliance with legislation. Eco-audits are management tools used to evaluate how well organisations, management and equipment are performing against defined environmental objectives. A recent EC regulation [lo] has established an eco-management and audit scheme which has been designed to promote continuous improvement in the environmental performance of industrial activities. The regulation gives guidance on a range of issues which should be addressed including assessment, control and reduction of the impact of the activity on the environment, energy management, raw materials management, waste avoidance, noise control, product planning, environmental performance and practices of contractors, sub-contractors and suppliers, prevention of environmental accidents and provision of information for internal and external use. Clearly it is very important that the best use is made of all the nation’s resources and that primary aggregate resewes are conserved. One way of doing this is to encourage greater use of waste and recycled materials. Whilst some of the environmental concerns associated with extraction of primary aggregate also apply to the utilisation of secondary materials (notably production of noise, dust, visual intrusion and transportation problems) [23 extraction of primary aggregate gives additional environmental concerns. These include permanent loss of land related amenities, loss of habitats and possibly damage to aquifers. Other arguments in favour of greater use of waste materials where possible are loss of land related amenities or landfill space as a consequence of tipping as well as the loss of potentially useful materials. 4. SPECIFICATIONS AND THE USE OF MINERAL WASTES 4.1. Aggregate for concrete Aggregates for concrete are covered by BS882 for natural aggregates, BS3797 for lightweight aggregate and BS1047 for air-cooled blastfurnace slag [ll-131. The use of waste materials is covered by BS6543 [141 but a survey of specifiers [31 found that this standard is little known. Specifications for building contracts refer to BS882 and frequently to BS1047 and BS3797, but never to BS6543. This

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essentially precludes use of crushed concrete and demolition waste even though theoretically it is not excluded by British Standards. The Department of Transport, however, in the recent revision of their Specification for Highway Works [15] have recently extended the use of crushed concrete (conforming to the grading and quality requirements of BS882) to use in pavement concrete. Full details of the current position of demolition waste with regard to British Standards and specificationsis in a paper presented at Odense in 1993 [161. Much of the mineral waste available in large quantity in the UK could without dfliculty be classified as natural materials as they have not been subject to processing other than crushing, washing and sieving. This would apply to china clay sand, slate waste, unburnt colliery spoil, dredged silt and various other quarrying wastes. This would not apply to pulverised fuel ash (pfa), burnt colliery spoil, spent oil shale, and various metalliferous slags, as well as to demolition wastes. Wastes classified as natural materials could be assessed for use in concrete according to the British Standard for natural aggregates (BS882 [ll])without reference to the guide for wastes (BS6543 [141). The use of an aggregate need not necessarily rely on aggregate Standards. The British Standard for concrete, BS5328 [17] refers to BS882, BS1047 and BS3797 but the use of aggregates to these Standard specifications is not mandatory in all circumstances. For "designed' and "prescribed' mixes it is possible to select aggregates outside British Standards as long as the properties of the concrete are satisfactory. This is rather too open-ended for producing job specifications because it places a responsibility on the specifier to guarantee long term durability. 4.2. Aggregates in unbound applications The main use of unbound aggregates is in road construction and this is covered in detail by the Department of Transport's Specification for Highway Works [151, in which specific reference is made to a wide range of situations where waste materials can be used. Roads are constructed in layers, so that an economical use can be made of materials, with the lowest quality materials at the bottom and the highest quality materials at the surface. Only a few waste materials are capable of use in all layers of road construction, but most are suitable for use in lower layers subject to certain minimum requirements (ie they do not contain appreciable quantities of compressible material, do not cause chemical attack or corrosion of other materials, do not pollute aquifers, and conform to minimum stability requirements). The main limiting factor for waste materials is availability and the cost of transport. A detailed analysis of the position of the major waste materials has been prepared for DOEMinerals Planning Division by BRE [4].

In building construction unbound aggregates are used as fill and hardcore; this is not covered by British Standards and the main source of advice is BRE Digests, and in particular BRE Digest 276 "Hardcore" 1181. This recommends the use of wastes such as colliery spoil, clean demolition waste, modern blastfurnace slags, pfa and oil shale residue (subject in all cases to limits on water-soluble sulphate content to

69 1

prevent attack on concrete floor slabs etc), but warns against the use of steel slags, old blastfurnace slags, refractory bricks and gypsum mine waste which could cause heave. 4.3. Bituminous bound aggregates. The Department of Transport’s Specification for Highway Works [151 currently permits the use of in-situ recycling for bituminous road materials, but for the production of bituminous materials in plant off site the maximum content of reclaimed bituminous material is limited to 10%. There is opportunity to use rubber in bituminous mixes, however this makes eventual recycling of such mixes more difficult due to burning of the rubber and consequent air pollution.

4.4. Cement replacement materials. The pozzolanic and hydraulic properties of pfa and ground granulated blastfurnace slag (ggbfs) are well recognised in the UK and partial replacement of Portland cement is commonplace and well covered by British Standards [19-221. Particular impetus to the use of these materials has been given by a desire to exploit their low heat and chemical resistance properties [23-261. Blending such materials with cement is the most effective way of saving energy in cement use and also in reducing C02 emissions. In addition to the opportunities for substitution of primary materials by wastes, cement kilns may use secondary fuels such as tyres, domestic refuse and methane gas from landfill sites [27]. 5. DETAILS OF MINERAL WASTES

5.1. Demolition waste Demolition materials are extensively recycled in the UK and it has been estimated that l l M t or nearly half of present arisings of old concrete and masonry are recycled [2]. The major use is as fill and hardcore. Demolition waste is frequently crushed on the demolition site by portable plant and used on the same site as a base for new construction. There is also a long history of recycling concrete from road and airfield pavements for use as road sub-base. This is also conveniently prepared by portable plant. There are fewer “fixed site” ie stationary plants in the U K although these sites should be capable of producing a higher quality product there is little information to corroborate this. The input to such centralised facilities is potentially more variable as there are no statutory requirements to separate waste before arrival at the recycling facility; the plant operator must rely heavily on visual inspection of the waste and on his charging policy for acceptance of materials. Economies achieved by larger scale operations on fixed sites are offset by costs of transport and the need to register material removed from demolition sites as waste.

It is UK policy to increase the recycling of demolition waste, and central to this is the need for universally acceptable standards [2,3] This would also have the effect of improving the viability of fixed site plants with regard to portable operations, where it is suspected that more of the crushed product is used on site than is

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strictly necessary just to avoid the need to classify it as a waste if it is removed from the site. Improvements in the efficiency of aggregate utilisation would thus be achieved by: (1)Setting up the conditions where some demolition materials could be used in higher grade applications (2) Increasing demand for demolition materials through [2] and an overall greater acceptance of these materials (3)Discouraging the use of more demolition materials on site than is strictly necessary for the construction process. Standards for aggregates are being developed by CEN under Technical Committee TC154, and specification standards for mortar, concrete and lightweight aggregate are mandated so that standstill applies to the production of national standards for these categories. It is hoped that the specification for aggregates for concrete will be ready for national comment in 1994; provision has been made for the specification of recycled materials as directed by a resolution of the CEN Technical Board. Recommendations with regard to recycled material are being made by an ad hoc group of TC154 specially for this purpose. This ad hoc Group on recycled aggregate is considering current national requirements where they exist, including a RILEM specification presented a t the Odense conference (24-27 October 19931, so that recycled materials can be specified with no less assurance of performance and quality as could be expected for natural aggregates. A variability trial on recycled aggregate is currently being carried out for BRE using the statistical methods being employed for the estimation of the precision of aggregate test methods for TC154. 5.2. China clay sand China clay sand, a residue of the winning of kaolin deposits in Cornwall (SW England), with a suitably adjusted grading, will pass BS882 and has frequently been used as an aggregate for concrete, although it reduces the workability. Some specifiers are worried about the mica content and some contractors have also experienced problems working with an unusual material so it needs to be offered for sale at prices considerably below the usual price for natural sands. A further problem arises as china clay sand deposits are located in Cornwall which is some distance from areas of high demand and transport costs are prohibitive [2]. 5.3. Slate waste

Slate waste fails the flakiness requirement in BS882 [ll],but with carefkl mix design can sometimes be used in concrete. Alternatively many sources of slate can be expanded to produce lightweight aggregates with excellent properties and covered by BS3797 [121. The British Standard Guide to the use of wastes for building (BS6543, [14]) in section 18.4 cites the case of a dam in SW England in which crushed slate waste was used in conjunction with a china clay sand. To obtain some workability the aggregate:cement ratio was reduced from 8:l to 7:l and a plasticiser was used. Even so, the concrete had no slump. Cubes cast with this concrete had a 28 day

693

strength of 27 N/mm2 and a density of 2500kg/m3. This dam was visited by BRE staff in 1990 and the concrete was found to be in excellent condition 17 years after construction. There is one further twist in the specifications which has particular relevance to Delabole slate which was used in the Crowdy Dam referred to above. Delabole slate contains some pyrite and matches almost exactly a type of rock described as deleterious in an Advice Note 1281which is referenced by the latest (1992) version of BS882 [ll].The Advice note was issued to combat the "Mundic" problem in Devon and Cornwall where serious deterioration has occurred in some houses about 40-70 years old; these were built with concrete blocks in which there was indiscriminate use of metalliferous mining wastes for aggregate. This has been a set-back to the use of wastes and other lower grade materials in that area and probably to some extent in the country as a whole. A number of different degradation mechanisms are involved in "Mundic" deterioration, but their relative importance has not yet been hlly elucidated. Such factors reinforce a deep underlying mistrust of waste materials by many specifiers. The recent DOE Advice Note [28] has attempted to encompass the "Mundic" problem but in the process has excluded from use certain materials that would be acceptable. Further advice to be published early in 1994 will more closely define those aggregates which are likely to be suspect. Slate waste, like china clay sand, is remote from areas of high construction activity, but Arup [2] in their report to the DOEconsider long distance transport (by sea) to have greater potential. Crushed slate has been established in North Wales as an excellent "Type 1" sub-base material specified according to the DOT specification [151 and its use for such purposes could release supplies of crushed rock for use in concrete. 6.4. Unburnt colliery spoil Unburnt colliery spoil is widely available in the UK but in general terms cannot be used in concrete without high temperature processing either as a part of the raw feed for cement manufacture or to form synthetic aggregates. A few unburnt spoils will in fact pass BS882 for concrete but the high content of clay and the susceptibility to water mean that the quality of the concrete is poor [4,29]. The main usefulness of unburnt spoil is in the availability of large quantities of filling material eg in road embankments which releases other sources of aggregate for higher grade use and reduces the need for "borrow" pits. Although high quality synthetic aggregates can be made from colliery spoil [30], the cost of processing plant currently makes this economically unviable [311. 6.6. Burnt colliery spoil and spent oil shale Burnt colliery spoil (from old tips which have caught fire) and spent oil shale (the residue after heating oil shale to remove oil - a now defunct Scottish industry) have some similarities in properties and potential. They are less susceptible to water than unburnt colliery spoil because clays have been converted to harder mineral phases, but sulphides are oxidised to sulphates so that there is a greater risk of

694

sulphate attack on concrete. Apart from BS6543 [14] these materials are not covered by British Standard, but there has been extensive use in the lower layers of road construction [41. 5.6. Dredged silt Dredged silt collected by port and harbour authorities is normally too fine to comply with the grading requirements of BS882, however it has been demonstrated that silts with low clay contents could be used successfully in concrete [32]. Some clay containing silts can be used to produce sintered lightweight aggregates [33]. 5.7. Quarry wastes Fine material excess to normal requirements is also available in large quantity at some crushed rock quarries. Natural sand is usually preferrred for making concrete and if a crushed rock sand is used the quanity of fine material is strictly controlled. Much of this sand however could be successfully be used in concrete. In a detailed study of concrete made with crushed rock aggregates at BRE it was found that although the overall tendency for fine material was to increase water demand, in a significant number of cases the addition of fines actually reduced water demand 1341. Opportunity also exists for some fine material to be added as part of a composite cement to BS12 [201 as well as part of the aggregate. 5.8. Pulverised fuel ash Pfa, as well as being well established as a cement replacement material (see 4.4 above) can be used to replace part of the fine aggregate. This is also suitable for fly ashes with little or no cementitious properties and is covered by BS3892 Part 2 [35]. Pulverised fuel ash can be used as a lightweight fill material which as well as saving on other aggregates on a volume-for-volume basis, saves on ground preparation where this has low bearing capacity. 5.9. Slags All blastfurnace slag currently produced in the UK is used, either for aggregate [12,13] or for cement (see 4.4 above) although some tips still exist which contain material produced before British Standard BS1047 was first introduced in 1942. Steel slag produced in the UK contains free lime and magnesia which will hydrate and expand when in contact with water. Surface degradation has made some steel slags particularly suited to use as skid-resistant roadstone. Some use of steel slag is possible in the lower layers of road construction but use as fill and hardcore in building construction has resulted in serious cracking [41. 6. OTHER USE OF WASTES IN CONSTRUCTION As an alternative to recycling, some of the construction and demoliton waste produced in the United Kingdom could be reused. This might necessitate some dismantling rather than demolition which would be labour intensive and hence costly. Expensive sorting, distribution, cleaning and testing operations might also

695

be required. In general, for these reasons the costs of reclaiming low price products such as bricks, stone, tiles etc are usually much greater than the price of new products. Other higher priced products such as timber and metals are already recovered and used to some extent. Much of the material which could not be reused directly such as concrete and mortars could be recycled as aggregate. In order to comply with the Building Regulations a reused product or material must be shown by experience to be capable of performing the hnction for which it is intended. Clearly, unless accurate records are kept of how and where specific products were used then some form of performance testing is needed in order to demonstrate fitness for purpose. This is clearly costly for small batches of products. For bricks a particular problem arises in that some bricks have only been fired at low temperatures making them unsuitable for external use. Their appearance is often similar to that of bricks used externally making them difficult to distinguish through visual means. In parts of Denmark where high disposal taxes are levied on each tonne of demolition waste, bricks from demolition may sometimes be economically reclaimed by refiring. This process makes it easier and cheaper to separate the bricks from the mortar (by brushing) and the firing is reported to eliminate the need to separate facing bricks from commons [36]. However, the process is costly in terms of energy consumption and is unlikely to be applied in the United Kingdom. Construction practice strongly influences the ease with which building materials can be recovered. The use of cement based mortars rather than traditional lime based mortars makes it more difficult to recover bricks without damaging them although the Danish process of refiring is reported to reduce the damage [36]. A related problem is that some old stock bricks can themselves be damaged through the use of cement based mortars which are stronger than lime mortars. At present work is in progress at BRE to design mortars with better bonding to brickwork in order to reduce rain penetration. Use of these mortars will make reusing bricks more difficult. Most of the metal content of demolition and construction waste is already recovered as it commands a high price [37]. Metal components are rarely reused but are usually recycled. The main exceptions to this are rebar, aluminium window frames with thermal breaks, wiring and other small items for which recycling costs are usually too great. Clearly, greater reuse could be promoted by a modular approach to design of components. This is being explored by some manufacturers. Whole timbers (floorboards, rafters, doors etc) are often recovered and may be reused for renovation or new construction purposes [37]. One of the major problems associated with reuse or recycling of construction timber is that it is has a wide range of contaminants such as nails, screws, heavy metal preservatives, paints and diseases. Timber fragments can be recycled in chipboard or low grade pulp applications even if they contain nails and screws, by using a hammer mill and separator. Chipboard manufacturers require a large continuing input of material

696

which is difficult to ensure from demolition. In Denmark [38] timber components are commonly recovered and reused or recycled. Treatment plants are available for stripping paint from window frames, doors etc and these can then be reused providing there is no evidence of decomposition. In the United Kingdom old timber is rarely used in new construction but there is a strong market for old timber for conservation and heritage applications. Plastic building products are diverse and in general have been designed to have very long lifetimes so only small quantities of plastic components are available for recovery. Some construction site scrap is recovered and reused or recycled and work is currently going on to modify technical standards to allow the use of recycled plastic construction components. 7. CONCLUDING REMARKS

Growing environmental concerns have produced demands for greater use of waste materials in construction. Whilst sufficient minerals exist for long term needs in the UK changes are needed to improve the efficiency of utilisation including an increased use of lower grade and waste materials where appropriate. Legislation, minerals planning, specifications, construction designs and site practice all need to be directed towards the efficient use of materials. Risk is often quoted as the reason why innovation is neglected, but unless the building industry is seen in a wider context, the overall cost both in real terms and in damage to the environment will be higher. Risk sharing, incentives, demonstration projects, ecolabelling and environmental audits all provide a way forward. 8. REFERENCES

HM Government White Paper, This Common Inheritance - Britain’s Environmental Strategy, HMSO, London, 1990. Arup Economics and Planning, Occurrence and utilisation of mineral and construction wastes, Report for the Department of the Environment, HMSO, London, 1991. Building Research Establishment, Efficient use of aggregates and bulk construction materials - the role of specifications. Volume 1: An overview; volume 2: Technical data and results of surveys, BRE Reports BR243 & 244, BRE, Watford, 1993. R.J. Collins and P. Sherwood, Use of waste and recycled materials as aggregates: standards and specifications, To be published 1994. Department of the Environment, Environmental Assessment - A guide to the procedures, HMSO 1989. European Economic Community Council Regulation No 880/92 (EEC), 23 March 1992 on a Community eco-label award scheme, Official Journal of the European Communities 11.4.92,No L 99/1.

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7 8

9

10 11

12 13

14 15

16

17 18

19 20 21 22

C. Atkinson, J. West and S. Hobbs, Life cycle assessment and ecolabelling of building products, CIB Conference on Buildings and the Environment, Building Research Establishment, Watford, May 1994. C.J. Atkinson and R.N. Butlin, Eco-labelling of Building Materials and Building Products, BRE Information Paper IP 11/93, Building Research Establishment, Watford, 1993. Building Research Establishment, BRE Environmental Assessment Method: Version 1/93 B R E E M e w Offices (1993); Version 2/91 An environmental assessment for new superstores and supermarkets (1991); Version 3/91 An environmental assessment for new homes; Version 4/93 BREEAMlExisting Offices (1993); Version 5/93 BREEAM/New Industrial Units (1993), BRE, Watford. European Economic Community Council Regulation No 1836/93 (EEC) of 29 June 1993 allowing voluntary participation by companies in the industrial sector in a Community eco-management and audit scheme, No L 168/1. British Standards Institution, Aggregates from natural sources for concrete, British Standard BS882: 1992, BSI, London, 1992. British Standards Institution, Specification for lightweight aggregates for masonry units and structural concrete, British Standard BS3797: 1990, BSI, London, 1990. British Standards Institution, Air-cooled blastfurnace slag aggregate for use in construction, British Standard BS1047: 1983, BSI, London, 1983. British Standards Institution, Guide to the use of industrial by-products and waste materials in building and civil engineering, British Standard BS6543: 1985, BSI, London, 1985. Department of Transport, Scottish Office Industry Department, Welsh Office and Department of the Environment for Northern Ireland, Specification for Highway Works, HMSO, London, 1991. R.J. Collins, Reuse of demolition materials in relation to specifications in the UK, in Demolition and reuse of concrete and masonry ed. E.K. Lauritzen, Proceedings of the Third International RILEM Symposium, held in Odense, Denmark, 24-27 October 1993. E & FN Spon, London, 1994, p.49-56. British Standards Institution, Concrete: Part 1. Guide to specifying concrete; Part 2. Methods for specifylng concrete mixes, British Standard BS5328: 1991, BSI, London, 1991. Building Research Establishment, Hardcore, BRE Digest 276 (minor revisions 1992), BRE, Watford, 1992. British Standards Institution, Pulverised fuel ash: Part 1 Specification for pulverised fuel ash for use as a cementitious component in structural concrete, British Standard BS3892: Part 1: 1982, BSI, London, 1982. British Standards Institution, Specification for Portland cement, British Standard BS12: 1991, BSI, London, 1991. British Standards Institution, Specification for Portland blastfurnace cement, BS 146: 1991, BSI, London, 1991. British Standards Institution, Specification for high slag blastfurnace cement, BS 4246: 1991, BSI, London, 1991.

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23 J.D. Matthews, Pulverised-fuel ash - its use in concrete parts 1 and 2, Building Research Establishment Information Papers IP 11/87 and IP 12/87, BRE, Watford, 1987. 24 G.J. Osborne, Durability of blastfurnace slag cement concretes, Building Research Establishment Information Paper IP 6/92,BRE, Watford, 1992. 25 Building Research Establishment, Sulphate and acid resistance of concrete in the ground, BRE Digest 363,BRE, Watford, 1991. 26 Building Research Establishment, Alkali aggregate reactions in concrete, BRE Digest 330,BRE, Watford, 1988. 27 P.J. Hoddincott, R.A.F. Macrory and N.Roberts, UK Cement Manufacture and the Environment, Institute of Concrete Technology Annual Conference, April 1993. 28 Department of the Environment, Advice on certain unsound rock aggregates in concrete in Cornwall and Devon, DOE(Buildings Regulations Division), London, February 1991. 29 Commission of the European Communities, Coal research reports - utilisation of colliery spoil in civil engineering applications, National Coal Board (London) contract no. 6220-73/8/805, CEC Directorate General Scientific and Technical Information and Information Management, Luxembourg, 1977. 30 W.Gutt, P.J. Nixon, R.J. Collins, and R. Bollinghaus, The manufacture from colliery spoil of synthetic aggregates for use in structural concrete, Precast Concrete (MarcWApril1980) 120-124and 183-185. 31 P.J. Nixon, and E.M. Gartner, An assessment of processes for the manufacture of synthetic aggregates from colliery spoil, International Journal of Lightweight Concrete 2(3) (1980)141-164. 32 P.F.G. Badill, Alternative materials for concrete - Mersey silt as fine aggregate, Building and Environment 15 (1980)181-190. 33 R.J. Collins, Dredged silt as a raw material for the construction industry, Resource Recovery and Conservation 4 (1980)337-362. 34 D.C. TeychennB, The use of crushed rock aggregates in concrete, Building Research Establishment Report BR18, BRE, Watford 1978. 35 British Standards Institution, Pulverised fuel ash: Part 2 Specification for pulverised fuel ash for use in grouts and for miscellaneous uses in concrete, British Standard BS3892:Part 2: 1984,BSI, London, 1984. 36 P. Kristensen, Recycling of Clay Bricks, in Demolition and reuse of concrete and masonry ed. E.K. Lauritzen, Proceedings of the Third International RILEM Symposium, held in Odense, Denmark, 24-27 October 1993. E & FN Spon, London, 1994,p.411-414. 37 P. Lindsell and M. Mulheron, Recycling of Demolition Debris, The Institute of Demolition Engineers, Virginia Water, Surrey, 1985. 38 B. Olsen, The "Recycled House" in Odense, in Demolition and reuse of concrete and masonry ed. E.K. Lauritzen, Proceedings of the Third International RILEM Symposium, held in Odense, Denmark, 24-27 October 1993. E & FN Spon, London, 1994,p.521-527.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, H A . van &r S l w t and Th.G. Aalbers (Editors) @I994 Elsevier Science B.V. AN n g h ~ sreserved.

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OVERVIEW OF COAL ASH USE IN THE USA

Samuel S. Tyson American Coal Ash Association 1913 I Street N.W. - Suite 600 Washington, DC, 20006 USA SUMMARY

This paper describes coal ash produced by electric utilities in the USA. An overview is presented of the various applications in which this coal ash is used. 1. INTRODUCTION

The American Coal Ash Association, Inc. (ACAA) is an organization of producers, marketers and other organizations involved with utilization of coal ash, or coal combustion byproducts (CCBs). ACAA’s goal since its founding in 1968 has been to gain recognition and acceptance of coal ash as an engineering material on par with competing virgin, processed and manufactured materials by advancing coal ash uses that are technically sound, commercially effective, and environmentally safe. The use of CCBs is affected by local and regional factors including production rates; processing, transportation and handling costs; availability of competing materials; and experience of materials specifiers, design engineers, purchasing agents, contractors, legislators, regulators and other professionals. 2. ANNUAL CCB SURVEY A n annual survey of electric utilities is conducted by ACAA to determine the quantities of CCBs produced and used in the United States (1). In 1992 approximately 82 million short tons (for metric tons multiply short tons by 0.9078) of CCBs were produced in the USA in the form of fly ash, bottom ash, boiler slag and flue gas desulfurization (FGD) material. Approximately twenty-five percent of the combined production of these byproducts was used, while the remainder went to disposal areas. The approximate use quantities for these by-products are summarized in Table 1.

Table 1. Use of Coal Combustion By-products [1992 data; million short tons] Tons Used ( % Use)

Fly Ash 13.1 (27%)

Bottom Ash 3.9 (28%)

Boiler Slag 3.1 (75%)

FGD By-product 0.3 (2%)

700 It is clear from survey data gathered by ACAA over the years that the annual use of CCBs represents a major continuing effort by a number of parties, including the electric utility producers of ash and their marketers. It is equally clear, however, that significant tonnages of coal ash are not used each year. Therefore it is essential for ACAA to promote the use of coal combustion byproducts in numerous applications that are technically sound, commercially effective and environmentally safe. 3. CCB USES

CCBs are engineering materials with uses similar to the uses for competing virgin, processed and manufactured materials. It is instructive to consider the total tonnages of CCBs (fly ash, bottom ash, boiler slag and FGD material) that are used in the four leading markets for coal ash based on ACAA's 1992 survey results. This information is presented in Table 2. Table 2.

Use of CCBs in the Four Leading Markets [1992 data; million short tons)

Markets

Amount

Cement and Concrete Products Structural Fills Road Base and Subbase Blasting Grit/Roofing Granule Other Markets Total CCB usage

*

7.9 2.7 2.4 2.1 5.2 20.3

% of Usaqe*

38.9% 13.2% 11.7% 10.2% 26.0% 100.0%

Total CCB usage was 20.3 million tons which was 24.8 percent of the 82.0 million tons produced.

This paper describes each of these four leading markets for CCBs which together account for 74 percent of total CCB use in the USA. Additionally, the several categories of CCB uses that make up the other markets are summarized. 3.1

Cement and Concrete Products 3.1.1

Tmical Concrete

In 1992 approximately 7.1 million short tons of coal fly ash was used in the USA in cement and concrete products (1). The amount of fly ash in typical structural concrete applications ranges from 15 to 35 percent by weight of the total cementitious material (cement plus fly ash), with amounts up to 70 percent for massive walls and girders, road bases and dams.

70 1

Various concrete mixtures are produced with coal fly ash including normal weight and lightweight concretes, high strength concrete, early strength concrete for form removal requirements, low-slumppaving concrete, controlled low strength material (CLSM), and architectural concrete. With the principal exception of high strength concrete, all of these fly ash concrete mixtures are routinely air-entrained for added workability and for resistance to freezing and thawing. A state-of-the-artreport on the use of coal fly ash in concrete has been prepared by the American Concrete Institute (ACI) (2). Fly ash for use in concrete is covered in an ASTM specification (3). 3.1.2 Mixture Proportioninq The selection of mixture proportions for fly ash concrete is accomplished through the use of the same standard practices that are applied to any portland cement concrete. A document detailing a standard practice for normal, heavyweight and mass concretes is available from ACI (4). The ACI document shows computations for fly ash content specified either as a weight percentage or as a volume percentage of the total cementitious material content. The first approach, using weight equivalency, is probably the most common method in use. If the trial batches with and without fly ash are made to have the same ratio of water to cementitious material, then, as demonstrated in the ACI example: w/cl

=

w/(c2 + f ) ; where w

=

weight of water,

cl= weight of cement only, c2= weight of cement when used with fly ash, and f

=

weight of fly ash.

Because many fly ashes will bring about a significant decrease in water demand for the mixture, an absolute volume calculation is used to determine the small increase in sand to accommodate this slight volume decrease. Similarly, because of the assumption in the above example that cl = (c2 + f), and because fly ash has a lower specific gravity than portland cement, the mixture with fly ash will have a slightly greater volume. Again, absolute volume calculations are used to determine the small reduction in sand to accommodate this slight volume increase.

702 3.1.3

Roller ComDacted Concrete and Concrete Road Bases

The amount of fly ash in roller compacted concrete and concrete road bases, and in dams and massive walls and girders may be 70 percent or more of the total cementitious material. In such mixtures, where the fly ash content exceeds the portland cement content by a weight ratio of two or more, substantially increased curing times may be needed before placing the structure in service. For typical paving applications the percentage of fly ash will frequently be from 20 to 35 percent by weight of total cementitious material content, and normal curing times can be applied. For roller compacted concrete in paving applications reference documents are available from the ACI (51, the American Society of Civil Engineers (6) and the U.S. Army Corps of Engineers ( 7 )( 8 ) . 3.1.4 Concrete Block and Pilse

Fly ash and bottom ash are used in the manufacture of concrete masonry units, i.e., concrete block. Fly ash, because of its contribution to workability, strength and durability, is an important ingredient in the stiff mixtures used for concrete block. Similar attributes are cited for the selection of fly ash as a component of the stiff concrete mixtures used for concrete pipe. The several ASTM specifications for concrete pipe allow the use of fly ash by reference to either ASTM C 618, as discussed above for typical concrete mixtures, and ASTM C 595 (9). The concrete pipe specifications from ASTM are available through the American Concrete Pipe Association in a three-ring binder for convenient updating (10). 3.1.5

Lishtweisht Assresate

An ACAA symposium publication contains a number of papers describing traditional as well as developing uses of coal combustion by-products (11). One developing market is the manufacture of pelletized lightweight aggregate from coal fly ash by incorporating chemical admixtures and either lime (12) or portland cement (13) as activators, and from a third process using fly ash and coal cleaning mixtures (14). These lightweight aggregates are produced without the use of heat energy for sintering, however there is another process that produces a The lightweight aggregates sintered fly ash aggregate (15). produced without sintering are used primarily in concrete block, however some may be used in non-structural and structural concretes. A sub-committee of ACI Committee 213, on lightweight aggregate and lightweight aggregate concrete, is collecting information for publication on lightweight byproduct aggregates.

703 3.1.6

Flowable Mixtures

ACI Committee 229 deals with certain flowable grout-like materials under a general designation, "Controlled Low Strength Materials" (CLSM) (16). Such materials have compressive strengths equivalent to well compacted soils and may represent a wide range of fly ash contents. Applications include but are not limited to: backfills, structural fills, insulating fills, road and slab base, trench bedding and so on. While flowable mixtures can be produced without fly ash, it is very easy demonstrate that economical mixtures with the most desirable characteristics, including flowability, cohesiveness, minimal bleeding, and controlled density, can be produced only with fly ash in combination with relatively small amounts of portland cement. The percentage of fly ash used in grout mixtures may be in a wide range from 20 to 95 percent by weight. To produce a flowable mixture having a flowable consistency without segregation of the constituents, coal fly ash is typically proportioned with portland cement and water, with or without aggregate or other fillers. Some fly ashes with hihg lime contents can be used to produce a flowable mixture without cement. The use of CLSM flowable mixtures is open to numerous innovative engineering solutions for everyday problems that would otherwise be viewed as traditional soils backfilling and foundations problems. Such mixtures help to achieve economies through reduced labor and inspection costs, and allow contractors to reduce or eliminate certain labor and equipment costs. 3.2 Structural Fill Numerous structural fill applications of CCBs have been designed, constructed and evaluated over the last several decades. A number of such projects are described in re-publishedpapers from the proceedings of ACAA's international symposia (17). Coal fly ash is readily available in many locations to be used as a borrow material in lieu of soils for the construction of fills. When fly ash is compacted in lifts, the resulting structural fill is capable of supporting parking lots, buildings and roadways. Moistened fly ash can be used alone for structural fill applications. As with ordinary soils, optimum and target moisture contents can be established, along with procedures for achieving required levels of compaction. Open trenches can be cut in the compacted, non-cemented, fly ash for the placement of building footings and for the installation of pipes and cables.

704

When used in structural fills and embankments, fly ash offers several advantages over soil and rock: Low Unit Weight--Thecompacted maximum dry density of fly ash is typically about 10 to 20 percent less than that of ordinary soils. Placing fly ash over weak, compressible foundation soils results in lower total settlement. High Shear Strength--One of the most significant characteristics of fly ash used as a fill material is its strength. Compacted fly ash is as strong or stronger than many compacted soils. Moisture Control--Althoughthe optimum moisture content of fly ash is greater than that of silty soils, the compaction behavior of fly ash is relatively insensitive to variations in moisture content when it is placed with a moisture content that is less than its optimum moisture content. 3.3

Road Base and Subbase

ACAA has published a manual on the design and construction of pavement systems incorporating fly ash stabilized bases. The project to produce the manual was reported at a 1988 meeting of the American Society of Civil Engineers (18) where advice and comments were solicited. The ACAA pavement manual (19) offers pavement design engineers, materials engineers, and construction managers guidance in the design and construction of low- to high-strength Ilpozzolanic stabilized mixturer1( IIPSM1l) base and subbase layers having coal fly ash in combination with activators, aggregates and water. Users can choose from three pavement thickness design methods included in this manual: o

Method A - Flexible pavement structural layer coefficients;

o

Method B - Mechanistic pavement design procedures, using resilient modulus values for the pavement layers;

o

Method C - A combination of Method A and Method B, using mechanistic concepts to determine pavement layer coefficients.

design

procedures

using

To capture the long-term service and cost-saving features of PSM design, the document details a mixture proportioning system, a thickness design procedure, and established mixing and construction techniques. The user can apply the contents of this manual with professional advice to produce satisfactory pavement structures of acceptable uniformity in accordance with typical specifications and quality requirements of individual departments of transportation.

705 3.4

Blastinq Grit and Roofins Granules

Blasting grit and roofing granule applications, with an annual usage of 2.1 million short tons in 1992 represents 10.2% of the total coal ash used in that year. This market is extremely important to the coal ash industry as high-quality blasting grit and roofing granules are in fairly constant demand. The largest users of blasting grit are the large shipyards that perform contract maintenance for the U.S. Navy and for commercial shipping lines. The other users of blasting grit are supplied by a small number of companies which collect, size and bag the boiler slag and distribute it in small lots to numerous locations for use. Because the boiler slag that can be used for blasting grit is typically limited to slag produced in wet-bottom cyclone boilers, the long-term supply of this material will be related to the life of those boilers. The use of boiler slag as a roofing granule is subject to some of the same limitations as found for blasting grit. The large investment in facilities and equipment are factors which make use of boiler slag for roofing granules a regional manufacturing application with shipments of a finished product in small lots to numerous locations for use by a multitude of individual users. Miscellaneous uses of boiler slag are found in several decorative aggregate applications. For example, boiler slag has been used as a sand-substitute in sandtraps on golf courses; as an aggregate in precast and cast-in-placeconcrete to which a surface treatment is applied to expose this visually attractive material; and in less glamorous uses such as a sand-substitute in ashtrays for public buildings. 3.5

Other Markets

The several market categogies which together consume annually about 5.2 million short tons of CCBs in the USA are: filler in asphalt; anti-skid material for snow and ice on roadways; grouting; coal mine applications; wallboard manufacture; waste stabilization and solidification; and other low-volume applications such as fillers in plastics and paints. 4. CONCLUSION

ACAA is committed to increasing the use of CCBs in technically sound, commercially effective and environmentally safe applications and will work to ultimately achieve full use of these materials.

706 5. REFERENCES 1.

1992 Coal Combustion Bv-product Production and Consumption, American Coal Ash Association, Inc., Washington, D.C., 1993, 1 page.

2.

Use of Flv Ash in Concrete, American Concrete Institute, Committee 226 Report, ACI Materials Journal, Detroit, September-October 1987, pages 381-409.

3.

Standard Specification for Flv Ash and Raw or Calcined Natural Pozzolan for Use As a Mineral Admixture in Portland Cement Concrete, ASTM C 618, American Society for Testing and Materials, Philadelphia, 1993, 3 pages.

4.

Standard Practice for Selectins Proportions for Normal. Heavweisht and Mass Concrete, Committee 211 Report, ACI Manual of Concrete Practice, Part 1, Detroit, 1989.

5.

Roller ComDacted Concrete Pavement, Publication C - 8 , American Concrete Institute, Detroit, 1987, 55 pages.

6.

Roller Compacted Concrete 11, Conference Proceedings, American Society of Civil Engineers, San Diego, February 29-March 2, 1988.

7.

Encrineerins and Desisn - Roller ComDacted Concrete, U.S. Army Corps of Engineers, Engineer Manual 1110-2-2006, 1985.

8.

Roller ComDacted Concrete (RCC) Pavement for Airfields, Roads, Streets and Parkins Lots, U.S. Army Corps of Engineers, Guide Specification 02520, 1988.

9.

Standard Specification for Blended Hydraulic Cements, ASTM C 595, American Society for Testing and Materials, Philadelphia, 1986, 5 pages.

10.

ASTM Standards for Concrete PiDe, Authorized reprints of the American Society for Testing and Materials, American Concrete Pipe Association, Vienna, VA, 1988.

11.

Proceedinss: Eishth International Coal Ash Utilization Svmposium, Volumes 1 and 2, CS-5362, Washington, D.C., Prepared by American Coal Ash Association, Published by Electric Power Research Institute, October 1987, 870 pages.

12.

Ibid., Hay, Peter, "Aardelite - An Economical Lightweight Aggregate from Fly Ash," Paper No. 57, 7 pages.

13.

Ibid., Styron, Robert W., "Fly Ash Lightweight Aggregate: The Agglite Process,Il Paper No. 58, 12 pages.

707

14.

Ibid., Burnet, George, "Experimental Studies of the Production of Lightweight Aggregate from Fly Ash/Coal Cleaning Refuse Mixtures," Paper No. 61, 17 pages.

15.

Pulverized Fuel Ash Utilization, Central Generating Board, England, 1972, 104 pages.

16.

Committee Rosters, Missions, Goals, and Activities, American Concrete Institute, Detroit, June 30, 1988, 142 pages.

17.

Structural Fill ADDlications of Coal Ash, American Coal Ash Association, Washington, DC, 1993, 100 pages.

18.

"Guidelines for Design and Construction of Pozzolanic Stabilized Base Course Mixtures", DisDosal and Utilization of Electric Utility Wastes, Session Proceedings, American Society of Civil Engineers, Nashville, May 1988, page 35-49.

19.

"ACAA Pavement Manua1,I' Recommended Practice: Coal Fly Ash in Pozzolanic Stabilized Mixtures for Flexible Pavement Systems, American Coal Ash Association, December 1991, 64 pages plus Appendix.

Electricity


Environmental Aspects of Construction with Waste Materials J.J.J.M. Goumans, H A van der Sloot and 7'h.G. Aalbers (Editors) 61994 Elsevier Science B.V. All rights resewed.

709

Environmental life cycle analysis of construction products with and without recycling M. Sc.A. M. Schuurmans-Stehmanna 'Intron, institute for materials and environmental research B.V., P.O. Box 5187, 6130 PD Sittard, The Netherlands

summary To evaluate the effects of (construction) products on the environment a standardized methodology called Environmental Life Cycle Analysis of Products (LCA), has been developed in the Netherlands. This methodology evaluates products in their specific function and during their entire life cycle. "Environment measures" are obtained, which are used for a large number of objectives, varying from product comparison, environmental management within industries, product improvement and certification of construction products. Various LCAstudies of construction products have already been performed. Effects of recycling can be assessed fairly well. 1. INTRODUCTION The production and use of products have an influence on the environment. This influence, or environmental impact extends itself to all phases of the product life, from the winning of raw materials to the processing of waste. In this account the life cycle analysis (LCA) methodology for evaluation of the environmental impact as developed in the Netherlands will be examined as well as the possibilities this methodology offers. Examples of the application of this "cradle to grave" approach on construction products and the influence of recycling on the LCA-results will be discussed. 2.

METHODOLOGY

In the Netherlands the first National Environmental Policy Plan (NEPP) has been published in 1989 in which the objectives are set to come to a sustainable development of the environment. The NEPP introduces the so-called product policy aimed at promoting the use of products with the lowest possible environmental impact. To enable an evaluation of the environmental impact a standardized methodology has been developed by the Centre for Environmentology of the (state) University of Leiden (CML). This project was ordered by the Dutch Ministry for Housing, Physical Planning and Environment (VROM). The methodology is named "Environmental Life Cycle Analysis (or:

710

Assessment) of Products", in short LCA [l]. The concept of this LCA-methodology was also initiated by international discussions on LCA's within the Society for Environmental Toxicology and Chemistry (SETAC) in which environmental scientists, policymakers, industrialists and interest groups from various countries are involved. In a LCA, as the word indicates, the entire life cycle of a product is evaluated. In this life cycle about 3 phases are to be considered: the production, usage and the waste phase. Subject to the product these phases can be subdivided. The life cycle of construction products for example ranges from the winning of raw material, through producing materials and products, construction, use, maintenance and demolition to the treatment of waste. In the LCA-method all environmental effects of the product during its life cycle are quantified. To do so the processes of all life cycle phases which together form a so-called "process tree", are evaluated. If this is done in all details the amount of data required is enormous and the method is not feasible. As a consequence choices have to be made. That is why for example capital goods (machines, buildings) are not taken into account. In the analysis a large number of environmental aspects can be taken into account. In Table 1 a summary is given of the aspects the Ministry of VROM has chosen in 1992 [2]. For each product a relevant number of these aspects is selected. When all data are collected the environment-related data are aggregated per environmental aspect into one identification number. Aggregation is only possible when the data for one environmental aspect are expressed in the same unit; such units are called identification numbers. These numbers are calculated by means of standards and indices, called classification factors. The contribution of a product to the greenhouse effect for example is calculated by dividing the emissions per greenhouse gas by the global warming potential (GWP) of the gas. If for example a 100 mg CO, emits of which the GWP is 100, the contribution to the greenhouse effect following the C 0 2 emission is 1 unit greenhouse effect contribution. The methodology provides such classification factors for a large number of environmental aspects. By reproducing these factors in identification numbers the so-called environment measures are created. Each environmental aspect corresponds with an environment measure. This environment measure gives information in quantitative form about the environmental impact of one specific environmental aspect. The set of environment measures is called the environmental profile, signifying a sort of "environmental characteristic" of a product. Quantification presents several advantages, in particular for the evaluation. In the evaluation similar environmental aspects are compared. As a result of the fact that the aspects are quantified, the comparison is objective. However, because of this quantitative approach, there is a risk that qualitative aspects, such as the affects upon the landscape, are left aside. Therefore qualitative aspects are mentioned separately. As a basis for product comparison a functional unit is applied. The functional unit defines the function of the product, its size, its required service life in the context of the structure, its actual service life, the maintenance required and the possibilities for reuse. A LCA is thus performed on a product in its function. Consequently one cannot

Table 1. General framework for environment measures in the building industry II

aggregatmn environment measures..

raw matenals

pollution

1 2 3 4 5 6 7 8 9 10 11 12

depktmn of searcety renewable raw matenals (e g tropral wood ivory) depletlon of non-renewable raw matenals (a o minerals) total amount used raw materlals acldfcatlon nubmcatmn greenhouse effect depklwn ofozone layer toxical substances for people toxical substances for flora en fauna waste heat radlalwn waste bef6re treamnt

*-

not possible m many cases environment measures rehted to Other measures

.*.

waste

13 14 15

IS 17 18 19 20 21 22

23 24

25

nuisance

energy

re-usability

waste after treatment (final waste) chemical waste stench and d o u r noise pollution for userlenvironrnenl calamles damage lo eco systerrmandscape/environmental quallty depletlon of non renewable energy caners total amount used energy re usabihly of total product re-usability ofproduct components recyclabiltf of matenals extent of repairabiltf of the product servw llfe of Droduct

repairability

lfe

712 determine environment measures of a material as such, but very well of the product manufactured out of that material. Herewith justice is done to the specific application of the material in a product and the specific function of the product itself. For the building industry this has to be considered a prior condition for the evaluation of environmental aspects [lo].

3. APPLICATION Obviously it is meaningful to deal with the question for what purpose evaluations made by means of a LCA will be used. Several applications are possible, each of them intended for and corresponding with a specific target group in the building industry. An LCA is first of all an instrument to obtain environment-related information about a product. In the Netherlands this information is used as: - a marketing instrument for producers and suppliers on behalf of their customers (”instruction leaflet” for sales argument); - a means for product comparison (only acceptable with standardized method), on behalf of designers, clients, customers and users; - a comparison of products with standards, or the development of standards, useful for government institutions; - a basis for product or process improvement or innovation having producers as a target group; - a starting point to set up and study policy strategies, on behalf of the authorities; - a management tool as part of the environmental managment systems within a company; - a basis for the eco-labelling of products (EEC council regulation NP 880/92 of March 1992); - a basis for the certification of environmental aspects. The initiative to have life cycle assessments made, was initially taken by the government. At present environment-related information obtained by means of LCAs is used more and more in the promotion and communication policy of companies. 4. LCA OF WINDOW FRAMES

One of the first construction products on which a life cycle assessment (LCA) was performed, was the window frame [3]. Compared are frames of hard wood, pine wood, PVC and aluminium. Next to the frames as such, all other materials/products used for the assembly of window frames have been included in this study. They are packaging foils, finishing materials, sealants, paints etc. The most important results are summarized in Table 2. When we arrange the various environment identification numbers in another way by assigning the value 10 to the highest number and then linearly extrapolate the lower numbers, Table 3 is created. From this table we can deduce that none of the window frames scores better than the other ones on all points. However it is clear that the aluminium frame has the most negative points in general and stands somewhat out from

713 Table 2. Environment identification numbers of the various types of window frames for the living room of a public housing unit; state on July 1. 1990 [3] environment ldenbflcalron number

aluminium

pine wood

PAW MATERIALS

-

.

total use energy carner (MJ) affected kopical forest (m‘)

23 195 3.1

10 774 0,625

EMISSION INTO AIR

I

I merantl

1 1 lroko

12 088

222

”’%

2 583 1.1

251 7.1

514 ~_______

DISCHARGE INTO WATER . toxical substances (I) - others (kgll) * 2-chloroelhanol * lnchloroethanol * vinyhc chlonde =

soflener

6 020

74 500

6 770

8.49404 3.4040’ 1.61 405 3.65 . l o 3

1.10.10‘ 4.41 .lo‘ 2.094 Oa 0

16.1 162

Table 3. Relative environment identification numbers of the various types of window frames for the living room of a public housing unit [3] environment ldentfcdtton number RAW MATERIALS . total use energy carriers affected trooical forest

.

EMISSION INTO AIR toxtcal substances aciddying substances others * CFK 1 1 * carbon dmxide

-

DISCHARGE INTO WATER toxtca~substances others * 2-chloro-elhanol * trichbro-elhanol

-

*

vinyl chbnde

* soflsner

WASTE - chemtcal waste - other waste

aluminium

el ol

pine wood

I I 1:

iroko

1;

meranti

I

wc

Table 4. Environmental impact concrete first span of bridge (period of 75 years) [6]

4 e

P deplemn raw

drying up

acdmicamn

greenhouse

air pollwn

water pollubon

malenals 1Oe-12

1oe-12

1oe +5

effect 1De*5

1&+6

(kg)

chemical

nonchemlcal

energy

waste

waste (ton)

(GJ) 1&+3

103 36 16 13

(ton)

Pmducban Semmanuf

46000Oe+3

1200e+5

435

76

86725

56

79712

23254

PmducMn

1342e+3

108 31

48

113

21460

0.5

765

44 15

13 6

38065 212438 26540 21967

31 0.2

30728 382

1547 312 5862

634

149

385735

200 7

133047

mpl-

5e+3

Maintenance Renmval

3768e+3 4e+3

286ei5 0 168e+5 0

Total

46511-3

1654e+5

6

Table 5. Sensitivity analysis use of concrete rubble to replace gravel (concrete first span of bridge) [6] 20% broken cnnwete. 80% gravel

acidifation ChemlCal waste (kg) energy (GJ)

40% broken concrete. 60% grave4

4.65119.104

- 2.5%

634 .lo5

+ 2.7%

133.047 ton 176.10’

+ 2.9%

+ 1.8%

1

8

30976

176

715

the others. But if we state that the aluminium frame is less environment-friendly than the other window frames we enter into the field of the weighing factors. However a weighing can only be made between similar environmental aspects. Dissimilar aspects cannot be compared; this would be like comparing "apples and oranges": how can m2 of affected tropical forest be compared with units of polluted water or solid waste? In order to reduce environmental impact to a minimum, the university of Amsterdam has developed software to determine the effects of alternatives on the environment. Besides some design and material alternatives, the effects of recycling on the environmental profile are determined. Recycling of the window frame (material) as well as the use of secondary raw materials are considered. The environmental yield due to recycling varies from appr. 20% when recycling PVC frames to a 50% for pine wood frames. When measures are to be taken one should always consider that a measure which has a positive effect upon one of the environment identification numbers, might adversely affect other identification numbers. The study of the environmental data proves that other initial hypotheses do not give cause for other conclusions, at least for the principal aspects. The Life Cycle Assessment of the window frames shows that none of the frames scores better than the others in all aspects. The information provided and considered to be objective, offers the customer only an objective starting point from which he is to make a subjective choice. 5. LCA OF A BRIDGE

For a bridge crossing the river Waal an LCA-study is made on the impact of one of the spans of the bridge [ 6 ] .Two alternatives have been compared: one of concrete (reinforced concrete), the second of steel with concrete for the bridge deck. In both alternatives asphalt is the road topping. The LCA covers the total span including coatings, pipes (HDPE), PVC tubes to protect electrical cables, etc. For the alternative in concrete 20% concrete granulate produced from demolished concrete structures is used. For the alternative with steel, it was assumed that 17% of the steel was produced from scrap iron. In Table 4 the environmental profile of the span made of concrete is given. The study shows that on a number of environmental aspects the alternative in concrete scores better than the steel structure. But in this case as well, it is difficult to decide upon which alternative is the most environment-friendly. The purpose of the study was a(mong) o(thers) to gain a clear insight in the way both alternatives affect the environment. An effect analysis should help to reduce the impact as effectively as possible. Therefore it has been analysed which factors contributed most to the environmental impact and also a sensitivity analysis has been made. For the concrete for example the analysis has revealed that an increased use of concrete granulate (40% instead of the 20% assumed in the study), even though reducing the use of gravel, did not have much influence on the final figures. The depletion of raw materials is somewhat diminished, because of a decreased need for gravel, but the other units slightly augment as a result of the production of concrete granulate, see Table 5 . The steel alternative

716 profits substantially from a higher use of scrap iron (a 100% instead of 17%). 6. LCA OF ROADS

Intron has in cooperation with TNO-Bouw performed an LCA-study of a concrete and an asphalt road [9]. One of the objects of the project was to assess the feasability of the LCA-method adopted by the Ministery VROM for the building industry and to discover areas which have to be improved. As the functional unit has been chosen a road section with a service life of 60 years. It was concluded that transport of road construction materials and energy for production of the materials were main sources of the environmental impact. Recycling of road construction materials at the road construction site when asphalt etc has to be renewed is identified as an important possibility for reducing the environmental impact. In the concrete road for example on-site crushing of concrete is possible for use as unstabilized roadbase or for preparing new concrete with this concrete ”waste”. On-siteheuse of asphalt is already common practice. Crushed asphalt is mixed with sand and cement for use as roadbase (cold reuse). However, off-site recycling, is still preferred. Techniques to obtain the same quality of secondary material on-site is still in development. In a follow-up of the project environmental profiles of alternative road constructing, the effects of recycling options, the use of industrial secondary materials such as replacement of gravel by secondary material or concrete aggregate, secondary asphalt, will be studied.

7. DEVELOPMENTS The Dutch ministry of VROM has commissioned LCAs of other building products such as roofing sheets and building paints [7, 81. LCAs are not only made on the initiative of the government, but also and frequently on the initiative of the industry. Intron has recently made an LCA of the building cladding material TRESPA G2. TRESPA G2 is a product of Hoechst Holland. Hoechst intends to use the environmental profile of Trespa for environmental management within the company and for certification. In the past year it is studied in which way LCAs can be used in the certification of building products and processes. A so called ”environmental paragraph” will be added to the already existing certificates. It is likely that products of which environmental data based on the adopted LCA-method are available and which meet environmental requirements will be granted such an additional environmental certificate. The first environment paragraphs are in development at the moment. The Dutch ministry of VROM plans to make operational the environment measures system in the building industry beyond 1994.

717

8. CONCLUSION The methodology for an environment-oriented life cycle assessment of products offers a potential basis for a standard method to measure the potential effects of a (construction) product on the environment. The LCA provides a set of environment measures, the environment profile, which represents the environment characteristic of the product. Only similar environmental aspects can be compared. Attempts to arrive at one figure for each product are deemed to be based on biased criteria. The examples show that a final judgement of the environment-friendliness of a product in relation to another product based on unbiased criteria cannot always be made. However analyses will offer well-founded and qualified information as an objective starting point for a subjective choice to be made by the purchaser of the product. Besides product comparison numerous other applications of LCAs are possible, from which environmental management within industries, product improvement, marketing and environment certification are already applied in the Dutch building branch. The effect of alternatives such as recycling can be measured fairly well.

9. LITERATURE 1. Guinee, J.B., Heijungs, R., Huppes, G., Lankreijer, R.M. (Centrum voor Milieu-

2. 3. 4.

5.

6.

kunde Rijksuniversiteit Leiden CML/Centre for Environmentology R. U.Leiden), Ansems, A.M.M., Eggels, P.G. (TNO),De Goede, H., Van Duin, R. (Bureau Brand- en grondstoffen B&G/Bureau for Fuels and Raw Materials), "Milieugerichte levenscyciusanalyses van produkted "Environment-oriented life cycle assessments. Deel I: handleiding/ Part I: Introduction. Deel 11: achtergrondedpart 11: Backgrounds", oktober 1992. DGM ministerie VROM, "Milieumaten in het milieubeleid-Stand van zaken per I September 1991/ Environment measures-State of affairs per September 1. 1992", 3 September 1991. Lindeyer, E., Mekel, O., Huppes, G., Hacke, R., "Milieu-effekten van kozijneniEnvironmenta1 effects of window frames", Centrum voor Milieukunde R. U. LeidedCentre for Environmentology U./Leiden, 1990. Hoefnagels, F.E.T., Kortman, J.G.M., Lindeyer, E.W., "Minimaliseren van de milieubelasting van buitenkozijnedTo minimize the environmental impact of outside window frames", Interfacultaire Vakgroep Milieukunde U. A./Interfaculty department U./Amsterdam, 1991. VNCI. "Integrated substance chain management", uitgevoerd door McKinsey & Company, december 1991. Fraanje, P., Jannink, H., De Lange, V., Lim, R., "Milieu-vergelijking van twee aanbruggedEnvironmenta1 comparison of two first spans of bridges", Interfacultaire Vakgroep Milieukunde Universiteit van Amsterdam (IVAM)/Interfaculty department Environmentology U./Amsterdam, in opdracht van /commissioned by VROM-DCB, IVAM-onderzoeksreeks N.57. oktober 1992.

718 7 . Tromp, W.F.T., Korenromp, R.H.J., Nieuwenhuis, J.W. ( T A W Infra Consult BV), "Milieumaten van dakplaten, een casestudie (concept)/Environment measures of roofing sheets, a case study (concept)", ministerie van VROM-DGMlIBPC, nog niet gepubliceerdlnot published yet. 8. Manders-Maanders, E.H.C., Technische Universiteit Eindhoven (Faculteit Bouwkunde, Vakgroep Fysische Aspecten van de Gebouwde Omgeving, Groep Materiaalkunde/Faculty of Civil engineering, department Physical Aspects of the built environment, Group Materials science), "Milieumatenstudie van vier bouwverven. Een oefenprojekt/Study of environment measures of four building paints. A work project", performed within the National Research program 'Re-use of Waste materials/ uitgevoerd in het kader van het Nationaal Onderzoekprogramma Hergebruik van Afvalstoffen (NOH), NOVEM, RIVM, mei 1992. 9. Schuurmans-Stehmann, A.M. (Intron), Siemes, A.J.M. (TNO-bouw), "Uitwerking milieumatenconcept voor de bouw aan de hand van een voorbeeld. Proefprojekt weg/Elaboration of environment measures concept for the building industry based upon an example. Road test project", CUR Gouda, november 1992. 10. Schuurmans-Stehmann, A.M., Hendriks, Ch.F. (Intron), "Naar een milieumaat voor bouwproduktedTowards an environment measure for building products", Cement nr. 718, 1992 p. 56-59.

Environmental Aspects of Conshcction with Waste Materials J.J.J.M. Goumans, H A . van &r SIoot and Th.G.Aalbem (Editom) el994 Elsevier Science B. K All tights reserved.

719

ASSESSMENT OF THE ENVIRONMENTAL COMPATIBILITY BY-PRODUCTS AND RECYCLED MATERIALS

OF INDUSTRIAL

R. Bialucha *, J. Geiseler and K. Krass **

Forschungsinstitut der Duisburg (Germany) **

Forschungsgemeinschaft

Eisenhuttenschlacken,

lnstitut fur Strassenwesen und Eisenbahnbau, Ruhr-Universitat Bochum, Bochum (Germany)

SUMMARY

Substantial quantities of industrial by-products and recycled materials can be used in road construction. This means a saving in the consumption of natural resources. The precondition for the utilization of industrial by-products and recycled materials is their technology and ecological suitability. Attempts have repeatedly been made to assess the environmental compatibility - in particular the impact on surface water and groundwater - of industrial by-products and recycled materials in the same way as for waste materials. However, a clear distinction must be made between waste materials which are to be disposed of by dumping and the industrial by-products and recycled materials which can be used as aggregates for road construction. The test methods which are used for waste materials therefore cannot be applied to industrial by-products and recycled materials that are employed in the building and construction industry.

1.

INTRODUCTION

The theme of this conference is "Waste materials in construction".The term "waste materials" can have a very broad meaning in English: it covers both waste materials which are disposed of by dumping and residual and by-products of a series of industries which are suitable for use in many different sectors, including road construction. A clear distinction must therefore be drawn between these two groups of materials. Materials which are to be used, for example, as aggregates for road construction must have a carefully defined and uniform composition. Their origin must be known, their production characteristics must remain constant over a lengthy period of time and they must satisfy the requirements laid down in the relevant specifications. On the other hand, waste materials which have to be disposed of by dumping are often of unknown composition and origin and certainly do not satisfy the

720 requirements of road construction specifications. These waste materials must therefore undergo a completely different process of investigation and assessment than materials whose origin and composition are known. To enable a clear distinction to be drawn between these two different groups of materials, we do not describe materials which are suitable for use in road construction as "waste materials" in this article but use instead the terms "industrial by-products" and "recycled materials" or, more generally, "aggregates".

2.

ASSESSMENT OF THE ENVIRONMENTAL COMPATIBILITY OF AGGREGATES

Various methods are available to assess the environmental compatibility of an aggregate. Firstly, the total content of all the individual components may be determined and secondly the leaching characteristics of a particular aggregate may be investigated. Information on the chemical composition enables the risks of the relevant material to be determined, but it remains unknown whether the individual components will ever be released. In Germany, it is therefore widely accepted that while the chemical composition can be used for general characterization of an aggregate, this information is not appropriate for an assessment of the acceptability of the material as far as effect on water resources is concerned. The potentially harmful substances which may be released under practical conditions tend therefore to be decisive in assessing the influence of an aggregate on the soil and water. The compatibility of an aggregate with water resources is therefore determined by reference to the concentrations of environmentally relevant components which may be leached out. It is only in the case of certain organic compounds for which the eluate values are insufficiently, if at all, relevant that the solid composition is partly also taken into account in addition to the eluate values. Based on the eluate contents there are two fundamentally different systems for determination of the compatibility of industrial by-products and recycled materials with the water resources. The first possibility consists of determining uniform limit values for the aggregates which may, for example, be guided by the leaching characteristics of natural soil and rocks. These limit values are considered to be environmentallycompatible and must then be respected by all the different industrial by-products and recycled materials. The second possibility is to determine the normal range of contents of environmentally-relevant components on the basis of extensive investigations and long years of experiences. It will then be possible to arrive at limit values for the specific substance which must be respected by a regular quality control. In practice, the uniform assessment of all industrial by-products and recycled materials on the basis of universal limit values is very unfavourable. The acquisition of extensive data on the leaching characteristics of all the industrial by-products and recycled materials which currently undergo quality control in North Rhine Westfalia has shown just how different these materials in fact are and how their potential uses

72 1 also vary as a result. A great many aggregates will not be able to satisfy universal limit values on every point. In consequence, the use of an aggregate may be ruled out because a single limit value is exceeded. The result of this approach is that a great many aggregates which would be particularly suitable for use in road construction, provided that certain background conditions are satisfied, cannot be used. The only remaining solution is to dispose of these materials by dumping. On the other hand, the definition of specific limit values for a particular material offers a much better possibility of finding suitable application areas for industrial byproducts and recycled materials. As a function of the leaching characteristics of an aggregate which are determined by the limit values specific to the particular material, the potential uses can be determined having regard to the engineering application areas and the hydrogeological circumstances. That is the concept underlying working document No. 28/1 entitled "Environmental compatibility of aggregates, Section: compatibility with water resources" [ l ] which was published at the end of 1992 by the Forschungsgesellschaft fur Strassen- und Verkehrswesen (FGSV)). That document deals with the compatibility with water resources of eight different industrial by-products and recycled materials which currently undergo quality control. The particular materials are as follows:

- Air cooled blast furnace slag - Granulated blast furnace slag

-

BOS slag Electric arc furnace slag (from bulk steel production) Slag tap (from coal fired power plants) Coal fly ash Municipal waste incineration ash (1,Il) Colliery spoil (I, II) Recycled material (I, II)

The three following types of aggregate: municipal waste incineration ash, colliery spoil and recycled material are further subdivided into two sub-groups whose leaching characteristics differ as a result of various possible ways of quality improvement. Specific limit values are determined for these aggregates and potential uses indicated as a function of the construction technique and hydrogeological background conditions. Fiaure 1shows, by way of example, the limit values determined for air cooled blast furnace slag, municipal waste incineration ash and recycled material. In general, a distinction will be drawn between the construction techniques shown in Fiaure 2 as far as the use of industrial by-products and recycled materials is concerned. Decisive factors for the potential uses of aggregates with reference to their influence on the water and soil include, in particular, the use of an aggregate in a bound or unbound layer and the accessibility of seepage water which will depend in part on the permeability of the layers above the aggregate.

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1) not limit values but typical values 2) value corresponds t o Thiosulphate sulphur 3) sum of the single compounds named in the drinking water supply regulation 4) for record only 5) eluate value is decisive BFS = air cooled blast furnace slag MWI = municipal waste incineration ash RCL = recycled material

m: Limit values for some aggregates Fiaure 9 shows the hydrogeological background conditions for the use of industrial by-products and recycled materials. The location of the site must be assessed so as to ascertain whether it is situated within or outside areas which are either particularly relevant from the aspect of water resources or hydrogeologically sensitive. In addition, the distance between the aggregate layer and the highest ground water level must be taken into account. A matrix is plotted for each individual aggregate with the construction technique (see Figure 2) and the location of the site (see Figure 3) as its coordinates.

123

T

. .

Y P E

0 F

road pavement

inbound layers

C 0 N

.

S T R U C

Iound layers

.

T

ioise barrier

. . .

I 0 N

earthworks

Lubgrade ;tabilization

as wearing course under waterproof wearing course (concrete, asphalt, sett paving with waterproof joints) under semi-pervious wearing course ( sett paving, plates, wearing course without binders) under water pervious wearing course (open porous sett pavina) as course with hydraulical binder as course with bitumen with surface water proofing with water pervious course

m: 3.

Possible applications for industrial by-products and recycled materials

LEACHING PROCEDURE

Working document No. 28/1 prescribes a modified DEV-S4 technique as the leaching procedure. The DEV-S4 procedure (DIN 38414, Part 4 [2])is currently the only leaching technique to be covered by a standard in Germany and is therefore the most widely used. It was originally developed for the investigation of sludges and sediments, i.e. for materials with a very fine particle size. This technique therefore only has limited suitability for the investigation of road construction materials which generally consist of larger lumps. The working document accordingly sets out a number of modifications in relation to the standardized DEV-S4 procedure; these modifications relate essentially to the grain size and quantity of the material to be investigated. The aggregates which are to be studied should be leached in quantities of up to 2,500 g in their original grain size. The tank leaching test (see Fiaure 4, 131) is more suitable for use in practice. 2 kg of the material under investigation in the original grain size up to a maximum grain size of 32 mm are leached with ten times their volume of demineralized water

124 for 24 hours in a tank made of polypropylene or glass with a capacity of about 30 litres. The material sample is placed on a mesh to permit the best possible flow rate.

LOCATION OF CONSTRUCTION PROJECT outside of areas important to water supplies and hydrogeologically sensitive 0,l < G W < l I GW > 1

I

I

restricted parts of catchment areas/ ,mineralspring 1 reserves GWe1 GW>1 GW>O,l

Fia. 3 :

aquifer with natural cover

fissure- and karst- aquifer

near to catchment area of surface waters

near to margins of sensitive waters

GW1 GW1 GWl GW>O,l GW>O,l GW>O,l

Hydrological conditions for the employment of industrial by-products and recycled materials

The advantage of the tank method, as compared with the modified DEWS4 procedure, lies in the fact that it is unnecessary to agitate the entire container; only the leaching medium is constantly circulated round the aggregate to permit intensive leaching within a short period of investigation. The leaching medium is circulated by means of a magnetic stirrer positioned on the base of the tank. This avoids severe mechanical stress on the material undergoing investigation in the tank method. Another advantage of the tank method is that both unbound and bound substances can be investigated. Figure 4 shows, by way of example, a test cube resting on the mesh. This permits direct comparison of the leaching characteristics of a material in both unbound and bound form. The procedural specification for this tank method is currently being incorporated into the FGSV working document. The intention is to use the tank method in future as a substitute for the modified DEV-S4 procedure for routine examinations. However, for that to be possible it remains necessary to define limit values. Previous comparative tests have shown that the results obtained by the tank method are of the same order of magnitude as the results of the modified DEV-S4 procedure.

725

tank

40 cm

test cube

I

I /lE

mesh /aperture:

2 mm

stopcock magnetic stirrer

not to scale

Fig.4 :

Tank leaching test

To permit the investigation of unknown, or inadequately known, substances, a comprehensive suitability test must first be carried out. For this purpose, routine methods such as the DEV-S4 procedure and the tank method are not sufficient on their own. Other techniques must also be used which will, for example, enable conclusions to be drawn in respect of the long-term behaviour of an aggregate. A percolation method and a pH-4-stat method are currently being considered. However, both these techniques are still in the development phase and cannot therefore be described in more detail.

4.

CONCLUSION

1.

A clear distinction must be drawn between waste materials that have to be disposed of by dumping and materials which can be used for road construction.

726 2.

Because of the imposition of uniform limit values and the assessment of all industrial by-products and recycled materials on the basis of those limit values, many of these materials are excluded from further processing, although they might be used under certain circumstances.

3.

The optimum use of industrial by-products and recycled materials is made possible by taking account of the special features of each aggregate by determining specific limit values for each material. If these limit values are respected in the framework of regular quality control, the aggregates can be used having regard to the prevailing construction engineering and hydrogeological conditions.

4.

In order to ascertain whether an aggregate satisfies the limit values for a specific material, a routine leaching method is required which can be used rapidly and easily and provides readily reproducible results. A modified DEV-S4 procedure is used as the routine technique and might later be replaced by the tank leaching test

5.

Unknown aggregates must first undergo more extensive investigation. Techniques such as the percolation and pH-4-stat method can be used for this purpose. Both these methods are currently undergoing further development.

REFERENCES

FGSV- working document no. 28/1 "Environmental compatibility of aggregates, Section: compatibility with water resources" Forschungsgesellschaft fur Strassen- und Verkehrswesen, 1992 DIN 38414, part 4: German standard methods for water, wastewater and sludge investigation; sludge and sediments (group S); Determination of the leachability with water, 1984

[31

R. Bialucha and G. Spanka: "Tank leaching test for aggregates" Report of the working group no. 6.4.1 "Leaching tests for aggregates" of the FGSV Strasse + Autobahn 5/1993, pp. 297 - 300

Environmental Aspects of Constmction with Wasre Materials JJJM. Goumans, H A van der Sloot and Th.G. Aalbem (Editom) @I994 Elsevier Science B. V: All rights reserved.

727

Environmental management in large construction projects. Erik K. Lauritzen DEMEX Consulting Engineers AIS, Hejrevej 26, 3rd floor, DK-2400 Copenhagen NV, Denmark

Abstract Based on experiences gained from the Great Belt Link and 0resund Link projects together with the work in the RILEM Technical Committees 34 and 121 on Demolition and Recycling of Concrete and Masonry, it is stated that much of the demolition and construction waste material generated in large construction projects can be reused. Construction and demolition waste management and handling is an important part of environmental management according to BS 7750. Recycled building rubble could substitute natural resources.

1. Introduction In December 1992 the construction of the 0resund Link between Denmark and Sweden started with the demolition of houses and site clearing before the proper construction work. Due to the high requirements of environmental protection and quality assurance, the management of the Oresund Link Company dealing with the Danish land structures decided to implement the Environmental Management System as described in British Standard BS: 7750: 1992 [l]. According to this standard, an environmental management policy was stated and certain goals for the environmental protection were specified for the construction work as well as the operation of the link-structures, Among the issues of the environmental policy, it has been stated that all generated demoliton and construction waste (C&D waste) should be reused as much as possible and handled in such a way that the load of the enviornment should be limited. In May 1993 another great project in Denmark, the Great Belt Link between Zealand and Fyn, reached an important milestone. The Great Belt Link consists of three major projects: the 6,800 m long bridge and the 8,000 m long railway tunnel under the eastern channel between Zealand and Sproge, and the combined road and railway bridge across the western channel between Sproge and Fyn. The construction of the 6.6 km long West Bridge was completed, whereafter, the demolition of prefabrication yard could be started. The two great projects clearly demonstrate what is typical for most modem construction projects: They start with demolition work and they end with demolition work. Furthermore, during the construction process a lot of waste is generated.

728

Fig. 1. The two giants of civil engineering in Denmark - The Great Belt Link between the Danish islands Zealand and Fyn, and The Bresund Link between Denmark and Sweden. A third project, m e Fehmam Belt Link to Germany, is also discussed.

2. Generation of C&D-waste During the life cycle of any building and construction, waste will be generated, and the disposal of the waste will require some considerations and money. Referring to the two mentioned construction projects the generation of the different types of waste can be classified as follows: a.

Preparatory works Demolition of buildings and structures Clearing of old or superfluous infrastructures (roads, sewers etc.)

b.

Construction works Spill of resources and materials Surplus of resources and materials Rejected resources and materials Demolition of provisional structures Demolition of structures due to failures, hazards and changes of the project Packing, containers, etc.

729 c.

Site clearing Demolition of provisional structures Different kinds of remains

-

d.

Operation of the structure Maintenance Repair work

e.

Reconstruction or demolition

Fig. 2. Demolition of one of houses before the construction works of the 0resund Link 1993 in Copenhagen. The timber is recovered for reuse, und the insulution material is removedfrom the walls and disposed of ar controlled 1und.fill. 2.1. Preparatory works The need for demolition during preparatory works depends on the the actual construction site. The connection roads and railways on the Danish side of the Oeresund Belt Link go through city areas which requires the demolition of more than 400 family houses, shops and other structures, comprising some hundred thousand tonnes of demolition waste. The demolition of the houses has been performed as selective demolition with a very high demand for the reuse of waste materials. Most of the windows, doors, boards and timber have been reused, and the concrete and masonry rubble has been recycled and used as construction materials. The recycling of materials has been very successful, 90-95 % of all building waste has been reused [2]. The construction of the Great Belt Link did not require the demolition of so many houses. However, a 5 year old motorway bridge with 11.OOO tonnes heavily reinforced

730

concrete has been demolished, and all the concrete has been recycled. Some of the concrete rubble has been crushed and used as aggregates in new concrete in "The Recycled House" in Odense [3]. See fig. 3. 2.2. Construction works Due to the strict requirements of concrete quality and to other difficulties, a considerable number of tunnel elements and some bridge elements were rejected in the initial stages of the tunnelling contract and the West Bridge contract. Many of the rejected tunnel elements were reused for other purposes, and the rejected bridge elements were demolished by use of explosives on site. According to Loosemore [4], the construction of the West Bridge involved the production and placing of some 480,000 m3 of concrete. Approximately 1% of the concrete produced, ie. some 12,000 t, had to be disposed of due to over-ordering of concrete and the rejection of mixed concrete. During the peak construction period, 7,000 m3 of concrete were produced per week. The concrete was distributed from two site batches using a fleet of concrete wagons each with a capacity of 6 m3 Certain plans for the management and disposal of the waste ready mixed concrete were necessary, and in the peak periods approximately 70 m3 waste concrete was produced! Initially, investigations took place to see if the concrete could be used to prefabricate small temporary works items as used by most contractors. This solution was not progressed because the supply of waste concrete was generally intermittent and, when available, usually in large loads (6 m3 per wagon). Estimates indicated that the cheapest solution would be to crush the concrete and sell it to other contractors for either haul roads on their sites or to upgrade temporary roads on farmland. The concrete was ideal for crushing as it contained no reinforcement or incast items. An area of approximately 50 m x 40 m was designated as the official tipping area for waste concrete. Once the storage area started to become full, a mobile crushing plant was hired to crush the concrete in two sizes, 0 to 32 mm and 32 mm to 60 mm, which was sold at 30-40 DKK per m3. Generally, from the construction work a lot of paper, plastic, insulation, coating etc. is produced which not is reusable and must be disposed of at controlled land fills.

2.3. Site Clearing After completion of the West Bridge project, the temporary Lindholm Concrete Prefabrication Yard was demolished. This demolition project, involving 35,000 m3 reinforced concrete, 7,000 t of steel and 5,000 t of asphalt, started in June 1993 and was finished by the end of 1993. Some of the demolition works were planned and prepared for blasting. For instance, parts of the structures have been supplied with pipes during the construction with the purpose that the pipes should be used as boreholes for the blasting work. Unfortunately, many of the pipes were wrongly placed and unfit for the blasting job. By the end of the entire Great Belt Link construction work, the temporary tunnel prefabrication yard in Korsm and the construction site in Kalundborg for the East Bridge will also have to be cleared. In considering the total amount of construction and demoli tion waste, spill, refuse, packaging etc. we are dealing with very large figures - several hundred thousand tonnes - which clearly indicates the need for planning, management and recycling.

73 1

Fig. 3. Photos showing reinforced concrete bridge which has been demolished because it was not applicable to the Great Belt Link. After demolition some of the crushed concrete was used as aggregates in new concrete in "The Recycled House" in Odense.

732

As a concluding remark concerning the Great Belt Link project we should also mention that the link will close the present ferry line across the Belt. This will make all f e q berths superfluous, and result in several hundred thousand tonnes more concrete waste!

2.4. Operation of the structure Maintenance and repair of the structure require a certain amount of structural work and will cause some waste product. However, we are not dealing with greater amounts of waste, but we should not forget to take the waste management into consideration. 2.5. Reconstruction and demolition Normaly nobody will think of reconstruction and demolition during the construction process of major structures. Unfortunately, it happens that bridges and other structures get damaged from hazards and disasters, which requires reconstruction work. Dealing with Environmental Managment according BS7750:92 it should be noticed that risk analyses of different hazard scenarios are recommended.

3. Selective demolition of houses In accordance to Law no. 590 of 19th August 1991 concerning the establishment of the land infrastructure for the Oresund Link, expropriation and demolition of a large number of buildings in Copenhagen has begun. This consists of approximately 200 family houses in T h b y borough and 150 detached houses in the Municipality of Copenhagen. The demolition is being carried out in a number of different contracts, each of 15 - 30 houses. The management and planning body concerned with the land infrastructure in Copenhagen, A/S Oresundsforbindelsen, has sub-contracted the project planning and supervision of the demolition work to DEMEX Consulting Engineers AIS. The separate contracts are carried out as the houses are expropriated and cleared for demolition. As a result, buildings to be demolished under any one contract are spread throughout the area, some of these being adjacent to still inhabited houses. This places considerable demands on the demolition techniques. Consequently, A/S 0resundsforbindelsen has decided that the demolition should be carried out in three steps: 1. Initially buildings are demolished to the foundation, and the cleaned demolition waste is temporarily deposited within the foundation area. This avoids the use of large machinery and thus reduces the environmental impact on the surrounding neighbourhood. The sites are cleared of trees and bushes, concrete and masonry rubble removed, 2. and buried oil tanks dug up. Roads and remaining structures which are not needed for temporary use are 3. removed. The initial demolition of the buildings is carried out as selective demolition, according to experience gained during demonstration projects performed with the Danish National Agency of Environment. Since A/S Oresundsforbindelsen emphasises the importance of the demolition not disturbing the surrounding environment, the demolition work is executed as follows:

733 -

-

All demolition products are dismantled and sorted on site with the intention of maximum recycling. All environmental nuisance is kept to a minimum. Movement of machinery and vehicles is carried out with great care and the least possible disturbance to neighbours. Disturbance to gardens surrounding the houses is kept to a minimum. Demolition and temporary dumping sites are kept in a clean and orderly manner.

Before the start of the separate contracts, the previous owners are asked to remove all possessions of personal interest, such as doors and fixed effects. Thereafter, the nearby youth clubs are given the opportunity to remove remaining effects for sale, the profits of which go directly to the operation of the clubs. It is the contractor’s duty to demolish the houses in the following order: Removal of remaining furniture and other efects. 1. Removal of all wastes for special treatment: e.g. asbestos, oil tanks, chemical 2. wastes etc. Removal of all indoor installations and building materials, doors, windows, floors 3. for reuse. All plaster, insulation and other dust-producing material must be removed by vacuum in closed containers. Dismantling of roof structure for reuse as rooting materials and timber 4. Demolishing of walls, leaving the rubble in proper heaps. 5. Sorting of the rubble for all impurities such as paper, wood, plastics etc. 6. All materials except foundation and the rubble must be removed without any noise or inconvenience to neighbours. Most of the materials are kept for reuse, and only very little has been deposited in controlled landfills. Fig. 4 shows a cross section of a typical Danish family house with some 100 - 150 mz floorage. It produces approximately 1.0 - 1.5 t building waste per square meter. Because situation concerning the acquisition of property under compulsory powers is politically sensitive, special consideration must be paid to the remaining inhabitants in the area. Demolition must be carried out with wheeled machinery under 12 tonnes net weight. Noisy tools are not permitted, and emission of dust is not accepted. The provision supply of electricity, heat, water, and sewage etc. must not be interrupted, and the roads must be kept clean and free of any obstructions. In fig. 4 the different classes of wastes are shown. Class A contains recyclable materials of which concrete and masonry rubble should be left on site, whereas Class B and C should be removed for special treatment, incineration or tipping. The figure shows the distribution of the different fractions of waste materials, also. The philosophy of leaving the concrete and masonry rubble was that it would be easier, and hence cheaper, to remove of all the rubble when the greater part of the houses has been demolished and no special considerations were needed any longer. Initially, it was planned to crush the concrete and masonry rubble into aggregate for temporary roads used in the project. Later, however, it was discovered that Copenhagen Harbour needed material for construction of new dams for a planned land reclamation project. Therefore, it was necessary to calculate the most feasible economic solution.

134

Sla-

Fig. 4 Cross section of a typical Danish.family house with indication of the dwerent kinds of building materials and classes of waste.

I74doond2u)-MU5W& =TCWONVi a i - - p l F a u m i a d ~ * * ~ ~

*

735

4. Recycling and cleaner technology In June 1992, the Danish Minister of Environment presented two action plans, "Waste and Recycling 1993-97" and "Cleaner Technology 1993-97", to the Danish Parliament's Environmental Planning Committee. The plans included initiatives to be taken in the next five year period in order to reduce the amount of waste and to ensure the development and implementation of cleaner technology. Attention was especially drawn to the increased goal for reuse of building and construction waste. The previous target of 50 % of all construction and demolition waste to be reused by the year 2000 was increased to 60 %. Furthermore, the disposal fees for waste were increased from 1 January 1993, the new values being 195 DKK/ton (32 US$/ton) for dumping and 160 DKK/ton (27 US$/ton) for incineration. The two action plans have been combined to form one action plan for the construction industry. This is due to the difficulty of separating the concepts recycling and cleaner technology in the field of building and construction. The long term aim of the plan is to promote the initiatives for reducing both the use of resources and also the environmental impact in all stages of the life-cycles of buildings and constructions. The basic strategic element of the plan is the consideration of the life-cycle of total resource utilisation and the resulting impact on the environment. Thus, we are able to show the possibility of introducing cleaner technology, thereby aiding the decisionmaking process by fixing an order of priority, classification and implementation of the necessary initiatives. The plan strongly emphasises the following areas: Investigation of materials and building components Investigation and development of minimal forms of construction Minimisation of excess and waste, combined with an increase in recycling Analysis of industry and construction Development of models for life-cycle evaluation Environmentally, friendly planning Economic and administrative control systems.

As examples of actual projects where considerations for cleaner technology are required, we have used the two above mentioned construction projects in Denmark. Due to the size and importance of these projects, the decision-making processes involved have been heavily influenced by the evaluation of the resources required and the resulting impact on the environment. During the project planning of building and construction projects, it is important that a very accurate evaluation is carried out of all the relationships concerning the extraction of raw materials, production of components, actual construction and operation. The immediate requirement for demolition concerns structures which either lie in the way of the project or ones which were specifically built for the purpose of the project. During the construction of The Great Belt Link, considerable resources were used for the construction of concrete mixing plants, foundations, roads and such; these will be removed when the project is completed. The same kind of temporary works are to be built for the Oresund Link.

736

5. Conclusions From the work performed in the the two RILEM Technical Committees 34 and 121 on Demolition and Reuse of Concrete and Masonory, which has been presented at three symposia on demolition and recycling (Rotterdam 1985, Tokyo 1988 and Odense 1993) [5,6 and 71, it has clearly been demonstrated, that there is no technical limit for the reuse of concrete and masonry rubble - in principle. However, at lot of questions and barriers will always exist, and the economical and legal aspects are not clearly described, yet. Thus, with the beginning of the Oresund Link project, much care has been taken in the conservation of natural resources and the impact on the environment. At the same time it has become clear that the terms Recycling and Cleaner technology are gaining more and more recognition and importance in the building and construction industry. Recycling and cleaner technology are no longer idealistic concepts which never reach the reality of the construction site. In this project 90 % of all C&D Waste has been reused. Cleaner technology concerns the rational principles and attitudes which aim to continuously reduce the use of resources and the load on the environment for the benefit of society as a whole.

References: 1

Environmental management systems, British Standard BS 7750:1992

2

Lauritzen. Erik K. and Jannerup, Morten: Guidelines and experiences from demolition of houses in connection with the 0esund Link between Denmark and Sweden, 3rd International RILEM Symposium on Demolition and Reuse of Concrete and Masonry, Odense, Denmark, 24 - 27 October 1993

3

Olsen, E.B.: The "Recucled House" in Odense,3rd International RILEM Symposium on Demolition and Reuse of Concrete and Masonry, Odense, Denmark, 24 - 27 October 1993

4

Loosemore, C.E.: The Great Belt Link Project, 3rd International RILEM Symposium on Demolition and Reuse of Concrete and Masonry, Odense, Denmark, 24 - 27 October 1993

5

Kasai, Y. (editor): Demoltion and Reuse of Concrete and Masonry, Vol. I and 11. Proceedings of the second International RILEM Symposium on Demolition and Reuse of Concrete, Tokyo, 7-11 November 1998, Chapmann & Hall, London

6

Hansen, Torben C. (editor): Recycling of Demolished Concrete and Masonry, Third State-of-the-art report 1945-1989, RILEM report No. 6, E & F.N.Son, London

7

Lauritzen, Erik K. (editor): Demolition and Reuse of Concrete and Masonry. Proceedings of the Third International RILEM Symposium on Demolition and Reuse of Concrete and Masonry, Odense, Denmark, 24-27 October 1993, E. & F.N. Spon, London

Environmental Aspects of Construction with Waste Materials JJJM Goumans, H A . van &r Slmt and n . G . Aalbers (Editors) el994 Elsevier Science B.V. AN rights resewed.

131

A CONCEPT FOR THE ENVIRONMENTAL EVALUATION OF WASTE MANAGEMENT BENEFITS A. Tukker and D.J.Gielena.b a Study Centre for Environmental Research TNO, P.O. Box 6013,2600 JA Delft, The Netherlands

Present address D.J. Gielen: Netherlands Energy Research Foundation (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands Abstract

For the removal of a certain waste stream in general several options are available. According to the common applied 'stair concept' prevention of waste should be the first option. If this is not possible the waste should be re-used and otherwise it should be incinerated or landfilled. Though a valuable rule of a thumb, scientific and public discussions show that this approach can be in quite a few cases too rough to make common accepted decisions. This paper presents a more sophisticated approach, called the Waste management benefit concept. It has been developed on the basis of methodologies used in Environmental Impact Assessment, (health) risk analysis and product Life Cycle Analysis. A system-approach is presented, in which all relevant environmental effects related to whole life-cycle of the waste removal process are analyzed and aggregated to an integrated judgement. The methodology has been tested in a case on the removal of polluted sediments. Four options have been compared: (1) no removal, (2) covering the polluted sediment with an isolating clay layer, (3)dredging and landfill of the sediment and (4) dredging the sediment and sintering it with sewage sludge to so-called 'eco-gravel'. Apart from the theme 'acidification' the re-use alternative (4) shows to be the most environmental friendly option. The case-study has shown that the approach in principle is suitable to perform a quantitative, integral and transparent comparison of the environmental benefits of waste management options. 1

INTRODUCTION

Achieving a sustainable development is in general considered as the central goal in environmental policy. The means to reach this goal are the closing of substance cycles in society and the minimization energy use [I, 21. With regard to waste management, central goals are to ensure 1) treatment with a high level of protection for the environment; 2) minimization of the danger of illegal treatment and 3) promotion of prevention and re-use [Z,31.

738 In general several options are available for the removal of a waste. As a rule of a thumb the so-called 'stair-concept' is widely used to choose between removal options [4]. According to this concept prevention of waste should be the first option. If this is not possible the waste should be re-used and otherwise the waste should be incinerated or landfilled. This concept implicitly assumes that in the sequence reuse, incineration and landfill the effects on the environment will enlarge. There is no scientific evidence for this implicit assumption. Scientific and public discussions show that in quite a few cases an environmental assessment of waste management options on the basis of the 'stair concept' is not sufficient. The preference for incineration above landfill is subject to an intensive discussion [5,6, 71. Common sense approaches have proven to result in conflicting conclusions. According to [7]in Switzerland incineration of domestic waste would be preferred, in order to solve the problem in one generation, where Swedish researchers argue that incineration leads to ashes that leach out, and for this reason direct landfill could be preferred. Also for some types of waste, e.g. plastic waste, the environmental benefit of re-use above incineration is thoroughly questioned [8, 91. These examples show that the charm of a simple concept, like the stair concept, is also its weakness. Counting the amount of kilo's of a certain waste that is removed according to a certain level on the stair is just a too simple yardstick to avoid discussions. If capital- and/or energy-intensive processes are necessary for pre-treatment of a waste before it can be re-used the problem arises that the pretreatment process might have more negative environmental consequences than there are positive consequences related to the re-use itself. In waste management strategic choices have to be made by authorities and waste management firms and big interests are involved. Decisionmaking by authorities can be totally frustrated when no common accepted criteria exist to make preferences between waste management options. Denied permit extensions can be easily attacked in court. An objectivated methodology for environmental assessment of alternatives can make discussions more transparant and enhance the quality of decisionmaking [lo]. The paper will present a methodology called the Waste management benefit concept. It has been developed on the basis of methodologies used in Environmental Impact Assessment, (health) risk analysis and product Life Cycle Analysis (LCA) [ l l , 12, 13, 141. The basic idea is that the evaluation of waste management options needs an approach in which a whole waste management system and all the relevant environmental impacts are analyzed and aggregated to an integrated judgement. Paragraph 2 gives an outline of this approach. 2

METHODOLOGY

2.1 Introduction

In Environmental Impact Assessment (EIA) the following steps in the evaluation of alternatives can be distinguished 1131:

139 A: 1) inventory of potential effects; 2) choice of relevant effects and target variables; 3) choice of criteria; B: 4) analysis of the process system; 5) inventory of relevant effects; C: 6) selection of relevant alternatives; 7) sensitivity analysis; 8) integrated judgement of remaining alternatives; 9) final choice of the alternative. This general evaluation scheme can be divided in three parts. Part A) defines how and on which criteria alternatives are judged. Actually in this phase the 'yardsticks' are chosen to score alternatives. Part B) analyzes the process chains that have to be included in the system and makes an inventory of the (according to part A) relevant effects. In part C) the aggregation and final evaluation takes place. In fact this introduction gives a general framework for environmental evaluations. Depending on choices made in the 9 steps given above concrete, quantitative evaluation frameworks like Health Risk Assessment and Life Cycle Analysis can be derived [ l l , 12, 15, 161. The following paragraphs will give a discussion on choices that can be made within this general framework.

2.2 Part A: selection of yardsticks and criteria The first part in the evaluation scheme involves the selection of yardsticks and criteria that will be used to analyze the waste management system. Basically these choices involve [ 13, 151:

-

the effects that are considered; the position in the emission-effect chain chosen as the basis for evaluation; the criteria used to evaluate effects.

For example, in health risk assessment only one effect of an activity is evaluated: the effect on human health. The whole emission-effect chain is taken into account and the actual or potential daily intake is calculated, taking into account the local situation. The criterium used to evaluate the risk is the exceedance of an intake related to the Maximum Tolerable Risk (MTR); this equals the Accepted Daily Intake (ADI) for non-carcinogenics and the chance on death for carcinogenics [14, 161. In LCA methodologies, whole series of potential effects are distinguished [l1, 121. Effects include the greenhouse effect, acidification, land use, ozonlayer depletion, ecotoxicity, use of biotic and abiotic resourses, etc. In LCA, effects in general are described on the level of emissions. Local situations and subsequent calculation of emission-effect chains are not taken into account [I 11. In the case to test this methodology we have chosen to evaluate a waste

740 management system on the basis of a limited set of classification factors, mainly based on those given in the first draft CML methodology for LCA [ l l ] . For Human Toxicity we used as classification factor the sum of the emission of toxic substances, weighted on the basis of the Tolerable Daily Intake. Table 1 gives a review of effects and criteria used. This part of the evaluation is location independent. We added a location-specific evaluation of risks for natural functions and human health [14, 161. Table 1 :Classification factors chosen II

I

Affected varlable Man Environment

Resources

E, TDI, k,

GWP,

I

I

I

Effect

I

I1

I

Target variable

I

Unit

Human toxicity

Emission of toxic substances

Potential Human Toxicity [kg.day] PHT=2 EJTOI,

Acidification

Emission of SO,. NO, and NH,

Acidification Unit [ha.jr] AU =Z

Greenhouse effect

Emission C,H, CO,

CO,-equivalent F g COJ CO,-equiv.= Z E,'GWP,

Squandering of energy msources

Energy use

MegaJoule [MJ]

Squandering of resources of sand and grid

Use of sand and/or grid

Ton

Use of scarce space

Land use

Hectare [ha]

= Emission substance x [kg] = Tolerable daily intake substance x [kg/kg.day] = Correction for effechviiy [ l l ] . in Fg/ha.yr] = Global Waning Potential substance x [-]

2.3 Part B: System analysis and inventory The waste management system consists of several operations, that together form the process chain for the alternative. Time and place of the operations can be of importance if these aspects play a role in judgement of the alternatives. The waste management system is analyzed according to a system approach. This means that all relevant process chains are inventoried and taken into account as a part of the system. This approach is similar to that followed in LCAs for products; the difference in this situation is that not a product but an amount of waste has the central position in the analysis. The input of the system consists of the waste, capital goods, energy and other materials. The output consists of emissions to the environment. Landfill is a part of the system. Only emissions from the landfill are taken into account as output of the system. Incineration processes are, like re-use, seen as operations that take part in the system [17, 181. In every operation capital goods, energy and other materials are needed. Each of these elements is a part of its own process chain. Figure 4 gives an example of the process chain related to the re-use of polluted sediments as eco-grid, one of

74 1 the alternatives in the case discussed in paragraph 3. In theory an infinite amount of process chains could be included in the system analyzed. In practice system boundaries have to be chosen. The boundaries should be such that the system includes all processes or operations that have significant effects. It is common practice to neglect the production of capital goods [19]. Quite a few LCA's follow a first-order approach; this means only the main process chains and main material inputs are followed (201. However, the best approach is to neglect input of materials only if there is good evidence from similar studies that they do not have significant effects. Problems can arise when processes have multiple-input or multiple-output flows. In that case the emissions out of the system have to be allocated to each of the waste inputs or material outputs. Allocation could take place on the basis of mass, the contents of toxic substances in the waste, or the costs related to removal of the waste. Every choice has its own advantages and drawbacks. Since in the presented case study the contamination in the waste streams that are treated in a combined process didn't differ too much we have chosen to allocate on mass basis In recycling situations primary material is replaced by a secondary material. This means that processes and effects related to the winning of the primary material do not occur if waste is recycled; we allocated these environmental benefits to the waste management option if recycling takes place. Actually we defined a combined system consisting of the waste removal process and the winning of primary materials. In product LCA's these process chains are separated [11,12]. In a product LCA effects related to waste treatment are allocated to the product that is responsible for the waste. When this waste can be re-used in a second product no effects for waste treatment have to be taken into account for the first product. Effects related to upgrading processes necessary for making the waste suitable for re-use are allocated to the second product. We avoided these allocation discussions but payed the price that we had to analyze a more extended system. 2.4 Part C: Comparison of alternatives

For each waste management option the analysis in paragraph 2.3 results in scores on the yardsticks defined according to paragraph 2.2. Options that score worse on every yardstick than other alternatives can be eliminated directly. Options that do not meet legal limit values for the score on one or more yardsticks can be eliminated as well. E.g., in the Netherlands limit values have been set for soil and water quality; if an option causes exceedance of these limit values it can not be taken into account. For the remaining alternatives the different scores somehow have to be weighted. In EIA and LCA this has proven to be a very problematic item. One of the problems involves the differences in time scale and location of effects. Some authors use a positive interest calculation, that means that effects in the future are seen as less severe than the same effects in present [22]. Other authors regard

742 this as creating a negative environmental heritage for future generations and see this more negative than effects in present [23].At this moment no consensus seems achievable on the weighting problems related to time, place and kind of effect. Therefore a political assessed judgement on weighting factors seems to be the 'cleanest' option. This approach has been followed in the project on priority setting of waste materials (PRIAF) [24]. In the VNCVMcKinsey study on the evaluation of alternative processes in the chlorine industry weighting factors on the basis of expert judgement were used [25].A sensitivity analysis can indicate the importance of uncertainities in data inventoried and calculations made.

3

CASE: THE REMOVAL OF POLLUTED SEDIMENTS

3.1 Introduction

The methodology has been tested in a case on the removal of polluted sediments [21]. Polluted sediments is one of the most voluminous waste streams in the Netherlands. Annually about 70 million tons of sediments are dredged from rivers, estuaries and lakes. The sediments in general are polluted with heavy metals, PCB's, PAH's and organic micropollutants. Four options have been compared: (1) no removal, (2) covering the polluted sediment with an isolating clay layer, (3) dredging and landfill of the sediment and (4) dredging the sediment and sintering it with sewage sludge to so-called 'eco-gravel', a material that can be used as an alternative for primary building materials. The next paragraphs will briefly discuss the alternatives. It has to be stressed that the case was mainly meant to evaluate the idea behind the method, and not to give precise calculations. For simplicity reasons we sometimes made assumptions in the data inventory and simplifications in the system analysis or related calculations. Results of calculations therefore have to be regarded as tentative. For the calculations reference is made to literature [21]. Final results are given in table 2 in paragraph 3.6. 3.2 No removal

Figure 1 gives the situation of the polluted location. At the bottom of a river about 880 ha is covered with polluted sediment. It is assumed that as a result of source-oriented measures no further deposition of polluted sediments will take place. Without any remediation measures, due to resuspension processes about 30 % of the toxicity equivalent of the hazardous substances in the sediment will be released to the water in a time frame of about 100 year. The rest, 70 YO,will be released to the ground water in a period of several thousands of years. A locationspecific risk analysis shows exceedance of the permitted level for ecotoxicity.

743

T

water 880 ha polluted sediment

~

30% in 100 year

A ,//// ,’,/’/,,’,//

I \L 70% in > IO.OOO year

Figure 1: Situation to be remediated

3.3 Covering with a clay layer The first possible remediation option is covering the polluted location with an isolating clay layer. Only during the period the cover is constructed (about 2 years) emission of substances to the surface water takes place. This counts for about 0,5 % of toxicity equivalent of the amount of toxic substances. The rest, 99,5Yo,will be released to the ground water in a period of several thousands of years. The remediation process involves several activities with effects that have to be taken into account. Clay has to be dredged and transported to the location to be isolated. The process chain is given in figure 2. In the calculation of effects the construction of capital goods and processes related to oil well operations and refining are neglecied. It is assumed that after clay winning a multifunctional surface remains; this means no land use arises from clay winning.

Input

Capital goods

outpul

(

Input

n day

)

Energy (luel) Capilal goods

Emissions

0

,T (

output

Emissions

sediment

clay winning

transport

sox c02

isolation

processes

Figure 2: Process chain option 2: covering with clay layer

.

Figure 3: Process chain option 3: disposal

toxic subst

144 3.4 Disposal

Another remediation option is dredging the polluted sediment and disposal of the sediment. It is assumed that disposal takes place in an old sand excavation location, below water surface. It is assumed the disposal site is filled in about 10 years. In this period, emission of substances to the surface water takes place. This counts for about 3 % of toxicity equivalent of the amount of toxic substances. The rest, 97 %, will be released to the ground water in a period of several thousands of years. The surface of the disposal site is about 88 ha.

The disposal process involves several activities with effects that have to be taken into account. The sediments have to be dredged, transported and disposed. The process chain is given in figure 3. In the calculation of effects the construction of capital goods and processes related to oil well operations and refining are neglected. The creation of this disposal site is allocated to sand winning. 3.5 Re-use as ecogrid

A re-use option that might be operational in the near future has been evaluated as the last waste management alternative. The polluted sediment is dredged, transported and separated in a sand and organic fraction. The sand can be re-used directly as a material in road construction or for other purposes. The organic fraction is mixed with sewage sludge and is converted in a thermic process to an artificial grid, the so-called eco-grid. During this process the organic components in the sludges are burned; the heavy metals are partially immobilized in the matrix of the eco-grid and partially emitted with the flue gases. Due to flue gas cleaning most of the metals in the flue gas are trapped with the fly ash.

Figure 4 gives the process beam of the eco-grid process. The ecogrid process results in production of 4,8 10' tons of sand and 3,2 lo6 tons of ecogrid. Processes related to the winning of primary building materials and treatment of sewage sludge are avoided. The related environmental effects are taken into account as benefits of this particular waste management option. Since in some cases the effects of winning of primary materials are bigger than those related to the ecogrid process, the overall result is a positive environmental effect of this ecogrid process (minussigns in table 2). E.g., in the Netherlands the winning of primaly grid and sand takes place near rivers, creating big lakes and thus uses scarce space. The emissions and effects after the moment of co-processing of sewage sludge and the organic fraction of the sediment are allocated on mass basis. It is assumed that only 1 % of the metals in the ecogrid leach out in a time frame of several million years.

145

atput:

sediment

)

separation

j

j

Enissions

use in ccncrete

Figure 4: Process chain option 4: the Eco-grid process

3.6 Comparison of options Table 2 shows the results of the calculations of effects. Apart from the theme 'Acidification', the re-use alternative scores better than all the other options. Note that the emission of toxic substances is the same in option 1 , 2 and 3. However, the time scale and location of emissions differ quite a lot. We made locationspecific calculations, that show that only in alternative 1 the risk limit values for ecosystems are exceeded [21]. Also methodological choices can have important influences on the comparison. We compared the land use on the basis of affected surface area. In that case, differences arise between alternative 1 or 2 and 3. If we would have compared on volume no difference could have been made. We allocated the co-processing of sewage sludge and sediment on mass basis. Allocation on another basis could have lead to different results.

746 Table 2: Comparison of options

a = original location b = elsewere

4

OVERALL CONCLUSIONS

Methodological problems still remain. We only partially made location- and timespecific calculations. By choosing the (time and location independent) total emissions for comparison, we avoided weighting discussions for time and location differences. The case doesn't give an alternative that scores best on all the yardsticks. This means that in fact a discussion on weighting factors should have been made. Similar, still unsolved problems are present in other sectors of environmental policy, specifically in product policy [ l l , 261. The case shows that in some situations a LCA-alike approach is not enough to make a final choice between options, but that local dispersion calculations are needed to choose between option 1 and 2 or 3. Further the description of the case shows that consensus on other methodological choices still is needed. Specifically the enormous time frame related to landfill emissions still needs methodological attention [17, 181. However, the case-study shows that the Waste management benefit concept is suitable to give a quantitative, integral and transparent comparison of waste management alternatives. The methodological approach forces to take into account all relevant effects, to take into account a whole system and to make transparent choices when simplifications are made. The method also gives the possibility to take country-specific preferences into account. E.g., the effect land use is regarded as very important in a densely populated country like the Netherlands. Since the Netherlands do not have much natural resources of building materials, this is another drive for re-use. In countries like Spain or France, with lots of space and natural resources of building materials these factors will not be seen as big advantages. By choosing country specific weighting factors these differences can be made transparant.

141 In the Netherlands, the method has been accepted by the Dutch committee on EIA for EIA's on waste management plans. Several waste management plans have or are being evaluated according to the approach presented here [27,281.We think the method can offer a framework for structuring consensus processes when a choice has to be made on waste removal options. This can specifically be useful for choices on tense subjects like incineration in rotary kilns versus incineration in cement kilns and immobilization of waste followed by landfill under light regime versus direct landfill under strict regime [I 0, 291. References 1

National Environmental Policy Plan (NEPP). Dutch Parliament, Lower house, year 1988-1989, 21137 nrs. 1-2

2

National Environmental Policy Plan Plus (NfPP+), Dutch Parliament, Lower house, year 19891990,21137 nr. 20

3

Paper on prevention and re-use of waste, Dutch Parliament, Lower house, year 1988-1989, 20877, nr. 2

4

Dutch Parliament. Lower House, year 1979-1980, 15800, nr. 21, chapter XVII.

5

Samson H.D. Tjeenk Willink, Alphen aan RIVM: National environmental forecast 2 (1990-2000), den Rijn. 1991, pp. 357-358

6

Duvoort, G.L.: Solid waste In : Koernan. N.; Winkel, P.: Code of practice environment, Kluwer. Deventer, 1977-....

7

Bresser, A.H.M.: Nagelhout. D.: Risk assessment as a basis lor integrated waste management , Paper presented a1 the Joint International Symposium on Environmental consequences of hazardous waste disposal, Stockholm, Sweden, 27-31 Mei 1991

8

ECOBiLAN, Ecobilans compares des sacs d dechets en polyethylene vierge et regenare. Paris, augustus 1991.

9

Cayla, A , , Association Francaise de Normalisation, personal communication

10 Mulfy-year Programme on Hazardous Waste, Ministry of Housing, Physical Planning and Environment and IPO, The Hague, July 1993. 11

Heijungs, R. el. al: Methodology for LCA's on products. Parf 1 to 3. CML, Leiden, concept 1991, (Final draft 1992).

12 Fava, J.; Denison, R.; Jones, B.; Curran, M.A.; Vigon. 8.; Selke, S . ; Barnum, J.: A technical framework for life-cycle assessmenf. SETAC workshop report. Smugglers Notch, Vermont, 1990. 13 EIA-series nr. 13, Assssment mefhods, theory and practice. Ministry of housing, Physical Planning and Environment and Ministry of Agriculture and Fishery, the Hague 1982 14

Paper on risk policy (Omgaan mef risico's). Dutch Parliament, Lower House, year 1988-1989, 21 137, nr.5.

15 W.T. de Groot. H.A. Udo de Haes. Estimations in the first phase of €/A, Milieu 1987/5 16 Berg, R. v.d.. Roels, J.M.: Risk assessment for man and environment in cases of contaminated soil. lntegration of aspects Report no. 725201007, RIVM Bilthoven. 1991.

748 17 A. Tukker: Waste management and LCA, Lecture on the SETAC-Europe symposium on case studies, Brussels, 7 December 1993 18

Finnveden, G : Landfilling . a forgotten parf of the life cycle assessment. 1992, as clled in Finnveden el al., Classification (impact analysis) in connection with Life Cyde Assessments - A preliminary study. Manuscript prepared for the Nordic Council of Ministers, IVL, Gothenburg, Sweden, 1992

19 APMEIPWMI, A methodology for ecoprofiles on commodofy plastics. Brussels 1993 20

Korenromp, R.J.H., de Zeeuw, J.H., de Zoeten, G . : Development of ecolabels, TAUW lnfra Consult, Deventer, 1991

21

Gielen, D.J., A new method for environmental assessment of alternatives in waste managemant, Report 92/103, SCMO-TNO, January 1992

22

Phung, D.L.; v . Gool. W . : Analyzing lndustrial Energy Conservation Folicies: The Method of CostEnergy Dynamics. Energy systems and Policy 6 nr. 1, 1982

23

Reijnders, L.: Limit values for environmental pollution with regard to sustainable development. Milieu 5 , 1990, pp. 138-140.

24

Kaltenbrunner, D. e.a.: Priory setting for waste materials, RPC, Delft, 1988

25

VNCCMcKinsey. integrated substance chain management, Leidschendam, 1991

26

Raad voor het Milieu- en Natuuronderzoek: Assessment of risks of new technologies. RMNOpubl. no. 60, the Hague 1991.

27

Waste management council (AOO), Environmental Impact Assessment on the Multi-year waste management plan 1990-2000, Utrecht, the Netherlands, January 1992.

28

Commission for the EIA, Terms of reference for the € / A on the third waste management plan of the province of South-Holland, Utrecht, the Netherlands, June 1993.

29

A. Tukker, R. Klein Entink: Standard setting for immobilization - an analysis on the basis of the concept of integrated substance chain management, Report 9311 60, TNO-SCMO, June 1993 (concept)

Environmental Aspects of Consbuction with Waste Materials JJJ.M. Goumans, H A . van der SIoot and Th.G.Aalbers (Editors) 01994 Elsevier Science B. V. All rights resewed.

749

TECHNOLOGICAL AND ENVIRONMENTAL PROPERTIES OF CONCRETES WITH HIGH PFA CONTENT

H.A.W. Cornelissen and R.E. Hellewaard KEMA Environmental Technology, KEMA Nederland B.V., P.O. Box 9035, 6800 ET Arnhem, The Netherlands

Abstract Concretes were made in which up to 60% of the amount of cement was replaced by PFA. In order to compensate the slow increase of strength several measures were taken. The water to cement ratio was reduced, rapid hardening cements were applied and the effect of curing at elevated temperature was studied. In all cases the addition of superplasticizers proved to be necessary. The compressive strength values were recorded over a period of two years. Also the efficiency factor (k-value) was determined as well as the development of permeability. Durability data were also gained from carbonation tests and chloride penetration. Leaching was determined by standard diffusion and availability tests on high volume PFA concretes in comparison with reference concretes. The results showed good quality concretes with properties which are highly sensitive to proper mix design. Furthermore it was found that mixtures containing up to 60% PFA as replacement of cement, did not exceed the limits for leaching.

1.

INTRODUCTION

The utilization in concrete of pulverized fuel ash (PFA) from coal fired electric power plants, is widely accepted. Normally about 20%-30% (m/m) of the amount of cement is replaced by PFA. However, in Canada and in the United Kingdom This is beneficial for reasons these replacement levels may reach 50% to 60% [l]. of reuse of byproducts, for economical reasons and for the realization of specific concretes where for instance heat generation must be limited. In the Netherlands PFA concretes have to meet the strict technical and environmental requirements as defined in the standards, CUR recommendations, certification documents and regulations with respect to among others leaching. In order to verify the results from the literature for these boundary conditions, an extended research project was carried out by KEMA [I-21.

750

2.

MATERIALS AND COMPOSITIONS

In this research project a typical Dutch PFA was used having a mean grain size of 22 micrometer. With respect to the chemical composition, the carbon content was 4.2% , the amounts of the other main components were 57% Si02, 26.4% A1203, 4.4% Fe203 and 1.8% CaO. The standard concrete composition (denoted as REF) contained 320 kg/m3 cement and the maximum quartz aggregate size was 31.5 mm. The water content was related to the total cement plus PFA content (water to binder ratio). For the tests 150 mm cubes were cast and stored in a fog room at 20 "C and over 95% relative humidity. In general compressive tests were performed in triplicate. The various PFA mixes are indicated like H40, in which 40 stands for the weight percentage cement replacement.

3.

CONCRETE HARDENING CONTROL

Preliminary tests learned that at increasing PFA contents, the development of concrete strength slowed down. Therefore various methods were applied to enhance the evolution of early strength. In the literature especially a low water to binder ratio is recommended for this purpose [ l ] . In those cases, however, a suitable superplasticizer is necessary. At KEMA also methods were investigated based on rapid hardening cements, curing at elevated temperature and the addition of chemicals which increase the alkalinity of the pore water. The addition of these chemicals being NaOH (2.5-30 grams per litre mixing water) and Na20.Si02 (2-92 grams per litre) proved not to accelerate strength development and will therefore not be further discussed in this paper. Curing at elevated temperature Standard concrete was made with 320 kg/m3 normal hardening Portland cement (PC-A). From this mixtures were derived in which 20%, 40% and 60% of the amount of cement was replaced by PFA. The water to binder ratio was about 0.50, resulting in fresh concrete slumps of 75-100 mm. A temperature treatment was chosen according the RMC method [4]. For that the moulded concrete cubes were stored for 16 hours at 82°C in a water storage tank, immediately followed by demoulding. After that three cubes were tested and the remaining three cubes were stored in the fog room and tested after 28 days. The results as presented in Table 1 are compared with the results of cubes cured at 20 "C. As durability parameter, the water penetration (DIN 1048/5 1991) at 28 days is given as well. As can be seen the temperature treatment results in practical strength levels for all mixes tested. For the H60 mix, however, the 28 days permeability proved to be relatively high. 3.1.

75 1

Table 1 Effect of temperature treatment (82°C for 16 hours) on concrete strength (f'c) T = 20 "C

T-treatment

REF H20 H40 H60

*

35.3 31.5 30.7 24.8

49.4 42.8 35.6 25.6

32.1 26.2 17.3 8.9*

16 20 13 92

41.8 37.2 28.4 15.5*

water to binder ratio = 0.54

3.2.

Effect of rapid hardening cement

It is obvious that by the use of rapid hardening cements early strength development can be accelerated. Therefore the results of concretes based on this type of cement (PC-C) were compared to PC-A based concretes. In the mixes 320 kg/m3 cement was replaced by 20%, 40% and 60% PFA. The slump was 70-90 mm at water to binder ratios of about 0.50. The results are presented in Table 2. The 7 and 28 days compressive strengths are higher for PC-C cements, as expected. After one year hardening, the PC-A concretes show higher strength values. It can be seen that for PC-C concretes with up to 40% PFA, compressive strength values are in the normal practical range. This is also true for H60 concretes after one year hardening caused by the pozzolanic effect of PFA. Table 2 Effect of type of cement on the development of strength (f'c) PC-A cement MIX

PC-C cement

f'c(7d) f'c(28d) f'c(l8fd) (N/mm 1

REF 32.1 H20 26.2 H40 17.3 H60 8.9

41.8 37.2 28.4 15.5

54.8 61.0 50.7 34.5

f'c(365d)

f'c(7d) f'c(28d) f'c(i82d) f'c(365d) "/mm 1

55.8 63.7 59.1 49.0

44.6 38.5 27.2 13.9

53.1 47.5 40.9 20.5

55.9 59.4 52.0 35.7

54.3 58.9 55.4 49.0

752

3.3. Effect of low water content In concrete technology the water to binder ratio is an important parameter for the strength (and also the durability) of concrete. A low water to binder ratio will generally result in high strength. However, a certain surplus of water is needed to reach sufficient workability of the fresh concrete. In order to fulfil these two conflicting requirements, additives such as superplasticizers are added. In this research project a naphthalene formaldehyde condensate was selected. In the mixes 320 kg/m3 PC-A cement was used; the water to binder ratios varied between 0.35 and 0.52 in order to realize slumps between 100 and 190 mm. Details of the mix composition are given in Table 3,in which results are given as well. In Figure 1 the development of strength for high volume PFA concretes with 0% and 2.5% superplasticizer (m/m binder) is illustrated. The results indicate the strong effect of the low water to binder ratio, as made possible by the superplasticizer. Because of the continuation of the pouolanic activity, the strength increases over time and the differences in strength diminish between the mixes with various PFA contents. Table 3 Effects of low water to binder ratio in combination with the addition of superplasticizer MIX

SP

WBR

SLUMP f'c(7d) f ' ~ ( 2 8 d ) ~f'c(365dJ f'c(730dJ (mm) (N/mm2) (N/mm 1 (N/mm 1 "/mm 1

REF

0

0.52

100

32.1

41.8

55.8

59.0

H20 H40 H60

0 0 0

0.51 0.51 0.54

125 130 150

26.2 17.3 8.9

37.2 28.4 15.5

63.7 59.1 49.0

66.5 63.7 56.3

H20 H40 H60

1.5 1.5 1.5

0.40 0.40 0.40

140 120 140

42.2 29.0 15.3

56.0 46.6 28.0

79.1 78.5 68.8

87.9 86.6 79.6

H20 H40 H60

2.5 2.5 2.5

0.35 0.36 0.37

120 190 190

53.1 39.3 18.1

71.6 56.0 32.3

95.5 93.9 81.5

104.6 100.6 92.6

("w

753 f’c (N/mrnz)

110, 100 90 80

-

70

-

60

-

50 40 -

30 20 -

0’

1

I

I

I

3

7

28

I

I

I

182 365 730 age (days)

Figure 1. Compressive strength development (f‘c) of high volume PFA concretes. For mixes with 20%, 40% and 60% cement replacement efficiency factors (k-values) were calculated. These factors represent the binder effect of PFA. Starting point for the calculation of the k-values was the compressive strength. The calculated k-values are shown in Table 4. The 7 days and 28 days k-values are affected by the PFA content. Even at 60% replacement levels the value exceeds the generally accepted value of 0.20. Table 4 k-values of hiah volume PFA concretes MIX

H20 H40 H60

SP

2.5 2.5 2.5

WBR

0.35 0.36 0.37

K-VALUE

7d

28d

0.73 0.48 0.23

1.17 0.67 0.31

The effects of methods to accelerate strength development are summarized in Figure 2 and compared to standard curing, no-treatment (NO). In the figure the methods are denoted as TEMP for temperature treatment, RHC for the application of rapid hardening cement and SP for the addition of superplasticizers (1.5% and 2.5%).

754 For concretes with 60% PFA, especially the temperature treatment proved to be effective for the enhancement of the 7 days strength. Reduction of the water to binder ratio proved to be most successful in all cases. The optimal method is of course dependent on the requirements under actual conditions. f'c (N/rnrn2)

182 days

0

23

60

1 2 3

-

40 -

20 0

8o 60

-

--

1

--

-

1

t

1 : 20% PFA 2 : 40% PFA 3 : 60% PFA

7 days

NO

TEMP

RHC

1.5SP

2.5SP

Figure 2. Effect of early strength control methods for high volume PFA concretes. 4.

CONFORMITY TESTS

For the assessment of high volume PFA mixes, conformity with the appropriate national documents for technical approval (BRL 1802/01 1992) was applied [5]. Concrete mixes were designed based on 340 kg/m3 PC-A and HOC-A (blastfurnace) cements. Replacement levels of l8%, 26% and 32% were chosen. The slump was held between 190 and 240 mm. The water to cement plus 0.2 PFA content was 0.45 for all mixes. For the reference mix (REF') no additives were necessary; for the mixes with PFA a combination of 0.5% plasticizer and 1.5% superplasticizer (for HI8 1.0%) was used. The plasticizer was a ligno sulphonate whereas the superplasticizer consisted of naphthalene formaldehyde condensate. Some typical results of compressive strength development are shown in Figure 3. At increasing age the strengths of the PFA concretes exceed the strengths of the reference concretes because of the pozzolanic reactivity of the PFA.

755

The results of durability tests like water penetration, carbonation depth and chloride penetration, as far as available up to now, are summarized in Table 5. In this Table chloride penetration is taken as the average of four readings from 0-5, 5-10, 10-15 and 15-20 mm depth.

f'c (N/mm2)

60

-

50 40

-

20 -

10 -

REF x

32% PFA

Figure 3. Compressive strength development (f'c) of high volume PC-A and HOC-A concretes The test results were compared to the requirements in BRL 1802/01. The assessment is based on comparison of the properties with reference mixes (REF'), taking into account the statistical variation in the results. In this research it was found that these variations were about equal for both the reference and PFA mixes. So mean values of the properties could be compared. According to the BRL strength and durability have to be checked. For strength the 28 days compressive strength must be taken, whereas for the durability the 7 days and 90 days strength values have to be taken into account, as well as carbonation and, depending on the environmental conditions, deicing salt resistance. For the 7 and 28 days strengths, the criteria are 95% of the reference mix strengths; the 90 days strength must be at least the 28 days strength of the corresponding reference mix. Further, the maximum accepted carbonation depth is the carbonation depth of the reference concrete exposed to similar conditions. In Table 6 an overview is presented of the comparisons. The criteria were calculated from the properties of reference mixes with the same type of cement (i.e. PC-A or HOC-A). As can be seen all HOC-A mixes fulfil the requirements. For the PC-A mixes, the H32 concrete does not reach the 7 and 28 days strength limits, also the carbonation depth is too much as was found for the H26 concrete as well.

156

According to the BRL, concretes must be compared to an accepted reference concrete. So strictly spoken the PFA concretes with PC-A may be compared to HOC-A reference concrete. In that case it can be seen that also the PFA mixes with PC-A cement meet the BRL requirements. Table 5 Results of tests to check the durabilitv of PFA concretes MIX

waterpenetration 28d 91d (mm) (mm)

CI--penetration carbonation 35 d depth (91d) (mm) (mm)

PC-A REF' HI8 H26 H32

30 29 32 36

22 10 10 27

2.4 1.8 1.7 1.7

2.0 1.5 2.5 3.0

HOC-A REF' H18 H26 H32

20 9 7 5

5 8 2 6

1.o 1.o 0.9

4.5 4.0 4.0 3.0

Table 6 Properties of high volume PFA concretes compared with the requirements MIX

PC-A criterion H18 H26 H32

compressive strength

carbonation

f'c(7d) (N/mm2)

f'~(28d)~

35.4 39.1 35.5 32.4*

43.1 54.1 46.1 42.9"

(Wmm

1

f'c(91d)2

"/mm 45.4 63.9 57.6 60.2

HOC-A criterion 27.4 42.4 44.6 H18 31.6 49.8 59.0 H26 28.1 45.5 60.1 H32 27.7 42.9 54.3 * exceed PC-A criterion, but comply with HOC-A criterion.

1

depth (90d)

(mm) 3.0 3.0 4.0* 4.5" 5.5 5.5 5.5 4.5

757 5.

ENVIRONMENTAL PROPERTIES

For the application of building materials, environmental properties have to be considered. With respect to leaching the corresponding Dutch regulations (abbreviated as BSB) have to be taken into account. In general the leacheability of numerous components must be checked. However, in previous research it was found that for PFA, mainly seven components proved to be decisive (see Table 7). Diffusion tests were performed according the Dutch Standard NVN 7345 (1992). The results have to meet the limits in the BSB. Another type of test is the availability tests based on the Dutch Standard NVN 7341 (1992). This type of test gives an indication of maximum possible leaching. Concrete specimens were subjected to both diffusion and availability tests at an age of 2 years. The results of high volume PFA concretes (20%, 40% and 60% PFA and 2.5% superplasticizer) were compared to the results of reference concrete. The test specimens originated from the batches as indicated in Table 3. The two sets of results are given in Tables 7 and 8. Table 7 shows that all PFA mixes investigated fulfil the BSB requirements. In the well accepted reference mix, however, the leaching of selenium slightly exceeds the limit. Also in the availability test a higher selenium content was found for the reference mix. This finding may be explained by the higher alkalinity of the reference mix compared to the PFA mixes. Table 7 Results of diffusion tests according NVN 7345 and corresponding limits (6%) Component BSB (mg/m2)

REF (mg/m2)

H20 (mg/m2)

H40 (mg/m2)

H60 (mg/m2)

As

25

< 0.8

< 0.8

< 0.8

< 0.8

Cr

90

U1 limit value - classification as C2-waste (+). The leachability of the residues was compared with these limit values in order to determine the classification of it. Table 1 Compounds for analysis of composition and leachability Untreated fly ash

Immobilised mixture

fly ash

mixture

L

L

L

L

Macrocompounds: aluminum ammonia calcium carbonate chloride fluoride iron magnesium organic carbon potassium silicium sodium sulphate sulphite

Microcompounds: antimony barium cadmium lead mercury molybdenum strontium zinc

C C C C,L C C C C C C C,L

C C C C,L C

816

4.

RESULTS

4.1. Introduction The five companies have carried out experiments using either fly ash or a 50/50 mixture of fly ash and APC residues. Since a tight time schedule had to be met, only a preliminary optimisation of the recipes by the companies could take place. The results which were obtained by the companies therefore only can be regarded as an indication. In this chapter the results of immobilisation are presented. The results of each single company are to be kept confidentially, therefore the results are presented anonymously. The results of the five companies will be presented in random order and they will be indicated as A to E. 4.2. Untreated residues The untreated fly ashes and the 50/50 mixture of fly ash and APC residues have been analyzed on both their composition and their leachability. The leached quantity (1.q.) has been compared with the limit values for classification. The 5060 mixture of fly ash and APC residues could not be analyzed by means of a shortened column test, because the flow through the column was blocked after a short period of time. The symbols which have been used for comparing the leachability of fly ash with the limit values are described in paragraph 2.3. Table 2 presents the results for the untreated fly ashes and untreated 50/50 mixture of fly ash and APC residues. Table 2 Results for untreated fly ash and 50150 mixture of fly ash and APC residues (in mglkg dry matter) limit values u1 value

uo value

fly ash composition

50150 mixture 1.q.

composition

Macrocornpounds: aluminum ammonia calcium carbonate chloride fluoride iron magnesium organic carbon potassium silicium sodium sulphate sulphite

> 17,000

34,000

50,000 280

50,000 25

110,000 3.2 >56,000

36,600(--)

11,000 9,500 16,000 25,000 5.800

> 750 115,000 2.2 213,100 > 13 >5,500 >4,750 > 8,000 > 12,500 >2,900

> 110,Ooo 80,000

80,000

>54,000

3,450(--)

>63,000

>275

817 limit values

Microcompounds: antimony barium cadmium lead

mercury molybdenum strontium zinc

fly ash

uo

50/50mixture

u1 value

composition

1.q.

composition

value

0.8 60 0.2 25 0.1 3 5 40

0.1 20 0.05 4 0.1 0.04 I 10

850 540 135 3,500 0.5 9 215 11,000

0.015(--)

595 350 103 2,800 1.9

2.05(--) 1.15(+) 12 (3 0.00005(--) 1.6(-) 9.9(+) 5. I(--)

115 8,150

From table 2 it can be seen that for fly ash the loads of both cadmium and strontium exceed the U1 limit value. Because of this the untreated fly ash has to be considered as C2-waste.

4.3. Treated residues 4.3.1. h o b i l k a t i o n of fly ash Four companies have carried out experiments on immobilisation of fly ash. The results of the leachability tests on the immobilised products are presented in table 3. Table 3 Results of leachability test for immobilised fly ash (in mg/kg dry matter)

antimony barium cadmium chloride*’ lead mercury” molybdenum strontium sulphate*’ zinc classification

untreated fly ash

immobilised fly ash

composition

1.q.

1.q.

A

850 0.015(--) 540 2.05(--) 1.15( +) 135 > 56 37(--) 3,500 W-) 500 0.05(--) 9 1.6(-) 215 9.9( +) > 85 3.5(--) 11,000 5 . I(--) c2

O.Ol(--) 0.215(--)

1.q. B

1.q.

1.q.

D

E

0.0005(--) 0.04(--) 0.4(+) 43(--) < O.l(--)

0.1(-) 0.275(--) 0.0002(--) 15(--) 2.9(--) 0.05(--) 1.75(-) l.O(-) 1.2(--) I.%(--) c3

47(--) 2.2(--) 0.03(--) 2.75(-) 2.4(-) 6.8(--) 0.78(--)

1.9(-) 2.4(-) 2.2(--) 0.4(--)

0.2 1(-) 0.54(--) < 0.0 1(--) 78(+) 16(-) 63 8.150

classification

275

1.4 0.9 220

-

820

Table 6 shows that the costs for immobilisation at full scale are moderate for company A, while both companies C and D are expensive. It can also be seen that the largest volume reduction will be achieved by both companies C and D, whereas company A has a lower volume reduction. 6.

CONCLUSIONS AND RECOMMENDATIONS

From indicative experiments on immobilisation of fly ash and of a 50/50 mixture of fly ash and APC residues, the following preliminary conclusions can be drawn: - In general, the leaching behaviour of fly ashes can be sufficiently reduced by means of immobilisation in order to classify the product as "C3-waste". Two companies meet these limit values, and two companies expect they can meet these limits after optimization. - The leaching behaviour of a 50/50 mixture of fly ash and APC residues could not be reduced sufficiently by means of the considered immobilisation processes. None of the companies could meet the U1 limit values for the compounds chloride and strontium. It is likely that the amount of chloride which has to be fixed in order to meet the limit values, can not be realised by means of immobilisation. Besides, the considered immobilisation processes mainly focus on immobilisation of metals. - The processes carried out by the companies appear to differ significantly in prices and the volume-reduction that may be achieved. On the basis of this research it can be stated that only immobilisation of the fly ash gives promising results which make further elaboration and optimisation useful. The two companies having produced the best results for these residues, may be invited for taking further steps. The next steps should be 1). optimization of the recipe, 2). a specification of the costs for immobilisation at a full scale and 3). the handling of the immobilised products.

[ 11

[2]

Tauw Milieu bv, Immobilisatie vliegas en rookgasreinigingsresidu AVI-Amsterdam, report number R3285790.T04/T05 (1994). Dutch Ministry of Housing, Physical Planning and Environment, Grenswaardennotitie Storten gevaarlijk afval (1993).

Environmental Aspects of Construction with Waste Materials 3.JJ.M. Goumans, H A van der Sloot and 7'h.G.Aalbers (Editors) a1994 Elsevier Science B.V. All rights reserved.

82 1

Certification system for aggregates produced from building waste and demolished buildings Ch.F. Hendriks Director of Intron, Institute for Materials and Environmental Research, P.O. Box 226, 3990 GA Houten, The Netherlands

')

Professor of Materials Science, Delft University of Technology, P.O. Box 5048, 2600 GA Delft, The Netherlands

b,

Abstract In the Netherlands per annum about 14 million tons of building and demolishing waste are produced. Nowadays about 8 million tons are recycled, mainly for unbound road base courses. This market is almost saturated and a further increase in re-use must be realized within other sections of the building industry. One of these is the use as an aggregate in concrete. However, quality requirements for concrete are more difficult to meet for various reasons. The concrete industry is rather reluctant to accept the material, in the first place because of a lack of confidence in the quality. Another aspect is that the government on the one hand stimulates the re-use for building and demolishing waste as much as possible but on the other hand also fears pollution of the soil if incidentally contaminated building and demolishing waste is applied. This has stimulated the implementation of quality assurance systems by the recycling industry. Initially this industry established its own foundation which camed out attestation of conformity with the requirements of a quality assurance guideline. In 1993 this system has been converted into a certification system which will be approved officially in 1994 by the Dutch Council for Certification. Within the tight quality control scheme of this third-party certification the customers can confidently rely on the quality of this recycling aggregate.

1. INTRODUCTION The extraction of natural (primary) building materials increasingly meets with environmental objections. Moreover, the amount of waste and industrial residues increases alarmingly, which also involves environmental and economic objections. However, a large part of these waste materials and residues can (after processing) be used to partly compensate for the shortage of primary building materials. As a result of efforts of the government these so-called secondary materials are also becoming economically attractive.

822 2.

THE BUILDING CYCLE

Maintenance, renovation and demolition of constructions produce a considerable amount of waste. Recent estimations for building and demolition waste indicate an annual amount of 14-16 tons, mainly consisting of asphalt (2.5 million tons), concrete (5.3 million tons) and masonry (3.8 million tons). These numbers might still increase in the near future. A similar development can be seen throughout Europe. Presently the EC countries produce 200 million tons of building and demolition waste, an amount that may well double in ten years time. Dumping these materials causes more and more problems because of the space it takes up and the costs of sufficient care. Moreover, the establishment of this type of dump sites causes the NIMBY syndrome. Reuse would be the ideal solution. The building cycle, which indicates how each phase is influenced by the input and output of resources and energy, would then be closed. Building waste mainly consists of miscarried productions, superfluous materials and packing materials. Research in combination with the inventiveness of some entrepreneurs, has shown that when building waste is collected separately a large number of sub flows could be re-used in a cost effective way. In fact separate collection should become part of the quality system or the environmental care system of the construction company. With demolition waste things are more complicated. Especially the demolition waste of houses and other buildings contains, apart from the stony main components, a number of side components of which wood, metals, rubber, glass, paper, cardboard, textile, synthetic materials, soil and paint, are the most important ones. Materials that cause problems in re-use are: gypsum aerated concrete fibre concrete some applications of synthetic materials asbestos tarry materials some coatings and paints The problems mainly arise when these materials are offered in combination with other materials or are even attached to them. -

A re-use friendly design should take this into account. Pollution in demolition waste is mainly brought in during the period a construction is used, this is even valid for houses. Although the situation is somewhat more favourable with demolition waste from road and hydraulic constructions, re-use of demolition waste is only possible after upgrading, usually in combination with selective demolition.

823 A modern and well equipped demolisher draws up his plan of action on the basis of information about the construction, inspection and if required additional research. Moreover, he has various mechanical, chemical and physical methods at his disposal to go about selectively and therefore environmentally sound. ’Peeling’ old concrete with radio waves is an example of this. Because of this the demands with regard to the demolisher’s competence have risen to a high level. Further treatment of demolition waste is done in processing installations. Since the end of the seventies this has become a growing branch of industry in the Netherlands, which makes 7-8 million tons of demolition waste suitable for re-use and puts it on the market.

3. ENVIRONMENTAL ASPECTS In the Netherlands the acceptable burden of building materials to the environment is subject of an in-depth discussion. Most attention is focused on: * $radon emission in the indoor environment * leaching to soil and (ground) water. The authorities are working on the establishment of limit values to acceptable ionising radiation from building materials on the basis of a general (health) risk policy. A final point of view has not yet been established, since both the calculation of the risks and the measuring methods are still subjects of intense discussions. Compared to the primary materials extracted in the Netherlands the radiation load of secondary materials is equal or somewhat higher. The significance of this small increase is being investigated. Eventually the result of this investigation will have to be balanced against the importance of the application. With regard to soil and ground water the preliminary assumption is that the average natural content may not increase with more than 1% over a period of 100 years. From this assumption, limit values have been derived with regard to leaching of building materials, dependent on the application conditions. Since the leaching of organic pollution cannot be measured very well, limit values have been formulated for the composition. By far most bound applications of building materials meet with the requirements. This means that the use of aggregates made of building and construction waste has no environmental limitations concerning soil and (ground) water.

824 4. REUSE OF BUILDING AND DEMOLITION WASTE Most of the material is sold as 0/40 fraction concrete granulates or mixed granulates (which is a mixture of concrete and masonry granulates) in road foundations. The material can be sufficiently compacted, has a good crushing resistance and both the plastic and the elastic stiffness make the material suitable for heavy duty roads. Research into this material, among others executed by the Delft University of Technology, has had a positive influence on the constructive knowledge of stone foundations in general. Although the Netherlands are the leader in Europe with the present amount of this type of re-use, further growth in this sector is improbable. The market is saturated and is even becoming smaller in view of the shift in road construction from new construction to maintenance. A recently published implementation plan for building and demolition waste, written by order of the ministry for the environment, aims at a re-use percentage of 90% in the year 2000. This can only be achieved if the granulates will also be used as an aggregate in concrete. That market, however, renders far more problems. Technically the application has been extensively studied. 5.

STANDARDS

In 1984 - 1985 preliminary standards were made based on several years of thorough research for the use of building and construction waste in roads and in concrete. Last year, under the responsibility of a Rilem group, a proposal for the European standard was made for the use in concrete. This document is at present discussed by CEN TC 154 "Aggregates" in order to see if a European specification can appear based on this document.

6. SCOPE OF THE RILEM DOCUMENT This document gives the framework for a Rilem guideline dealing with recycled coarse aggregates 2 4 mm for concrete. These guidelines are based on the assumption that the fine ( < 4 mm) fraction of the concrete is composed of materials where traditional specifications for this material are applicable. Consequently, recycled materials may be used as substitute for the natural sand or parts hereof as long as above mentioned material specifications are complied with for the total sand fraction. In addition hereto the same requirements concerning content of sulphate and PAC as for coarse aggregate according to table 1 apply if the sand fraction contains recycled materials. This specification classifies different categories for the recycled coarse aggregates and indicates the field of application for concrete containing these recycled aggregate classes in terms of acceptable environmental exposure classes and strength classes for concrete in accordance with Eurocode 2; Design of concrete structures.

825

Eventually, the design values to be adopted for the different concretes are defined in relation to the applied aggregate class. The document gives the framework for use of recycled coarse aggregates in concrete. The use of recycled fine aggregates is limited for the following reasons: - The recycled fine materials do often contain large amounts of contaminants. It has been assessed that operational testing procedures and acceptance criteria are not readily available. Further research in this field is recommended. - The impact of the recycled fine materials on durability and strength of concrete is not sufficiently documented. Further research in this field is recommended. - A relevant test method for determination of the strength of the fine recycled aggregates is not available. - A reliable test method for determination of residual alkali reactivity of the fine recycled aggregates is not available. - Use of recycled fine aggregates has been reported to lead to production problems, e.g. in the control of free water and in the flow of materials during production. It is recommended to consider the use of recycled fine aggregates in the fraction 2 - 4 mm by change of definition of coarse aggregates.

7. CLASSIFICATION Recycled coarse aggregates are classified into three categories, i.e.: - Type I aggregates which are implicitly understood to originate primarily from masonry

rubble. - Type I1 aggregates which are implicitly understood to originate primarily from concrete

rubble.

III aggregates which are implicitly understood to consist of a blend of recycled aggregates and natural aggregates. This classification of the materials is based on the mandatory requirements stated in table - Type

1.

For the production of these 3 types of aggregates the following additional rules apply: The composition of type 111 aggregates shall meet the following requirements; Min. content of natural aggregates ( m h ) : 80% Max.content of aggregates type I ( m h ) : 10%.

In table 2 is given a list of material properties for which requirements may be specified. Such requirements are not mandatory unless specified in national documents or CEN standards.

826

7.1 Classification of aggregates The reason for introduction of a class of aggregates as defined in type I11 is that the application of traditional construction rules and design values can be accepted as indicated in table 3. Table 1 Classification of recycled coarse aggregates for concrete (RCAC) RCAC Type I

RCAC Type 11

RCAC Type 111

Test Method

1800

2200

2500

ASTM C123

20

10

3

IS0 6783

10

10

ASTM C123

10

1

1

ASTM C123

1

0.5

0.5

ASTM C123

5

1

1

Visual

Max. Content of Metals (46 d m l

1

1

1

Visual

Max. Content of Organic Materials (9% d m )

1

0.5

0.5

NEN 5933

Max. Content of Filler (< 0.063 nun) ('% d m )

3

2

2

prEN 933-1

5**

5**

5**

prEN 933-1

M~datofy Requirements Min. SSD Density* (kglm3) ~

Max. Water Absomtion

(46 d m ) Max. Content of Material with SSD < 2200kglm3

(46 d r n ) Max. Content of Material with

SSD < 1800kg/m3 f % m/m) ~~~

~

~

Max. Content of Material with SSD < 1OOOkgld (% d m )

Max. Content of Foreign Materials (metals, glass, bitumen, soft material, ...) (96 d m )

Max. Content of Sand ( < 4 mm) (96 d m ) Max. Content of Sulphate

1

(96 din)*** ~

Max. Content of PAC @pm)

50

1

1

BS 812, Part 118

______~

~

50

50

Dutch Building Materials Order

*) **)

***)

Water Saturated Surface Dry condition If the maximal allowable content of sand is exceeded this part of the aggregates shall be considered together with the total sand fraction Water soluble sulphate content calculated as SO,.

827 Table 2 Properties of recycled materials which have to comply with the requirements of national or implemented CEN documents Static Strength Grading Form Index Abrasion Value ~~

Chloride Content

Iron and Vanadium Content for Clean Concrete Applications Pop out Potential (Ca, Fe content) Content of swelling Clav ~

~~

Frost Resistance (if different from requirements in table 3) Leaching and Radiation The recycled aggregates must not contain any material or any other substances which retard the setting of the concrete by more than 15% compared to the setting time of the identical composition with traditional aggregates or which are detrimental or harmful to the concrete. The indicated test methods are introduced to exemplify the type of testing which is suggested. These methods may be applied until relevant CEN standards are implemented. However, the use of the specific standards is not considered to be mandatory. Existing national standards may be used if applicable.

828

8. FIELD OF APPLICATION Recycled coarse aggregates, complying with the specifications mentioned in paragraph 1, can be used in plain and reinforced concrete under the provision that the restrictions mentioned in table 3 are satisfied. If additional testing is required in accordance with table 3 the specifications given in table 4 shall comply. Table 3 Provisions for the use of recvcled concrete Recycled aggregates

RCAC Type I

Max. Allowable Strength Classes Required additional testing when used in the exposure class 1”

RCAC

RCAC

IJ

Type m

C 16/20”

C50l60

No limit

None

None

None

Type

Mortar bar expansion test. Use in class 4a not allowed

*

Mortar bar expansion test

*

Mortar bar expansion test

Required additional testing when used in the exposure class 2b and 4b

Usein class 2b and 4b not allowed

*

Mortarbar expansion test Bulk frost thaw test

*

Mortar bar expansion test Bulk frost thaw test

Required additional testing when used in the exposure class 3

Use in class 3 not allowed

*

Mortar bar expansion test Bulk frost thaw test Deicing salt test

*

Required additional testing when used in the exposure class 2a and 4a

*

*

* *

*

*

*

Mortar bar expansion test Bulk frost thaw test Deicing salt test

1) However, the strength class may be increased to C30J37 conditioned the density of the recycled aggregates exceeds 2,000 kg/m3. 2) Conforming with ENV 206.

829

Table 4 Specifications and compliance criteria for the additional testing

Test procedure

Criteria

Mortar Bar Expansion Test

50°C Sodium hydroxide, 20 weeks ....

Max. expansion < lOlW

Bulk Freeze Thaw Test

ASTM C666

Durability factor > 80%

Deicing Salts Test

SS 137244

Max. Weight Loss < 500 g/m2

For concrete with recycled aggregates used in the exposure classes 2, 3 and 4 attention should be paid to the durability aspects of reinforced concrete as the speed of carbonation and chloride ingression may be larger than in conventional concretes. If these properties are relevant, more accurate values for the concrete to be used should be determined.

9. DESIGN VALUES For concrete with recycled aggregates the same design and application rule principles apply as those stated in prENV 1992-1-1 for conventional concrete. Due account must, however, be taken of the possible influence of density of the aggregates on the strength and deformation characteristics of the concrete. In the absence of more accurate experimental data, a worst case estimate of these material characteristics, can be obtained by multiplying the values stated in prENV 19921-1 by the coefficient given in the following table 5. Table 5 Factors for the evaluation of the material properties of recycled concrete.

RCAC Type 1

RCAC TYPen

RCAC TYPm

Tensile strength (f,d

0.85

1

1

Modulus of Elasticity (E,,,,)

0.65

0.8

1

Creep coefficient (0(m ,to))

1

1

1

Shrinkage ( E J

2

1.5

1

Where accurate data are needed, e.g. where deflections are of great importance, tests should be carried out.

830

For design of a structure more parameters may be of importance than the ones given in table 5. It is recommended to use procedures for light weight aggregates in such cases (Eurocode 2). 10. EVALUATION OF THE PRESENT SITUATION

Technically the prospects are good and yet there are a lot of bottle necks in the market. * Users hold the opinion that the quality demands with regard to pollution are not met. * There are extra costs, such as extra quality controls, extra storage, adaptation of the production process or the concrete composition. * The costs of transport are unfavourable because crushing plants are usually not situated on the waterfront. * On balance the material is sometimes more expensive than gravel. * People are prejudiced: it is waste material and it may not be environmentally sound. * The producers of granulates are careful with investments required to improve sale on the concrete market. There are also opportunities:

* The government policy is increasingly aimed at sending building and demolition waste

*

* * * *

to processing installations. Dump sites and agricultural application in the ballasting of private grounds fade into the background. The production costs of granulates for road construction and for concrete are getting closer together; in both cases the material has to be clean, which can for example be achieved by washing. The authorities stimulate contacts between suppliers and users of granulates and in some cases even impose the use of granulates. The establishment of regional consultants may help to remove all sorts of reservations. The issuing of quality declarations will also support this development. The authorities try to make things clear by drawing up environmental demands. When these are univocal they may stimulate the acceptance of re-use of waste. These demands are based on specifications for leaching and radon exhalation and will be available in a final draft within one year.

For reasons mentioned above a certification system is developed which is yet in an operational phase.

83 1 11. THE ORGANIZATION OF CERTIFICATION IN THE NETHERLANDS

The total process can be divided into separate constituent processes. There is a quality control and assurance (quality system) for each constituent process. By definition, any party carrying out a constituent process has a quality system. The delegation of constituent processes can only be controlled after three questions have been answered. 1. If the secondary process consists of supplying a product, is it clear which characteristics the product has to possess and which requirements have to be satisfied with regard to supplies?

2. If the constituent process consists of performing work, is it clear which quality requirements the work has to satisfy? 3.

If the party who is delegated to carry out the constituent process capable of maintaining proper control over it.

Therefore, the essential points in quality management are: Product specifications 2. Process specifications 3. Quality-system specifications 1.

Certification affects these essential points. In quality control, which is an important part of quality management, it is important to check products against product specifications and processes against process specifications. The certification of products and processes takes care of this. What is certification? Certification involves having an independent third party in addition to the first party (the supplier) and the second party (the customer). The third party declares that the product or service supplied may be considered to meet the specifications. One of the advantages of certification is that there is no need for a new second party to carry out a check on the first party every time. The control can be carried out much more efficiently by one party, provided that party can be relied on to do the job properly. Quality systems can also be certificated, as well as products and processes. In certification, there is symbiosis between the first party (the supplier) and the third party (the certifier). The symbiosis is laid down in the certification system: this is a sort of quality system for which the third party is responsible. So, certification adds another essential point to the three essential points of quality management already mentioned.

832 12. CERTIFICATION SYSTEM SPECIFICATIONS

In the Dutch situation, the certification bodies are accredited by the Council for Certification (Raad voor de Certificatie) and the certification scheme for which they are accredited is laid down. This covers the product certification, the attestation, the process certification and, of course, the quality-system certification. The basis for certification issuing certificates for each product or group of products is laid down in a document which is usually referred to as the assessment guidelines. This states that the manufacturer’s method of production and the control of the production process must be arranged so that the products produced by that process meet the requirements. It also states how and how often the certification body has to inspect the production-process controls carried out by the manufacturer and the products produced by that process. It is important that these principles for product certification but also those for qualitysystem certification are aligned, that is to say, that the bodies that work in the same field also employ the same assessment principles. It is also important that the intrinsic technical aspects as well as the quality-assurance aspects are properly named at the right level. This applies to statutory requirements and also the requirements agreed on according to private law. A lot has been done over the past few years to incorporate paragraphs on the environment and working conditions into these assessment guidelines.

The assessment guidelines clearly state the difference between statutory requirements and the requirements agreed on privately in society in general. This action will make it possible for the conversion in Europe to take place imperceptibly in the future. 13. CERTIFICATION OF GRANULATES, MADE OF CONSTRUCTION AND BUILDING WASTE

The basis for the certification of granulates is an assessment guideline. This document is developed as a follow up of some years of experience with internal requirements for quality systems for the producers of granulates. In the assessment guideline all relevant specifications are given with regard to: - acceptance of rough building and demolition waste; -

upgrading of this material;

- properties of the granulates produced after upgrading; - the quality system of the producer.

For an integral quality system guidelines will be made for selective and environmental friendly demolition being the step before the acceptance of the waste which is of great importance for the final quality of the granulates.

833 The assessment guideline deals with the application of granulates: for subbases as unbound material in road constructions as aggregates for asphalt as aggregates in lean concrete or cement of bitumen stabilized subbase layers. b. in concrete as aggregates c. in hydraulic works as unbound material. a.

Furthermore, the assessment guideline deals with different qualities of aggregates: - masonry granulates; - concrete granulates; - mixed granulates consisting of a mix of masonry and concrete granulates; - hydraulic granulates consisting of mixed granulates and hydraulic slags; - asphalt granulates. The following scheme supplies a summary of the standards used as a base for the assessment guideline. description

standard

acceptance criteria type and origin of waste control and assurance of upgrading proces of the waste (sieving, handpicking, crushing, magnetic separation, other separation techniques such as washing, windsifting etc.

remarks including how to handle if criteria are not met

EN 29002

granulates for road constructions

National RAW Standard 1990

granulates for concrete

NEN 5905

granulates for hydraulic constructions

no specifications available

specifications are agreed upon between producer and client

A testing scheme is made in which the frequencies are laid down of sampling during production.

834 For road constructions this scheme deals with: size distribution composition content of plain particles crushing value durability for frost and moisture density CBR (only unbound application) - organic components.

-

-

For concrete constructions this scheme deals with: size distribution particle density content of concrete particles content of non stony materials dust content crushing value content of plan particles chloride content sulphate content alkali-silica reactive components content of organic substances content of weak components

14. CONCLUSIONS Certification of granulates made of building and construction waste is a very important step forwards for the reuse of these materials. The assessment guideline in the Netherlands consists all relevant technical properties and will be completed with environmental properties within one year.

Environmental Aspects of Constnrction with Waste Materials JJJ.M. Goumans, H A . van der SIoot and l71.G.Aalbers (Editors) 01994 Elsevier Science B.V. AN rights resewed.

835

Sampling and sub sampling of primary and secondary building materials: a statistical treatise A.M.H van der Veen, D.A.G. Nater Materialenbank Nederland MBN, P.O.Box 15 1 , 6470 ED Eygelshoven, the Netherlands Abstract The statistics of sampling and sub sampling of primary and secondary building materials are reviewed. A Monte Carlo model is described, which is capable of describing the sub sampling process of granular materials at a particle level. The model is demonstrated for the socalled cross-riffling process and for distribution heterogeneity. It is concluded from the computational results as well from experiments, that the model is capable of describing the statistics of a sub sampling process. However, the model should be extended in order to study the influence of the distribution of the critical parameter(s) over the sub samples. 1. Introduction

In order to do experiments, reliable starting materials are required. The processes of sample taking and sample preparation from primary and secondary building materials are far from simple. Many steps are involved, and each of them steps may be of influence on the properties of the material. The property of interest, usually called the critical property, should be maintained during the process as good as feasible. When preparing a sample, the only objective is to reduce the amount and the particle size of material in such a way, that a portion suitable for the experiment remains. Under strict controlled conditions, it is possible to do both maintain the property of interest and to make the material suitable for the experiment. In a previous paper [I], an outline over standardised sample preparation and use of reference materials has been given. In this paper, emphasis will be put on the statistical aspects of sample taking and sample preparation. Special attention is being paid to the heterogeneity concept, which is of great importance when sampling construction materials.

2. Sub sampling

When sampling a material, it should be considered that any practical sampling process is to be treated as sampling from a finite population. This observation is very important, since it has great practical implications. After a sample is taken from the population, the properties of the population may have changed. If sampling takes place under strictly controlled conditions, it is possible to minimise this effect, but it may never be excluded that the sampling process itself changes the properties of the population. The effects become stronger as the ratio between the sample mass and the population mass increases. Thus, for sub sampling, the observation of a finite population becomes even more important. If a sub

836 sampling fails, than both the sub sample and the remainder of the original sample become useless. In a sub sampling process, the orders of magnitude of the sub samples and the population (the sample before subdividing) are comparable. Usually ratios between 1:2 and 1:20 are observed. For the preparation of reference materials, it is even more important that the properties of the sub samples are as equal as possible. Although the material being subdivided may be very heterogeneous with respect to its constitution, the objective of a subdividing process is always to distribute the properties of the material equally over the sub samples. If this attempt succeeds, then it is said that the sub samples are homogeneous The distribution heterogeneity (DH), which only exists if there is also constitution heterogeneity (CH) [ 2 ] should be minimised in the sub sampling process. If a bulk material is to be sampled, it is usually desirable to have a sample that amounts a few 100 kg, depending on the sampling conditions. If, for instance, a depot is sampled that contains about 100 tonnes of fly-ash, it is no use to take only a few kilograms of material. A sample of 100 kg for instance allows to design a sampling process that is suitable to the purpose. In practice, a severe problem is how to prepare samples of good quality from such an amount. Any treatment by hand will not meet the quality requirements stated in the introduction. For this type of operations, specially designed large-scale equipment can be used [I]. However, the accuracy of this type of equipment is lower than that of a laboratory riffler. Experiments have shown, that weight differences in the 10 sub samples from the large scale riffler of about 10% may be observed. The differences in particle size distribution, as well as the properties of the sub samples are far less fortunately. The sample size and the particle size distribution may indicate whether a sub sampling step may be successfbl or not. These indicators are not sufficient however when preparing materials for a special purpose. Then the critical parameter should be investigated. In order to guarantee that the samples are homogeneous after sub dividing the 10 sub samples (of 10 kg on average in the example), a special procedure has been developed. Since the process originates from using spinning rifflers, it has been called cross-rij’jing (X-riffling), and it is carried out as follows. The 10 sub samples (labelled #01..#10 in the scheme on the next page) are riffled each into 10 sub samples. After riffling each of the 10 sub samples, a matrix of 100 samples is constructed. The samples are arranged in such a way, that 1. in each column the samples from one sub sample appears 2. in each row from each of the 10 tubes just one sample appears (indicated by the second pair of digits in the scheme) Finally, 10 new sub samples are created by recombination of each of the rows. The recombined samples are labelled #A..#J. The X-riffling process is very efficient with respect to reducing the random error. The Monte Carlo model, to be introduced shortly, has been used to investigate the statistics of this process. The reason for recombining samples from different tubes from the riffler is quite obvious: if samples were taken from one tube (the samples #01.05, #02.05, ,,,,#10.05 for instance), propagation of a systematic error in the riffler is possible.

837

u

u

u

u

u

u

u

u

u

u

3. Segregation

Segregation is the greatest potential risk in the sub sampling process. Segregation is favoured by two factors: 1. a particle size distribution 2 differences in density Segregation due to the particle size distribution is only possible as long as the particles move. The process favoured by density differences is a slow process, but it can proceed even if the material is in rest. There are two ways to circumvent the problem of segregation while sub sampling, in fact mixing or sub sampling with a technique that is not sensitive to differences in constitution or particle size. Mixing will solve only a part of the problems, since any method of sub dividing will allow the particles to move, and thus favouring segregation of the first type. It can be proved that using a vibrating feeder will certainly cause this type of segregation to occur. The Monte Carlo model is also used to investigate the influence of gradually changing properties when subdividing.

4. Monte Carlo model

In order to enable a thorough study on various aspects of the sampling and sub sampling of granular materials, a Monte Carlo model is developed [ 3 ] . The model was intended to be a tool for validation of the cross-riffling procedure, as implemented at MBN for several years. The model was tested first on coals [4], and after that the applicability was tested for other materials. The results of the first computational experiments are that promising, that a fbrther development of the Monte Carlo model is planned. The model developed so far is based on the riffler mechanism. A riffler consists of a head, which turns around an axis. This head allows the material being fed by a continuous feeder to pass one tube at a time. If the rotational velocity of the riffler head and the feeding rate are constant, then it may be expected that all sub samples have about the same properties

838

Inpul

1

N. a v e r a g e . slaridard devlitllon L,Se Po,sso,,,B,no Cpne,.n,o,.s

,,,,",

.~~ -

DrLrrrnine # c1ustcrs

~ i i u s s r a n ene erst or

{_-# _par11cies i z z J &J& ;: D e te 1.111 I" e # "red"

8"' """s'

Omeralor

I

Oulpul

~ i ~ , 1, ,..Algorithm ~ of the Monte

Model

carlo

If the particles stick together, it still must be expected that the average volume of the through-put is constant. The distribution of the average number of particles differs however. Depending on the strength of the clusters, these clusters can be treated as if they were single particles, just of a larger radius. The cluster size will not be distributed normally. Especially at low average cluster sizes, it must be expected that the distribution function of this size will not be symmetrical. The Poisson distribution seems to be suitable for modelling this feature.

Heterogeneity is probably the most complex property to describe. A true quantitative approach would require the knowledge how the various components are distributed over the particles. The theory of Gy [2] provides us with a general treatment on heterogeneity, but this theory is not readily applicable in calculations. In the Monte Carlo model, a method has been sought for, which allows the simulate heterogeneity, without demanding for a true quantitative description. So far, only distribution heterogeneity has been taken into account. The implementation of the distribution heterogeneity (DH) is quite straight forward. DH can simply be regarded as having particles of two types (e.g. red and white particles). In statistics, normally experiments with two possible outcomes are described by means of the binomial distribution. In the MC model the binomial distribution is used in the final step to fix the number of particles of one kind (the number of particles of the other type is fixed then automatically). Figure 1 summarises the algorithm. 5. X-riflling

The first task for the Monte Carlo model was to evaluate the statistics of the X-riffling procedure. From round robin tests, it was known that the process yielded sufficiently homogeneous sub samples. However, one of the questions still remaining was how many times the

839 scheme should be applied before a sufficiently homogeneous batch of samples was prepared. The results of the simulations are shown in figure 2. The figure clearly shows that the standard deviation of the samples is effectively reduced to a level specific for the equipment. The variations after the first cycle are due to the fact, that a stochastic process is being investigated. The various values of n in the figure (where n is the average number of particles falling through a tube per cycle) can be translated to different angular velocities

X-riffling performance at various feeder speeds

10,000 1,000

The larger the value Of n, the greater is the angular velocity. A simulation where the initial standard deviation was lower than that of the riffler yielded exactly the same result as in figure 2. The standard deviation of the samples after the first cycle was equal within the precision of the simulations 6. Blending and heterogeneity

Both blending and distribution heterogeneity can be described accurately by using the binomial distribution. The greater the similarities between the particles in the blend, the better the description will be. I f a material is sampled which can be regarded as a blend (like metal particles in soil, or a mixture of sand and clay in a soil sample), the Monte Carlo simulation f d l y applies. DH increases when the probability to obtain a particle from one part of the sample decreases. Figure 2 shows the results of the MC calculation, where the total number of particles is 100000, the average is 100, the riffler standard

840

deviation is 10, and the number of sub samples is also 10. At the y-axis, the standard deviation divided by the 'binomial' probability is plotted. This correction is made to correct for the number of particles involved for which the probability applies. Two important observations have been made when testing the modelling of DH. First of all, the riffler mechanism allows to treat materials with gradually changing properties. This observation is very important, since it implicates that segregation will not be of influence on the riffling process. Secondly, when the total number of particles is increased, the relative standard deviation decreases. Depending on the requirements of the samples, the minimum sample size can be determined. It is a clear demonstration of a well-known fact, that an insufficient amount of material will not result in sensible analytical data.

7. Discussion and conclusions

The Monte Carlo model under development provides a flexible basis for sampling and sub sampling modelling. Depending on the assumptions made when sub sampling, the algorithm can be modified to be applicable for other equipment. One of the main issues is how to translate the results from the Monte Carlo model to the real world. One of the features to be implemented is to study how the value of the critical parameter is affected by (1) the distribution of this parameter in the material, (2) the distribution heterogeneity, and (3) blending. The approach of the model becomes somewhat different when implementing these features, since the 'analysis' of the sub samples has to take place also by the Monte Carlo principle. On the other hand however, the model comes closer to the real world, and thus the quality of the predictions will become better. Parallel to the development of the model, the knowledge of how certain sources of errors are translated into the final results on analysis will help to improve the quality of environmental measurements. The model is at this stage already a valuable tool in design, development and validation of sampling and sub sampling strategies. Additional refinements of the model in this direction will certainly be beneficial to our knowledge on how to sample in environmental studies.

8. Literature

1 . F.J.M. Lamers, G.J de Groot, "Standard sample preparation and reference samples as a

tool for determination of the environmental quality of building materials", Waste Materials in Construction, Proceedings of the WASCON Conference 1991, Elsevier, Amsterdam 1991, pp 375-378. 2. P.M. Gy, "Sampling of particulate materials", Elsevier, Amsterdam 1982. 3 . A.M.H. van der Veen, "Computer simulations of subsampling with use of spinning rifflers", final report, SBN/MBN Eygelshoven, the Netherlands 4. A.M.H. van der Veen, D.A.G. Nater, "Sample preparation from bulk materials: an overview", Proc. Third Rolduc Smyposium on Coal Science, Elsevier, Amsterdam pp 1-7

Environmental Aspects of Construction with Waste Materials J.J.J.M. Goumans, H A . van der Sloot and Th.G.AaIbers (Editors) Q1994 Elsevier Science B.E All rights resewed.

84 1

Industrial scale application of the alkali activated slag cementitious materials in the injection sealing works Brylicki Witold, Malolepszy Jan and Stryczek Stanislaw University of Mining and Metallurgy, Al. Mickiewicza 30, 30-059 Cracow, POLAND

Abstract As it results from many years observations and studies, the alkali activated vitreous calcium and magnesium aluminosilicates give cementitious materials of very good properties. These materials can be produced for special purposes, e.g. for the cementing and sealing works by injection method. Their parameters, such as setting time, shrinkage and rheology can be controlled in a wide range depending on the activators and mineral admixtures used. The alkali activated slag pastes show many advantageous properties: they interact well with the rocks surrounding a bore hole, they are resistant to chemical corrosion and filtration. They can immobilize heavy metals and other detrimental substances. The low cost of the slag cementitious materials should be also of importance. The properties of the alkali activated slag pastes will be presented together with the examples of their application on a large scale in hydrotechnics drilling, sulphur mining and as a stabilizer of subsoil under the industrial and hydraulic structures. 1. INTRODUCTION

The effluent of drilling fluid in the zone of absorptive rocks is one of the serious technical difficulties in drilling. The effective methods of the absorptive area separation consist in the utilization of proper sealing agents. The sealing of the rock mass is of significate importance not only in drilling but also in geotechnology and hydraulic engineering. The pastes can be classified into 3 groups [ 1-31: - mineral suspensions, - organic and inorganic gelation agents, - organic emulsions and dispersing media. The following parameters must be taken into account when the sealing substance, particularly the cementing component, is selected: - the mineral and petrographic composition of the rock mass,

842

- the tectonic of walls, - the strength parameters of rocks,

- the absorbing capacity of surrounding rocks, - the occurrence of deposit wastes and chemical composition of wastes. The traditional sealing (walling) of injects are produced from the ordinary or metallurgical portland cements. The clay-cements pastes can be also used. The most important features of these pastes are: - possibility to control their fluidity, - setting and strength. The good adhesion to the surrounding rocks, compactness, low shrinkage and high corrosion resistance are required also. In many cases the portland and metallurgical cement pastes can meet the above requirements. As it results from our studies the better effect can be archived when the alkali activated slag materials are used as injection pastes [4, 51. The properties of the alkali activated slag pastes can be controlled in a very wide range [5, 61. First of all they exhibit very high corrosion resistance and low porosity [7]. The prevailing pores are the gel ones of diameters less than 2 nm. The alkali activated slag pastes show also a very good adhesion to the rock mass. Therefore these materials can be successfully used in the formation of the cut off walls. The effect of the alkali activated slag pastes on the industrial scale application, in different conditions, will be presented in the next part. 2. THE INDUSTRIAL MATERIALS USED IN THE ALKALI ACTIVATED SLAG PRODUCTION The granulated blast furnace slag of the specific surface 3500 cm2/g(Blaine) has been used on the industrial scale. The chemical composition of slag is given in table 1, Table 1 Chemical composition of slag Component

Percentage wt [ %]

CaO SOz

41.1 38.1 9.6 8.4 0.4 1.1 1.2 0.1

A1203

MgO Fez03

so3

+

Na,O K,O residuum

843

The OPC has been used as a mineral admixture; the sodium carbonate and water glass or their mixture - as activators. The Na,O content calculated in relation to the slag binder was 5%.

2.1. Some applications of the alkali activated slag pastes on the industrial scale The antifiltration cut off wall at the Wisla river dam is an example of the alkali activated slag paste utilization in geotechnology [9]. This cut off wall has been formed on the depth 60 m, in the rock mass consisting of the metamorphized shales, sandstones sand and gravel. The conditions in the rock mass were difficult: the proportions between the components varied and in some places the underground water invasion appeared. Therefore the high and variable absorbing capacity towards the injection media, in which the different proportions of activators and water to Solid ratio from 2.5 to 0.45 have been assumed. The properties of the alkali activated slag paste injections are given in table 2.

Table 2 The properties of the slag injection Parameter Sample No

WIS

Density [kglm']

Fluidity test [mml

Viscosity, test Ford [s]

1

2.5

1279

260

10.8

2

1.85

1356

260

10.8

3

1.47

1413

270

11.9 ~~

~~~~

4

1.14

1492

260

12.3

5

0.75

1646

260

12.5

6

0.48

1838

190

28

7

0.58

1753

240

18.5

8

0.57

1761

220

25.5

9

0.45

1872

200

33.7

The sealing works under the reinforced concrete pillars supporting the overbridge are the other example of the alkali activated slag paste injections. The pillars were embedded into the ground on the bottom of the river, consisting of the gravel, sand and clayey sludge. After a time, the dangerous falling down of the construction could be noticed. The sealing of the rock mass to the depth 12 m using the OPC paste failed because of the high absorptivity of the surrounding rock towards this medium and, in some places, the paste out flow on the surface ("volcanos"). The alkali activated slag paste applied subsequently produced a concrete plate under the pillar, as a result of quick setting and hardening of the paste with gravel and

844

sand filler. The paste thus used revealated high fluidity and rapid hardening. The exploition of sulphur in Poland is carried out by a hole method [Fig. 13.

10 /---

1. Water filter, 2. Technological column, 3. Superheated water (115.5"C),4. Melted sulphur from raw, 5. Floor, 6. Main filter, 7. Column of pipes, 8. "Air" lift, 9. Column of facing pipes, 1O.Top of layer (sand, clay, gravel).

Figure 1. Scheme of hole exploition conditions. Because of difficult geological conditions, the cementing works are strongly disturbed [ 101. The OPC pastes used earlier in the lining pipes columns cementing did not form any stable joint with the clayey rocks covering the walls of the holes. The cement seals between the lining pipes columns and the walls of holes undergo a deformation under the influence of the past-exploition settlement of the rock mass. This process results in the shearing and break of exploition pipes. Subsequently, the outflow of deposit water can take place. The consequences are very serious: the pollution of natural environment by sulphur compounds and hydrogen sulfide on one side and economical losses on the other side. The hydrothermal conditions in the rock mass and in the holes favorite the alkali activated slag setting and hardening [7]. These slag pastes have been successfully used in the cementing works during the petroleum and gas deep exploratory drilling. The particular compositions of pastes are worked out every time depending on the depth of cementation, technical and geological conditions of the bore hole and underground water mineralization. The alkali activated slag pastes are used in the cementing works on the depth up to 2000 m

845

in extremely difficult conditions, to prevent the outflow of drilling fluid and in preliminary cementation of fissured rocks as a drilling fluid [ 111. The alkali activated slag paste has been used at the outflow of drilling fluid on the depth 1716-1796 m during the exploratory drilling on the hole Wysoka 3. The rock mass was so full of cavities, as the drilling could not be continued without preventing the drilling fluid outflow. The earlier attempts with OPC-clay, OPC-gypsum, bentonite, oil-bentonite pastes failed. Only when the alkali activated slag paste was used, the absorptive zone became sealed.

2.2 The characteristics of cares from control bore holes The cores from the control bore holes were examinated. The macroscopic evaluation and microstructure observations were carried out. One can notice the good adhesion between the paste and rock mass (Fig. 2,3). The SEM-EDAX studies and porosity measurements prove that the paste meets the requirements for the injection sealing medium. A substantial amount of the compact gellike material, consisting mainly of C-S-H phase (Fig.3,4,5). In the presence of clayey minerals in the rock mass, the sodium and calcium zeolites are formed (Fig.6,7). The microporosity measurements show the occurrence of gel pores of diameters less than 2 nm, without capillary pores ( > 100 nm) practically.

Figure 2. Sandstone cemented with slag - alkaline binder (bore hole W-6,depth 41.5 m -left; bore hole W-7, depth 39 m - right).

846

Figure 3. Sandstone cemented with slag - alkaline binder (bore hole W-9, depth 48 m)

Figure 4. EDAX diffractogram of paste.

847

Figure 5. SEM. The microstructure of pastes. Visible C-S-H phase.

Figure 6. SEM. The microstructure of pastes after 2 months curing in bore hole. Visible sodium zeolites. ~5000.

848

Figure 7. SEM. The microstructure of pastes after 2 months curing in bore hole. Visible calcium and sodium zeolites.

3. CONCLUSIONS Some years lasting industrial practice and experience indicate that the alkali activated slag pastes can be successfully used in sealing works and cut-off walls formation (Fig.9,12). The properties of pastes particularly the setting and fluidity can be controlled in a wide range. Their hydration products are highly corrosion resistant. For this reason they can be applied in the cementing works to stop the eruption of hydrogen sulfide. The OPC pastes cannot be used for this purpose. One should underline the good adhesion between the paste and different rocks. The slag pastes react with the clayey substance forming the zeolites mentioned above and hydrogarnets. The zeolites give the possibility to immobilize the heavy metals by the hydrated slag matrix [ 131. The alkali activated slag pastes can be applied, with good results, to stop the overflow of drilling liquid, as it was been confirmed in industrial practice [ll]. This fact is important from the environmental point of view. Because the works described above are the human interference to the environment, they must be effective. It means that the best material should be used for cementing works. Alkali activated slag pastes guarantee the high effectiveness of cementation.

849

4. REFERENCES 1 2

3 4 5 6 7 8

9

10

11 12

13

J. Bernsted, World Cement, 2 (1987). W.G. bielikov, A.T. Bulatov, R.F. Uhanov, Promyvka priburienii i kreplenii i cemientirowaniju, Moskva 1974. S. Stryczek, Criteria of selection technical parameters of the monoportland cement pastes for the sealing of absorptive zones in the rock mass through bore-holes, Wiertmictwo, Nafta, Gaz, Krakbw, 12 1993 (in polish). W. Brylicki, J. Malolepszy, S. Stryczek, 9th I.C.C.C., New Dehli, VoI.111, (1992) 312. Polish patent NO285 071, Paste for bore holes sealing and cut off walls construction. W.D. Gluchovski, Gruntosilikatni virobi i konstrukcji, Budivitnik, Kiev, 1967. J. Malolepszy , Hydration and properties of alkali activated slag cementitious materials, Zeszyty Naukowe AGH, Ceramika, 53, 1989 (in polish). J. Deja, J. Malolepszy, 3rd Int. Conf. on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Trondheim, Vol.11, (1989) 1547. J. Dziewahski, W. Brylicki, A. Gonet, S. Stryczek, Z. Olszamowski, Utilization of alkali Activated Slag Cement For Antifiltration Screens in Hydrotechnics, Proc. 4th Int. Symp. On the Reclamation Treatment And Utilization Of Coal Mining Wastes, Krakbw, Vol.11 1993, 41 (in polish). A. Gonet, S. Stryczek, W. Brylicki, J. Malolepszy, Liquidation blow out deposit water for example the Mine of Sulphur "Jeziorko", Proc. Int. Conf., Krakow, 1992, 41 (in polish). S. Stryczek, W. Brylicki , J. Balasz, J. Sztorc, Practical aspects of the utilization of new, alkali activated slag materials assailing agent in drilling operations, Oil Industry Prospect - Year 2000, Tripoli, Libya, 1992, 590. W. Brylicki, S. Stryczek, J. Malolepszy, Properties And Use of alkali activated Slag Paste, Proc. 4th Int. Symp. On the Reclamation Treatment And Utilization Of Cool Mining Wastes, Krakbw, Vol.11, 1993, 925. D. Breck, Zeolites Molecular Sieves, New York (1974)


Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, HA. van der SIoot and Th.G. Aalbers (Editors) 91W4 Elsevier Science B. V. All rights reserved.

85 1

THE USE OF MSWl BOlTOM ASH IN ASPHALT CONCRETE. M.M.Th. Eymael', W. de Wijs', D. Mahaded

' Feniks Recyclingmaatschappij B.V., P.O.Box 9265, 1800 GG Alkmaar, The Netherlands * Hoogovens Technical Services E&E, P.O. Box 10.000, 1970 CA idmuiden, The Netherlands ABSTRACT Municipal Solid Waste Incinerator (MSWI) bottom ash has been used by Feniks Recyclingmaatschappij (Feniks) as a mineral aggregate in asphalt concrete for more than five years. Several projects with asphalt concrete containing MSWl bottom ash have been carried out. In the year 1991 Feniks started a research program which included laborato tests and two pilot projects. This research program was guided by a CUR/CROW research committee. The objective was to find out whether it is possible to produce and apply asphalt concrete with MSWl bottom ash that meets the normal requirements for stability and durability. Problems were expected due to the moisture and filler content in the MSWl bottom ash. The pilot projects with asphalt concrete containing MSWl bottom ash provided the opportunity to learn more about the behaviour of this asphalt concrete during production and paving.

Y

1. INTRODUCTION

The annual amount of MSWl bottom ash produced in The Netherlands is about 700,000 tonnes. It is expected that this amount will strongly increase in the next

tonnes. The major part of the MSWl bottom ash will be used in decade to 1,500,000 large scale land fill projects and in road and railway embankments. However, an increasing amount might be used in cement treated base courses and in asphalt concrete if the products containing MSWl bottom ash can meet the requirements for leachate and mechanical properties. In this paper the results of a research program towards the use of MSWl bottom ash in asphalt concrete will be discussed. The research was carried out as a part of a more comprehensive research program "Application of MSWl bottom ash in cement treated base course and in asphalt concrete" which was initiated by Feniks Recyclingmaatschappij (Feniks) in 1990 and was guided by the 657 CUR/CROW committee. history In the early seventies in the USA some reports were published dealing with the application of MSWl bottom ash in bituminous base courses (asphalt concrete). The

'

CUR: Centre for Civil Engineering Research and Codes CROW: Centre for Research and Contract Standardisation in Civil and Traffic Engineering

852

experiences with the asphalt concrete containing MSWl bottom ash were quite good but it never became a standard application due to the availability of cheap new aggregates all over the country. There was also no reason for searching new applications for MSWl bottom ash as it was easy and cheap to bring the MSWl bottom ash to waste disposals. In The Netherlands there was not so much space and the costs of waste disposal were already rising in the early eighties, so it became interesting to search for new applications. Some projects with asphalt containing MSWl bottom ash were carried out in the late eighties [2]. Feniks has been studying the possibilities of using MSWl bottom ash in asphalt concrete extensively since 1988 and carried out laboratory tests and pilot projects. The annual production of asphalt concrete in The Netherlands is about

6,000,000tonnes. To produce these 6,000,000 tonnes about 1,500,000 tonnes of old asphalt is used. So, in The Netherlands new asphalt concrete contains on the average about 25 % of recycled material and this percentage will increase in the next decade to a practical maximum of about 35 %. It is not dutch policy to exchange the old asphalt in new asphalt concrete by MSWl bottom ash, but Feniks believes that there might be a role for MSWl bottom ash. 2. RESEARCH PROGRAM

obiectives The main objective of the research program was to find out whether it is possible to use MSWl bottom ash as a mineral aggregate in asphalt concrete for base and binder courses. The aim is to add as much MSWl bottom ash to the asphalt concrete as is theoretically and practically possible. The research program consisted of: - literature research; - environmental research to determine the chemical composition and the leachate of MSWl bottom ash and asphalt concrete containing MSWl bottom ash; - laboratory tests to determine the mechanical properties of MSWl bottom ash and asphalt concrete containing MSWl bottom ash; - pilot projects with asphalt containing MSWl bottom ash. This paper deals with the results of the research program and the experience with the pilot projects. Presented is also a technology to improve the environmental properties of the MSWl bottom ash by processing it. With this technology the MSWl bottom ash can be treated and will become a kind of mineral aggregate that can be used in asphalt concrete. pilot DrOf all Pilot projects with asphalt concrete containing MSWl bottom ash, two will be discussed as the results were used in the research program. The first pilot project was carried out in Enkhuizen (1991) and the second in Rotterdam (1993).

853

In Enkhuizen a parking area of 3500 m2 for trucks has been paved by order of a private company. In the asphalt concrete for the base course 50 % (by weight) of the mineral aggregate has been substituted by MSWl bottom ash. On this base course a surface course of normal dense asphalt concrete was applied. In Rotterdam an area of 5000 rn2 for handling contaminated soil was constructed using a pavement consisting of two layers of asphalt concrete containing 25 % (by weight) of MSWl bottom ash: 70 mm asphalt concrete base course and 50 mm asphalt concrete wearing course. In both pilot projects the asphalt layers were put on a base course of cement treated MSWI bottom ash.

3. PROPERTIES OF MSWl BOlTOM ASH general MSWI bottom ash is the solid residual result of the incineration of domestic waste and similar light industrial waste, without fly ash. MSWI bottom ash should meet standard requirements in The Netherlands. When the MSWI residue leaves the incinerator and has been cooled down, it is sieved on a 40 mm sieve and deironed. After this treatment the MSWl bottom ash is stored for a period of at least 6 weeks before it may be used in landfill or other applications. During this storage period several chemical and microbiological processes take place resulting in an increase of the environmental properties of the MSWl bottom ash. MSWl bottom ash is a continuously graded mixture containing filler, sand and gravel. The biggest particles are about 20 mm and about 8 % is smaller than 0.063 mm (filler). The filler can absorb a relatively high amount of asphalt binder and the sand-fraction is relatively coarse.

The unit weight of MSWl bottom ash is lower than the unit weight of conventional mineral aggregate, due to the properties of the particles and the porosity of the coarse aggregate. This has to be taken into account on designing a recipe for asphalt concrete containing MSWl bottom ash. Theoretically, an asphalt mix design is based on a volumetric composition using the particle size distribution of the mineral components. However, usually asphalt mixes are designed by weight composition of the mineral components. This does not give problems when homogeneous aggregates with a constant and known unit weight are applied. So, on using MSWl bottom ash the specific mass of all components to be used in the asphalt mix must be determined. The standard method to determine the specific mass of mineral aggregate 'Pycnometer test' could not be used for MSWl bottom ash because the porosity of the MSWl bottom ash is very high. Asphalt binder can not penetrate the small voids in the mineral aggregate so the water in the pycnometer is exchanged for oil. The

854 viscosRy of the utilized oil at 25 "C is the same as the viscosity of asphalt binder at 150 "C. Having determined the specific mass by using this method, it is possible to calculate the amount of voids in the aggregate and the amount of voids in the asphalt mix to be designed. In table 1 the specific mass of the components in MSWl bottom ash is listed. Table 1. Specific mass of MSWl bottom ash. Size of aggregate

Density In water [ks/m31

in oil

[ks/m31

Difference in Air Void

[%I

8-40

2321

2334

4-8

2349

2264

3.6

2-4

2302

2167

5.9

63 pm 2 mm

2483

2377

4.3

0-63m

2449

2246

8.3

-

The pycnometer is filled with water or with oil. The viscosity of the utilized oil (at 25 as the Viscosity of bitumen sO/lOO at 150 "C.

"C)is the same

chemical comDosition The average chemical composition of the MSWl bottom ash is given in table 2. Most of the elements are present as an oxide or as a hydroxide. On the other hand, also metal salts, chlorides, sulphates and carbonates are available within the MSWl bottom ash. Iron, aluminium and zinc, but also some other non-ferrous metals may be present as a metallic. The MSWl bottom ash is being formed at a relatively high temperature and thereafter quenched in water. Consequently, the MSWl bottom ash is not stable and during storage several reactions will take place. Due to these reactions the chemical composition of the MSWl bottom ash will change, pH will decrease to 9 -10 and the temperature can rise to 60 - 70 "C. The chemical composition and leachate of six weeks old MSWl bottom ash have to meet requirements to get a certificate. However, also MSWl bottom ash with a certificate may only be applied under certain conditions in landfills or in road and railway embankments. The MSWl bottom as must remain at least 0.50 m above the highest groundwater level and must be covered with an impermeable layer, which must be inspected regularly. Also the environmental quality of the groundwater must be monitored.

855

4. ASPHALT CONCRETE MIX-DESIGN

general The requirements for dutch asphalt concrete are specified in the standard requirements “De Standaard 1990”[3].All standard asphalt concrete mixes contain asphalt binder (bitumen), ground particles of limestone and mineral aggregate. The mineral aggregate consists of fine (sand) and coarse (gravel or stone) aggregate. The standard requirements specify the composition and the mechanical properties such as Marshall stability, Marshall flow and durability. MSWl bottom ash can replace a portion of the filler and the mineral aggregate (sand and stone). The particle size distribution, the density and the void content of the MSWl bottom ash were determined. It appeared by calculating that the amount of MSWI bottom ash in asphalt concrete mixtures can reach a maximum of 65 % by weight. Practically the amount of MSWl bottom ash will be lower than 65 %. The maximum amount has to be estimated during production. Table 2. Marshall properties of asphalt concrete containing MSWl bottom ash.

I

As~haltconcrete for base course 125% MSWl bottom ash)

I

856

laboratoy tests In the laboratory a number of samples asphalt concrete containing up to 65 % MSWl bottom ash was made and the mechanical properties (Marshall) of the samples were determined. Also samples with 50 and 25 % MSWl bottom ash were investigated. The use of MSWl bottom ash in asphalt concrete has a good impact on the Marshall stability while the Marshall flow decreases. So asphalt concrete containing MSWl bottom ash has a high Marshall quotient, which is a parameter for the material's resistance to permanent deformation. The durability of asphalt concrete with MSWl bottom ash is determined with the retained Marshall test. The decrease of the Marshall stability after immersing in water of 60 "C during 48 hours is comparable to conventional asphalt (table 2). The amount of filler in the MSWl bottom ash is about 8 % and exceeds the specific maximum for filler in mineral aggregate. The amount of natural filler from the aggregate in the asphalt concrete is also too high. However, asphalt concrete mixtures with MSWl bottom ash meet most of the dutch requirements for asphalt concrete. The mechanical properties of asphalt concrete containing MSWl bottom ash are as good as the properties of new asphalt concrete. Table 3. Retained Marshall stability of asphalt concrete with 25 % MSWl bottom ash. Asphalt base course Immersing time

Stability

Asphalt wearing course

Retained

Stability

Retained

10,962

N

t=O

9,565

N

t = 24 hours

8,636

N

90 %

10,910

N

99%

t = 48 hours

8,278

N

86%

10,440

N

95%

The Marshall Stability of the asphalt concrete with 25 % MSWl bottom ash is measured at 60°C.

environmental research The leaching behaviour of asphalt containing MSWl bottom ash was investigated by an environmental laboratory. Marshall tablets were tested by the diffusiontest (Standtest NVN 5432). Two mixtures of asphalt concrete containing MSWl bottom ash with different asphalt binder content were tested (asphalt binder content 6.0 % and 6.5 %) and the results were compared with the results of tests on a reference asphalt concrete without MSWl bottom ash. The composition of the tested asphalt concrete mixtures are presented in table 4.

857

Table 4. Composition of the asphalt concrete mixes for environmental tests.

After analyzing the chemical composition of all components the concentrations of elements in asphalt concrete containing MSWl bottom ash were calculated and are summarized in table 5. The contribution of asphalt binder (bitumen), limestone filler, sand and gravel to the metal content in the asphalt concrete is, except for the metal Chromium (Cr), of no significance in relation to the contribution of MSWl bottom ash. Table 5. Environmental properties of asphalt concrete with and without MSWl bottom ash. Element

Na

Concentration Asphalt with bottom ash in m g / h

I

I

284

Bottom ash

Reference 5.5% bit.

I

0.66*103

Bottom ash 6.5% bit.

6.0% bit.

I

4.0*103

I

3.5*103

4 A10; -> 6 H,

+ 8 H,O + + 12 OH

-> 4 A10;

+

12 e

6H,

The above reactions can only take place if water and OH- ions are present near aluminium particles. Another reaction, which is also likely to take place instead of the reduction of water, is the reduction of iron. Investigations in this field have proved that expansions are often found near iron particles. The aluminate ions can diffuse through the MSWI bottom ash. The amount of diffusion will depend on the moisture content in the bottom ash and on the period of time in which diffusion can take place. The aluminate ions will convert to aluminium hydroxide if the alkalinity of the ash decreases to a pH lower than 9 - 10. Aluminium hydroxide is not mobile in the bottom ash. This reaction can be described as follows: A10;

+

2H,O

-> Al(OH),

+

OH

The conversion of aluminium into aluminium hydroxide gives rise to an increases of volume of about 3 . 2 .

2.4. Testing programme The investigation has been focused on the reaction of non-ferrous metallics under alkaline conditions. The effect of the following parameters on the expansion were investigated in this research programme: the incineration plant from which the MSWI bottom ash originated; the composition of the cement mixture; the kind of cement used; the conditions during storage of the ash. Several kinds of proctor testing cylinders were produced to determine the effect of these parameters on the development of expansions. Eight series of 9 cylinders were made and kept under different circumstances. The 72 cylinders were produced as follows: 4 different MSWI

868

*

bottom ash >t 2 kinds of cement * 3 storage conditions 3 cylinders per series. In Table 2 more details are given on the various parameters. Furthermore, 20 cylinders were made with Portland cement B and Spanish cement. Table 2. Different parameters which were investigated Parameter

Levels

origin of MSWI bottom ash

incineration incineration incineration incineration

kind of cement

Portland cement A Blast furnace cement A

storage conditions

under water, 25 O C wet/dry cycles, 25 O C in air, relative humidity 70 % , 25 O C

-

plant plant plant plant

Alkmaar Amsterdam-Noord Roteb Rotterdam Rijnmond

The samples of the MSWI bottom ash were taken in accordance with quality control systems. The composition of the cylinders (as to the amount of cement, MSWI bottom ash and sand) was kept constant: 80 X MSWI bottom ash, 20 % sand and - on the basis of 100 % aggregate - 3 X cement. The proctor cylinders were prepared by compacting the mixture in a PVC cylinder with a serrated edge. The formation o f expansion followed by measuring the circumference.

3 . RESULTS 92 testing cylinders were produced to investigate the effect of three parameters on the expansions in cement-treated base courses. The development of expansion was followed by measuring the circumference of the cylinders. After 72 days, the circumference and the compression strength of the cylinders was measured and the materials were visually evaluated. After 259 days, the circumference was measured a second time. The results of this test programme are given in Appendix 1. An expansion is shown in Figure 1.

869

Figure 1. Testing samples with expansion To understand the effect of the parameters on the expansion of the cylinders, a statistical analysis was carried out on the results. The analysis clearly showed that o n l y the conditions under which the cylinders had been kept during the testing period had a significant effect on the expansion. The largest expansion was found for cylinders which have been kept in air with a relative humidity of about 70 % . After the test programme (259 days), some additional tests were carried out :

-

-

some of the cylinders that were given wet/dry cycles during 259 days, were brought in air; some of the cylinders that were kept in air for 259 days, were given wet/dry cycles; several of the other cylinders were kept under the same conditions as during the first 259 days.

It appeared that the proctor cylinders reacted on the changing testing conditions:

-

-

more expansion increase than found in the first 259 days, could be found for cylinders which were given a wet/dry cycles for 259 days and then, afterwards, kept in air; less expansion increase than before, was measured for cylinders kept in air for 259 days and, thereafter, were given wet/dry cycles; the cylinders having the same conditions after 259 days as before this time, showed an continuous increase in the amount of expansion,

870 The proctor testing specimen, in which no expansion could be measured, contained a lot of humidity and seemed to consist of relatively small particles of MSWI bottom ash.

4.

DISCUSSION

On the basis of the data gained in this research programme, a theory has been formulated. This theory tries to explain the formation of expansions in cement-treated base courses. As well as on the data, the theory is based on literature and on experiences from asphalt pavements which are already used at the moment. The theory has to be verified in an additional research programme. Background information has been given in Chapter 2.

4.1. Theory bottom ash

regarding

the

formation of

expansion

in MSWI

Aluminium will be oxidised in (cement-bound) MSWI bottom ash resulting in the formation of soluble aluminate ions. The aluminate will diffuse only a little if the moisture content in the base course is low. Therefore, the concentration of aluminate could be high near aluminium particles. After some time, the pH of the (cement-bound) ash will decrease, if carbonation is taking place. Aluminate will be converted into aluminium hydroxide under the changing conditions. This will result in an increase in volume. The increase in volume causes unevenness in the asphalt pavements if the aluminate ions are concentrated around an aluminium particle. If enough diffusion of the aluminate has taken place (because of a high moisture content), the increase of volume can be absorbed by the CTBC. Expansions can be seen in MSWI bottom ash in depot as well as in cementtreated MSWI bottom ash:

MSWI bottom ash in depot From experience it is known that expansions in depots are found mainly in the ash on the outside of the depot. At this place, more carbonation will occur and therefore, the pH of the ash decreases. This will result in the conversion of aluminate into aluminium hydroxide causing an increase in volume. It is expected that the dispersion of the aluminate is low as the moisture content in the ash will be relatively low: the high temperature in the ash (see above) will cause the evaporation of water (only near the surface). Cement treated MSWI bottom ash Also cement-treated MSWI bottom ash may have a low water content, The water is used during the hydratation of the cement. Furthermore, the base course layer is generally covered quickly to prevent leaching of elements. Consequently, the dispersion of aluminate ions will be small and expansion of the ash will be significant. The expansion will take place at the time the pH has reached the

87 1 critical value, because aluminate is then converted into aluminium hydroxide. The critical pH value will be reached if the free lime from the cement has been carbonated or has been bound in another way. This theory gives an explanation for the results of the experiments described in Section 3 . Test samples which were kept under a relative humidity of 70 % , show significantly more expansion than cylinders which were kept under water. In the cylinders which were kept under water, the diffusion of the aluminate ions will be high as a lot of water is present. In that case, the expansion of the ions can be absorbed by the cement matrix and expansion cannot be seen on the surface. The other cylinders (at r.h. of 70 %) will have a smaller amount of dispersion and therefore expansion is found. In addition to this, it is expected that carbonation within cylinders (and so the decrease of pH) is faster under a relative humidity of 70 % than when kept under water, as more air is present. If this theory is correct, the content of metallic aluminium in the MSWI bottom ash, the pH and the humidity are the most important parameters that determine the occurrence of expansions.

5.

GUIDELINES TO PREVENT EXPANSION

Based on the theory discussed in Chapter 4 , one may conclude that expansion will mainly occur near aluminium particles and if iron particles are available as well, the expansion will be more likely to happen. Furthermore, the development of expansions is dependent on the circumstances in which the ash is stored. Therefore, guidelines to prevent expansions can be divided into guidelines which are aimed at the removal of the causes of expansion and guidelines which are aimed at the realisation of conditions under which expansion can not occur. Both kind of guidelines are given hereafter.

5.1. Quality of the MSWI bottom ash MSWI ash from which the non-ferrous metals have been removed, will not expand, because the expansion is mainly caused by aluminium particles. At the moment, separation o f non-ferrous metals in MSWI bottom ash is practically possible for particles larger than about 10 nun. With this, the possibility of expansions resulting in unevenness will be reduced. However, non-ferrous particles smaller than 10 nun can still give rise to significant expansions. The amount of digestible material in the ash is another characteristic of the ash which can affect the formation of expansions, for a low pH o f the ash (as an effect of a large amount of digestible materials), increases the probability of the formation of unevenness in the asphalt. To sum up, if ash is used containing only a small amount of digestibles (1 - 2 %) and in which non-ferrous particles are removed as much as possible, the chance of the development of expansions is reduced. The aluminium particles should be removed before the bottom ash is stored to mature.

872 5.2. Conditions during storage of the MSWI bottom ash In the previous section it is concluded that small particles (< 10 mm) of non-ferrous metals have to be expected in the ash which can cause expansion. Perhaps, it will be possible to control the circumstances in the depot of the ash in such a way that the chance of expansion is reduced. This could be effected if the aluminium is converted into aluminate during storage: the aluminate will be distributed with the cement during the construction of the base course layer and consequently small expansions can be absorbed by the matrix. The conversion from aluminium into aluminate will be most successful under the following conditions:

-

the initial pH of the bottom ash in high; the pH of the bottom ash in the depot is kept high; a relatively long storage time will enlarge the dispersion of the aluminate in the ash (more time available for diffusion); the relative humidity must be high, as this will give a more rapid diffusion (and therefore a greater dispersion); remove aluminium particles as much as possible before storage. The best way to keep the pH of the ash high (pH > 11) is to start with ash containing a small amount of digestible material. If this is not sufficient, lime can be added to the ash. Furthermore, the contact with air must be avoided as much as possible, as carbonation gives a decrease in the pH. A s a result, the depot has to be large. A s has been explained before, the humidity is another parameter which might influence the formation of expansions. The humidity in the depot can be kept high by sprinkling the bottom ash. However, it must be kept in mind that the percolation water may contain some hazardous materials.

5.3. Conditions in the base course layer The conditions in the base course layer can be focused on prevention of the formation of aluminium hydroxide. The best conditions to prevent the formation of aluminium hydroxide are: low initial pH in the base course layer containing the ash; a rapid decrease of the pH in the base course layer. A low initial pH in the base course layer results in a slower conversion of aluminium into aluminate ions. The concentration of OH- ions is too low for a fast conversion. To reach a low initial pH, the amount of cement has to be as low as possible. Furthermore, the use o f Blast Furnace cement is preferable compared with Portland cement, as the initial pH o f Blast Furnace cement is lower. A quick reduction of the pH will give a rapid formation of aluminium hydroxide. This will result in less conversion of aluminium into other structures as the aluminium hydroxide may give a layer around an aluminium particle that can prevent further oxidation. However, it is not sure that the conversion of aluminium will indeed stop after a reduction in the pH. Therefore, another option, to prevent the unevenness in asphalt is t o create conditions in the base course layer in which all the aluminium is converted and dispersed through the base course before the pH has been reduced below the critical value. This will

873 give less local expansions. The best conditions in this situation are probably: a high initial pH in the base course layer containing bottom ash; a high humidity in the MSWI bottom ash; the pH of the base course must be reduced after all the aluminium has been converted into aluminate. A high initial pH in the base course results in a fast conversion of the aluminium in aluminate as a high proportion of OH^ ions is available. A high pH can be reached by the addition of a relatively large amount of Portland cement (see above). If the pH reduces slowly, the dispersion of the aluminate will be high if sufficient moisture is available. A high amount of cement will give a long period of time before the critical pH is reached. If the base course layer is covered directly with bitumen after construction, the humidity in the base course will remain relatively high. However, this can give less bond between the base course and the covering asphalt layers. Furthermore, fast construction of the base course layer is also desirable, because the contact with carbondioxide (resulting in carbonation) will be small.

6. CONCLUSIONS The results of the research programme clearly demonstrate that the conditions of the cement-treated base courses containing MSWI bottom ash, have a significant effect on the formation of expansions in this kind of base course layer. Furthermore, it was found that the o r i g i n of MSWI bottom ash and the k i n d of cement used seem to have a less significant role in the development of the expansions. On the basis of this information as well as literature data and experiences from asphalt pavements with MSWI bottom ash which are already used nowadays, a theory on the formation of unevenness has been formulated. If this theory is correct, a few guidelines to prevent the formation of expansions can be given.

*

*

The amount of aluminium in the bottom ash; The local expansions are caused by metallic aluminium and therefore the number and size of the particles of metallic aluminium in the MSWI bottom ash will have a large effect on the possibility of expansion in the base course. The moisture content of the CTBC material; The research has made clear that expansion will occur when the base course is relatively dry. This can be explained as follows. Water can give rise to a faster diffusion of the ions in the material. If the ions are dispersed in the bottom ash, the expansion can be absorbed by the CTBC.

874 >k

*

*

The period of storage of the MSWI bottom ash in the depot; During the period of storage in the depot, the aluminium-ions can be dispersed through the bottom ash. Again, this will lead to a better dispersion o f the ions and therefore will give less local expansions. Consequently, this will lead to less expansion in the CTBC . The cement content; In base course material with a high amount of cement, the pH will decrease more slowly than in a material with a relatively low cement content. A slow decrease o f pH in the cement-treated material is desirable because more time is available for the ions to diffuse through the bottom ash. A s explained above, this will reduce the chance of expansion of the base course. The digestible material content. If the digestible material content in the MSWI bottom ash is low, a slow decrease o f pH of the material is found, resulting in a slower conversion of aluminium into aluminate and consequently in less local expansion of the CTBC.

In a future research programme attention will be given to the validation the described theory and to the development of a quick testing procedure to determine whether bottom ash will expand. of

8.

REFERENCES

1

Notice of Ing. P. Leenders, Veabrin, The Netherlands

2

J . Hartlen, Incineration ash utilization in some countries Europe, Proc. Ash I - Conference, Philadelphia (1988)

3

Zwellen van AVI-slakken. Tussenrapportage van CUR-studiecommissie B57, Feniks Recycling Maatschappij B.V., Alkmaar, report T&A 91/009/n/5, (1991)

4

Dip1.-Ing. G . Kluge, Prof. Dr. H. Saalfeld, Dr. W. Dannecker, Untersuchungen des Langzeitverhaltens von Mullverbrennungsschlacken beim Einzatz im Strassenbau, Texte Umwelt Bundes Amt.

5

NOH-report, Veabrin kwaliteitscontole van AVI slakken 1987-1988, T A W rapport RAP-305/JJS/avd, Deventer, (1988)

in

7.

APPENDIX

Rijnmond

Table 1 Increase of circumference

BF-A

w/d/ cycles = wet/dry cycle r.h. = relative humidity

BF-A = Blast Furnace cement A PL-A = Portland cement A

PL-B = Portland cement B Sp.A = Spanisch cement A

Compression strength

Characterisation of sample

Compression strength after 12 weeks Investigated on 1 sample per section Disposal condition

Cement

yield strenth

yield stress [N/mn’l

“1 under water

BF-A F

I w/d PL-A

BF-A

PL-A

BF-A

PL-A

16.500

Sp.A

I

Expansions near iron particle

1.75

No expansion, strong nucleus

under water

11.200

1.49

No expansion, Strong nucleus

w/d

13.200

1.75

cvcle

I

70 X

9.800

I

1.30

Cristallisation near iron Darticle

I Large

expansions

near iron particle

1.59

Small expansions

14.000

1.86

A1 particle with small expansions

18.900

2.51

Small expansions near iron particle

under water

21.600

2.87

Small expansions

w/d cycle

23.100

3.06

No expansions

r . h . 70 X

22,200

2.94

No expansions

under water

12,800

1.70

Small expansions near iron particle

w/d cycle

16.800

2.23

No expansions

r . h . 70 I

14.100

1.87

No expansions

under water

7.000

0.93

No expansions or compression strength

w/d cycle

8,100

1.07

Small expansions, no Compression strength

r . h . 70 1

7.000

0.93

No expansions, a lot of iron, no compression strength

under Water

12,000

w/d cycle r.h. 70 X

under water

17.100

15.600

2.27

I

2.07

No exDansions

I Smalle

expansions

near iron particle

r . h . 70 I

18.600

2.47

No expansions, a lot of iron

under water

23.400

3.10

Small expansions

w/d c v c l e

26.000

3.45

No exDansions

2.92

I No exDansinns

3.34

No expansions

I r.h. PL-A

2.19

13.200

I w/d c v c l e I BF-A

No expansions

1.51

I

r.h. 70 Z

I r.h. PL-B

11.400

I

cycle

Visual aspects

1

70 X

22.000

under water

25.200

I

w/d cycle

13.500

1.79

Very small expansions

r.h. 70 I

20,000

2.65

No exmnsions

under water

29.200

3.87

No expansions

8.900

2.51

Small expansions

21.300

2.83

Small exoansians near iron oarticle

w/d cycle r.h. 70 w/d/ cycles = wet/dry cycle r.h. = relative humidity

%

BF-A

=

PL-A

=

Blast Furnace cement A Portland cement A

PL-8 = Portland cement B Sp.A = Spanisch cement A

Environmental Aspects of Constnrction with Waste Materials J1J.M. Goumans, H A . van der SIwt and Th.G.Aalbers (Editors) 61994 Elsevier Science B.V AN rights resewed.

811

Microstructure of concretes containing artificial and recycled aggregates J.A. Larbi and P.D. Steijaert

TNO Building and Construction Research, Department of Building Technology, P.O. Box 49, 2600 AA Delft, The Netherlands

Abstract The microstructure of concrete specimens containing various artificial aggregates have been characterized by means of polarizing and fluorescent microscopy (PFM) and scanning electron microscopy (SEM). The artificial aggregates in question were Lytag, Aardelite, Liapor, incinerator-source slag, recycled masonry and recycled concrete. The concrete specimens examined had prior to this study been subjected to carbonation tests for various periods of time ranging from 2 to 5 years. Of specific importance to the study were the pattern of carbonation in the concrete specimens, the capillary porosity and homogeneity of the cement paste, the intensity and distribution of microcracks, and the characteristics of the cement pasteaggregate interfacial zone. Results of the fluorescent thin section analyses revealed that the use of specific sizes of certain types of these artificial aggregates tend to influence the pattern of carbonation of the concrete. With the exception of a few distinct features associated with the concretes studied, their microstructural characteristics are in general comparable with concretes containing conventional natural aggregates. These distinct features and characteristics have been presented in this article with photomicrographic illustrations. 1 INTRODUCTION

The use of artificial aggregates, mostly specially processed lightweight aggregates and secondary (recycled) aggregates is gradually increasing not only for economic reasons but also for practical purposes. In the Netherlands, for instance, environmental constraints on exploitation of good quality river aggregates and the high costs of importation of alternative natural aggregates outside the country have necessitated the use of artificial or recycled aggregates for preparing concrete. Although there is a growing interest and need for use of these materials in concrete, not very much is known about the internal structure of these materials and the microstructural characteristics of concretes prepared with these aggregates. It is generally known that the microstructure of concrete plays an important role with regard to the performance of concrete [ 11. The characteristics of the paste-aggregate interfacial zone which determines the type of bonding between the cement paste and the aggregate particles and the structure of the external layer, a few centimetres from the surface are known to influence the strength and the durability concrete [2,3]. With regard to concrete prepared with artificial aggregates, information about the microstructure is not only useful for predicting the performance of such concretes but is also important for optimising the use of such materials in concrete in order to enhance the quality and performance of the concrete. Concrete microscopy, which is based on the study of thin sections of concrete specimens by

878 means of polarizing and fluorescent microscopy (sometimes supported with scanning electron microscopy) has been found to be one of the most useful techniques for acquiring such information. It enables on the one hand information regarding the mineralogical omposition of the materials used to be determined and on the other hand the porosity and microstructure of the concrete to be characterized without disturbing the integrity of the concrete. The aim of this study was to characterize the microstructure of some concretes prepared with artificial or recycled aggregates (used as coarse aggregate) as a way of providing more insight into the behaviour of these alternative aggregates in concrete. Three microscopic techniques, including stereo-microscopy, polarizing and fluorescent microscopy (PFM) and scanning electron microscopy (SEM) were used for this investigation. 2 MATERIALS AND METHOD OF INVESTIGATION 2.1 Materials

In all, six concrete specimens each containing one artificial or recycled aggregate material were examined in this investigation. The artificial aggregate materials included a Liapor (expanded shale), Lytag (a sintered fly ash), Aardelite (an artificially-processed fly ash-lime composite), incinerator-source slag (AVI-slag), recycled masonry and recycled concrete. In all cases the fine aggregate used was river sand. All the concrete specimens used had, prior to this investigation been subjected to carbonation in two climate conditioned rooms of either 20"C, 50% relative humidity (RH) or 20"C, 65% RH. Each of the specimens had before the carbonation test been cured in a fog room for 28 days. The composition and some properties of the concrete specimens used have been presented in Table 1 .

2.2 Methods of investigation A preliminary investigation involving examination of fractured surfaces of the specimens with the aid of a stereo-microscope was performed. The cement paste was found to be well bonded to the aggregate particles. There were no cases of detachment of the cement paste from the these particles. Further, a zone measuring approximately 50-200 pm wide, with a distinct brown colour was found bordering some of Lytag, Aardelite and in the case of Liapor, all the particles as an outermost layer or 'skin'. The microstructure and composition of this layer have been given in Section 3. The stereo-micrographs of Figures 1 and 2 for the Liapor and Lytag specimens reveal some of these features. For the PFM analysis, small blocks of the concrete specimens, each measuring approximately 50x30~15mm3 were sawn from each of the samples listed in Table 1 . After sawing, the blocks were glued to an object glass and vacuum-impregnated at approximately 40°C with an epoxy resin containing a fluorescent dye. The impregnated specimens were then left at room temperature overnight which allowed the resin to harden. Following this, one thin section was prepared from each of the blocks for the PFM analysis. Each thin section had an approximate thickness of 30 pm. Preparation of thin sections in this manner enables the specimens to be examined by means of both polarizing and fluorescent microscopy. The latter technique is especially useful in studying the microstructure (capillary porosity and microcracks) of the specimens. For the SEM-EDAX analysis, small samples of the specimens concerned were first dried under vacuum at a temperature of about 35°C overnight. They were then coated with a very thin layer of gold, mounted onto metal stubs and examined with a Philips 515 Scanning Electron Microscope (SEM). The SEM used was equipped with an Energy Dispersive X-ray Analyzer (EDAX). The investigation was performed on fractured surfaces of the specimens.

879

Figure 1. Stereo-micrograph showing an overview of the Liapor specimen - a Liapor particle

Figure 2 . Stereo-micrograph showing an overview of the Liapor specimen - a Liapor particle

880 Table 1 Composition of mix and some properties of the concrete specimens used in the investigation. Composition and properties

Aardelite

1 1 1 Liapor

i l l -

1

Crushed masonry

Crushed concrete

Artificial aggregate

50

Cement type

BFSC

~~

Cement (kg/m3)

pr

Silica fume (% m/m) Superplasticizer Melment (% m/m of cement)

320

375

I0.7

Water absorption after 30 minutes

9.1

Water absorption after 24 hours

11.5

Water-cement ratio (total) Water-cement ratio (effective)

0.48

10.8

-

14.3

0.66

0.57

0.58

0.59

0.3 1

0.5 1

0.50

Bulk density (kg/m3)

1975

2050

1780

2247

2155

Air content (%)

3.5

1.1

3.0

2.1

3.7

28-day compressive strength

58

Room condition for the carbonation test (“C, %R.H.)

20; 50

0.55

0.40

> 20; 65

20; 50

20; 50

20; 50

3.2

20; 50

This cement is the similar to OPC except that the particles are finer in size than those of OPC. (2) Blast furnace slag cement containing about 70 % by mass of cement as slag. (1)

3 RESULTS AND DISCUSSION 3.1 Internal structure of the aggregate particles Figures 3 and 4 are SEM micrographs showing the internal structure of particles of Liapor and Lytag respectively in the concrete specimens examined. It is clear from these micrographs that both the Liapor and Lytag particles have a porous internal structure. This applies also to

88 1 the Aardelite and most of the AVI-slag particles as shown in the PFM micrographs of Figures 5 and 6 but does not apply to the specimens containing the recycled aggregates. For the latter aggregates, the internal structure was found to be very much dependent on the type of masonry or concrete used. Remarkable features found about the recycled concrete particles were that they contained many microcracks and very often completely carbonated. These features apply especially to the concrete aggregate particles obtained from blast furnace slag cement concrete. Most of the pores have an irregular structure with only a few being interconnected with each other (see also Figures 1 and 2).

Figure 3. SEM micrograph of a fractured surface of the Liapor specimen showing the internal structure of the Liapor particle.

Figure 4.SEM micrograph of a fractured surface of the Lytag specimen showing the internal structure of a Lytag particle.

882

3.2 Microstructure of the cement paste The cement paste of all the concrete specimens was found to have a heterogeneous structure (variation in capillary porosity). This heterogeneity is believed to be related to the size and microstructure of the surface layer of the various porous aggregate particles. The structure of the pores of the outermost surface of the aggregate particles (whether open or closed and if open, to what depth) will control the rate and degree of sorption of fluid from the concrete when the latter is in the plastic stage. The hypothesis is that larger particles with open pores at the surface which are interconnected deeper into the aggregate particle are likely to absorb a lot more materials from the fluid phase of the concrete and at a faster rate (if not saturated prior to mixing) than similar particles but with closed pores [4-61. This process will tend to draw very fine particles of the cement together with the pore fluid into the aggregate particle. Larger grains will accumulate at the surface of the particle and hydrate which in the long run will cause a gradient in capillary porosity from the aggragte surface into the bulk of the cement paste.

Figure 5. Thin section (PFM) micrograph showing the internal structure of an Aardelite aggregate particle (plane polarized light; micrograph = 2.7 x 1.8 mm2). One remarkable feature about the specimens examined was that the density (microcracks/mm2) and distribution of microcracks in concretes containing these artificial aggregates were found to be different from similar concretes prepared with river aggregates. A semi-quantitative analysis of the microcracks present in the thin sections specimens by means of fluorescent microscopy revealed that the density of microcracks is, in general, higher in the concretes prepared with river aggregates than those prepared with any of the artificial aggregates for the similar water-cement ratios and cement contents. An average of 14 (microcrackslmm’) was obtained for the specimen containing Liapor, 7 for the rest as opposed to values between 28 and 36 for similar specimens containing river gravel and sand [7,8]. The discrepancy is likely to be due to the fact that microcracks in normal weight concretes prepared with river aggregates occur as paste cracks and adhesion cracks, which are cracks

883

that occur in the cement paste and along the cement paste-aggregate particles (sand and gravel) interface [2]. In the present study only paste cracks and cracks along the cement pastesand particles interface were observed. Cracks separating the cement paste and the coarse aggregate particles as well as those traversing through the coarse aggregate particles were not observed.

Figure 6. Thin section (PFM) micrograph showing the internal structure of an AVI-slag aggregate particle (plane polarized light; micrograph = 2.7 x 1.8 mm2). 3.3 Characteristics of the paste-aggregate interfacial zone A distinct zone of about 0.5-2 mm extending into the coarser aggregate particles was found in the specimens containing Lytag, Aardelite and some of the AVI-slag particles. The fluorescent thin section analysis showed clearly that the capillary porosity of this zone was lower than deeper in the aggregate. Differences in the capillary porosity (effective watercement ratio) of the cement paste bordering these aggregate particles and the bulk of the cement paste was not clear. Clear differences were found in the case where the concrete specimens were prepared with blast furnace slag cement. In such cases, the carbonated areas bordering the coarse aggregate particles were found to have higher capillary porosity than the uncarbonated areas. In general, the bond between the cement paste and the coarse aggregate particles was found to be very good. In the case of Lytag, Ardelite and especially Liapor, the bond was so good that the boundary separating the aggregate particles and the cement paste could hardly be traced. These observations were made from both the fluorescent microscopy and the SEM analysis. Figure 7 is a SEM micrograph of the paste-aggregate interfacial zone for the specimen containing Liapor. With the exception of this specimen, all the other specimens showed direct evidence of transport of some cement hydration products into the porous aggregate particles. Figure 8 is an SEM micrograph of the interfacial zone between a Lytag particle (left) and the cement paste (right) showing cement hydration products in the particle. Figure 9 shows

884 a representative EDAX spectra showing the bulk composition of a Lytag particle. Figure 10 shows a similar one for the outermost layer (a few hundreds of microns) of the particle in Figure 8.

Figure 7. SEM micrograph showing the microstructure of the cement paste-Liapor aggregate interfacial zone (a = aggregate; c = cement paste). The aggregate-paste boundary can hardly be distinguished.

Figure 8. SEM micrograph showing the microstructure of the cement paste-Lytag aggregate interfacial zone showing evidence of cement hydration products in the porous aggregate particle (a = part of Lytag particle; c = cement paste). The higher contents of Ca and to a less extent K support the observation made about transport of cement hydration products into the aggregate particles (see further Section 3.4). Cement grains were, however, not identified in any of these porous particles presumably because they were too coarse to penetrate the pores at the surface.

885

For the Liapor particles, there was no evidence found for penetration of cement hydration products or silica fume particles. The present investigation shows that there is a brown layer of about 50-100 pm thick bordering almost all the particles (Figure 1, 11 and 12). Analysis of this brown layer revealed that it contained closed pores within which iron oxide had crystallized (see the EDAX spectra of Figure 13). Calcium hydroxide, (Ca(OH),) crystals which are known to occur at the paste-aggregate interface were not observed at the aggregate interface for any of the specimens studied. This evidence is in agreement with observations made by Sarkar et. al. [4] and Zhang and Gjorv [ 5 ] which they attributed to pozzolanic reaction between the aggregate particles and the cement paste.

4

- L y t a g

f

2.00

0

t

O

:

B

.

6.00 0 0 K E V

4.00

O C N T

0

l

e

t o e s l a g

l

1

5

k

V

8.00 lOeV/ch

4

E 0

4 X

Figure 9. EDAX spectra showing the bulk composition of a Lytag particle.

4

- - L y t a g

f o t o : 1 6 2 2

2 00

O C N T

4.00

0

1

6 00 0 0 K E V

1

5

k

V

8.00 10eV/ch

4

E D 4 X

Figure 10. EDAX spectra showing the composition of the outermost layer of a Lytag aggregate particle of Figure 8.

886

Figure 11. Thin section (PFM) micrograph showing the internal structure of a Liapor aggregate particle (plane polarized light; micrograph = 2.7 x 1.8 mm2).

Figure 12. SEM micrograph showing the structure of the brown layer around the Liapor particles.

887

I AlKe

O C N T

0

.

0 0 K E V

lOeV/cn

A

E 0 A X

Figure 13. EDAX spectra and composition of the outermost layer of the Liapor aggregate particle in Figure 12. The crystals in this layer consist of iron oxide.

3.4 Carbonation Carbonation was found to have taken place in all the specimens examined. The depth and pattern of carbonation were, however, found to vary within a single specimen and very often among the specimens. Examination of the thin sections of these specimens in the polarizing mode and under crossed nicols revealed that the carbonation processes in these specimens proceeded mostly in the cement paste and to a lesser extent via the porous aggregate particles. Carbonation products in the form of finely-divided calcite (calcium carbonate) crystals with high interference colours were observed in almost all of the porous aggregate particles. From the PFM analysis, it became clear that the size of the aggregate particles and the microstructure of the surface layer, that is the structure of the pores of the outermost surface of the aggregate particles were the controlling factors, among others, for penetration and eventual carbonation in the particles. For smaller particles, ranging in size up to about 4 mm and occurring close to the surface of the concrete, carbonation was found to have penetrated the entire particle. For particles greater than this size, carbonation was found to be limited to a few millimetres of the outermost part of the particles. On the basis of these observations, it quite clear that for the same cement composition and effective water-cement ratio, the depth of carbonation will be greater for porous (lightweight) aggregate (with interconnected pores) concrete than for normal (dense) aggregate concrete. From durability point of view, it may be necessary to have an extra cover for the reinforcement in case porous aggregates are used to prepared concrete. From the results of this study, it may be concluded that the 5 mm extra cover specified in the Dutch Concrete Standards for concretes prepared with lightweight aggregates may not be an overestimation. 4 SUMMARY OF CONCLUSIONS From the results of the present microscopic investigations, the following conclusions ragarding the microstructure of lightweight aggregate concretes may be drawn: 1. The artificial aggregate particles of Lytag, Liapor, Aardelite and most of the AVI-slag were found to have a porous internal structure. A considerable number of these pores has an irregular structure. Most of them are not interconnected with each other.

888

2. The cement paste of all the concrete specimens was found to have a heterogeneous structure (variation in capillary porosity and water-cement ratio).

3. The density of microcracks in the artificial or recycled aggregate concretes was found to be considerably lower than the density in similar concretes but prepared with river gravel and sand. 4.A zone of about 0.5-2mm extending into the coarser aggregate particles was found in the specimens containing Lytag, Aardelite, and Liapor. In this zone the capillary porosity was found to be lower than deeper in the aggregate particle. 5. There was no difference in capillary porosity (effective water-cement ratio) of the cement paste bordering the artificial or recycled aggregate particles and the bulk of the cement paste. Clear differences were found in the case where the concrete specimens were prepared with blast furnace slag cement. In such cases, the carbonated areas bordering the coarse aggregate particles were found to have higher capillary porosity than the uncarbonated zones. 6. The bond between the cement paste and the coarse aggregate particles was found to be very good. In the case of Lytag, Aardelite and especially Liapor, the bond was so good that no boundary could be traced between the aggregate particles and the cement paste. 7. There was direct evidence of transport of cement hydration products into the porous aggregate particles. No evidence was, however, found for transport of cement grains into the aggregate particles. 8. For the Lytag, Aardelite and Liapor particles, there was direct evidence of some pozzolanic activity between the aggregate particles and the cement paste. Calcium hydroxide crystals which are known to occur at the paste-aggregate interface were not observed at the aggregate interface for any of these specimens. 9.The carbonation processes in the concrete specimens containing the porous aggregate particles was found to proceed mostly in the cement paste and to a lesser extent via the porous aggregate particles. The size of the aggregate particles and the microstructure of the surface layer, that is the structure of the pores of the outermost surface of the aggregate particles are believed to be the controlling factors for penetration and eventual carbonation in the particles. For smaller particles, ranging in size up to about 4 mm and occurring close to the surface of the concrete, carbonation was found to have penetrated the entire particle. For particles greater than this size, carbonation was found to be limited to a few millimetres of the outermost 'skin' of the particles. 5

REFERENCES

1 S. Mindess, Proceedings of the Materials Research Society Symposium, 114 (1988)3. 2 J.A. Larbi, Microstructure of the interfacial zone around aggregate particles in concrete, Heron, 1993. 3 R.I.A. Malek and D.M. Roy, Proceedings of the Materials Research Society Symposium, 114 (1988) 325. 4 S.L. Sarkar, S. Chandra and L. Berntsson, Cement and Con. Composites, 14 (1992)239. 5 M.H. Zhang and O.E. Gjorv, Cement and Concrete Research, 20 (1990)610. 6 M.H. Zhang and O.E. Gjorv, Cement and Concrete Research, 20 (1990)884. 7 R.B. Polder, R. Walker and C.L. Page, Int. Conf. on Con. and Corr. Protection of Steel in Concrete (1 994). 8 R.B.Polder, Investigation of Concrete Exposed to North Sea Water for 16 years. TNO Building and Construction Report, 93-BT-R0619-02 (1993).

Environmental Aspects of Construction with Wmte Materials J.J.J.M. Goumans, H A . van der SImi and Th.G.Aalbers (Editors) el994 Elsevier Science B.V. AN rights reserved

889

Frost Susceptibility of Recycled Aggregate M.M. OMahony Department of Civil, Structural and Environmental Engineering, Trinity College, Dublin 2, Ireland.

Abstract

An important requirement for sub-base and capping materi;il i n road construction is that it should not be susceptible to frost. Therefore if recycled aggregate is to be used in either of these cases, it also must not be susceptible to frost. Frost susceptibility is largely dependent on the flow of water to an aggregate from the soil below but tests were also conducted to determine if frost susceptibility was influenced by the moisture content of an aggregate at the time of placement. Crushed concrete was tested to represent ;Ihigh quality recycled aggregate whereas demolition debris (an unsorted demolition waste materiul) wits much lower in quality. The results, presented in the paper, show the response of these recycled ygregates to frost and highlight a strong relationship between frost susceptibility and moisture content for crushed concrete, in particular. The itim of the research was to provide additional information on the behaviour of recycled aggregates in freezing conditions and to compare this response with that of naturnl aggregates.

1. INTRODUCTION

Materials placed within 450nim of any road surfitce should not be susceptible to frost as defined by the Transport and Road Research Laboratory test described by Roe and Webster (1984). I t has been found t h a t there is an increase i n the number of road failures during and following severe winters. This deterioration can occur in three ways. a)

When water penetrates the road surface, damage can be caused by the expansion of water as ice fomis. This type of deterioration cun be avoided by better construction and maintenance techniques and p;iniculnrly if the road is adequately sealed.

b)

A more serious type of damage can be caused to rotid surfaces by the formation of ice

c)

When a pavement has been damaged by either of the ways described in a) and b), a further loss of strength may occur when the ice thaws because the material will have a higher moisture content and therefore reduced bearing capacity.

lenses i n the lower layers which cuise the road to heave.

890 Point b) is the most relevant when discussing unbound aggregates placed in the lower layers of a road pavement such as in the sub-base layer or the capping layer. It is imperative that these layers include materials which are not susceptible to frost. The pore spaces between the unbound aggregate particles itre generally large enough to accommodate the expansion of water contained in them when freezing starts. However, as the zero isotherm penetrates deeper into the pnvement, a presslire gradient is set up between the ice in the upper layers and the water table. Under this pressure gradient, water ascends towards the zero isotherm by means of ciipillnry action. The pore spaces do not have the capacity to hold this extra water when it expands on freezing nnd so ice lenses develop. Two important factors which effect this flow of water are the quantity of water present and the amount of fine particles in the material (less than 75 p i ) . The greater the ;mount of these tine particles, the easier water will be able to ascend by capill;uy nction. The object of this research was to examine the ability of recycled aggregates to match the performance of their natural counterparts with respect to the requirements of unbound aggregates for use in sub-base and cupping layers. This included a n examination of the frost heave of crushed concrete and demolition debris ;ind a coniparison of the results with those of limestone.

2. EXPERIMENTAL WORK The frost heave experiments were cnrried out in a frost heave appnratus as described by Roe and Webster (1984). The experiments involved placing compacted specimens of aggregate, of height 154mm and diameter 100mm. in a chnmber with the lower ends of the specimens in indirect contact with water by me;tns of a porous disc. The specimens were surrounded by dry pea gravel and the top of the specimens were not covered. The chamber was closed and the temperature of the water was maintained ;It 4OC but the air temperature was reduced well below freezing to -17°C. The heave was measured by the movement of brass rods placed touching the top of the samples and protruding through the top of the chmber. Although it is recommended by Roe and Webster (1984) that snmples be tested at optimum moisture content (OMC) and peak dry density (pel), testing ;it 0.5 OMC and 1.5 OMC was also attempted. Some adjustment WGS nixie to these moisture contents when stitbility of the compacted samples could not be achieved. 2.1 Test conditions of liniestone spccinieiis

Three samples at ench test condition were tested i n accordance with Roe and Webster (1984). Table 1 includes the moisture content and density values ;It which the limestone specimens were tested.

89 1 I

I

COMPACTION TARGET VALUES

TEST NO. REF.

I

pb (kdrn3)

2361 240 1 2442

Moisture Content (%)

(kg/m3)

1.75 3.5 5.25

2320 2320 2320

Pd

MEASURED VALUES Moisture Content (%) I .98 (0.56 OMC) 3.34 (0.95 OMC) 3.8 (1.08 OMC)

Pd

(kdniR) 2074 23 16 207 1

Table I . Test conditions of the limestone specimens Note: pb and pd denote bulk density and dry density respectively The target density and moisture content for L2 were peitk dry density and OMC. Although samples L1 and L3 were prepnred ;tt different moisture contents, the target density remained at 2320kg/m3 so that stable snmples could be obtained. However, it was clear during compaction that this density could not be achieved using these test conditions. compaction of these samples was continued u n t i l ;in increase i n compaction time did not change the volume of the material. When this stage w a s reached, the specimens were extruded. As they remained stable, i t was decided to use these samples i n the frost heave test. I t c;in be seen i n Table 1 that L3 had a moisture content much lower than the target v:ilue. This was due to a bleeding from the sample during mixing.

2.2 Test conditions o f the demolition debris specimens Initially, the choice of test conditions for demolition debris was siniilnr to that of limestone. The demolition debris had ;I water absorption value of 8% which was much higher than the value of 0.45% for limestone and consequently the moisture contents of the samples of demolition debris were ;tko higher. However, it w i i s difficult to obtain stable samples at a moisture content of 0.5 OMC. The OMC for demolition debris was fotind to be 13% using the BS 5835 (1980) compaction test and consequently 0.5 OMC was lower than the water absorption value. Hence, there wits not enough water present i n these samples to help compaction. It was also impossible to obtain stable samples of the material ;it it moisture content of 1.5 OMC. To rectify this situation, new target moisture contents were calculated as follows:Low moisture content = OMC - (OMC-WJ2

(1)

High moisture content = OMC+ (OMC-WJ/2

(2)

where W, is the water absorption of the aggreg;ite, It was possible to create stable snmples when these moisture contents were used. The test conditions of the demolition debris specimens are listed i n Table 2.

892

COMPACTION TARGET VALUES

pb Moisture (kg/m3) Content (Q)

TEST REF. NO.

2010 2060 2090

D1 D2 D3

10.5 13.0 15.0

MEASURED VALUES

Pd (kgjn13)

Moisture Content (5%)

I820 1820

Pd

(kgjni3)

10.94 (0.84 OMC) 1 X 15

13.0 (OMC) 14.6 (1.12 OMC)

1820

1824 1802

~~~

2.3 Test conditions of the crushed concrete sptc’.imens The crushed concrete had ;I water :ibsorption v;ilue lower thxn 0.5 OMC so the same approach was adopted a s that for limestone i t . the t:irget nioistiire content v;ilues were 0.5 OMC, OMC and 1.5 OMC. When trial specimens were prepared, ii w a s concluded, after several attempts, that the target density of 2000kg/m3 for C3 could not be achieved. Therefore the target value for C3 was changed to the m;ixiniiini density which could be oht;iined for this test condition in the trial samples. The moisttire content mid density v;ilues of the crushed concrete samples are listed i n Table 3.

COMPACTION TARGET VALUES rESTRT NO

I

ph Moisture (kg/ni3) Content (%,)

I

MEASURED VALUES Moisttire

(kg/ni?)

2000 2000

I

6.3 (0.6 OMC) X.3 (0.8OMC) 13.2 (1.2X OMC) -

Table 3. Test conditions of the crtislird concrete specimens

I838 2002 1904

893 3.

RESULTS AND DISCUSSION

The following c1assific;ition system was presented by Roe and Webster ( 1 9x4). a)

If the mean frost heave is less that 9mm, the materiiil is classed as not frost susceptible.

b)

If the mean is greater than ISmm, the materinl is classed iis frost susceptible.

c)

However, if the mean is i i i the range 9.1mm to 14.9mm. the material shall be regarded as 'not proven' and is reqtiired to be tested at other laboratories for cl;uific;ition.

The results of all frost heave tests are listed in Table 4. If L2, D2 and C2 iire examined firstly i.e. the specimens closest to Oh4C ;ind peak density, i t C;LII be seen t h a t the frost hewe measured in the L2 s;imples is quite low with :t mean of 3.Smm. However, the mean frost heave of the demolition debris (D2) samples is 12.3mm which indicated that it was in the 'not proven' range. The nioisttire content of the crushed concrete samples (C2) was 0.8 OMC which was much lower than expected. To obtain an indication of the likely frost heave at OMC, the frost heave results were plotted agiiinst moisture content i n Figure 1. By interpolation of the results, i t c m be estimsted that ;I frost heiive of IXmm might be obtained :it OMC (10%). On this basis. crushed concrete would be clxsszd ;IS frost susceptible. -

~~

TEST MOISTURE REF. ZONTENT No.

SAMPLE HEAVE (mnl)

SAMPLE 2 HEAVE (mm)

1

LI L2 L3

0.56 OMC 0.95 OMC 1.OX OMC

5.5 5.0 4.0

7.0 2.5 3.5

DI D2 D3

0.X4 OMC 1 .OO OMC 1.12 OMC

12.0 12.0 10.5

12.5 12.0 10.5

CI C2 C3

0.6 OMC 0.9 OMC 1.2X OMC

4.0 10.0

3.5 10.0 30.0

-

Table 4. Frost heave results.

30.0

~

SAMPLE 3 HEAVE (n1m)

MEAN FROST HEAVE (mm)

9.0

1.2

3.0 3.0

3.5 3.5

1.43 I .08 0.41

13.0 13.0

12.5 12.3 10.7

0.4 1 0.47 0.48

3.7

0.24 1.41 1.41

1 1 .o

3.5 13.0

33.0

1 1 .o 3 1 .o

STANDARD DEVIATION (n1111)

894 It is apparent i n Figure 1 that there is ;I strong relationship between moisture content and frost heave for the crushed concrete samples where, as the moisture content increases so does frost heave. The relationships for demolition debris and limestone ;ire much different, in that as the moisture content increases, frost heave reduces to ;I much lesser extent. Further work would need to be conducted to investigite these relntionships further. Considering the high frost heave of 30mm - 33mm recorded in the crushed concrete samples, i t can only be concluded that it would be unwise to place this material in areas where water is likely to ingress into the pavement. Increasing moisture content in the other rnvterials does not appear to incrense the probability of frost heave.

95

3025

-

CRUSHED C O N C R m

20-

15

-

DEMOLITION DEBRIS

. + 10

+

LIMESTONE

5-

o

! 0

,

, 2

,

, 4

,

, 6

,

, 8

,

, 10

,

, 12

,

, 14

, 16

MOISTURE CONTENT (%)

Figure 1. Relationship between frost heave mid moisture content. The two main factors effecting frost heave are considered to be the quantity of water below the layer of material which might ascend when freezing stiirts and the amount of fine material in the sample. Normally high frost heave is associated with large quantities of fines in the material (Jones and Hurt, 1980). The proportion of the particles possing the 7Spm sieve was close to 10% which is the m;iximum percentage allowed for sub-bnse materi:il according to the Specification for Roadworks (1981). However, the fines content of the crushed concrete samples was not significantly different to the other materials so this could not be the reason for the higher frost heave exhibited.

895 The moisture content present in the :iggreg:ite ;it pl;icernent can be considered further. It can be divided into two parts; the first being the water absorbed by the particles and the other the free water between the particles. I t is likely, upon freezing, thot the free water would be the main cause of any global damage to the layer particularly by the fonnotion of ice lenses. In the case of the crushed concrete at 1.28 OMC, it was calculated t h a t the water between the particles would induce a heave of 2mm-4mm upon freezing. A volume increase of water upon freezing of 9% was used, ;is suggested by Neville (1973, . The heave cnlculated is relatively small in comparison with the heave of 3~~l11111 - 33mm measured i n tlie smples and therefore does not serve to clarify this excessive frost heave. Additional work would be required to investigate the susceptibility of crushed concrete to frost. I t was surprising that the demolition debris, which was a lower quality aggregate with a higher water absorption, did not exhibit high frost heave values similar to those of crushed concrete. It should be noted that these results were also more consistent than those of the other materials. Croney and Jacobs (1967) found t h a t the addirion of cement to aggregates reduced frost heave. I t was found by Sweere (1989) i n ;I field triiil that crushed concrete and demolition debris, used as sub-base materinls i n m i d piveiiients, exhibited better resistance to rutting three months after construction that when the msterisl was first placed. This led Sweere (19x9) to believe that recycled aggregxes hiid it self-cenirnting effect. It may be thnt this binding effect might also reduce frost heave and so it is proposed to examine this in ;i later study. In general, crushed concrete wid demolition debris both contain relatively large quantities of cement but the self-cementing effect might not be easily identified i n tlie Roe and Webster (1984) test because the samples are rested directly after placement.

4.

CONCLUSIONS

(i)

On the basis of the results presented i n this paper. limestone would be classed as not frost susceptible but it was :ipp;irent tli;it crtished concrete would be highly susceptible to frost. The frost heave results of demolition debris indicated that i t was in the inconclusive range but its results were more consistent than those of the limestone or crushed concrete. Further testing ;it other hborntories would be required to confimi its susceptibility to frost.

(ii)

Although the frost heave of crushed concrete appeared to be directly influenced by the initial moisture content of the specimens, the increase i n volume of the material due to the expansion of this water on freezing w;is cnlculated and found to be relatively insignificant. The app:irent dependence of frost henve on the initial moisture content was not noticed for tests conducted on limestone and demolition debris and further testing therefore would be required to determine other contributing fxtors to frost heave.

(iii)

Following the conclusion of Sweere (1989) that recycled aggregates exhibit a selfcementing effect some time after placement, i t is proposed to examine whether this effect would also improve the susceptibility of these materi;ils to frost.

896 REFERENCES British Stnndnrd 5835 (1980) Compactibility test for gr;ided aggreg:ites. Pnrt I . British Standards Institution. London. Croney, D. and Jacobs, J.C. (1967) The frost susceptibility of soils and road materials. LR90. Transport and Road Resznrch Loborotory. Jones, R.H. and Hurt, K.G. (1980) The prediction of the frost susceptibility of limestone and sub-base materials. The Highway Engineer. Neville, A.M. (1973) Properties of Concrete. Pitmnn. London. Roe, P.G. and Webster, D.C. (1981) Specification for the TRRL frost henve test. SR829. Transport and Rood Research 1,;iborntory. Crowthorne, Berkshire, U.K. Specification for Roadworks ( 1981 ) Publications Office. Dublin.

Dep;irtment of the Environment.

Government

Sweere, G.T.H. (1989) Structural contribution of self-csnisnting granular bases to asphalt pavements. Proc. frd Symposium on Unbound Aggreg;itrs i n Roatls (UNBAR 3). University of Nottinghani.

Environmental Aspects of Consmction w'th Waste Materials JJJ.M. Goumans, H A , van der Slmt and Th.G.Aalbers (Editors) 01994 Elsevier Science B. K All rights reserved.

897

Use of crushed tile and concrete as filling in pipe trenches Jan Folkenberg Department of Cleaner Technology / Institute of Building Technology Danish Technological Institute, P.O.Box 141, DK-2630 Taastrup, Denmark

Abstract On the basis of detailed laboratory work and full-scale pipe work, studies have been effected to establish whether it is possible to use crushed tile and concrete in 0-4 mm fractions as filling in pipe trenches. The results of the studies prove that crushed material can be used for levelling and filling material in pipe trenches. The results have been gathered through video inspection and inclination measurements. In addition, deformation measurements were carried out on the plastic pipes in the test field. The compression of the material used in the pipe trenches does not always comply with the minimum requirements to road construction, but damage/deformation has not been demonstrated. The results only prove that the technical conditions of the piping have been observed. No studies have been carried out concerning any up-down movements in the road surface.

Objective and background On average 4.5m tonnes of building waste are generated in Denmark annually. Forecasts show that the volume will increase to reach 5.3m tonnes annually in 2015, / l / . Tiles and concrete rubble make up approximately 75% of the waste. Experience gained in practise concerning crushing of both tiles and concrete with a view to applying the material as stabilised gravel in road constructions shows that there is a large surplus of the fine 0-4 mm fraction /2/. In connection with tiles this sulplus reaches as high as 35 weight per cent of the basic material. This percentage has been confirmed by effected test crushings. To find an application field for the "surplus" material, a decision was made to study whether the material could be used as filler in pipe trenches.

898

The requirements of the existing standards of the field presuppose that the used filler predominantly consists of sand 13, 41. However, it is possible to use other materials as long as it can be documented that the alternative materials fulfil the requirements set up for the field of application. Studies were carried out to this effect, partly as laboratory studies, partly as effected pipe works. In connection with the execution of the mentioned pipe works a detailed measurement programme was executed. Execution of thorough monitoring of the compression of the materials has ensured that the materials were applied correctly in the pipe trenches. Correct application ensures that any settlement or damage/deformation of the installed pipes is attributable to the crushed material.

Applied construction machinery One of the prerequisites of the project was that the machinery used both in the laboratory tests and in the full-scale tests of the crushed materials should be the machinery which is normally used in the handling of traditional materials. This decision was spurred by the wish that the project was also to show that crushed tiles and concrete can be applied under the same circumstances as the traditional fillers, and that it will not be necessary to acquire new machinery because crushed filler is to be used.

Preliminary tests The following laboratory tests were carried out in connection with the studies of crushed tiles and concrete of the 0-4 mm fraction: Distribution of grain size at screening Determination of sand equivalent Determination of capillary absorption Standard Proctor tests. Because pipes can be made of both plastic and concrete, studies were carried out to determine whether the crushed materials fulfilled the prevailing requirements in relation to the pipe material. The results of the laboratory tests show that crushed concrete meets the requirements to base course gravel in roads 121 and that the material may thus probably also be used for this purpose. However, supplementary studies must be carried out to determine this.

899

As the results from the laboratory tests showed that crushed tiles and concrete - based on the existing requirements to fill materials - could be used as fill materials in pipe trenches, the next phase was to determine whether handling and application of the materials in practise would cause any problems. On the basis of the results a full-scale test field was then established in a gravel pit.

Full-scale test Across the entrance to a gravel pit the test field was established consisting of four parallel pipe trenches, see figure 1. The average daily traffic load was 105 trucks.

Road

Point 1

o~~~pvc

point 2

1

0 200 concrete

Point3

0-1

PdntC Point 7

0°200pvc I Point6 02ooconcrete 0-1 Point 8

Point9

00 200 PVC

Point4

Point i a

I

0 200 concrets

Pdnt 11

0-1

Pipetrench 1 wshed tiles

Pipetrench 2

mshed Concrete

Pipetrench 3

crushed tiles Point 12 :rushed Concrete

................................... Point 13

00200 Pvc

Point 14

I

0mconaete

Point 15 0 -1 Point 18 ...................................

Pipe trench 4

gravel (reference)

Road sign 0

-

inspeaionhole

Figure I Outline of the test area. The figure also contains information on the fillers used in the pipe trenches and specijies the materials and sites of the piping.

900 In principle the test fields were constructed as shown in the sectional view below.

Only the conditions in the piping trench area have been studied and documented. The four piping trenches in the field were constructed as follows:

Pipe trench no. I , construction: Construction

Thickness of layer

Stabilised gravel

0-32 mm gravel

Filling around piping

0-4 mm crushed tiles

Base course

0-4 mm crushed tiles

10 cm

Pipe trench no. 2, construction: Construction

Thickness of layer

Stabilised gravel

0-32 mm gravel

Filling around piping Base course

0-4 mm crushed concrete 0-4 mm crushed concrete

Construction Stabilised gravel Added filler/levelling course Filling around piping Base Course

Thichness of layer 0-32 mm gravel o-4 mm gravel

0-4 mm crushed tile and crushed concrete (1:l) 0-4 mm crushed tile and crushed concrete (1: 1)

30 cm 20 cm 30 cm 10 cm

90 1

Dipetrench no. 4, construction. Reference: Construction Stabilised gravel 0-32 mm gravel Filling around piping Base course

I

Thickness of layer

0-4 mm gravel

0-4 mm gravel

Execution of the work The pipe trenches were approx. 1 metre wide and approx. 0.80 metre deep. At a distance of 20 cm from the sides of the pipe trench a concrete pipe of 0200 mm was installed and in the opposite side a PVC pipe measuring 0200 mm was installed. The pipes were installed horizontally on the base course. One end of the pipes was corked up whereas inspection holes were mounted at the other end for subsequent video inspection and measurement of inclination, see figure 2.

Figure 2 The figure shows PVC and concrete pipes with mounted inspection holes.

902

When the pipes were laid, a filler course around the pipes was established measuring 30 cm, and compression was carried out with a vibration punner of the brand "Wacker", type BS65Y. After each two passings, compression was measured with an isotope probe of the brand "Troxler", type 3440. The measurements were carried out at the same points through the courses. When filler had been laid around the pipes, the levelling filler was laid, and the materials were once again compressed. This compression was carried out with a vibratory plate of the make "Wacker", type 3345. After each two passings compression was measured with the isotope probe. The measurements were repeated until twelve passings had been made of the materials with the compression machinery. When the filler had been added around the pipes, and in this case the filler and the base course of the road surface were made of the same material because of the low level of laying, 30 cm of stabilised gravel of 0-32 mm, type 2, was applied. The material was compressed and checked in accordance with the guidelines applying to the filler material. Uniform methods of laying, compression and checking were used in all four pipe trenches. In January 1993, two years after the establishment of the test field, video inspection and inclination measurement were again carried out on the pipes to determine any damage. The results of the video inspections showed that there was no visible damage to the pipes. The results showed that all pipes had settled a few centimetres. Nothing seems to indicate that there is a difference in the settlement of the pipes laid in crushed tiles and concrete and the pipes laid traditionally in gravel. After another interval the television inspection was repeated of the test field. The result showed that no visible damage to the pipes had occurred. Because it is not possible in a TV inspection to recognise deformation to plastic pipes, deformation measurements were carried out of the plastic pipes. The results of the studies at the test field show that the deformation to the PVC pipes after two years never exceeds 8%. To find a relative measure of how much the pipes "settled" in the test period, inclination measurements of the pipes were carried out simultaneously with the video inspection, see figure 3.

903 Distance from first inspection hole (metres)

I

0

-5 un

-

POim I

+5 an

2

3

4

5

6

.

7

x

POOUZ

-5 an

Paia 3

t

+5

POiDl.1

an

-5 cm

Poim 5 *5

cm

.

'

Point6

8

1

m

7

-5 cm

mm 10

mM 9 +5 on -5 cm

mint I I

+5 cm

-5 cm

mint 13

. . x

+5

M

perm 12 Y

polat 14

-5 an pdm

I5

&

mm 16

Figure 3 Thefigure shows the relative conditions of thepipes, 6 months and 2 years, respectively, afer the establishment of the test jield. The results of the studies prove that the pipes installed in crushed materials had "settled"3-5 cm in relation to the original installation, whereas the pipes in the reference field which were installed in traditional gravel had "settled"2-4 cm. The settlement had had no influence on the pipes.

904 Thus the conclusion was made that the use of the alternative tile and concrete materials entailed no increased risk of damaging the pipes in comparison to the traditional gravel materials as filler in the pipe trenches. The experience gained in the establishment of the test field also shows that the crushed concrete and tile materials can be handled in the same way as the traditional materials.

Future studies The project only proves that the technical conditions of the pipes have been complied with in connection with the use of the alternative materials. Documentation of whether the materials fulfil the technical requirements of road construction - e.g. bearing capacity, deformation resistance, permeability and application conditions -

would require further detailed studies. Furthermore, it would be necessary to study whether the pipes are tight in relation to the settlements of the materials. As a consequence an application has been submitted to the Danish Environmental Protection Agency for financial support of a continuation of the project, and it is expected that a consecutive project will start in 1994.

Literature Environmental project no. 150 (1990).Forecast of building and construction waste main report. The Danish Environmental Protection Agency (not translated). Danish Standard DS 401.Standard of sand, gravel and gravel aggregate, 2 edition 1977 (not translated). Danish Standard DS 437 (1986).Installation of rigid pipes of concrete etc. in soil (not translated). Danish Standard DS 430 (1986).Installation of flexible pipes of plastic etc. in soil (not translated).

Environmental Aspects of Consttuction with Waste Materials J.I.J.M. Goumans, H A . van der SIoot and Th.G.Aalbers (Editors) 691994 Elsevier Science B.V. All rights resewed.

905

USE OF ASHES FROM MSW INCINERATION IN CEMENTITIOUS BUILDING MATERIALS A. Gerdes and F.H. Wittmann Institute for Building Materials ETH Zurich Switzerland SUMMARY A technology has been developed which allows to separate most hazardous materials in MSW from the organic components. The so purified organic components can be incinerated. Ashes obtained from this new technology have been analysed. It was found that they contain a small and tolerable amount of heavy metals only. In addition it was shown that both the bottom and fly ashes have a puzzolanic action. Different concrete mixes in which part of the Portland cement has been replaced by these special MSW ashes have been tested. With the most promising concrete mixes concrete blocks have been produczd under industrial conditions. About 25 % of the cement content can be replaced and acceptable mechanical properties are still obtained. First leaching test have shown that these concrete blocks can be used as a usual building material. In a second test series glasses produced from traditional MSW fly ashes after vitrification have been finely ground and used in mortar prisms. Up to 20 % of the Portland cement has been replaced by these ashes. The mechanical properties are hardly influenced. 1. INTRODUCTION

A few years ago a method to separate MSW into different components has been developed Ill. Ecomat operates in Moudon, Switzerland, one factory which uses this new technology. Metals, batteries, glas and ceramics are separated consecutively from the remaining organic components. The dried organic components can be burnt in a modem heat generating power plant. It is obvious that both the bottom ash and the fly ash from this incineration contain much less hazardous elements as compared to a conventional MSW incineration station. In Tab. 1 the range of heavy metals in two different fly ashes, a Dutch and a Gennan one, are shown together with the result of the analyses of a typical bottom ash of a conventional MSW incineration station (Hagenholz, Switzerland). For comparision the corresponding values of the Ecomat ashes are also given in Tab. 1. Finally the range of the elements as observed in the earth’s crust are added. Table 1: Range of trace elements in different ashes, give in mgkg Trace Elements Cd Cr CU Ni Pb

I I

Dutch fly ashes /2/ 2.1 f 1.4 139f43 144f 37 _l h _ 7+2 _ _6 ~

143245 Zn 38Of ISO n.a. = not analysed

German fly Hagenholz ash (CHI Powerplant MSW ash Ensdorf 131 141 I 3.6-16.0 I 22 550 176-365 2300 165-380 130 91-104 1800 660-1670 n.a. 970-1990

I

I

ECOMAT Fly ash

I

I

ECOMAT Bottom ash I51 I51 ca. 10 % ca. 90% 72.8 I 0.71 406 527 27 479 263 298 < 12 16 5.86 12.7

I

I I

Minerals in the Earth’s crust 141 0.03-0.3 4-2980 4-87 2-2000 1-20 n.a.

906 In a totally different approach fly ashes of conventional MSW incineration stations are heated above 1200 "C. Under these conditions most heavy metals evaporate and can be recovered by condensation. The remaining molten mass is relatively clean and can be quenched in order to obtain a puzzolanic reactive glass 161. In this contribution it will be shown that Ecomat ashes and the vitrified fly ash can be used in concrete technology in order to replace part of the Portland cement. 2. EXPERIMENTS A N D RESULTS 2.1 Concrete blocks prepared with Ecomat ashes Many different concrete mixes have been tested in the laboratory in order to find some promising compositions. With these optimized concrete mixes concrete blocks have been produced in a specialized factory. the maximum aggregate size in these blocks is 12 mm. Strength and elastic modulus have been determined on these concrete blocks and on prisms cut from the walls of the blocks. The strength evolution is shown in Fig. 1 for different concrete mixes. It can be seen that concrete blocks in which up to 25 % of the Portland cement have been replaced by Ecomat bottom ash show a reasonable strength development. These blocks can be used in load bearing and non load bearing masonry walls. 40 35

5

n 0

50

100

150

200

250

300

350

400

timeld

Fig. 1: Development of compressive strength of concrete blocks as prepared with different amounts of Ecomat bottom ash replacing part of the Portland cement. The percentage of bottom ash in hydraulic binder is given in the box. In all mixes the binder content (cement plus bottom ash) was 280 kg/m3 and the waterhinder ratio was 0.4. Similar concrete blocks containing relatively high amouiits of Econiat ashes have been tested with respect to leaching. Results obtained on blocks with four different compositions are compiled in Tab. 2. The heavy metal ions observed in the leaching tests according to DEV-S4 /7/ as obtained on concrete blocks containing significant amounts of Ecomat ashes hardly differ from those from blocks prepared with Portland cement exclusively. Further research on the leaching behaviour is going on at present.

Specimen

A

B

C

D

Binder composition

280 kg/m3 PC

210 kg/mj PC + 140 kg/m3 BA

210 kg/mj PC + 140 kg/m3 PFA

I

Al

cu

5.6 0.008 n.d. 0.023 n.d.

Ni

0.024

5.5 n.d. n.d 0.083 n.d.I. n.d.

210 kg/mj PC + 56 kg/m! BA + 28kg/m3PFA 3.5 n.d.

I I

0.098 n.d. . . 0.14

Pb Cd Cr

I I

I

5.1 n.d. 0.18 n.d. . .-

0.02:5

I II I

I 2.2 Mortar prisms prepared with vitrified fly ash Mortar prisms in which an increasing percentage of the Portland cement has been replaced by vitrified fly ash have been prepared. The maximum aggregate size of the mortar was 4 mm. Compressive and bending strength of the obtained material has been determined on standardized prisms (40 x 40 x 160 mm). Some results are shown in Fig. 2. It can be seen that the strength evolation is hardly affected by replacing up to 20 % of the Portland cement by the finely ground vitrified fly ash. These preliminary result indicate that possibly up to 40 % of the Portland cement can be replaced without dramatic influence on the mechanical behaviour.

0

P

41

60

BD

100

1P

tinrJd Fig. 2: Development of the compressive strength of mortar prisms containing different amount of vitrified fly ash. In all mixes the binder content (cement plus finely ground vitrified fly ash) was 586 kg/m3 and the waterbinder ratio was 0.5. The percentage of the finely ground vitrified fly ash in the binder is given for each mix in the box.

908 3. CONCLUSIONS It has been shown that it is possible to separate most hazardous components of MSW with an appropriate technology. If the remaining organic components are burnt in an advanced incinerator full advantage of their heat content can be taken and the resulting bottom and fly ashes can be used profitably in cementitious materials. Further research is needed to optimize the mix composition and to further elucidate all environmental aspects. 4. LITERATURE /1/ Z. Zhang and F.H. Wittmann, Use of proccessed garbage in cement concrete, in: Proceedings of the International Conference on Environmental Implications of Construction with Waste Materials, Editor: J.J.J. Goumans, H.A. van der Sloot, Th. G. Aalbers, Elsevier Verlag, Amsterdam, pp. 643-644, (1991) /2/ CUR Report 144, Fly ash as addition to concrete, A.A. Balkema, Rotterdam, (1992) /3/ F. Kiefer, Untersuchungen zur UmweltvertrBglichkeitund Verwendung von Kraftwerksnebenprodukten, Dissertation, Saarbrlicken, (1989) /4/ Amt f i r Gewlsserschutz und Wasserbau des Kanton Zlirich, Emisionsabschiitzung f i r Kehmchtschlacke (Projekt EKESA), (1992) IS/ Laboratoire d analyses, Energie et Environment, Strtlmsund, Schweden Rapport des Tests de Combustion Eneco Laborbericht Nr. 166Y91

/6/ H. Jodeit, J. Jochum and Ch. Wieken, Das ABB-Schmelzverfahren zur Behandlung von Filtersuuben aus der thermischen Abfallverwertung, in: VGB-Kraftwerkstechnik GmbH (Hrsg.), RiickstBnde aus der Miillverbrennung (VGB-TB-221), Essen

/7/DIN 1164, (1986) Part 5 (German Standard) : Standardized German procedure for water, wastewater and sludge testing, sludge and sediments (Group S), (1986)

Environmental Aspects of Constmction with Waste Materials JJJ.M. Goumans, H A . van der SIoot and Th.G. Aalbers (Editors) a1994 Elsevier Science B.V. AN rights resewed.

909

Effect of grain size composition of the calcium-sulphate fly ashes on the properties of autoclaved building materials Z. Pytel and J. Malolepszy

University of Mining and Metallurgy, Al. Mickiewicza 30, 30-059 Cracow, Poland

Abstract The bulk of fly ashes in ambient temperature is insufficiently chemically active in relation to water, independently on the kind of burnt coal. Nevertheless, some of them after suitable activation shows the hydraulic properties merging features of such binders as lime and cement. First, the calcium-sulphate fly ashes start as by-product in the burning of a brown coal reveal above properties. They make the chance in their application as a binder and microaggregates for the production of some kind of building materials. The pozzolanic properties of fly ashes depends on their granulation and show improvement when they are finer. The granulation effect of "Patn6w" fly ashes on the physical properties, texture and structure of autoclaved calcium-silicate brick is presented. Also, results of the investigation of the effect of the quartz sand additives on the quality of an autoclaved material get on the base of fly ashes binder is shown. 1. INTRODUCTION

The hydraulic properties of calcium-sulphate fly ashes depend on their chemical and mineral composition. Fly ashes characterized with an increase content of calcium compounds. Some amounts of free lime (CaO) is also found. Free CaO can be subjected on the slow hydration into Ca(OH), after the contact with water and then can react with active silica. The hydrated calcium silicates resulted due to such reactions and depending on the hydration conditions, mainly temperature and pressure of water vapor, can be formed into kinds ['I. Also, the glassy phase contained in fly ashes have an influence on their hydraulic properties. The pozzolanic properties of fly ashes consisting in the ability of association of Ca2+ ions from solution with the formation of hydrated compounds. According to Diamond [*I the pozzolanic reaction in 20°C starts itself tardily and shows a such slow run that the C-S-H phase is not visible before 28 days under the electron microscope. Uchikawa ['I revealed that the C-S-H phase get in such conditions shows the lower ratio of C/S equal about 1 and contain considerable amounts of Mg and Al, than in the portland cement paste where CIS is about 2 .

910

However, the distinct progress of pozzolanic reaction is seen in hydration of fly ashes in hydrothermal conditions, The glassy phase of fly ashes faster hydrolyze at an increase temperature under the pressure of the atmosphere saturated with water vapor and in highly basical environment. Resultant silicate (H,SiO;, H2SiO:-) and aluminate (H,AIO;) ions get into the solution and react with ions of Ca2' forming hydrated calcium silicates or calcium alumina silicates Also, hydrogamet can be expected among the products of hydration of fly ashes containing alumina beside silica [ 5 ] . Therefore, the free CaO and glassy phase contained in the mineral composition of fly ashes affect binding properties. It is also known, that the hydraulic activity of fly ashes increase with their degree of comminution ['I]. The pozzolanic reaction begin in the earlier stage of hydration and shows faster run. The earlier crystallization of hydrated calcium silicates and calcium alumina silicates having the chief influence on the strength properties of autoclaved material is the result that process ['I. The dry grinding of fly ashes in the ball mills is the simple and an efficient manner for their activation.

r].

2. EXPERIMENTAL 2.1. Raw materials The fly ash from the brown coal electric power station "Patn6w" (EPS) was used as a basal raw material in this investigations. The dust collection system installed in EPS "Pqtn6w" consists of three zones of electrofilters, so the fly ash exists in the three particle fractions. The degree of dust collection is highest in I zone of electrofilters and amount of 85% of a total yield, while in I1 and 111 zones is equal of 10 and 5 % , respectively. The particle size analysis of fly ash was checked by sieve test using the following set: 1.O, 0.5, 0.25, 0.12 and 0.063 mm. The sieve test was carried out for each fraction of fly ash and results is given in figure 1.

Undersize 6o material (P(d))

. . . . . . Fraction II

[%I

._ Fractlon Ill

0

0.063

0.12

0.25

0.5

1

Partlcle size (d) [mm]

Figure 1. The particle size distribution. The specific surface of the original fly ash as well as the disintegrated one was calculated according to Blaine procedure after 2h grinding in the laboratory ball mill and results are given in Table 1.

91 1

Table 1 Specific surface of "Patnbw" fly ash Specific surface S, [cm2/g]

Tested fraction Fraction I

before grinding

after grinding

600

3000

Fraction I1

1700

3400

Fraction I11

2600

4200

The chemical composition of examined fly ash (Table 2) depends on the particle size distribution. The coarse particle coming from I zone of dust collection are rich in Si02 and poor in CaO (also free CaO), MgO and SO,. The middle and fine fraction (from I1 and 111 zones) consist of highest amount of CaO, MgO, SO, and smallest amount of free SO2. The mineral composition of investigated fly ash was described by XRD method and revealed that is similar for each particle fraction, however, the participation of an individual minerals were changed. The quartz, CaO, anhydrite, periclase, hematite, magnetite and small amount of calcite belong to crystalline phases. The amorphous phase consisted mainly from glass. The unburnt coal is also seen. Table 2 The chemical composition of "Patnbw" fly ash. Chemical analysis wt (%) Component Fraction I Fraction I1 Fraction 111 L. 0.i. ( 1000 C)

2.47

2.38

2.92

SiO,

70.10

33.03

29.85

Fez03

4.59

6.02

6.08

O

A1203

2.79

4.46

4.16

CaO

15.28

37.01

37.33

MgO

2.52

6.03

6.73

so3

2.32

8.92

10.41

CaO,

2.47

8.13

7.99

residuum

2.40

4.53

5.44

2.2, Procedure The fly ash binder was used in preparation of samples designed for the testing of a new material. The binder was prepared in three different variants. The first one was made using a separate particle fraction of the natural fly ash.

912 The second one was made using the mixture of three particle fraction of the natural fly ash. Three mixtures was next collected with variable content of a given fraction. One of them had the particle size distribution similar to the structure of fly ash from the one of zone of dust collector. The moisten fly ash was matured according to I as well I1 variant at 120°C during 6h under the normal pressure. The third variant of binder was fabricated using fly ash disintegrated up to 3400 cm2/g according to Blaine. Next, it was initially hydrated in an autoclave at the temperature not higher than 150°C in the atmosphere saturated with water vapor under the pressure below 0.5 MPa during 2h. After hydration of tested fly ash, the produce binder was then mixed with a quartz sand. An addition of the quartz sand was ranged from 10 to 50%. Next, the cylinder laboratory samples was modeled using binders get according to I and I1 variant as well as using the fly ash and sand mass with a binder of the third variant under the maximum compression pressure of 20 MPa. Samples was next directly autoclaved under the conditions used in the production of the lime-sand brick.

2.3. Properties of the building material Autoclaved samples of a new building material were tested in respect of the following features: compressive strength, absorbability, density and frost-resistanceand results are given in Table 3. Table 3 Physical properties of a material with an addition of the natural and disintegrated fly ash. Properties Binder Sample variant symbol Comp.strength Absorbability Density Frost R, [MPa] Nm [%I sp [g/cm2] resistance Natural "Patnbw" fly ash I

I1

F- 1

10.7

22.3

1.65

None

F-2

18.2

29.3

1.52

None

F-3

22.1

33.2

1.51

None

M-1

14.4

23.5

1.61

None

M-2

19.3

26.7

1.54

None

M-3

25.7

29.9

1.52

None

Disintegrated "Patnbw" fly ash

111

P-10

31.8

23.3

1.64

Full

P-20

36.8

14.3

1.79

Full

P-30

34.6

12.1

1.87

Full

P-40

34.8

11.1

1.91

Full

P-50

33.5

10.9

1.92

Full

913 Results show that disintegration of fly ash is effective. In each case, material get in variant I and I1 characterized in lower compressive strength in contrary to material obtained according to variant 111. Also, samples show the higher absorbability and could be a reason of its lack of the frost-resistance.

2.4. Microstructure and material texture The texture of an autoclaved material was observed in Joel 5400 and is given on figure 2 and 3. Results show amorphous as well as crystalline hydration products. The C-S-H phase belong to the first one, and is seen under the high magnification as a submicroscopic substance similar to colloid particles resembling a gel. The tobermorite is a dominated product among the crystalline phases. The morphology of the tobermorite crystals is discriminated but usually looks in the form of slats, bands or needles. However, the tobermorite in the shape of plates is seen scarcely. It is typical, that crystals are found in the interior of the pore walls and grow up into the inside. The pore is charged with crystallization products and make the structure to be condensed. The direction of the crystals growth is different, so they make the net of the crossed and disordered themselves needles. This phenomenon is clearly demonstrated in figure 3. Also, observations under the electron microscope show the differences in the quantity of induced products during the reactions running in the hydrothermal conditions. The C-S-H gel is the dominant reaction product in samples prepared with a mass of fly ash (sample F and M). However, tobermorite is the principal product in samples get from a mass of ground fly ash and sand (sample P). Also, small quantity of C-S-H phase is observed.

Figure 2. Material produced from mass of fly ash (binder of I1 variant).

914

Figure 3. Material produced from mass of fly ash and sand (binder of 111variant).

3. SUMMARY Recapitulating, the brown fly ash prepared in a suitable procedure, instead of lime,

can be used in the production of the autoclaved building materials such as calcium-silicate brick. The fly ash plays the role as a binder and microaggregate but it should be dry disintegrated up to 3000+4000 cm2/g according to Blaine before usage. The disintegration is not only a process for an increase of the specific surface of a material but also make that That cover is a little permeable the glassy shield of fly ash particles is destroyed prohibiting the entrance of water into the inside of particles and rendering hydration of CaO and MgO. Thus, the disintegration of fly ash increase its hydration activity. Results of investigations of samples of series P, prepared with disintegrated fly ash, confirmed that fact. The samples characterize with the highest compressive strength between tested materials and the full frost resistance. Also, results of the microstructure testing of produced material proved the positive effect of a disintegration process. They show a higher quantity of the hydration products, beneficial morphology of a microcrystals of C-S-H phase and an attendance of fibrous crystals of tobermorite. It is also useful, to subject the disintegrated fly ash on a beginning hydration in hydrothermal conditions. Some of fly ash components, mainly CaO and MgO almost entirely hydrate and portlandite and brucite is formed in result. The negative soundness phenomenon being usually observed in later period of a hardening of the fly ash binder is caused by

915 retarding hydration of CaO and MgO and is eliminated by this way. As a result, the active binder is produced after started hydration of the ily ash in the atmosphere saturated with water vapor under pressure. The binder blended with a proper quantity of a quartz sand makes a raw mixture for the production of the pressed silicagel elements. The addition of a quartz sand containing an appropriate amount of a coarse and a middle size of a particle effects positively on the granulometric composition of the fly ashsand mixture improving their rheological properties. It make the direct influence on the compaction degree of molders during pressing and is related with their final porosity.

4. REFERENCES 1.

H.F.W. Taylor, Cement Chemistry, Academic Press, London 1990.

2.

S . Diamond, 7th I.C.C.C., Paris 1980 111 IV-19.

3.

H. Uchikawa, 8th I.C.C.C., Rio de Janeiro 1986 1 249.

4.

K. Takemoto, H. Uchikawa, 7th I.C.C.C., Paris 1980 I IV-2/1.

5.

J. Malolepszy, Hydration and properties of alkali activated slag cementitious materials, Ceramics, Bulletin 53, Cracow 1989 (in Polish).

6.

M. Regouord, 8th I.C.C.C., Rio de Janeiro 1986, I 199.

7.

J.B. Jambor, 6th I.C.C.C., Moscow 1974, I1 315.

8.

S. Diamond, D. Ravina, J. Lovell, Cement and Concrete Research, 10 (1980) 279.

9.

S. Diamond, Cement and Concrete Research, 16 (1986) 569.


Environmental Aspects of Consttuction with Waste Materials JJJ.M. Goumans, H A . van der Sloot and l3.G. Aalbers (Editors) el994 Elsevier Science B. V.All rights resewed.

917

SULPHATE AND ACID ATTACK ON CONCRETE IN GROUND AND LANDFILL C. Plowman UK Analytical Ltd, Vicarage Terrace, Kirkstall, Leeds LS5 3HL UK

ABSTRACT Disposal of industrial waste as landfill can give rise to chemicals in the groundwater which may damage concrete foundations. Possible aggressive agents include sulphate and acids. Cement replacements such as flyash or ground granulated blast furnace slag influence the mechanism and rate of attack. Mechanisms of attack by thaumasite formation, and sodium sulphate crystallisation, are briefly described. Potential for attack by low-calcium flyashes has been shown generally to be limited. Recommendations of BRE Digest 363 regarding classification of sevefity of sulphate conditions, and appropriate concrete specifications are given. Damage caused by volume expansion of industrial fill is described. 1.

INTRODUCTION

In the disposal of industrial wastes as landfill, considerable emphasis is given to the content of constituents such as heavy metals which may pollute the environment. The landfill is then considered environmentally safe to build on. It is, however, not necessarily possible to assume that concrete foundations built on such fill will be immune from chemical attack. Waste material may contain sulphate, sulphide, nitrate, chloride, or other species which, in addition to being pollutants, are capable of causing severe damage to concrete foundations. Aggressive species may occur naturally, and many clay strata contain sulphates. Industrial wastes can include materials considered suitable either in the past or at the present time as sub-base materials, such as fly ash, blast furnace slag, unburnt coal shales, or bricks and mortar used as hardcore, all of which can give rise to potentially aggressive species towards concrete, or cause very damaging volume changes. 2 CLASSIFICATION OF SOIL CONDITIONS

Table 1 of BRE Digest 363 [l] classifies soil or water conditions which may lead to sulphate attack (Table 1). The most widely found form of attack involving sulphate, is by sulphate in groundwater, which diffuses into the concrete and attacks the hydrates formed by the hydration of tricalcium aluminate to form ettringite, [ 3CaO.Al 0 .3CaSO .32H20], with consequent disruption by eqnsion. Following dishgtion 04 the cement paste by the ettringite expansion, the sulphate solution can then attack the calcium hydroxfde present in the cement paste to form gypsum, resulting in further expansion. The relationship between the tricalcium aluminate content of cement and vulnerability to sulphate attack is generally recognised and has led to the development of sulphate-resisting cements, whose predominant feature is their low tricalcium aluminate content. The mechanisms of attack where the solution is effectively sodium sulphate, were discussed by Cabrera and Plowman [ 21 , both for materials containing Ordinary Portland cement alone, and also for materials containing flyash as a partial cement replacement. Essential differences found where flyash was included were:1. Diffusion of sulphate into the matrix was at a much lower rate than for the cement alone. This was attributed to a reduction in the permeability of

918

Table 1 Classification of concentrations of sulphate and magnesium In soil or fill

In groundwater

the paste by the pozzolanic reaction. There is only limited formation of ettringite; the principal reaction products are monosulphate [4Ca0.A120 .CaSO .12H 0 ) and other members of the solid solution series of hexagonal h#dratej forded between the monosulphate and tetracalcium aluminate hydrate [ 4CaO.Al 0 ,1314 01 , which are stabilised by the incorporation of sulphate into the2s$ruct&e. Consequently, less disruption of the matrix occurs. 3. Less calcium hydroxide is present in the cement matrix due both to the presence of less cement, and the pozzolanic reaction. Subsequent studies of flyash concretes have confirmed the formation of stabilised hexagonal hydrates under a variety of site conditions, In concretes where some of the cement is replaced with ground granulated blast furnace slag, a pozzolanic reaction also takes place, resulting in a reduction in permeability, and also a reduced calcium hydroxide content. The improved performance of slag cements compared with cement alone for sulphate resistance has long been known [ 3 J , Table 2 gives the requirements in BRE Digest 363 [ I ] in terms of cement type, and content, and waterlcement ratio for the different conditions in Table 1 (for well compacted cast-in-situ unreinforced concrete 140mm to 450mm in thickness exposed on a l l vertical faces to a permeable sulphate soil or fill). The cement types are currently to the appropriate British standards, which are in the process of replacement by the corresponding European standards, Modifications to Table 2 are necessary for certain situations of exposure to sulphates. For instance, for concrete floors, a membrane is recommended between fill or hardcore and the floor for Class 1 or 2 conditions, and Classes 3, 4, and 5 are not recommended for use as a base for concrete floors. Classification is increased by one class for basement, embankment or retaining walls where there is a hydrostatic head by the groundwater greater than 5 times the thickness of the concrete (unless other precautions are taken). The conditions in Table 1 refer to permeable soils which give rise to mobile groundwater: if the water is considered essentially static, a reduction of one class may be made. 2.

919

Table 2 Cement type and content, and water/cement ratio Class

Cement type

Minimum cemegt content kg/m (Notes 1 and 2)

Maximum free water/cement ratio (Note 1)

1

A/B/C

Note 3

0.65

4A 4B

B C

360 380

0.45 0.45

5A As for Class 4 t surface protection 5B ........................................................................ Note 1. Cement content includes flyash and slag. Note 2. Cement contents relate to 20mm nominal maximum size aggregate. Minimum cement contents should be increased by 4Okg/m for lOmm aggregate, and decreased by 30kg/m for 4 0 m aggregate. Note 3. Cement type A is Portland cement, or Portland cement/blastfurnace slag or flyash. Cement type B is sulphate-resisting Portland cement. Cement type C contains Portland cement/blast furnace slag or flyash, with specified ranges for slag or ash contents. 3. MAGNESIUM SULPHATE ATTACK Magnesium sulphate attack is more aggressive, since not only is there reaction with the calcium aluminate hydrates as in sodium sulphate attack, but a direct reaction with the calcium silicate hydrates and calcium hydroxide. Ettringite, gypsum, hydrated magnesium silicate, and brucite [Mg(OH) ] are found in the reaction products. The more aggressive nature of magnes& sulphate attack is reflected in the more stringent requirements given in Table 2: however in severe conditions neither the use of sulphateresisting cement nor incorporation of cement replacements will provide lasting protection. Lawrence [ 41 has discussed magnesium sulphate attack in the overall context of sulphate attack. 4.

ACID ATTACK

Sulphuric acid and sulphates in acid solution frequently result from industrial wastes. These include colliery waste, ash from the combustion of coal from older power stations or from refuse incineration, or gasworks waste. Other acid solutions containing hydrochloric or nitric acid can result from particular industrial processes. In land previously used for the carbonisation of coal, a weak acid is formed from the solution of phenol in water. Waste creosote may also give rise to phenols, cresols, and other organic acids. Other organic acids may be produced which also cause attack. Lactic acid has caused severe attack on concrete dairy and cheese factory

920

floors, and also on mortar in tile floors; citric, malic, tartaric, and acetic acids cause similar attack to lactic acid [5]. Harrison [ 6 J reviewed recommendations for the type of concrete suitable for acid conditions and presented data on performance in field and laboratory studies. Virtually all acid conditions will attack concrete in the ground: the cement paste and calcium hydroxide which is produced as a result of the cement hydration are directly attacked. Well-cured concrete with a low water/cement ratio, and a pozzolanic replacement such as flyash or slag, with low permeability will be beneficial, although to a limited extent only. Severity of attack depends primarily on the ground conditions; in particular the pH, but also the mobility of the groundwater. For ground containing wastes, a pH above 5.5 in static ground conditions is considered to be relatively non-aggressive, but slightly aggressive if the groundwater is mobile. A pH of 4.5 to 5.5 is moderately aggressive, and less than 4.5 is highly aggressive, again, particularly with mobile groundwater. In low pff conditions, surface protection will be necessary. 5.

THAUMASITE FORMATION

Thaumasite [CaSiO .CaCO .CaSO .15H20] has been identified in a number of sites where detdriorakon 40f cementitious materials has occurred. Thaumasite is structurally similar to ettringite, and may occur together with ettringite. Crammond and Nixon [ 71 described field investigations and studies of laboratory mortars. The optimum conditions are consistently cold, wet environments, along with readily available supplies of calcium silicate, sulphate ions and carbonate ions. Where concrete contains a finely divided source of carbonate ions, the reaction can proceed very rapidly, even where the concrete is of good quality, or a sulphate-resisting cement is used. A source of magnesium ions, even in small amounts, encouraged thaumasite formation. Although it is not clear whether degradation by thaumasite formation is a widespread phenomenon, the use of concretes, mortars , etc containing limestone fines in cold, wet conditions, where sulphate is present in groundwater, should be treated with caution. 6.

SODIUM SULPHATE CRYSTALLISATION

Novak and Colville [ E l reported the formation of efflorescent salts on the surface of degrading concrete slabs in California. They attributed a possible cause of the degradation to pore pressure exerted by crystallisation of thenardite [Na SO ] , and the conversion of thenardite to mirabilite [Na SO .10H 01. A like?y dource for the sodium was weathered and poorly crystalhsdd sadium plagioclase feldspar in the soil, but found no source of sulphate. No gypsum, ettringite, or thaumasite was detected. Plowman [ 9 ] found degradation of concrete bricks in a housing scheme in the UK due to thenardite crystallisation. No mirabilite, gypsum, ettringite, or thaumasite was detected. Although the soil contained only relatively low concentrations of sulphate, the proposed mechanism was by concentration of salts in the groundwater due to capillary action in a boundary zone at ground level, with evaporation of the solution within the bricks. Matsushjta and Suga [lo] described a similar formation of thenardite and mirabilite in building foundations built on land reclaimed with unaltered coal waste in Japan. They found that deterioration was due largely to the formation of gypsum and ettringite, but considered that sodium sulphate crystallisation was also an important contributory factor.

92 1

It is significant that this mechanism can apparently occur where ground conditions would not necessarily be regarded as deleterious, i.e. a low sulphate content of the groundwater, The presence of sodium sulehates in efflorescence salts has been observed in low sulphate ground conditions; a concentration mechanism by capillary action was demonstrated in the laboratory by Matsushita and Suga. The mechanism appears to depend upon continuously wet ground conditions, with damage occurring where drying and crystallisation is within the concrete rather than on the surface. 7

FLYASH USED AS LANDFILL OR STRUCTURAL FILL

The use of flyash as landfill or structural fill involves the addition of water - typically 20-25% by weight - which causes a limited amount of hardening and development of a low strength. A comprehensive survey of the soluble alkalies in UK ashes was carried out by Sherwood and Ryley [ l l ] , in which they showed that only trace quantities of sodium, potassium, and magnesium ions were taken into solution, and that the principal soluble ions were calcium and sulphate. Gibergues and Vaquier [ 1 2 ] also found that the principal ions leaching out were calcium and sulphate: solution of calcium and sulphate was rapid and simultaneous, and gypsum precipitated on standing. Raask [ 1 3 ] reported an immediate 'acid flash' due to the faster solubility of sulphate, but calcium subsequently went into solution, and the final pH was 8-9; for a more alkaline ash, the pH rose immediately above 11. Cabrera and Plowman [ 1 4 ] studied the rate of solution of calcium and sulphate, and the rate of change of pH in detail for a typical low calcium ash. The pH and solubility study was carried out with a 5 : l water:ash ratio. Gypsum formation was studied by X-ray diffraction using a 1 : 5 water:ash ratio. The pH/time relationship is shown in Figure 1, the concentration/time relationships for calcium and sulphate are shown in Figure 2 , the increase in gypsum formation with time is shown in Figure 3 . The low initial pH is the result of very rapid solution of sulphate adsorbed on the surface of the ash particles in the electrostatic precipitators in the power station. Release of calcium into solution causes a gradual rise in pH. The solution becomes supersaturated with respect to gypsum, which then precipitates, and further sulphate and calcium dissolve. The rate at which the solution becomes saturated depends on the water/ash ratio; at the lower ratios which occur in landfill, the precipitation of gypsum is extremely fast, as can be seen in Figure 3 . The formation of gypsum is responsible for the hardening of the ash, and since calcium and sulphate are the only ions released in significant quantities, the material will give rise to only limited sulphate conditions (Class 2 in Table 1): the limit for Class 2 conditions is in fact deliberately set at the solubility of g y p s p . This mechanism is responsible for the fact that in the UK, ash used as fill in contact with concrete foundations does not cause a significant rate of sulphate attack. The same mechanism holds for almost all low calcium ashes, but care must be taken in applying the same criterion to high lime ashes, since these may have a significant level of soluble sodium or potassium, which have more soluble sulphates. It is suggested that a solubility test should be carried out if the aggressive potential of the ash is in doubt. 8

VOLUME CHANGES DUE TO PYRITES OXIDATION

Many waste materials such as colliery shale contain iron pyrites (FeS ). Where atmospheric weathering can take place, there is the possibility tiat the pyrites can be weathered to give products of greater volume, which may lead to expansion [ 1 5 ] . Grattan-Bellew and Eden found that drainage of

922

9

8

7

P" 6

5

4

3

b

I60

do

4 k TIME

Figure 1.

10.

- sbo MIMS.

TI0

Joo

Variation of pH with time for water:ash ratio of 5 : l .

0

so3

A cao 25.

Figure 2.

Solubility of CaO and SO3 with time for 5:l water:ash ratio.

923

U Y

A

.-t v) c

W t

c -

Figure 3 .

Rate of formation of gypsum for a 1:5 Water:ash ratio.

marshland led to oxidation of pyrite in shale beds, and the resulting formation of gypsum between the shale layers led to a volume increase which caused floor heave. They also proposed a series of oxidation and base exchange reactions for the oxidation of pyrite to jarosite [KFe (SO ) (OH) 1, which also results in a volume increase. The reactions can h s o 4 jiberite sulphuric acid, with the potential for both sulphate and acid attack on concrete with which it is in contact. An investigation was carried out by Nixon [16] into floor heave in houses built on shales which were both from a quarried source and waste from an ironstone mine. Deposits of both gypsum and jarosite were found in the quarried material, but only jarosite in the ironstone shale. Nixon recommends that shales likely to cause heave may be identifed by X-ray diffraction, together with total sulphur, acid-soluble sulphate, and calcium contents. The shale should be regarded as potentially troublesome if the total sulphur content (as sulphate) is greater than the acid-soluble sulphate, and a significant quantity of acid-soluble calcium is present. The author has investigated instances of pyrites oxidation of shales where both gypsum and jarosite were formed, and had caused floor heave. In most instances oxidation was virtually complete, but an X-ray diffraction examination, and analysis as recommended by Nixon is always necessary to ensure that no significant amount of pyrites remains. 9

VOLUME CHANGES DUE TO EXPANSIVE STEEL SLAG

Crawford and Burn [17] described an example of building movements due to an expansive steel slag backfill under a floor slab. Fresh slag contained substantial quantities of unslaked lime (Cao) and periclase (MgO). The

924

determine a total MgO content, since in many materials this is largely, or even entirely, present in the form of magnesium silicates, or other magnesium compounds which are not susceptible to the hydration reaction. 10 CONCLUSIONS

The disposal of industrial waste as landfill can give rise to chemicals in the groundwater which can cause damage to concrete foundations. Sulphate can arise from a number of sourcesI including pyrites oxidation. If the groundwater contains magnesium, or is acidic, more severe attack may occur. Different mechanisms of attack may be observed: in addition to the conventional form of sulphate attack by the formation of ettringite and gypsum, thaumasite formation can occur, or sodium sulphate crystallisation, The use of pozzolanic cement both of which cause severe damage. replacements such as flyash or ground granulated blast furnace slag can alter the permeability and mechanism of the severity of attack, If the landfill is a low-calcium flyash, the sulphate content of the groundwater will generally be limited to the solubility of gypsum. BRE Digest 363 classifies the severity of sulphate conditions, and recommends concrete specifications for the different classes. In addition to attack on concrete, industrial fill can cause disruption to buildings constructed on it by volume changes within the fill due to pyrites oxidation or expansive steel slag. Extracts and Tables from BRE Digest 363 are included by permission of the Director of the Building Research Establishment. REFERENCES 1 2 3

BRE Digest 363, July 1991. J, G. Cabrera and C, Plowman, Adv. Cem. Res,, 1 (3) 1988, 171. W. Gutt, W. Kinniburgh and A. J. Newman, Mag. Concr. Res., 19 (59), 1967, 71.

4 5 6

7 8 9 10 11 12 13 14

C. D, Lawrence, Mag. Concr. Res., 42 (153) 1990, 249. F. M. Lea, The Chemistry of Cement and Concrete, 3rd ed. 1970, 661. W. H. Harrison, Concrete, 21 (2) 1987. N. J. Crammond and P. J. Nixon, Conf. Durability of Building Mat. and Comp. 6, 1, Japan 1993, 295. H. Matsushita and I. Suaa. Conf. Durability of Buldina Mat. and ComD. 6. 1, Japan 1993, 647. G. A, Novak and A. A. Colville, Cem. and Concr. Res., 19, 1989, 1. C. Plowman, An investigation of the cause of degradation.of concrete bricks (unpublished), P. T. sherwood and M. D. Ryley, Road Res. Lab. Rep. no. 49, 1966. A. C. Gibergues and A. Vaquier, Mat. Const. no. 32, 1973, 141. E, Raask, Int. Symp. Use of PFA in Conc., Leeds, 1982, 5. J. G. Cabrera and C. Plowman, Int. Symp. Use of PFA in Concrete, Leeds a

1982, 15 P. E. 1975, 16 P. J. 17 C. 8.

.

I

111.

Grattan-Bellew and W. J. Eden, Canadian Geotechnical Journal, 372.

Nixon, Chemistry and Industry, March 1978, 160-164. Crawford and K. N. Burn, J. Soil Mech. and Found. Div., Am. SOC. Civ. Eng., NOV. 1969 pp. 1325-1334.

.

Environmental Aspects of Construction with Wute Materials J.J.J.M. Goumans, H A . van &r S h t and Th.G. Aalbers (Edtors) el994 Elsevier Science B.V. AN rights reserved.

925

Contaminated soil cement stabilizations for application as a construction material. P.J. Kroes' and J. van Leeuwen2 IWACO B.V., Consultants for Water & Environment, P . 0 . b ~8520, 3009 AM Rotterdam, The Netherlands

*

Gemeentewerken Rotterdam, Ingenieursbureau Geotechniek en Milieu, P.O.Box 6633, 3002 AP Rotterdam, The Netherlands

Abstract Possibilities for using non-cleanable contaminated soils as an alternative for sand in cement stabilizations, have been studied with respect to physical properties (compressive strength and durability) and leachability. Typical soil parameters like organic matter content, clay content and contaminant type and concentration that may effect the compressive strength have been investigated. It can be concluded that contaminated soil cement stabilizations conform to the construction engineering criteria and leachability standards and have potential application as an alternative for sand cement stabilizations. 1. INTRODUCTION

The excavation of primary surface minerals like sand meets more and more opposition as a result of the negative environmental aspects. The excavation policy in the Netherlands strongly advocates the application of alternative materials, including waste materials and industrial residues. The policy of the national government regarding waste materials in general offers an additional strong stimulus towards minimizing the dumping (landfilling) of waste materials and where possible, an efficient reuse. In the city of Rotterdam @art of the highly industrialized and densely populated area of the Rijnmond in the west of the Netherlands) large quantities of contaminated soil are being excavated because of remediation of sites and earth works. For the category noncleanable contaminated soil that is being landfilled the possibilities for application as an alternative for sand in cement stabilizations have been investigated [l]. These soil cement stabilizations can find there application in civil engineering constructions as can be shown in figure 1.

In the Netherlands there is little experience with respect to stabilizing contaminated soil with cement. Factors that can influence the compressive strength are the contaminants and the more heterogeneous matrix of soil (organic matter, lutum) in comparison with sand.

926

Figure 1. Application of cement stabilization in a road bed construction

2. MATERIALS AND METHODS Soil samples from 13 different sites in the Rotterdam region, from the above mentioned category, have been selected for this research. Each soil sample consisted of about 150 kg. The typical soil parameter contents and contaminant contents researched are summarized in table 1.

Soil samples 1-13

Dry matter

Organic matter

(%)

(%)

72-94

1-14

Lutum

Pb

cu

(%)

@pm)

(ppm)

0.34

7-11500

13-790

Zn (ppm) 83-900

Cd (ppm)

Environmental Aspects of Construction with Waste Materials

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