Recycling of Demolished Concrete and Masonry (Rilem Report, No 6)

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Recycling of Demolished Concrete and Masonry

Other RILEM Reports available from Spon Press 1 Soiling and Cleaning of Building Façades Report of Technical Committee 62-SCF Edited by L.G.W.Verhoef 2 Corrosion of Steel in Concrete Report of Technical Committee 60-CSC Edited by P.Schiessl 3 Fracture Mechanics of Concrete Structures: From Theory to Applications Report of Technical Committee 90-FMA Edited by L.Elfgren 4 Geomembranes—Identification and Performance Testing Report of Technical Committee 103-MGH Edited by A.Rollin and J.M.Rigo 5 Fracture Mechanics Test Methods for Concrete Report of Technical Committee 89-FMT Edited by S.P.Shah and A.Carpinteri 6 Recycling of Demolished Concrete and Masonry Report of Technical Committee 37-DRC Edited by T.C.Hansen 7 Fly Ash in Concrete: Properties and Performance Report of Technical Committee 67-FAB Edited by K.Wesche Publisher’s Note This RILEM Report has been produced from the typed chapters provided by the members of RILEM Technical Committee 37-DRC, whose cooperation is gratefully acknowledged. This has facilitated rapid publication of the Report.

Recycling of Demolished Concrete and Masonry Report of Technical Committee 37-DRC Demolition and Reuse of Concrete RILEM (The International Union of Testing and Research Laboratories for Materials and Structures) Edited by

T.C.Hansen

London

First edition 1992 by E &F N Spon Transferred to Digital Printing 2003 Spon Press is an imprint of the Taylor & Francis Group This edition published in the Taylor & Francis e-Library, 2005. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk”. © 1992 RILEM ISBN 0-203-62645-1 Master e-book ISBN

ISBN 0-203-63031-9 (Adobe e-Reader Format) ISBN 0-419-15820 (Print Edition) 0-442-31281-4 (Print Edition) (USA) Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organisation outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the UK address printed on this page. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication data available A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication data available

Contents

List of reports issued by RILEM Technical Committee 37-DRC Preface

PART ONE RECYCLED AGGREGATES AND RECYCLED AGGREGATE CONCRETE. Third State-of-the-art Report 1945–1989 Torben C.Hansen Building Materials Laboratory, Technical University of Denmark PART TWO RECYCLING OF MASONRY RUBBLE Dr R.R.Schulz Institute for Building Materials Testing, Waldkirch, Germany Dr Ch.F.Hendricks Road Engineering Division, Rijkswaterstaat, Delft, The Netherlands PART THREE BLASTING OF CONCRETE: LOCALIZED CUTTING IN AND PARTIAL DEMOLITION OF CONCRETE STRUCTURES C.Molin Trimex, Sweden (formerly Swedish National Testing Institute) E.K.Lauritzen Demex, Consulting Engineers Ltd, Denmark

Index

vii viii

1

139

240

284

List of reports issued by RILEM Technical Committee 37-DRC 1 Nixon, P.J. (1978) Recycled concrete as an aggregate for concrete—a review. Materials and Structures, 11 (65) September-October, pp. 371–8. 2 Task Force 1—RILEM Technical Committee 37-DRC (1985) Demolition Techniques. European Demolition Association, Wassenaarseweg 80, 2596 CZ Den Haag, The Netherlands, Special Technical Publication, May, 1985. 3 EDA-RILEM (1985) Demolition Techniques. Proc. First International EDA-RILEM Conference on Demolition and Reuse of Concrete, Rotterdam, 1–3 June, 1985, 1, European Demolition Association, Wasenaarseweg 80, 2596 CZ Den Haag, The Netherlands. 4 EDA-RILEM (1985) Reuse of Concrete and Brick Materials. Proc. First International EDA-RILEM Conference on Demolition and Reuse of Concrete, Rotterdam, 1–3 June, 1985, 2, European Demolition Association, Wassenaarseweg 80, 2596 CZ Den Haag, The Netherlands. 5 Demolition and Reuse of Concrete and Masonry. Proceedings of the Second International Symposium on Demolition and Reuse of Concrete and Masonry, Tokyo, Japan, 7–11 November, 1988. Two Volume Set. Edited by Y.Kasai. Volume 1. Demolition Methods and Practice, 520 pages. Volume 2. Reuse of Demolition Waste, 296 pages. Hardback (0 412 32110 6 set). Chapman & Hall, 1988.

Preface It is becoming increasingly difficult and expensive for demolition contractors to dispose of building waste and demolition rubble. For environmental reasons, public authorities are looking for ways of reusing these materials. The purpose of this book is to make the construction industry and public authorities aware of the technical possibilities for recycling of demolished concrete and masonry. It also shows how localized cutting and partial demolition of concrete structures can be carried out. Recycling of Demolished Concrete and Masonry consists of three state-of-the-art Reports which have been prepared by members of an international RILEM Committee: • Recycled aggregates and recycled aggregate concrete • Recycled masonry as aggregate for concrete • Blasting of concrete: localized cutting in and partial demolition of concrete structures. The three Reports review a very wide range of research and practical experience on the subjects, much of which has not been easily accessible before. They are intended for use by building industry professionals involved in design and construction at all levels. It is the authors’ hope that they will be of particular use to demolition and recycling contractors, and to concrete technologists and ready mixed concrete producers. The three reports are the final result of work which was carried out over many years by RILEM Technical Committee 37-DRC on Demolition and Reuse of Concrete. The Committee was formed in 1976 and held its first meeting at the Building Research Station in Garston (UK) in June of 1977 under the chairmanship of Dr L.H.Everett. In 1978 the first RILEM TC-37-DRC state-of-the-art report was published on recycled concrete as an aggregate for concrete [1]. After the Committee was reorganized in 1981 and the author of this preface became chairman, a second Committee meeting was held in Copenhagen in December 1982. Since then the Committee has held meetings in the Netherlands, England, Belgium, France and Japan. The following general terms of reference of the Committee were agreed on at the meeting in Copenhagen in 1982. 1. To study the demolition techniques used for plain, reinforced, and prestressed concrete and to consider developments in techniques. 2. To study technical aspects associated with reuse of concrete and to consider economical, social and environmental aspects of demolition techniques and reuse of concrete. Three task forces were formed, each with its own specific terms of reference. Task Force 1 surveyed, on the basis of the existing literature, methods of demolition and fragmentation including economic, social and environmental aspects. It published its

findings in a general state-of-the-art report on demolition techniques [2] and a more specialized report on localized cutting in and partial demolition of concrete structures, which appears as Part 3 of this Volume. Task Force 2 collected and surveyed codes and regulations concerning demolition in various countries. It did not issue a separate state-of-the-art report. Instead its findings were included in Part 1 and 2 of this volume. Task Force 3 studied technical aspects associated with reuse of concrete and considered economic, social and environmental factors. It is the findings of Task Force 2 and 3 which are published as Part 1 and 2 of this Volume. The Committee arranged the first international symposium on demolition and recycling of concrete in Rotterdam in 1985 in co-operation with the European Demolition Association (EDA). The symposium proceedings were published in [3] and [4]. The symposium gave valuable input to the work of the Committee from an industrial point of view. Developments were fast, and it was soon decided to hold a second international RILEM symposium on demolition and reuse of concrete already in 1988 in Tokyo in order to make it possible for persons from science and practice from all over the world to communicate and exchange experience before the Committee was dissolved at a final meeting in Tokyo in 1988. The Proceedings of the Symposium were published in [5]. As chairman of RILEM TC–37–DRC 1 wish to thank the following persons who have served as members and corresponding members of the Committee over the years. Members: Mr R.C.Basart (NL), Dr Ch.F. Hendriks (NL), Professor P.Lindsell (GB), Professor Y.Kasai (Japan), Dr K. Kleiser (D), Dr R.R. Schulz (D), Professor Y.Malier (F), Mr R. Hartland (GB), Mr T.R.Mills (GB), Mr P. Mohr (DK), Dr C.Molin (S), Mr G.Ray (USA), Mr C. de Pauw (B), Mr E. Rousseau (B), Mr E.K. Lauritzen (DK), Secretary from 1982–1985, and Dr M.Mulheron (GB), Secretary from 1985–1988. Corresponding members: Mr F.D.Beresford (AUS), Mr M. Whelan (AUS), Mr A.D.Buck (USA), Dr S.FrondistouYannas (USA), Mr J.M.Loizeaux (USA), Mr J.F. Lamond (USA). Our very special thanks go to the European Demolition Association for its loyal co-operation in the work of the committee. The work of RILEM TC-37-DRC is being continued in a new RILEM Technical Committee 121-DRG on Guidance for Demolition and Reuse of Concrete and Masonry. RILEM TC-121-DRG will prepare Technical Recommendations leading to guidelines for production of concrete from recycled concrete and masonry, and guidelines for demolition and processing of demolition rubble with respect to the reuse of concrete and masonry. In addition the Committee will prepare a State-of-the-art Report on site clearing and demolition of damaged concrete structures with respect to the reuse of concrete and protection of the remaining structure. Special emphasis will be placed on earthquake and war damaged structures. TC-121-DRG is supporting the 1st International Conference on Concrete Blasting in Copenhagen in June 1992. Torben C.Hansen

PART ONE RECYCLED AGGREGATES AND RECYCLED AGGREGATE CONCRETE Third state-of-the-art report 1945–1989 TORBEN C.HANSEN Building Materials Laboratory, Technical University of Denmark

Recycled aggregates and recycled aggregate concrete

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The extensive, but fragmented research on recycled concrete aggregates and recycled aggregate concrete, which has been carried out in various parts of the world from 1945 to 1989, has been collated to form a comprehensive state-of-the-art document. A thorough analysis of the data has been made, leading to guidelines for the production and evaluation of recycled concrete aggregates as well as the design, production, and use of recycled aggregate concrete.

1. Introduction It has been estimated that approximately 50 million tons of concrete are currently demolished each year in the European Economic Communities (1). Lindsell and Mulheron (87) have estimated that 11 million tons of demolished concrete are dumped at landfill sites each year in the United Kingdom. Equivalent figures are 60 million tons in the United States (2, 3), and in Japan (12) the total quantity of concrete debris available for recycling on some scale is about 10 to 12 million tons. Karaa (93) has estimated that approximately 13 million tons of concrete is demolished in France every year. Very little demolished concrete is currently recycled or reused anywhere in the world. The small quantity which is recovered is mainly reused as nonstabilized base or sub-base in highway construction. The rest is dumped or disposed of as fill. For environmental and other reasons the number of readily accessible disposal sites around major cities in the world have decreased in recent years. Both disposal volume and maximum sizes of wastes have been restricted. In Japan disposal charges from 3 to 10 US dollars per ton were not uncommon in 1985. Moreover, distances between demolition sites and disposal areas have become larger and transportation costs higher. At the same time critical shortages of good natural aggregate are developing in many urban areas, and distances between deposits of natural material and sites of new construction have grown larger, and transportation costs have become correspondingly higher. It is estimated that between now and the year 2000, three times more demolished concrete will be generated each year than today. For these reasons it can be foreseen that demolition contractors will come under considerable economic and other pressure to process demolished concrete for reuse as unscreened gravel, base and sub-base materials, aggregates for production of new concrete or for other useful purposes. Large-scale recycling of demolished concrete will contribute not only to the solution of a growing waste disposal problem. It will also help to conserve natural resources of sand and gravel and to secure future supply of reasonably priced aggregates for building and road construction purposes within large urban areas. It is the purpose of this report to examine the current state-of-the-art for what concerns recycled aggregate and recycled aggregate concrete and to point out areas where research is needed in order to promote safe and economical use of such concrete.

Recycling of demolished concrete and masonry

4

Two literature searches were carried out in June 1987 in order to check whether the author of this state-of-the-art report had missed any major publications in the field. One search was carried out on a data base in the English language (COMPENDEX) and the other on a data base in the French language (PASCAL). Neither of the two searches gave satisfactory results. Keywords used in the two data bases were CONCRETE, RECYCLING and REUSE for COMPENDEX, and BÉTON RECYCLAGE for PASCAL. Neither of the two data bases covered the recycling of concrete in a comprehensive manner, and very little new literature was found, which had not previously been known to the author.

2. First state-of-the-art report 1945–1977 On behalf of RILEM Technical Committee 37-DRC, Nixon (5) prepared a state-of-the-art report on recycled concrete as an aggregate for concrete, covering the period 1945–1977. A list of literature reviewed by Nixon is presented in Appendix A. In 1977 Nixon concluded that a number of workers have examined the basic properties of concrete in which the aggregate is the product of crushing another concrete. Most have concentrated on uncontaminated material, often old laboratory test specimens. There is good agreement on most aspects of the behaviour of such recycled concrete. The most marked difference in the physical properties of the recycled concrete aggregate is higher water absorption, and it seems likely that this is due to absorption by cement paste adhering to the old aggregate particles. There is general agreement that the compressive strength (and judging from limited evidence, the flexural strength) is somewhat lower (up to about 20% lower in some cases, but usually less) compared with control mixes, but there does not seem to be any correlation between the loss in strength and the water-cement ratio of the final concrete. There is only limited evidence (and some disagreement) on the effect of the strength of the original concrete on the strength of the new concrete made with it as aggregate, but it seems probable, that when the concrete fails, it is the adhering mortar on the crushed concrete aggregate that is the weakest link. The use of crushed concrete fines does not seem to have any great effect on the compressive strength of the concrete, but it does seem to reduce the workability significantly. When only crushed concrete coarse aggregate is used, the workability is little different from control mixes. Again, when using recycled coarse aggregate, there is little difference in the modulus of elasticity; there is no information on the effect of fines on this property. The durability of the recycled concrete has been examined mostly with respect to the freeze/thaw resistance of the concrete, and the results suggest that with uncontaminated concrete there is no problem. In fact with concrete containing a highly porous frost susceptible aggregate there may actually be an improvement probably because the cement paste blocks up the pores. Drying shrinkage has been found to be somewhat


5

greater in the recycled concrete. There is no information on creep, wetting expansion or resistance to aggressive solutions such as sulfates of recycled concrete. Less work has been carried out on the effect of impurities in the crushed concrete on the properties of the final concrete. Most of that which has been done has been devoted to sulfate impurities, presumably originating from gypsum plaster. This would certainly be a major problem with the recycling of mixed demolition rubble. The results published suggest that for concrete placed in a position where it is likely to be wet for much of the time, a limit on the total soluble sulfate content of the aggregate of between 0.5 and 1% is advisable if ordinary Portland cement is used. Most workers have used finely powdered gypsum in their experiments. What little evidence there is on the effect of particle size has suggested that larger-sized pieces of gypsum cause less expansion. There is some conflict of evidence on the effect of pozzolanic cements including fly ash, and more work is needed. In 1977 Nixon concluded: There seems to be a reasonable knowledge of the basic engineering properties of the recycled concrete, and the main penalty in its use is a slightly lower compressive strength compared with a control mix made with the same original aggregate. A more thorough investigation of the effect of the strength of the original concrete would seem to be needed, however, and also a fundamental investigation of the mode of failure of the recycled concrete which may enable the reason for the lowered strength to be understood and counteracted. The main field in which more information on the behaviour of the recycled concrete is required is its durability. Creep, wetting expansion, and porosity all need to be examined as does the effect of aggressive solutions.’ The above remarks apply to uncontaminated concrete from a known source. If, however, recycled concrete aggregate is to be used on any scale, then the rubble from general building demolition would have to be exploited. Here there is a basic lack of knowledge of what might be expected to occur in the output from a particular method of processing the rubble. Possible methods of controlling impurities, e.g. magnetic separation of metal reinforcement and means of reducing the amount of gypsum, need to be explored and the effect of the remaining contaminants examined. Once identified, there is some knowledge of the behaviour of common contaminants, but much investigation will be needed in order to deal with all the possibilities, for example the effects of mixtures of cement other than Portland cement in the crushed concrete.


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3. Second and third state-of-the-art reports 1978– 1989 A second state-of-the-art report on recycled aggregates and recycled aggregate concrete was prepared by Hansen and published in Materials and Structures Vol. 19, No 111, May-June 1986, pp. 201–246, covering developments between 1978 and 1985. The current third state-of-the-art report is an updated version of the second state-of-the-art report including developments in the period 1985–1989. More than 80 new publications have been reviewed. In its scope this report is limited to review developments to 1989 concerning the use of crushed concrete as recycled aggregates for production of new, plain and reinforced, normal-weight concrete in building and road construction. By crushed concrete is meant concrete made with Portland cements, Portland-pozzolan cements or blast furnace slag cements, and with natural or manufactured sand or a combination thereof and with aggregates consisting of natural gravel, crushed gravel, crushed stone, air-cooled blast furnace slag or combinations thereof. Crushed concretes made with high-alumina cements or with lightweight aggregate, brick-waste aggregate, or aggregates made from other waste products are not dealt with in this review. Crushed concretes which contain more than 5% of other substances than concrete are also excluded from this review.

4. Terminology Partially based on a Japanese Proposed Standard on ‘Recycled aggregate and recycled aggregate concrete’ which was prepared by the Building Contractors Society of Japan in 1977, B.C.S.J. (6), the following terminology is suggested: Waste concrete Concrete debris from demolished structures as well as fresh and hardened concrete which has been rejected by ready-mixed or site-mixed concrete producers or by concrete product manufacturers. Conventional concrete Concrete produced with natural sand as fine aggregate and gravel or crushed rock as


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coarse aggregate. Original concrete Concrete from reinforced concrete structures, plain concrete structures or precast concrete units which can be used as raw material for production of recycled aggregates (or for other useful purposes). Original concrete is occasionally referred to as old concrete, demolished concrete or conventional concrete. Recycled aggregate concrete Concrete produced using recycled aggregates or combinations of recycled aggregates and other aggregates. Recycled aggregate concrete is sometimes referred to as new concrete. Original mortar Hardened mixture of cement, water, and conventional fine aggregate less than 4–5 mm in original concrete. Some original mortar is always attached to particles of original aggregate in recycled aggregates. Original mortar is occasionally referred to as old mortar, or conventional mortar. Original aggregates Conventional aggregates from which original concrete is produced. Original aggregates are natural or manufactured, coarse or fine aggregates commonly used for production of conventional concrete. When no misunderstanding is possible, original aggregates may also be referred to as virgin or conventional aggregates. It is suggested to use the notation Ns for natural sand, Ng for natural gravel, Ncs, for sand produced by the crushing of natural materials, and Ncc for natural crushed aggregate. N stands for natural, g stands for ‘gravel’ while cs stands for ‘crushed sand’ and cc for ‘crushed coarse aggregate’. Recycled concrete aggregates Aggregates produced by the crushing of original concrete; such aggregates can be fine or coarse recycled aggregates. Fine recycled aggregate is sometimes referred to as crushed concrete fines. When no misunderstanding is possible, recycled concrete aggregates may be referred to as recycled aggregates. This is the case in the present state-of-the-art report. It is suggested to use the notation Rs for recycled fine aggregate and Rc for recycled coarse aggregate. R stands for ‘recycled’ and s stands for ‘sand’, while c stands for ‘coarse aggregate’.


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5. Original concrete Demolition methods for plain and reinforced concrete are dealt with in another part of this book, and in a separate state-of-the-art report (78) published by RILEM TC-37DRC. Demolished concrete may be mixed with soil or other wasted building materials, or it may be contaminated by impurities. However, by observing a few simple precautions during the demolition process, the potential for recycling demolished concrete can be improved and the value of the debris increased.

5.1 Separation of different qualities of original concrete Records of composition, quality, and history of the original concrete are valuable documents in determining the recycling potential of any concrete structure. Even when such records are not available, but it can be shown that mix proportions and strengths of original concretes are different, such concretes should not be treated as equal during demolition.

5.2 Demolition of original concrete and removal of reinforcing steel Concrete in structures to be demolished may have various types of finishes, cladding materials, lumber, dirt, steel, and hardwares attached to them. It is an advantage if such concrete, which is to be used for production of recycled aggregates, is made free from foreign matter before demolition. Early concern that steel reinforcement in waste concrete would ball up and jam crushers has apparently been somewhat exaggerated. It has proved to be fairly easy to separate steel reinforcement from concrete, at least for what concerns lightly reinforced concrete pavement slabs. This is best demonstrated by describing a set of operations used in the successful break-up, removal, processing, and rehabilitation of the concrete pavement of Edens Expressway in the midst of the metropolitan area of Chicago, Illinois, (Dierkes (7a) and Krueger (7b)). The 25 cm mesh reinforced pavement was broken by two large mobile diesel hammers. This equipment fractured the old slab into pieces about 60 cm maximum size at a rate of between 460 m and 600 m of 11 m wide pavements during a twelve-hour work shift. Each diesel hammer had an enclosed bounce cylinder and a 1750 kg piston to yield a maximum impact on the breaking shoe. The hammer cycled at over 100 strokes per minute and broke the mesh effectively in one pass. The diesel hammers were towed at


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about 15 m/min so as to strike the pavement at 15 cm intervals. The next operation used a rubber tyred hydraulic excavator with a large curved, pointed hard-steel picker tooth (a so-called ‘rhino-horn’) mounted where the bucket usually is. The excavator was positioned along the side of the pavement. By reaching to the opposite side of the pavement with the hoe arm, the tooth could be pulled transversely up and through the shattered concrete. This pulled the concrete pieces towards the centre line and separated most of the reinforcement. The operation was repeated at given intervals from both sides of the old pavement. (Other contractors load trucks with backhoes directly off the grade without the rhino-horn. They are likely to pick up more of the base material and incorporate it in the recycled aggregate, which is undesirable.) Workers followed this operation along with hydraulic shears, cutting and pulling out loose reinforcing steel and putting it on the shoulder for pick-up and salvage. The hydraulic shears were also used to cut the reinforcing, once on the shoulder, into shorter length for easier handling and better salvage value. 90–95% of the reinforcing was removed this way. The remainder was still embedded in the concrete and had to be removed by crushing. When the reinforcing in the old pavement was mesh rather than bars, it was somewhat more difficult to handle. More cutting was required to separate the concrete pieces after the tooth had gone through, than was necessary for bar reinforcing. However, nearly the same percentage of reinforcing could be removed on grade. The broken pavement was then loaded on to trucks for hauling to a crusher and screening plant which was set up at a clover-leaf type interchange. If the concrete was properly sized when it was shattered, it was put in a stockpile. When an inordinate number of large pieces of broken concrete came from the grade, a wrecking ball was used to break these into a size that the crusher could accommodate. Concrete was then fed into a primary jaw crusher. 30–40 cm pieces were reduced to 64–76 mm top size. A smaller jaw crusher plus a hammer mill was used for secondary crushing which reduced the top size to 19–25 mm and produced an aggregate which met specifications, with less than 2% passing the ASTM No. 200 sieve. Remaining reinforcement and dowel bars presented no problems to the primary crusher. A large self-cleaning electromagnet was placed over the belt coming from the primary crusher to collect any reinforcing that had remained embedded in the concrete. About two semi-loads of wire per shift were removed from the broken concrete. It is reported that the proceeds from the sale of salvaged steel from a pavement recycling job usually more than pays for recovery and for loading and hauling it away. Several other projects where steel reinforcement has successfully been removed from recycled pavement concrete are reported in (7) and by Chase and Lane (59), McCarthy and MacCreery (67), and Strand (68). The main concern when removing broken concrete is not to pick up material which is not wanted in the concrete mix. If the construction site is on clay soils, the loading, hauling and stockpiling operation can incorporate clay into the salvaged concrete pile; and the reclaiming operation from the salvage pile to feed the crusher can pick up still more. Once clay balls are incorporated there is no reasonable way to get them back out. Extreme care should be taken if the pavement being salvaged or the stockpile, crusher or plant site rests on a clay subgrade (108).


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While most projects in the US employ conventional pavement breakers such as diesel hammers or wrecking balls, the Europeans have tried other types of equipment. The Wirtgen machine, made in Germany, was used for two major recycling projects on motorways near Paris, France. More recently a Wirtgen CB 7000 guillotine concrete shattering machine was used when recycling Detroit’s Lodge Freeway, (109) and (110). These pavement beakers use a 6.3 ton, 170 cm wide guillotine-type drop weight which can generate more than 160 000 Joules of energy, and can be controlled to provide as little as 16 000 Joules of energy. The crack spacing and amount of breakage are varied by controlling the machine’s speed and the drop height of the weight. The newest machine to show considerable promise as a recycling tool is the Resonant Pavement Breaker. This self-propelled 50-ton machine employs a 12-feet beam that vibrates approximately 1 1/2 inches 44 times a second. This huge ‘tuning fork’ is equipped with a special knife-like tool that shatters the concrete without transmitting vibrations to the subgrade, underground utilities, or adjacent slabs. One of the more interesting uses for this new machine was in the reconstruction of the San Francisco cable car tracks where it shattered the concrete around the tracks and cableway. In North Dakota the same machine was used to recycle 12 miles of two-lane pavement on Interstate-94 (20). The Resonant Pavement Breaker creates much less earth vibration than the drop hammer. It also operates at lower production rates and breaks the pavement into smaller pieces. Strand (68) concluded that machines which are used to break up concrete pavements are either impact or resonant breakers. Hironaka et al. (117) presents an extensive table of pavement breakers which were available on the commercial market in 1987. Impact breakers consist of diesel hammers, mechanically, pneumatically or hydraulically activated falling weights, or leaf spring whiparm hammer breakers. Each type has unique characteristics. Diesel hammers impact the greatest energy and are the fastest; their disadvantage lies in the depressing of the broken pavement into a yielding base. The mechanically, pneumatically or hydraulically activated falling weights seem to be slower, but the braking patterns are finer, resulting in easier removal of reinforcing steel. The resonant breaker is the slowest in production although its use has resulted in more efficient and effective removal of reinforcing steel and less base disturbance. The resonant breaker is probably most effective where the sub-base is deteriorated and no longer provides good support. The diesel hammer appears to perform best on pavement where the sub-base is still firm. However, Hironaka et al. (117) concludes that the effectiveness of pavement breaking equipment depends on factors, that could vary from site to site. Therefore, to determine the best systems it is necessary to conduct a controlled experiment of those systems that appear to have the best production rates to determine, on a given pavement, the actual rates, percentage of separated reinforcing steel, maximum size of broken fragments, and amount of fines generated. Pavement breaking is likely to generate complaints from local house owners if the houses are near the pavement that is being removed. Complaints sometime occur when maximum earth vibrations exceed 0.03 inch per second and are likely when vibrations are 0.06 inch per second or more. Vibrations caused by 18 000 foot pound hammers get down below this probable complaint level at roughly 140 feet from the source. The 30


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000 foot pound hammer reaches the 0.06 level at about 200 feet. But it is many hundreds of feet from the guillotine-type drop hammer before that low a level is attained (108). Although the presence of steel reinforcement in concrete does not represent a major problem in the recycling of pavements, it does slow down operations. When attempting to recycle heavily reinforced structural concrete, the problem is more severe, as reinforcement bars and mesh tend to ball up and jam crushers. The problem was overcome on pavement projects in Michigan and Iowa (59, 67) where reinforcement was effectively separated from concrete by means of an impact crusher hammer and selfcleaning magnets. Practical experience has shown that very large jaw crushers (8), and even better impact crushers (9) are capable of handling heavily reinforced chunks of concrete without excessive difficulties, provided each chunk can be accommodated by the respective crusher. After primary crushing most steel can be removed from the product on its way to the secondary crusher by means of self-cleaning electromagnets which are placed over the conveyor belt. De Pauw (10) reported that 0.30 x 0.30 x 0.90 m heavily reinforced chunks of concrete were fractionated by means of explosives. Steel was cleanly separated from concrete and the resulting recycled aggregates had a particle size distribution which is suitable for concrete production. Although this process is still at the experimental stage, it could become a desirable alternative to mechanical crushing of concrete. De Pauw (11) also reported that up to 1.2×1.2×2 m reinforced concrete blocks can be successfully fractionated using a type of equipment which is commonly used to crush discarded aircraft engines and other large machinery. Hafemeister (54) reports on an impact roll crusher, produced by Klöckner-Becorit in West Germany, which is capable of processing 300–500 t/hr of 1100 mm maximum size reinforced concrete debris, see also (61). Zagurskij and Zhadanovskij (83) report that a crushing device has been developed by SKTB Glavmospromstroymaterials and is currently being used in 18 recycling plants in the USSR. The device is capable of crushing the concrete and sorting out the reinforcement from up to 24 m long, 3.5 m wide and 0.6 m thick precast concrete units. The units to be demolished are placed on a stationary bar-type grizzly by a lifting device, and a hydraulic press which is equipped with a lever knife is moved along the grizzly. Periodically the knife is lowered and crushes the concrete unit. Crushed concrete is discharged through the bar grate of the grizzly on to a belt conveyor which takes it to a primary jaw crusher. The clean reinforcement cage is lifted from the grizzly by means of a magnet and reused as scrap for the production of new reinforcing steel. Ridout (119) reports on a machine capable of safely demolishing pre-tensioned and post-tensioned structures.


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6. Production of recycled aggregate 6.1 Layout of production plants Plants for production of recycled aggregates are not much different from plants for production of crushed aggregate from other sources. They incorporate various types of crushers, screens, transfer equipment, and devices for removal of foreign matter. The basic method of recycling is one of crushing the debris to produce a granular product of a given particle size. The degree of reprocessing carried out after this is determined by the level of contamination of the initial debris and the application for which the recycled material will be used such as: (1) General bulk fill; (2) Base or fill in drainage projects; (3) Sub-base or surface material in road construction or (4) New concrete manufacture. Boesman (62) has discussed problems associated with the design of recycling plants for demolition waste. Drees (95) has published a comprehensive review of the lay-out of recycling plants for demolished concrete, their equipment, treatment of raw materials and economy. Hironaka, Cline and Shoemaker (117) studied different aspects of the recycling process of pavement including breakup and removal, steel reinforcement removal, crushing, screening, stockpiling, mix design, testing, placing, finishing and performance. They conclude that recycling of portland cement concrete require some specialized equipment such as pavement breakers and electromagnets for steel removal; however, all other equipment and procedures are those commonly used in the construction industry. A number of different processes are possible for the crushing and sieving of demolition waste which mainly consists of concrete, such as would be the case for example on a pavement rehabilitation project. Some of these possibilities are illustrated in the block diagrams which are shown in Figures 6.1a and 6.1b, from (62). Installations working according to the principles of one of these schemes are regarded as first generation processing plants. They are characterized by the fact that there are no facilities for removing contaminants, with the possible exception of a magnet for the separation of reinforcement and other ferrous material. Such plants are frequently used on pavement rehabilitation and recycling projects. Figure 6.1a illustrates the closed system which is generally recommended. The open system of Figure 6.1b is advantageous in one way only, because the capacity is greater than that of the closed system, even though the same basic equipment is used. However, the maximum particle size is less well defined when an open than when a closed system is used, and this can lead to larger variations in the size of the end product, particularly when the input flow varies.


13

Fig. 6.1 a Flow chart of typical plant for production of recycled aggregate from concrete debris which is free from foreign matter, from Ref. (62). Closed system.

Fig. 6.1 b Flow chart of typical plant for reproduction or recycled aggregate from concrete debris which is free from foreign matter, from Ref. (62). Open system.

However, clean concrete cannot always be supplied from the demolition site. Demolished concrete often contains foreign matter in the form of metals, wood, hardboard, plastics, cladding, and roof coverings of various kinds. On the basis of first generation plants, the process scheme can be adapted for small amounts of contaminants by removing larger pieces of foreign matter mechanically or manually before crushing, and by cleaning the crushed product by means of dry or wet classification. Installations working according to such principles are regarded as second generation processing plants. Incidentally, a pilot project which was carried out in Denmark (79) showed that,


14

when properly organized, manual sorting of demolition rubble on the site and sale of reusable items can be done as economically as plain dumping of demolition rubble. All second generation plants are similar in basic design, as shown in principle in Figure 6.2. Large pieces of debris arriving from demolition sites are typically reduced to 0.4–0.7 m maximum size, for example by means of a wrecking ball and hydraulic shears to cut reinforcement. Large pieces of steel, wood, plastics, and paper are removed by hand. Incoming material is then crushed in a primary crusher which is usually of the jaw or impact type. Products from the primary crusher are screened on a deck typically consisting of a 10 mm scalping screen. Minus 10 mm material is wasted in order to eliminate fine contaminants such as dirt and gypsum. Plus 40 mm material is passed through a secondary jaw, cone, hammer or impact crusher in order to reduce all products to 40 mm maximum size. 40–100 mm material from the primary crusher bypasses the secondary crusher. All material is then washed or air-sifted in order to remove remaining lightweight matter such as wood, paper, and plastics, and the clean product is screened into various size fractions according to customer specifications. All iron and steel is removed by self-cleaning magnets which are placed at one or more critical locations above conveyor belts. Recycled and processed aggregates which are made from mixed building rubble will usually contain less than 1 percent of impurities, which may be good enough for road construction purposes, but not necessarily acceptable for concrete aggregates. However, when recycled aggregates are made from raw materials which contain more than 95% of old concrete, the end product will usually be clean enough to meet specifications for concrete aggregates without being washed. In ideal future third generation plants all demolished material should be supplied to the installation, processed and sold without there being any need to transport large quantities of residual matter to city dumps either from the demolition site or from the processing installation. This would be an ideal situation both from an environmental and an economic point of view. The first third generation recycling plant in the world where both rubble and wood wastes are processed is already operating in Rotterdam, the Netherlands (81). Bauchard (135–1) reports that two types of recycling plants operate in France, those that produce aggregates by primary crushing only, and those that employ both primary and secondary crushing. Products from plants that produce aggregates by primary crushing only, depend to a large extent on the quality of the demolition material. From an analysis of the products of the four plants which were in operation in France in 1987 it may be concluded that the demolition materials in fact are carefully selected. Only plain and reinforced concrete is accepted. This ensures that the quality of the aggregates is adequate for the purposes intended. All four plants utilize impact crushers but from different manufacturers. (Bergeaud, Blaw-Knox and Hazemag).


15

Fig. 6.2 Processing procedure for building and demolition waste.

Two plants are in operation in France, which produce aggregates by primary and secondary crushing. These are more permanent installations which are designed for the processing of demolition debris of varied origins. However, only one plant makes use of this possibility. It crushes only reinforced and unreinforced concrete. In their overall designs these plants are not much different from the Dutch plants, earlier described. According to Schulz (135d) there are more than 100 recycling plants in West Germany. Most of these are small with only installations for crushing and screening of preselected rubble. Compared with the USA more impact crushers are used in Germany


16

without secondary crushing. These simple plants are not capable of removing contaminants, with the exception of iron and steel by self-cleaning magnets and rubble fines by screening. Only a few larger plants in more populated areas apply washing or air sifting procedures for removal of lightweight particles such as dirt, clay lumps, wood, paper, plastics and textiles, so that frost resistant subgrade material or base course material can be produced which may justify higher prices. Schulz (135d) discusses how homogeneous higher grade materials might be produced in the future. Trevorrow et al. (135r) report that a typical site set-up in the UK to produce crusher run material consists of the following items of plant: 1. 360° tracked, hydraulic backactor. 2. Jaw crusher, single or double toggle. 3. Straight or swing conveyor with screen. 4. Tracked or rubber wheeled loader. Kabayashi and Kawano (135r) report that the Keihan Concrete Company in Kyoto, Japan, has developed a crusher which will remove much of the mortar which remain bonded to crushed concrete aggregate, thus refining the material. No details are given for what concerns the machine. The papers shows that a higher degree of refining for the recycled aggregate can produce higher quality concrete, but that this requires higher manufacturing costs and lower economical efficiency.

6.2 Crushers A number of different crushers such as jaw crushers, such as impact crushers, hammer mills and cone crushers, were studied in a Dutch investigation (11) in order to determine how well they performed when crushing old concrete. The results can be summarized as follows: Jaw crushers provide the best grain-size distribution of recycled aggregate for concrete production. The cone crusher is suitable for use as a secondary crusher with 200 mm maximum feed size. Swing hammer mills are seldom used. Impact crushers provide better grain-size distribution of aggregate for road construction purposes, and they are less sensitive to material which cannot be crushed, such as reinforcing bars. The first use of an impact crusher on a pavement rehabilitation project in the US was in Michigan in 1984 (59). Reinforcement mesh was effectively removed from concrete by means of two revolving magnetized drums after the crusher. When it comes to other properties of recycled concrete aggregate than grain-size distribution, jaw crushers perform better than impact crushers because jaw crushers which are set at 1.2–1.5 times the maximum size of original aggregate will crush only a small proportion of the original aggregate particles in the old concrete. Impact crushers, on the other hand, will crush old mortar and original aggregate particles alike and thus produce a coarse aggregate of lower quality. Another disadvantage of impact crushers is high wear and tear and therefore relatively high maintenance costs. All crushers investigated produced approximately the same percentage of cubical


17

particles in recycled aggregates and it appears that the properties of recycled concrete aggregates always are improved by secondary crushing, (135m), (135s), (135v) and 135x). A large proportion of the end product less than 40 mm from a crushing and sieving plant comes directly from the primary crusher. This can cause problems if the primary crusher supplies a product which does not satisfy the requirements laid down by the customer. Therefore, it should be possible to adjust the primary crusher so that the ratio between coarse and fine products can be reduced in the end product. This implies that the secondary crusher should have a relatively large capacity. Economy of coarse aggregate production can be maximized by balancing the crushers. The primary crusher should be set to reduce material to the largest size that will fit the secondary crusher without requiring tertiary crushing. A similar investigation of crusher efficiencies was carried out by B.C.S.J. (12). Table 6.1 shows that, except for grain-size distribution, the physical properties of recycled aggregates

Table 6.1 Physical properties of recycled aggregates produced by various kinds of crushers, from Ref. (12).

Type of Crusher

Type of Grain Size Concrete of Crusher Product

Specific Density in SSD Condition kg/m3

Water Absorption Percent

Sulphate L.A. Soundness Abrasion Loss Loss Percent by Percent Weight by Weight

max. minus fine coarse fine coarse fine coarse size, 5 mm agg. agg. agg. agg. agg. agg. mm

coarse agg.

Jaw Crusher

w/c=0.45 w/c=0.55 w/c-0.68

25 25 25

19.2 18.2 20.8

2100 2100 2100

2350 2350 2330

11.0 11.3 11.1

5.8 6.2 6.4

15.5 20.8 18.8

58.9 48.4 60.8

30.5 31.0 31.2

Horizontal Shredder

unknown

30

33.1

2040

2260

10.5

5.3

12.3

40.9

unknown

Continuous unknown Mill

25

41.7

2130

2340

8.7

4.6

9.9

29.9

unknown

such as specific gravity, water absorption, sulfate soundness, and Los Angeles abrasion loss percentage were not significantly affected by different types of crushers and crusher settings. The results of this investigation is described in detail by Kakizaki et al. (135s). Svensson (101) has dealt with the theory of action of jaw crushers. Schroeder (114) has analysed removal and reprocessing technologies as they apply to reconstruction of rural highways and airports.


18

Results from different countries are difficult to compare because different investigations have been made with different types of original concretes. However, it appears that there is a large difference in percentage of sands produced by different crushers. For the same maximum size of coarse recycled concrete aggregate (25 mm), shredders produced twice as much or 40% of undesirable crusher fines below 4.8 mm, compared with 20% for jaw crushers. This is important. It appears that jaw crushers should be used for the processing of plain or lightly reinforced concrete, while heavy impact crushers of various designs appear to be the best choice for normal or heavily reinforced concrete. If demolition waste is to be recycled, methods of demolition should be used which will reduce individual pieces of debris on the site to a size which will be accepted by the primary crusher in the recycling plant. This is 1200 mm at most for large stationary plants and not more than 400–700 mm for mobile plants. Thus the recycling of demolition waste requires careful planning on the part of all parties involved in such an enterprise. For those readers who are particularly interested in new developments within the field of concrete crushers a number of access numbers to patents registered in the World Patent Index are given in Ref. (118). In February 1988 the author of this state-of-the art report conducted a literature search in the following databases: Compendex, NTIS, World Patent Index and ESA. Keywords used were: ‘Crushers’ and ‘Concrete’. However, the papers turned out to be too specialized to merit a detailed discussion in this report.

6.3 Sorting devices and screens In line with specifications for natural aggregate and crushed stone, recycled aggregate is required to be free from dirt, clay lumps, gypsum (from plaster), asphalt, wood, paper, plastics, paint, textiles, lightweight concrete, and other impurities. The first stage at which demolition debris can be sorted is during the demolition process itself. Thus, if given the incentive the demolition contractor can, by the use of selective demolition methods, recover much of the material from a site in a relatively clean and uncontaminated form. In most cases, such orderly demolition procedures are not viable given the confines of an urban demolition site and the realities of time-penalty clauses. As a result, selective demolition is only carried out where both conditions and time allow and the operation has clear financial advantages. It is significant that demolition contracts involving the dismantling of structures consisting of only one type of material, such as a concrete runway, are highly sought after, since they provide an excellent source of clean debris requiring the minimum amount of processing. Once demolition has been completed and the debris taken to the recycling plant opportunities for sorting the debris are confined to selective stockpiling and primary screening. Selective stockpiling is simply the storing of incoming material in separate stockpiles according to its type and degree of contamination. This gives the plant operator the opportunity of dealing with oversize and undersize material separately. In addition, by building up a sufficient stockpile of a single clean material it becomes viable to optimize


19

the crusher set-up for that material and crush it in a single run. Such stockpiling is only practical on sites with sufficient space. A desirable minimum area is 1 hectare (87). In most recycling plants larger objects such as pieces of metal sheeting, wooden boards and beams, pieces of asphalt, loose reinforcing bars, and sheets of paper, cloth, and plastics are removed by hand before primary crushing of the debris. After primary crushing, dirt, gypsum, plaster, and other fine impurities are eliminated by passing the crushed materials over a set of scalping screens and wasting all material below 10 mm. Self-cleaning magnets which are positioned in various patterns of strategic locations over conveyor belts effectively separate bits of reinforcing bars and other pieces of iron and steel from the stream of crushed aggregate. Simple dry sieving only separates on differences in size and form. It can only be used succesfully to separate material crushed with a jaw crusher, because an impact crusher will crush in a non-selective manner. According to a Japanese study (12), coarse materials are separated more effectively by inclined screens vibrating at low frequences and large amplitudes, whilst horizontal screens vibrating at high frequencies and small amplitudes are more effective in separating fine material. Dutch results (62) indicate that for separating lightweight material, adapted flat sieves are the best, giving little loss of the stony material whilst removing some 80% of the wood. Nix (55) reports that most lightweight matter can be removed from crushed building debris and the aggregate brought to specifications by wet classification. Heimsoth (56) claims that the same can be achieved by dry processing when impurities are heavier than water. In principle, fine-grained and lightweight contaminants can be removed from rubble by air classification processes. The most frequently used of these techniques is dry-sifting, a process which can be carried out both vertically and horizontally. An important condition for obtaining a sufficient degree of separation is that the crushed product must be divided into fractions. This implies that when the product is of a size between 0 and 40 mm, four or five sieved fractions must be obtained; each of which is sifted separately, then remixed. It is a distinct disadvantage that dry-sifting produces an excess of dust which must be controlled. Alternatively, lightweight contaminants can be separated from heavier bulk material by the use of directly applied water jets in combination with a float-sink technique. The socalled ‘Aquamator’ is based on this principle. It is produced by UBA/BMFT in West Germany, and it is briefly described by Pietrzeniuk (72) and Drees (95). By the application of wet classification techniques, wood, hardboard, plastics, straw, and roofing felt as well as suspended sulfates and asbestos fibres can be effectively removed from the size range of 10–40 mm. Sieving on a 10 mm screen prior to washing is recommended, because the 0–10 mm fraction produces large quantities of undesirable sludge in the washing water. Drees (95) has provided an excellent review of the various methods available for sorting of crushed demolition debris. Efficiency of various types of screens was studied by B.C.S.J. (12). It has been suggested by BCSJ (6) and (12) that it should be possible to separate most brick rubble and other deleterious particles from recycled aggregate in a heavy medium of 1950 kg/m3. In principle, such a technique would allow the processing of highly


20

contaminated and mixed demolition debris to produce clean, graded aggregates.

6.4 Environmental problems in the recycling of concrete Recycling of Portland cement concrete presents both environmental advantages and disadvantages. The advantages are that substances are reused which would otherwise be classed as waste; reduction of fuel use, reduction of trucking, and reduction of the use of non-renewable resources. The disadvantages include the intrusion of trucking into locations where this is undesirable; aesthetic concerns, and potential noise and dust control problems. Operation of a crushing and screening plant is always accompanied by the generation of noise, vibrations and dust. Therefore, in the selection of plant location, environmental conditions of the vicinity and legal requirements must be carefully studied and necessary counter-measures taken. However, the early concern about noise and dust problems when crushing concrete in mobile plants in urban areas has apparently been exaggerated. Dierkes (7a) reports on a mobile plant which was set up near a local commercial and residential area in Chicago, Illinois. The only complaints received concerned night-time operations, the banging of tailgates to clean trucks, and the noise from back-up alarms on mobile equipment. Such practices were stopped, and stockpiles and earth berms were built around the perimeter to reduce the noise. The hoppers of the primary crushers were lined with rubber pads to reduce the impact noise, diesel generator engines were equipped with quieter mufflers, and sound absorbing panels were placed around the generator trailers. Copple (7c) reports on a crusher which was set up on a busy urban street in a suburb of Grand Rapids, Michigan, where no complaints were received about either dust or noise from the plant. Environmental concerns in recycling of concrete are discussed in detail by Munro (7d) who concludes: 1.A single purpose job site installation, for example for the purpose of recycling a pavement, is easier to locate than a permanent commercial type installation, but a permanent site has the advantage of being able to recycle slabs and footings from building demolition as well as pavement. 2.To recycle the aggregates into concrete, the best location of a permanent plant is adjacent to a ready-mixed concrete batch plant in an area of heavy industrial zoning. The recycling plant should be located on a road which is already used for heavy commercial or industrial trucking. Once located, there must be sufficient control exercised over the trucks to ensure that they are always using acceptable heavy duty roads. 3.Emission of dust should be limited to Number 1 Ringlemen (which is about 20% opacity) for a period not exceeding three minutes in any one hour. Any discharge less than this is essentially not visible and can be measured only with sophisticated devices. The easiest control is water. Roads around the site should be continuously watered


21

as should be stockpiles of broken concrete. Fine mist water should be used at the crusher feed and screens. This spray must be very fine or the material will be too wet and the fine screens will blind. A wetting agent added to the water will give better dust control with less water. Also watering the material at the head pulley of the stockpiling conveyor is helpful in controlling dust as the product is loaded into trucks. 4.The plant should be screened from view. A combination of grade difference and mature scrubs can almost totally shield the view of a plant and its stockpiles. 5.Personnel noise exposure should be limited to 90 decibels for an 8-hour day. In the case of front-end loaders, bulldozers and the like, this can be done by installing noise attenuated cabs. Plant operators can likewise have well-located enclosed operating positions. Personnel which must be around the plant during operation must be protected either by administrative or engineering controls. Administrative controls involve rotation of personnel during the working day from noisy to quiet environments. Engineering control involves enclosing the crushers and screens. Ear muffs should be used only as a last resort. 6.Community noise, i.e. noise at the receiving property, should be limited to no more than 55 decibels for daytime hours or 50 decibels during the evening. This limit should be exceeded for no more than one minute by no more than 15 decibels. The simplest way of controlling noise is distance. Noise impact will be reduced by 6 decibels for each doubling of the distance, but distance is not a very practical means of noise control in urban areas, considering the noise level of a typical crushing and screening plant which is serviced by front-end loaders. It may be necessary to enclose the machines or to shield the receiving property from the machines by means of noise attenuating walls. Controlling the exterior noise from bulldozers and front-end loaders is extremely difficult until manufacturers of such equipment realize that their equipment must meet the noise standards, and act accordingly. Until then, the most effective system is to restrict the operating time to reasonably convenient daytime hours. Kakizaki M., Harada M. and Motoyasu (135s) have studied the noise levels of different crushing machines. They conclude that in city areas the noise levels ought to be lowered below those regulated by current noise control-regulations by means of acoustic barriers of various kinds, or complaints are certain to be received. While demolition wastes earlier could be used without problems as fill or built into acoustic barrier walls or used for foundations or erosion protection, this is no longer possible under many environmental laws (95). At earlier times demolition wastes were considered non-toxic wastes which could be disposed of at any city dump because they consisted almost entirely of mineral products. This is no longer true. Many building materials now contain components which are considered toxic from environmental points of view, such as chlorinated carbon-hydrogens, phenoles and heavy metals. Because noise, vibrations and air protection are of primary concern during demolition and processing of demolition wastes, the operator of a recycling plant must now convince authorities that there is no danger of pollution of ground water before he can safely sell the reprocessed materials. However, in order to keep things in perspective it should be remembered that roads have long been built with asphalt as a surfacing material without


22

this having given rise to any problems at all. It is difficult to visualise why a small contamination of demolished concrete with asphalt should give rise to concern. The fear seems somewhat exaggerated. Dohmann (130) studied the chemical oxygen requirement and the concentration of phenols before and after treatment of demolition wastes in two different recycling plants. One plant removed contaminants by dry-sifting and one by wet processing in an Aquamator. Unfortunately for the recycling industry the investigation showed no significant difference between the contents of dangerous chemicals before and after processing of waste in the two plants. It may be concluded that the only way an operator of a recycling plant can be certain that his products will be free from dangerous contaminants is to make sure that the contaminants do not get in there in the first place. Such certainty can only be obtained by refusing any demolition debris which is contaminated with (impregnated) wood, paper, plastics, textiles, cable, non-iron metals, steel (except for small amounts of reinforcing steel), soil and clay, domestic or industrial waste, gypsum and other deleterious mineral products, oil, grease, rubber or components which in any way are contaminated by chemicals. This poses a responsibility on the individual operator, and it forces the demolition contractor to carry out selective demolition at least to a certain extent. Moreover, it increases the cost of processed demolition waste, thus severely restricting the quantities that can be recycled. Therefore, authorities should make certain that their requirements are justified, which is not always the case.

6.5 Grading of crusher products Table 6.2 shows a typical grading of the total output of recycled aggregate from a laboratory jaw crusher which was set at an opening of 25 mm with the jaws in a closed position (13). The crusher was fed three original concretes of different qualities in the form of old 15×30 cm test cylinders which had been split in halves. For all practical purposes the overall gradings of the crusher products are independent of the concrete quality in the entire range of water-cement ratios from 0.40 to 1.20. It is generally assumed that natural rock when fed to a crusher will break according to a’straight-line distribution’ (14) where 15% of the crusher product will be of a size above the crusher setting as shown in Figure 6.3.

Table 6.2 Overall grading of crusher products from Ref. (13).

Size Fraction in mm

Measured Weight Percent of Total Crusher Product 11 w/c=0.40

M w/c=0.70

L w/c=1.20

Estimated Weight Percent of Total Crushed Product According to Figure 6.4


23

> 30

3.0

4.2

3.2

0

30–20

27.4

31.9

27.6

32

20–10

35.9

33.2

33.5

34

10- 5

14.7

13.4

13.2

17

38

3

3

38

29

34

25

15

15


24

19

19

19

12.5

8

6

9.6

13

12

4.8

13

11

It will be seen from Table 6.2 that the actual particle size distributions of crushed concretes are in reasonably good agreement with the predictions that can be made on the basis of Figure 6.3. Similar results have been obtained by Fergus (7e) as shown in Table 6.3. Usually grain-size distributions of crusher outputs approximate Fuller curves. Thus, it may be concluded that the crushing characteristics of hardened concrete are similar to those of natural rocks and not significantly affected by the grade of original concrete. Japanese studies which have been reported by B.C.S.J. (12) confirm that approximately 20% by weight of fine recycled aggregate below 5 mm is produced when old concrete is crushed in a jaw crusher with an opening of 33 mm, also independent of concrete quality (see Table 6.1). With jaw openings of 60, 80, and 120 mm, corresponding percentages of fine recycled aggregate produced were 14.1%, 10.6%, and 7.0%. With a jaw opening of 20 mm Ravindrarajah and Tam (65) found the quantities of fine material below 5 mm to be 23.1, 25.7, and 26.5% by weight for 37 MPa, 30 MPa, and 22 MPa concretes, respectively. In order to be cohesive and workable, fresh concrete requires between 25 and 40% of fine aggregate by weight of total aggregate, depending on the type of sand and its fineness, concrete consistency, water-cement ratio, and maximum size of coarse aggregate. Thus, it may be concluded that by the crushing of old concrete in one pass through a jaw crusher there is not generated enough fine recycled aggregate to produce new concrete of good quality when the maximum size of crusher output is between 32 and 38 mm. The normal procedure in current American practice is to proportion fresh recycled aggregate concrete mixes so that coarse and fine recycled aggregate may be consumed in the same ratio that they are produced. However, due to the fact that insufficient quantities fine recycled aggregate is produced by the jaw crusher in order to make new concrete of good workability, it is necessary to add a certain amount of conventional fine aggregate. As will be seen later, this may also be necessary for other reasons. At a recycling project in Iowa (7f) it was found that optimum finishing properties and workability of fresh recycled aggregate concrete was obtained when 25% of natural sand was mixed with 75% of fine recycled aggregate in a standard pavement mixture which contained a 50–50 mixture of fine and coarse aggregate of 38 mm (11/2 inches) maximum size. It is interesting that the recycling of an existing pavement will produce a total of about 50% more recycled aggregate than is needed to produce the quantity of new concrete which is required to replace the same section with a pavement of equal thickness (7a). However, it will be seen later in this state-of-the-art report that, for reasons of durability, it may not be advisable to use fine recycled aggregate less than 2–3 mm for production of new concrete. However, even if all fine recycled aggregate below 5mm is rejected it is


25

likely that more than enough coarse recycled aggregate will be produced to replace the same section with a pavement of equal thickness. Dutch investigators have developed a concept which they call ‘Crusher Characteristics’ as a useful tool for control of the crushing and sieving processes of old concrete. Crusher Characteristics are graphic representations of the relations between a so-called reduction factor, R, and the sieve residues of the crusher output on various size sieves. The reduction factor, R, is defined as the ratio between the particle size of crusher input and crusher output for the same weight percentage of residue on a given size sieve. Different types of crushers yield different crusher characteristics. If for a specific plant the crusher characteristic is known, the grading of the crusher output can be forecast when the grading of the crusher input is known. The use of crusher characteristics can best be shown by means of a numerical example as follows: In order to determine the crusher characteristic for a given impact crusher, the particle distributions of crusher input and crusher output must be determined. For the fragmentation of concrete demolition waste in a specific impact crusher, these are plotted in one and the same graph as shown in Figure 6.4. In our example the reduction factor, R, for a sieve residue of 35% equals 59.5 mm grain size of the crusher input, divided by 9.9 mm grain size of the crusher output, or

By calculating the reduction factor R for a number of sieve residues and plotting them in another graph with the reduction factor along the ordinate and sieve residue along the abscissa, the crusher characteristic (labelled 3) is obtained as shown in Figure 6.5 for the impact crusher which was used in our numerical example. For purposes of comparison, typical examples of crusher characteristics are also shown in Figure 6.5 for a jaw crusher, labelled 1, a cone crusher, labelled 2, and a swing-hammer mill, labelled 4. It will be seen from Figure 6.5 that impact crushers and swing-hammer mills which both affect crushing by means of different kinds of impact, have greater reduction factors than jaw- or conecrushers, which affect crushing by the application of pressure only.


26

Fig. 6.4 Grain size distribution of crusher input and output for determination of crusher characteristic of impact crusher (example).


27

6.6 Storage and handling of recycled aggregates The Japanese Proposed Standard for the ‘Use of recycled aggregate and recycled aggregate concrete’ (6) includes the following recommendations for storage and handling of recycled aggregates: 1. Recycled aggregates produced from original concretes of distinctly different quality, and recycled aggregates produced by means of different production methods shall be stored separately. 2. Recycled coarse aggregate and recycled fine aggregate shall be stored separately. 3. Recycled aggregate shall be stored and transported in a manner to prevent breakage and segregation or otherwise cause change in quality of the recycled aggregate concerned. 4. Water absorption ratio of recycled coarse aggregates is large; therefore, such aggregates should normally be used in a saturated and surface dry condition. For this reason recycled aggregate storage yards should be provided with water sprinkling facilities so that recycled coarse aggregates can be maintained at the required moist condition. However, some unhydrated Portland cement and hydrated lime is present in fine recycled aggregates, and there is danger that such fine aggregates in time shall become caked. Therefore, fine recycled aggregates should not be kept in storage for any longer period of time. It is left to the ready mixed concrete manufacturers to solve this problem. We recognize that this, as well as the provision of extra sil capacities are important production problems, but they are beyond the commissorium of this committee to deal with. 5. Recycled aggregates shall be stored separate from other types of aggregates. 6. It is recommended that if different types and qualities of recycled aggregate are produced, the plant should not process coloured material such as brick rubble together with concrete rubble because of the extra cost which is involved in the cleaning of processing units when changing from brick to concrete rubble.


Fig. 6.5 Crusher characteristics (example).

28


29

7. Quality of recycled aggregates Simply producing a clean, crushed and well-graded material is not sufficient to ensure effective recycling. The recycled material produced must be suitable for specific applications and it should comply with certain grading limits, contain minimal levels of contaminants and meet other requirements of stability and durability. Once the concrete has been crushed, sieved and if necessary decontaminated, it can find applications as 1) general bulk fill, 2) fill in drainage projects, 3) sub-base or base material in road construction or 4) aggregate for new concrete. In this section we shall primarily discuss recycled aggregate for production of new concrete. Aggregate for other purposes are briefly dealt with in sections 7.9, 8.9, 12 and 13.

7.1 Grading, particle shape, and surface texture of recycled aggregates After screening on an ASTM No. 4 (5 mm) sieve, the grading of an average crusher products is compared with ASTM C-33 grading requirements for a 25 mm (1 in) maximum size aggregate shown in Figure 7.1. Data are from Danish (13) and Japanese (15) investigations. Both of the coarse aggregates were produced by the crushing of original concrete in a jaw crusher. It is evident that both aggregates could have been brought within ASTM grading requirements by slight adjustments of the opening of the crusher. Apparently it is easy to produce reasonably well-graded coarse recycled aggregate by means of a jaw crusher. The grading of fine crusher products below 5 mm from three different investigations (13, 15, and 7e) are compared in Figure 7.2. All gradings fall within the shaded area of the sieve diagram in Figure 7.2. All were produced by the crushing of old concretes in a jaw crusher. It will be seen that all gradings are somewhat coarser than the lower limit of ASTM grading requirements. Some are even lower than the lowest permissible grading limit of zone 1 sand in British Standard 882, 1201, which is considered to be the coarsest grading of sand from which concrete of reasonable quality can be produced. It may be concluded that fine recycled aggregates, as they come from the crusher, are somewhat coarser and more angular than desirable for production of good concrete mixes.


30

Fig. 7.1 Range of gradings of 25 mm coarse recycled aggregates produced by jaw crusher in one pass (from literature reviewed).


31

Fig. 7.2 Range of gradings of crusher fines < 4 mm (fine aggregate) obtained when 25–30 mm max. size coarse recycled aggregates are produced by jaw crusher in one pass.

As fine recycled aggregates also consist of angular particles, it is not surprising that concretes which are produced exclusively with coarse and fine recycled aggregates tend to be harsh and unworkable (7f). However, by adding a certain amount of a finer natural blending sand it is possible to bring fine recycled aggregates within the grading limits of ASTM C 33. At the same time, concrete workability is greatly improved (7f). Gerardu and Hendriks (70) report that the best recycled aggregate for concrete production is obtained when it is graded within the limits specified in the German Standard DIN 4163 for the recycling of rubble (71) which was in force in the 1950s, but which has now been withdrawn. Fergus (7e) found that the quantity of material finer than 75 micron in 38 mm (1½ in)


32

maximum size coarse recycled aggregates ranged from 0.3% to 0.5%. In fine recycled aggregate below the ASTM No. 4 sieve; material finer than 75 micron ranged from 4.1% to 6.6% depending on concrete quality. In one particular case where original concrete consisted essentially of cement mortar, the corresponding value was 9.1%. Hasaba et al. (16) found that 25 mm maximum size coarse recycled aggregate to contain between 1.3% and 1.7% particles finer than 88 micron, depending on the quality of concrete. Hansen and Narud (13) found that material finer than 75 micron in fine recycled aggregates below 4 mm ranged from 0.8% to 3.5%, depending on concrete quality. Considering that ASTM C 33 allows 1.5% dust of fracture in coarse aggregate 5% dust in fine aggregate in concrete which is subject to abrasion, and 7% in all other concrete, it may be concluded that recycled aggregates in most cases can be used for production of concrete without being washed. In the main these results are confirmed by Karaa (93). Schulz (135d) concluded that recycled concrete aggregates will be adequate for production of new concrete only if particle sizes below 2 mm are screened out. Morlion (135t) presented grading curves of recycled concrete aggregates used for production of new concrete at a large recycling project in Belgium. In this large scale practical project it was also decided to use coarse recycled aggregate and natural sand, because recycled sand gave poor strength results.

7.2 Attached mortar and cement paste When old concrete is crushed, a certain amount of mortar from the original concrete remains attached to stone particles in the recycled aggregates. Table 7.1 shows the volume percentage of old mortar which remained attached to original gravel particles in recycled aggregate, as reported by Hansen and Narud (13) on the basis of the results of an investigation by Hedegaard (17). A representative sample of various grades and size fractions of recycled aggregate was mixed with red-coloured cement and cast into cubes. After hardening, the cubes were cut into slices and the slices polished. Mortar attached to natural gravel particles in recycled aggregates could be clearly distinguished both from the original gravel particles and from the red cement matrix. The volume percentage of old mortar, which was attached to gravel particles in each grade and size fraction of recycled aggregate, was determined on a representative number of samples by means of a linear traverse method, similar in principle to the method which is described in ASTM C 457–71, ‘Standard recommended practice for microscopical determination of air-void content and parameters of the air-void system in hardened concrete’. Hansen and Narud (13) found the volume percentage of mortar attached to natural gravel particles to be between 25% and 35% for 16–32 mm coarse recycled aggregates, around 40% for 8–16 mm coarse recycled aggregates, and around 60% for 4–8 mm coarse recycled aggregates (see Table 7.1). However, it appears that for the same cement


33

and original aggregate the volume percentage of old mortar attached to recycled concrete aggregates does not vary much even for widely different water-cement ratios of original concrete. Hasaba et al. (16) found 35.5% of old mortar attached to natural gravel particles in 25– 5 mm coarse recycled aggregate produced by the crushing of original concrete having a compressive strength of 24 MPa. Corresponding figures were 36.7% mortar for 41 MPa concrete and 38.4% for 51 MPa concrete. Figure 7.3 shows the results of a Japanese investigation reported by B.C.S.J. (12) where the hydrated cement paste adhering to recycled aggregates was determined by immersing the particles in a dilute solution of hydrochloric acid at 20° C. It will be seen that the amount of cement paste attached to sand or stone particles, as determined from the weight loss due to dissolution of cement during the test, increases with decreasing particle size of aggregate. Approximately 20% of cement paste is attached to 20–30 mm of aggregate, while the 0–0.3 mm filler fraction of recycled fine aggregate contains 45– 65% of old cement paste. Old cement paste and mortar in many cases unfavourably affect the quality of recycled concretes, and it should be avoided to use the finer fractions below 2 mm. Perhaps it should be avoided to use any fine recycled aggregate at all, for a number of reasons which will be apparent later in the report.

Table 7.1 Properties of natural gravel and recycled aggregates according to Ref. (13).

Type of Size Specific water Los Los B.S. Volume Aggregate Fraction Gravity Absorption Angeles Angeles Aggregate percent of in mm SSD in percent Abrasion Uniformity Crushing mortar cond. Loss Number Value Percentage L100/L500 percent attached to Ratio natural gravel particle Original natural gravel

4–8 8–16 16–32

2500 2620 2610

3.7 1.8 0.8

25.9 22.7 18.8

0.28 0.22 0.20

21.8 18.5 14.5

0 0 0

Recycled aggregate (H) (w/c=0.40)

4–8 8–16 16–32

2340 2450 2490

8.5 5.0 3.8

30.1 26.7 22.4

0.30 0.25 0.24

25.6 23.6 20.4

58 38 35

Recycled aggregate (M) (w/c— 0.70)

4–8 8–16 16–32

2350 2440 2480

8.7 5.4 4.0

32.6 29.2 25.4

0.31 0.28 0.25

27.3 25.6 23.2

64 39 28

4–8

2340

8.7

41.4

0.38

28.2

6

Recycled


34

aggregate (L) (w/c— 1.20)

8–16 16–32

2420 2490

5.7 3.7

37.0 31.5

0.39 0.38

29.6 27.4

39 25

Recycled aggregate (M) (w/c— 0.70)

31.5

> 16

>8

>4

>2

>1

> 250µ

> 63µ

0–4

–

–

–

0–0

25– 31

50– 62

80–87

96– 100

4–16

–

0–5

55–

85–

95–

–

–

99–


4–31.5

0–5

32– 44

57

100

100

70– 75

90– 100

–

104 100 –

–

99– 100

Table 13.6 Maximum allowable contents of water-soluble chlorides (Cl−) in recycled aggregates according to (11).

Fraction mm

Unreinforced Concrete

Reinforced Concrete

Pre-stressed Concrete

0–4

–

0.1%

0.015%

>4

–

0.05%

0.007%

9. The content of calcium carbonate in recycled aggregate as determined according to the method presented in NEN 3542 should not exceed 25% by weight of the 0–4 mm fraction and 10% by weight of the fraction above 4 mm. 10. The content of sulfate in recycled aggregates, as determined according to the method presented in NEN 3542, should not exceed 1 weight per cent of particles dried at 98°C. 11. For some applications, such as exposed concrete surfaces, recycled aggregates must be free from constituents which are objectionable from an aesthetic point of view (for example asphalt, water-soluble iron or vanadium compounds). 12. The content of wood and other matter of organic origin in recycled aggregates, as determined according to DIN 4226 (Test for Lightweight Particles), should not exceed 0.5% by weight of the 0–4 mm fraction and 0.1% by weight of the fraction above 4 mm. 13. Certain requirements and limit values are introduced concerning dimensional stability, retardation, staining, cubicity, and frost resistance of recycled concrete aggregates. 14. On the basis of information of the origin of the demolition rubble and the visual analysis, it must be determined whether there are impurities in the rubble which may give rise to internal expansion of the concrete (for example particles of calcium or magnesium oxide, as determined by the autoclave method for detection of lime instability (BS 1047), iron instability (BS 1047) or alkali-reactive materials (ASTM C–586, C–295, C–289, and C–227)). 15. If the origin, the visual analysis, or the result of the test which is described under Item 7 gives rise to doubt, a water extraction of the rubble must be made in order to determine whether the material contains water-soluble or acid-soluble compounds which could adversely affect setting or hardening of concrete. Adverse effects on setting time are determined by preparing two sets of cement paste specimens, one with the extracted water, and one with distilled water. Any difference in setting time as determined by the standard Vicat test is assumed to be due to contaminants in the extracted water. Similarly, the compressive strength is determined on two sets of


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specimens made from the same standard mortar, but with extracted water, respectively distilled water. Differences in setting time and compressive strength of specimens prepared from extracted water and distilled water should not exceed 15% for the recycled aggregate to be accepted. 16. The content of flat pieces in coarse recycled aggregates as determined according to the vibration table test of the Organization for Applied Scientific Research in the Netherlands (TNO) should not exceed 30% by weight of total coarse aggregate. 17. If the rubble is to be used in asphaitic concrete, the requirements laid down in Items 5, 7 to 11, 13, 14, and 15 shall be waived. If used for construction of highway subbases, recycled aggregate must satisfy the requirements under paragraph 3.8 of the Dutch 1978 Requirements. For use in base courses or surface layers, the rubble must satisfy the requirements under paragraph 3.7 of the Dutch 1978 Requirements. 18 A proof of origin must be supplied with the rubble. The certificate must state: a) date of dispatch by the supplier b) name of the haulage contractor c) type of aggregate d) size fraction e) standard requirements which the material is guaranteed to satisfy f) location and type of origin When these product specifications are used, it is required in the draft of the new Dutch concrete code VBT 1986 that ‘for stuctural members whose dimensions are governed by the maximum permissible deflection it will be necessary to allow for 10% greater thickness or depth in order to ensure adequate stiffness’. This is required in order to account for the lower modulus of elasticity and creep of recycled aggregate concrete compared with natural aggregate concrete. However, if only 20% of natural aggregate instead of 100 percent is replaced by recycled concrete aggregate, this additional thickness or depth of the members is not required.

13.5 United Kingdom The new British Standard Guide 6543, ‘Use of industrial by-products and waste materials in building and civil engineering’, covers the use of demolition waste and other waste materials in both road construction and buildings. While not up to date in terms of technology, it does consider crushed concrete to be suitable for a wide range of sub-base and base course applications. It even goes as far as approving, in principle, the use of clean concrete and brick rubble for use as aggregate for concrete subject to minimum strength requirements. This is a considerable step forward for recycling in the UK. The current situation in the UK has been reviewed by Lindsell and Mulheron (87) and by Mulheron (135h).


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13.6 USSR In 1984, NllZbh of the USSR Research Institute for Concrete and Reinforced Concrete has published the first Russian ‘Recommendations on the recycling of sub-standard concrete and reinforced concrete products’. According to the recommendations, coarse recycled concrete aggregates can be used for: 1. macadam bases for the floors and foundations of buildings and structures and for asphalt pavements of all grades, 2. production of 5–15 MPa concrete and reinforced concrete, 3. production of up to 20 MPa concrete and reinforced concrete when mixed with 50% conventional crushed aggregate. It is recommended that the crushed concrete fines be used as filler in the production of asphalt concrete. It is not recommended to use crushed concrete fines for production of new concrete. It is not allowed to use recycled concrete aggregates for production of prestressed concrete due to high shrinkage and creep as well as low modulus of elasticity.

13.7 Federal Republic of Germany In the Federal Republic of Germany it is not allowed to use recycled concrete aggregate for production of new concrete. Because of their density, such aggregates are too heavy to be classified as lightweight aggregates, and with a crushing strength of less than 100 MPa, they are too weak to be classified as natural or crushed aggregate for production of conventional concrete. At the present time permission is required for each individual project to use recycled concrete aggregate for production of new concrete, but no permissions have yet been granted. However, during the period 1945–1955 large quantities of brick rubble were reprocessed and used in the production of new concrete. This resulted in the publication of a German Standard DIN 4163, written specifically to cover the production and use of concrete made with crushed brick. Under this Standard, concrete of a density between 1600 and 2100 kg/m3 could be obtained with a maximum strength of 30 MPa and an elastic modulus of 15 GPa. Authorities in the Federal Republic of Germany are now reconsidering their position on use of recycled aggregate concrete. It is worth mentioning that there exists a West German Standard Specification for the use of recycle demolition waste in road construction (128).


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13.8 Denmark In 1990 Denmark will issue an amendment to the regular concrete code (116) which will allow the use of recycled aggregate concrete for certain structural purposes in mild environments. The amendment distinguishes between concretes having characteristic compressive strengths up to 20 MPa (GP1) and concretes having characteristic strengths up to 40 MPa (GP2). GP1 recycled materials are required to have saturated and surface dry densities above 2200 kg/m3. Such materials typically consist of crushed structural grade concrete. GP2 materials are required to have densities above 1800 kg/m3 and typically consist of clean demolition rubble, typically a mixture of masonry and concrete. Both materials are required to conform to the regular Danish codes for aggregate and concrete for what concerns freedom from deleterious materials. For the purpose of structural design the modulus of elasticity of GP1 concrete shall be assumed to be 80% of the prescribed values for conventional concrete and 50% for concrete made with GP2 materials. Alternatively the true modulus of elasticity can be determined experimentally. The same coefficients of safety can be used for GP1 and GP2 as for conventional concrete. It has been established by experiments that the stress-strain relationship of recycled aggregate concrete is not significantly different from that of conventional concrete. Therefore, the same design criteria can be used for recycled aggregate concrete as are prescribed in the concrete code for conventional concrete. However, there are differences for what concerns design for instability of columns and walls as well as for deformations in general. It is also assumed that the coefficient of variation of compressive strength test results will be somewhat larger for recycled aggregate concrete than for conventional concrete.


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14. Economic aspects of concrete recycling Economic aspects of recycling of concrete have been analysed by Frondistou-Yannas (44, 45, 50) for what concerns the United States, by CUR (11) for what concerns the Netherlands, and by Drees (95) for the Federal Republic of Germany. The following conclusions can be drawn on the basis of these three studies: Conditions which are conducive to successful operation of recycled aggregate plants include: 1. Abundant and constant supply of demolition rubble 2. High dumping costs for demolition rubble 3. Easy access for heavy trucks 4. Suitable industrial land available, preferably next to a sanitary land fill. 5. Inaccessibility or scarcity, and therefore high cost of good quality natural sand and gravel or crushed stone. 6. Ready market for products. Considering these factors, it is not surprising that one of the largest recycling plants in the world is located in West Berlin (54) and that densely populated countries such as parts of the United States, the Netherlands, Belgium, West Germany, and Japan are among the first to consider large-scale recycling of demolition waste. Pavements and runways present favourable cases for recycling of concrete because large quantities of relatively clean concrete rubble are generated over a short period of time. It is generated within a very limited area, and transportation along still existing parts of pavements presents no problem. Moreover, such rubble can be processed in simple plants without washing or elaborate sorting and cleaning. In almost all practical cases where concrete pavements or runways have been crushed and recycled, considerable savings have been achieved compared to the combined cost of dumping the old concrete and hauling in new base or sub-base material from pits and quarries or producing new concrete from conventional aggregate (7). Obviously, the largest savings have been achieved where conventional aggregate was locally unavailable, and for that very reason most of the recycling projects that have been carried out so far have been located in areas with a shortage of natural aggregates. However, concrete used in streets and highways typically accounts for only about 15– 20% of total concrete consumption in industrialized countries (44, 45). In order to operate recycling plants at high capacities, thereby realizing economies of scale, the large quantities of concrete rubble generated from the demolition of old buildings, pavements, sidewalks, driveways, curbs, gutters, etc. are also required, and it must be processed into aggregate for production of new concrete which can be accepted by the construction industry as a reasonable alternative to conventional aggregate.


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The economy of large-scale recycling of mixed concrete rubble in metropolitan areas is very much different from the economy of recycling of pavements and runways. For one reason it introduces the problem of contamination as the demolition rubble is mixed with gypsum, wood, plastics, and steel (49) which must be removed before the recycled product can be used for production of new concrete. Thus, much more elaborate plants are required to process mixed demolition rubble than clean concrete from highway pavements. A flow chart illustrating the design of a plant which is capable of producing concrete aggregate from mixed demolition debris is shown in Figure 6.2. The macro-economics of plants capable of processing mixed concrete debris in the United States were studied by Frondistou-Yannas (44, 45, 50). Frondistou-Yannas found that a prerequisite for the economic justification of concrete rubble recycling is the presence of sufficiently large quantities of concrete debris so that a recycling plant of optimal size can be operated at high utilization factors. Accordingly, several researchers (48, 49) have assessed the quantities of concrete debris produced locally in the United States. It has been found that, on the average, 0.27 tons of concrete rubble per capita are generated each year in the United States. It follows that in urban areas with a population greater than half a million people, the amount of concrete debris generated annually is of the order of a few hundred thousand tons. By contrast, a single highway demolition project produces only a few tens of thousand tons of debris. On the basis of an economic analysis, Frondistou-Yannas found that in order to realize economics of scale, a plant should process at least 110–275 tons of debris per hour, and in order to produce a reasonable return on investment, the plant should process and sell no less than 200 000 tons of recycled aggregate per year. This implies that urban areas of at least one million people are needed to support the operation of a concrete recycling plant in the United States. There are no reasons to believe that this requirement would be substantially different in other industrialized countries. Frondistou-Yannas suggests for economical and other reasons that the most favourable location of a recycling plant would be at a fixed position near a large city, preferably next to a sanitary land fill so that trucks that bring in debris on their way back will carry aggregate. The adjacent sanitary land fill additionally reduces transportation costs as concrete contaminants do not have to be transported to a distant dump. Portable units should be used so that the plant can be relocated to a different site next to a new sanitary land fill when the capacity of the old fill is exhausted. However, recycled concrete aggregate can be sold only if it compares favorably with its competitor, natural aggregate. CUR (11) has analysed economic aspects of recycling of concrete in the Netherlands and attempted to make a comparison between the two types of aggregate on the basis of two concrete members of equal performance, one made with recycled concrete aggregate and the other with natural aggregate. Table 14.1 shows the main factors adding up to the total cost of recycled aggregates. CUR (11) found that: 1. The extra work on the demolition site which is required in order to prepare demolition debris for recycling is equivalent to 25% of the regular demolition costs (S1). 2. Dumping charges (s2) depend very much on local circumstances. In the Netherlands in 1982 they varied from 3 Dfl (Dutch guilders) to 30 Dfl per m3. 3. The extra costs for preparation, processing, inspection, storage, and sale of recycled


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aggregates, s7=12 Dfl, which appear in Table 14.1 and later in Table 14.2, are based on an average of estimates made in 1982 by a number of Dutch companies actually engaged in commercial processing and sale of recycled aggregates. Table 14.2 gives the Dutch cost comparison between concretes of equal strength, produced with natural gravel and recycled concrete aggregate. All costs quoted are based on experiences from real productions in the Netherlands, and they are quoted in 1982 prices in Dutch guilders. Costs of transportation are assumed to be equal for all four concretes. It will be seen from Table 14.2 that when dumping charges for demolition debris are left out of consideration, recycled building rubble was not competitive for concrete production in the Netherlands in 1982 as compared to natural gravel. The 1982 market prices which are quoted in Table 14.2 for recycled aggregates apply to rubble aggregates used as road-base materials. For such purposes rubble aggregate is competitive because crushed natural rock which is required for road construction is more expensive than natural gravel. In 1982 nearly two million tons of demolition rubble were processed into recycled aggregates and used for unstabilized road bases in the Netherlands. In order to be competitive for concrete production it appears from Table 14.2 that in the Netherlands, recycled aggregates would have to sell for approximately 25% less, instead of 50% more than natural gravel in order to compete with natural gravel for concrete production. In 1982 recycled concrete aggregates produced by the only large scale plant in France at Limeil-Brevannes near Paris was selling at twice the cost of natural materials (94). For

Table 14.1 Comparison of cost elements in the processing and handling of natural aggregates and recycled aggregates (D.fl.=Dutch guilders).

Natural Aggregates

D.fl. Re-Use of Rubble Granules

D.fl.

Excavation costs

n1

Extra treatment of debris at the demolition site

s1

Production costs (including interim storage)

n2.

Dumping charges (negative) for demolition debris

s2

Bulk transport costs

n3

Costs of transport of demolition debris to dump (negative)

s3

Costs of transport to building site

n4

Costs of transport of debris to processing plant

s4

Processing costs for recycled aggregate

s5

Costs of transport of recycled aggregate to building site

s6

Extra costs for inspection, storage, and sale of recycled aggregate

s7

Recycled aggregates and recycled aggregate concrete Total

111

Total

Requirement for recycled aggregate to be competitive provided the buyer is unbiased: ∑s ≤∑n i

i

Table 14.2 Cost comparison between concretes made with natural gravel, recycled concrete aggregate, brick rubble, and mixed concrete and brick rubble aggregate in the Netherlands (1982). 1.

Natural gravel concrete with 1080 kg of gravel at Dfl 22/ton

2.

Concrete made with recycled concrete aggregate

–

900 kg of recycled concrete aggregate (4–32 mm) at Dfl 17/ton (production and processing costs)

– –

Dfl 23.76/ton

Dfl 15.30/ton

40 kg of cement at Dfl 125/ton Dfl 5.00/ton Extra costs for inspection, storage, and sale) at Dfl 12/ton

Dfl 12.00/ton

Total

Dfl 32.30/ton

comparison, Frondistou-Yannas found that in the United States recycled aggregates would have to sell for at least 50% less than natural gravel in order to compete on equal terms with natural gravel for concrete production. Even at this price an unprejudiced person would be indifferent to natural aggregate or recycled aggregate. However, there are good reasons why a person could be prejudiced against recycled aggregate. For one, experience with it is limited and uncertainties remain concerning the performance of recycled aggregates in concrete. Secondly, extra costs and inconveniences are involved in the use of recycled aggregates for concrete production such as for example costs of pre-soaking, extra inspection, and costs of compensating for lower strength and higher creep, shrinkage, and elastic deformation of recycled aggregate concrete. Some of these costs may be offset by lower density or better thermal insulation of recycled aggregate concrete. Even so, the price of recycled aggregates will have to come down from today’s level in order for the material to be competitive with conventional aggregate. There are two ways in which this can come about. 1. The extra cost of 12 Dfl/ton, which was charged in the Netherlands when the report was prepared for the processing of old concrete and building rubble into recycled aggregate, can be lowered once the initial developing phase is over. Already in 1982 this would have brought the price of recycled aggregate down to a level where it would have been competitive with natural gravel provided the customer was unbiased.


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2. The price of conventional aggregates will continue to rise as raw materials get scarcer and transportation costs higher. More important, dumping charges for demolition debris are expected to rise steeply as the quantity of demolition debris and particularly that of concrete debris will continue to increase rapidly throughout the next decades. Without crushing, concrete debris packs very poorly and tends to render sanitary fills unsuitable for future use as building sites. All in all it can be expected that the use of recycled aggregate for concrete production will increase in the future as both the demand for roadbase material and the price of recycled aggregate is foreseen to decrease in most industrialized countries. Drees (95) found that in West Germany one may count on the generation of 0.3 tons of demolition rubble suitable for recycling per person per year. This makes for a total of 18 million tons per year. It is considerably less than what is assumed in the optimistic estimates which have been made by other authors. Compared to a total yearly production of 500 million tons of raw materials of mineral origin in West Germany, 18 million tons is a small part. However, it is significant, because demolition waste amounts to 2/3 by weight, or 1/4 volume of the total yearly deposits on city dumps. The costs of manually sorting the demolition waste would amount to 25 DM/m3 in 1989 prices. Mechanical sorting would reduce the costs to 8–10 DM/m3 in 1989 prices. At the present time economical use of clean demolition rubble is only sensible for road construction or as fill. Use of crushed and cleaned demolition rubble as aggregate for production of structural concrete is not economically viable and probably not technically desirable because of its lower quality compared to conventional aggregates. When building structures are demolished and it is desired to reuse the concrete, all components which contain deleterious materials such as wood, plastics, glass, lightweight materials and metals should be removed as far as this is economically possible before demolition of the load carrying structure itself. However, Drees (95) does not believe in total selective demolition based on the demounting of buildings in the reverse order of construction. He feels that this is considerably more expensive than pre-sorting of the mixed demolition rubble at the recycling plant and later wet or dry separation of deleterious components in the recycling plant itself. After a thorough review of different lay-outs and equipment of recycling plants for demolition waste, Drees (95) arrives at the conclusion that the total cost of a stationary plant itself would be 3.2–4.5 million DM in 1989 prices without including the cost of real estate. This is considerably more than what has been assumed by others, but probably a realistic estimate. Mobile and semimobile plants would cost between 700 000 and 900 000 DM in 1989 prices according to Drees. Production costs of marketable recycled demolition rubble depends on the required quality of the material produced. The least expensive is demolition rubble produced by a mobile plant on the demolition site, where the product is only intended for use as fill. The same is true for reuse of demolition rubble on site for road construction purposes. According to Drees (95) production costs for such materials would typically be somewhere between 5 and 7 DM/t in 1989 prices. For cleaned and processed building demolition waste produced to high quality requirements in stationary plants the costs would typically be 10–12 DM/t and could rise to more than 15 DM/t if the plant runs at lower than optimum capacity.


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Charges for receiving demolition rubble at dumps, and sales prices for end products depend on local conditions. If there is a long distance to the nearest dump, high dumping charges of 8–11 DM/t can be expected for reception of the rubble. If at the same time transport distances for virgin fill and aggregates are long, crushed and clean recycled materials can possibly be sold for 10 DM/t. Under less favourable conditions charges for receiving demolition waste may be as low as 3–4 DM/t and the sales price for processed material may have to be as low as 6–8 DM/t. In order to break even, it is estimated that the difference between dumping charge and sales price should be at least 10 DM/t for a stationary plant. For existing plants this difference was frequently only 9–9.5 DM/t in 1989. Thus, the processing of demolition rubble is not yet a profitable business. Drees (95) is not in favour of government interference, but he does recognize that government regulation of dumping charges for demolition waste in heavily populated areas must be regulated if recycling plants are going to have a realistic chance to survive. He also recommends that any requirements to recycled products which are superfluous from a technical point of view, should be abandoned. Furthermore, he belives that the risk of pollution of ground water by seepage from clean demolition waste is exaggerated and that many current requirements to cleanness of such materials could be relaxed. This would certainly promote more extensive use of recycled demolition waste.

15. Energy aspects of concrete recycling Copple (7e) compared the energy required for production of recycled aggregate concrete with the energy required for production of conventional concrete with virgin aggregate. Energy requirements which are common to both types of concrete as well as energy requirements which are unique to each type of concrete were considered. Energy requirements which are unique to conventional mixes include hauling and disposal of old concrete, production of virgin aggregates, and hauling of virgin aggregates. Energy requirements which are unique to recycled aggregate concrete include moving crusher to the job site, crushing and screening of concrete, and transporting old concrete to crusher and from crusher to plant if machines are at different sites. Results are plotted in Figure 15.1. It will be seen that energy savings are realized for recycled aggregate concretes even when virgin aggregates must be hauled only a few miles. As haul distances increase, so do savings.


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16. Practical case histories Ray (20) has traced developments in recycling of concrete pavements through current demonstration projects sponsored by the Federal Highway Administration in the United States. Projects discussed include highways and airports. The use of recycled concrete in

Figure 15.1 Energy savings (per cent) of recycled as compared to conventional concrete, from Ref. (7e).

sub-bases, cement-treated sub-bases, lean concrete bases, and concrete pavements is also described. At Love Field, Dallas, Texas, a new runway was placed on a 15 cm cement treated sub-base in 1964. The mix used 72% of crushed concrete from the old pavement on the site of the new runway, 28% natural sand, and 4% cement by weight.


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The first use of recycled concrete in a lean concrete (Econocrete) sub-base for a new concrete pavement was in California. The lean mix concrete which used a mixture of recycled concrete and asphalt required 8% cement. The average 28-day compressive strength was 5 MPa. In 1977 crushed concrete was used as aggregate in a lean concrete sub-base for a keel strip at the Jacksonville, International Airport, Florida. The first successful use of recycled aggregate for production of new concrete was in Iowa in 1976. A 41-year old concrete pavement was crushed and used as aggregate in production of concrete for a new one-mile long and 22.5 cm thick highway pavement. In another project in Iowa in 1978, crushed old concrete was used as aggregate for production of a new 17-mile long and 20 cm thick highway pavement. The mix design called for 638 kg/m3 of recycled coarse aggregate, 375 kg/m3 of recycled fine aggregate, 551 kg/m3 of natural fine aggregate, and 369 kg/m3 of cement. In Connecticut in 1980, a 1000-feet long section of a 24–year old reinforced concrete pavement was recycled into a new 22.5 cm thick reinforced concrete pavement. The resulting mix showed flexural strengths over 3.5 MPa at 28 days. Also in 1980, the Minnesota Department of Transportation recycled a 16–mile plain concrete pavement into a new concrete pavement on a trunk highway. The pavement was suffering severe distress from ‘D’ cracking. Studies in the Department laboratories proved that concrete made with the recycled concrete would provide suitable durability if the maximum aggregate size was set at 19 mm. The use of recycled concrete in the new pavement has saved the Minnesota Department of Transportation in excess of US$ 600000. The largest concrete pavement recycling project to date is the Edens Expressway reconstruction job in Illinois. Here 15 miles of six-lane pavement was recycled and placed as new sub-base material in 1979 and 1980. In 1983 the Minnesota DOT awarded two adjoining projects on Trunk Highway 15—a total of 11 miles. These were also a ‘D’ cracked pavement—similar to the 1980 project. The equipment and techniques for these projects corresponded to those used before. Oklahoma became the first state to recycle a full-size project on the Interstate System. They took alternative bids on a 7.7-mile, 4-lane project on Interstate-40 east of Oklahoma City. The base bid called for three layers of asphalt totalling 8 3/4 inches. The alternative was for removal and recycling of 220 382 square yards of the existing 9-inch plain concrete using the crushed ‘D’ cracked pavement as the aggregate in a new 10-inch slab. As in Minnesota, the maximum size specified for the coarse aggregate was 1 inch (90% to 100% of the material passing the 3/4-inch sieve) to prevent ‘D’ cracking in the new pavement. This work was carried out by paving alternate roadways in two 4-mile sections while traffic used the opposite side. Michigan also awarded a major Interstate recycling project in 1983. In less than five months 5.7 miles of four-lane divided pavement (‘D’ cracked 25-year old concrete) was replaced. The bid prices on this project were so good that Michigan advertised a second project on Interstate 75. The new 10-inch pavement with tied shoulders was built one roadway at a time to accommodate traffic. Information on developments in the United States was received from Gordon K.Ray (20) who also provided a list of additional pavement recycling projects in the U.S. in 1984 and 1985, see Table 16.1.


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Table 16.1 Concrete recycling projects in the US in 1984 and 1985.

State

Route

Location

Length in miles

Quantity in square yards

1984 Wisconsin

1–90/94

Madison N.

31.70

798500.00

Wyoming

1–80

Oregon

1–5

Evanston

4.50

200000.00

N. Albany

7.00

210250.00

Michigan

1–75 NB

Monroe Co.

6.00

211134.00

Michigan

1–94

Van Buren

9.20

402312.00

Michigan

1–75

Wayne Co.

10.00

381977.00

Illinois

Fwy 412 Macon Co.

3.34

100220.00

Minnesota

1–90

Austen

2.50

82196.00

Minnesota

1–90

N.D. line

3.80

122663.00

North Dakota 1–94 EB Eckelston

13.10

311634.00

1985 Wyoming

1–80

Green Ri.

5.90

263000.00

Wyoming

1–80

Pine Bluff

7.10

315000.00

North Dakota 1–29 NB

Blanchaard

10.40

84400.00

Michigan

1–94

Kalamzoo

8.66

443976.00

Kansas

1–70

Abilene

9.30

420000.00

Kansas

1–235

Wichita

15.50

700000.00

Wyoming

1–80

Rock Springs

9.50

As a result of these and other pioneering efforts, the Federal Highway Administration has set up several two- or three-man teams to travel around the United States contacting State Highway Departments to encourage them to recycle old pavements and offering to underwrite part of the costs involved. Also, as mentioned in Chapter 13, the ASTM and the US Army Corps of Engineers have removed all national barriers to the use of recycled Portland cement concrete as concrete aggregate. In just one construction season, the Michigan Department of Transportation (MDOT) has removed, recycled and replaced more than 400 000 m3 of 10 in. concrete pavement on one of Detroit’s busiest highway stretches (109) and (110). MDOT made use of the


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lessons learned from 14 previous recycling jobs where more than 2 500 000 m3 of old concrete were recycled. The old concrete from the Lodge Freeway recycling project produced 200,000 tons of coarse aggregate, more than enough for 380 000 m3 of 25 cm thick reinforced concrete pavement and 84 000 m3 of reinforced concrete shoulders placed during reconstructions. The 67 000 tons of crushed concrete fines below 5 mm were not used in the concrete mix, but the steel recovered from the old pavement was clean enough to be melted down and recycled. From a technical as well as an economical point of view the fact that this project was successfully carried out is evidence that the recycling of concrete has moved from an experimental stage to a cost effective way of conserving resources. With approximately 60 million cubic yards of concrete now utilized yearly in US road building, and with more expected for rebuilding of 3.8 million miles of roads and highways under the additional $5.5 billions a year provided by the Surface Transportation Assistance Act of 1982, the volume of recycling is expected to increase rapidly in the US (113). With barriers removed, the many concrete recycling plants which operate in and around major cities in the United States are brought into focus. Here old concrete salvaged from old buildings, pavements, sidewalks or curbs and gutters is crushed, stockpiled, and sold to contractors. Most of this material is used as unstabilized base or sub-base at the present time, but as concrete aggregate becomes scarcer and more expensive, its use may be extended to new concrete. Tests by many agencies on recycled concrete as aggregate for new pavement show excellent strength and durability. The numerous commercial concrete recycling plants in major metropolitan areas around the United States are of greater economic significance than concrete pavement recycling projects. The economic feasibility of concrete recycling is discussed in Section 14. The technology of concrete recycling is well established in the United States and is well documented in Anon. (97). Recycling of Portland cement concrete has proven itself to be a cost effective alternative for road construction purposes. In 1987 there had already been over 1000 lane miles of portland cement concrete pavements recycled into new pavements. Whenever reconstruction of a concrete pavement is contemplated, recycling should be considered as an alternative. In most cases recycling of concrete has proven more economical than the alternative of using virgin aggregate. However, in some cases the condition of the existing pavement and local aggregate availability and cost, will indicate that recycling of the in-place concrete is not the best option. Life cycle cost studies may result in a complete reconstruction using new concrete pavement with virgin aggregates. There always remains the option of using the old concrete in the sub-base or as improved granular subgrade or for reconstruction of appurtenances other than pavements such as drainage, side slopes, shoulders or backslopes. There is a paucity of published information on recycling projects in the rest of the world. Yrjanson (7g) reports that an urban expressway north of Paris, France, has been recycled and used in a lean concrete base and porous concrete shoulders. A number of other recycling projects in France are reported in Refs. (131)–(134) and an excellent general review of the state-of-the-art in France including case histories is presented by Bauchard (135l).


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Hendriks (64) reports that in Europe by far the largest quantities of demolition debris are recycled in the Netherlands. It is estimated that 0.43 tons of debris is generated each year per person, and more than 60 stationary and mobile recycling plants have been established in the Netherlands. The largest stationary plant with a yearly capacity of 200 000 tons is located in Rotterdam. Van Eck (81) reports that wood is sorted out from concrete and masonry rubble which is then crushed, washed, screened, and sold for road construction purposes. In the future 50,000 tons of wood waste a year from the Rotterdam plant will be processes in a pyrolysis plant which will generate charcoal, tar, and wood gas. From January 1985 it has also been allowed to use recycled aggregates for production of concrete for general construction purposes in the Netherlands. Hendriks (57) reports that the first use of recycled aggregate concrete in the Netherlands was in Amersfoort where such concrete was used for partition walls in an apartment building. The concrete was produced with the same cement content as regular concrete and met requirements to a characteristic strength of 22.5 MPa. The water requirement was slightly higher than would have been the case for regular concrete, and the concrete required vibration for a somewhat longer time. Relatively high drying shrinkage of recycled aggregate concrete did not result in any cracking of walls. Hendriks (64) also reports that at the Volkel Airfield in the Netherlands coarse recycled aggregate concrete was used for a lean concrete base course and concrete pavement. The compressive strength was 10% to 20% lower than what would have been expected for a conventional concrete of the same mix proportions. At Maastricht Airport, also in the Netherlands, a concrete pavement was made with recycled aggregate concrete. The concrete met requirements to a characteristic strength of 37.5 MPa. At the Copenhagen International Airport in Denmark recycled concrete aggregate has been used as base course for a new runway and on an experimental basis in the concrete pavement for new aprons (79). Schulz (82) reports that there are 60 recycling plants in the Federal Republic of Germany with a total capacity of 10 million tons a year or more than two-thirds of all available demolition rubble. However, only 2.7 million tons a year of recycled aggregate is used primarily as sub-base material, so the plants are working much below their full capacity. In the Federal Republic of Germany it is not allowed to use recycled concrete aggregate for production of concrete. Such aggregates are too heavy to be classified as lightweight aggregates; and with a crushing strength of less than 100 MPa, they are too weak to be classified as natural or crushed aggregate for production of concrete. It is regrettable that outdated concrete specifications prevents the use of recycled concrete in new concrete in the Federal Republic of Germany. Schulz (135d) reports on an abortive attempt in 1987 to obtain a single permit to reuse 5 000 tons of recycled concrete for production of new concrete in West Berlin. However, such materials is being extensively used as unbound as well as cement bound sub-base material in road construction as evidenced by two recent publications (111) and (112) which describe the use of such materials in the restoration of motorways in Western Germany. Kasai (66) reports that recycled aggregate is used for road construction in Japan. There is no production of recycled aggregate for concrete production because the authorities have not yet approved the Japanese Proposed Standard for the ‘Use of recycled aggregate


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and recycled aggregate concrete’ (6). However, Kasai (66) reports that the Building Research Institute of the Ministry of Construction in Japan has constructed a small house as part of its technological development work on reusing construction waste for construction activities. In this test recycled concrete aggregate was used for ready-mixed concrete, and no problems developed regarding slump, air content, workability or compressive strength. The behavior of the concrete in the structure is currently under observation. Zagurskij and Zhadanovskij (83) report that in the USSR, recycling plants with a total yearly capacity of 720 000 m3 are currently in operation. The plants are located at 18 different precast concrete factories in various parts of the country, including four in Moscow. Coarse recycled concrete aggregate is used for foundation purposes and for production of new structural concrete up to a characteristic strength of 20 MPa. Crushed concrete fines are also used as mineral filler in asphalt. Krejcirik (122) reports that the Czechoslovakian State Railways crush reinforced concrete sleepers that can no longer be used for track construction. This paper describes the recycling process and shows how the materials recovered can be put to economical use. Trevorrow et al. (135r) has reported on the current situation in the UK and they have included some case histories in their paper. Morlion et al. (135t) reports on the successful construction of the embankment walls of the new ‘Berendrecht’ lock using demolished concrete from the old ‘Zandvliet’ lock in the harbour of Antwerp in Belgium.


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17. Recycling of fresh concrete wastes Recycling of alkaline waste water and waste aggregate from ready-mixed concrete plants are important from the point of view of preventing public nuisance and the saving of natural resources. About 50 million m3 of ready-mixed concrete is produced in the Federal Republic of Germany each year. Roughly 3% of this quantity (i.e. 1.5 million m3) arises as waste concrete, which at the present time is largely disposed of by dumping. Riker (73, 74) and Friesenborg et al. (75) describe in detail how fresh waste concrete can be recycled. However, it is beyond the scope of this state-of-the-art report to deal with requirement for recycled fresh waste concrete. A survey which was carried out in the United States revealed that dumping was the most practical method of disposal of left-over ready-mixed concrete (123). However, some recycling does take place. If waste water was recycled in all of the ready-mixed concrete plants in Japan with an annual production of 150 million m3 of concrete, over 25 million m3 of fresh water and more than 2.5 million m3 of aggregate could be saved annually. The Japanese Standard Specifications for Ready-mixed Concrete, JISA 5308, has been modified to make this possible, and at the present time 52% of all Japanese plants are recycling clarified water and 17% successfully recycle slurry water. Results of investigations which led to this development are reviewed by Kasai (76). Grelk (124) has prepared a comprehensive state-of-the-art report on the recycling of concrete waste reviewing 34 literature references from all over the world. He has also conducted his own research (125). Grelk concludes that only slump and setting time of fresh concrete are affected by the use of up to 15 weight per cent of waste concrete fines < 0.3–0.5 mm suspended in the mixing water for new concrete. No other properties of fresh concrete or properties of hardened concrete were significantly affected. However, setting time of fresh concrete can be reduced by more than one hour and slump of the fresh concrete was typically reduced by 10 mm for each 2% of waste concrete fines in the mixing water. An amendment to the Danish Concrete Code is being prepared allowing the use of waste-water from ready-mixed concrete plants containing up to 15 weight per cent of waste concrete fines to be used for production of new concrete provided proper precautious are taken. Reclaimed, washed and screened sand and gravel from waste ready mixed concrete can be used as normal aggregates without further treatment. Culuknoise (77) has studied the recycling of rebound from shotcrete.


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18. Conclusions and recommendations 1. Numerous laboratory experiments, field tests, and full scale pavement rehabilitation projects have shown that it is possible to recycle concrete to produce aggregate for drainage material, shoulders, stabilized as well as unstabilized base courses, bituminous concrete, lean mix, and econocrete sub-bases as well as new concrete pavements. Recycling of concrete to produce structural grade concrete for other purposes than pavements is technically feasible provided certain precautions are taken. Giving contractors the option to recycle will determine the economic feasibility of such operations. 2. Plants for production of recycled concrete aggregates are not much different from plants for production of crushed aggregate from other sources. First generation processing plants incorporate various types of crushers, screens, and transfer equipment. With the possible exception of a magnet for the separation of reinforcement and other ferrous matter, they have no facilities for removal of contaminants. Such plants are frequently used on pavement rehabilitation and recycling projects. In most cases uncontaminated recycled concrete aggregate can be used for production of new concrete without being washed. Second generation plants incorporate various kinds of sorting devices for dry or wet removal of foreign matter from concrete. Such plants are in commercial operation. In the third generation processing plants of the future all demolished material should be supplied to the installation and processed into saleable products without there being any need to transport residual matter to dumping sites either from the demolition site or from the processing installation. Such plants are not yet in operation. 3. Operation of a crushing and screening plant is always accompanied by the generation of noise and dust. Therefore, in the selection of plant location, environmental conditions of the vicinity, and legal requirements must be carefully studied and necessary countermeasures taken. However, the early concern about noise and dust problems when crushing concrete in mobile plants in urban areas has apparently been somewhat exaggerated. 4. Plain as well as reinforced concrete can be crushed in various types of crushers to provide a crushed aggregate with an acceptable particle shape. When crushed in one pass, the grain size distribution of recycled concrete aggregate frequently approximates a Fuller curve. 5. Impact crushers provide the best grain size distribution of recycled concrete aggregate, and they are less sensitive than jaw crushers to material which cannot be crushed such as reinforcing bars.


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When it comes to other properties of recycled concrete aggregates, jaw crushers perform better because they crush a smaller proportion of original aggregate particles in the old concrete than impact crushers. 6. There was some concern expressed initially about the removal of steel from reinforced concrete, particularly pavements with heavy mesh. Through the innovation of contractors in developing breaking, removal and crushing equipment and procedures, this problem has largely been overcome. 7. Approximately 30% by volume of old mortar is attached to 16–32 mm coarse recycled aggregate. Corresponding figures are 40% for the 8–16 mm fraction and 60% for the 4–8 mm fraction. Fine recycled aggregate below 4 mm contains approximately 20% by weight of old cement paste, while the filler fraction 0–0.3 mm may contain as much as 65% of old cement paste. 8. Because of the large content of old mortar in the crushed material, the density of recycled concrete aggregates are from 5 to 10% lower than the density of corresponding original aggregates. Water absorptions of 5–10% are typically found for recycled aggregates. Relatively high values are found for fine recycled aggregate. Relatively low values are found for coarse recycled aggregates. Due to high water absorption of recycled aggregates, it is sometimes recommended to use pre-soaked aggregates for production of recycled aggregate concretes in order to maintain uniform quality during concrete production. However, it has not been studied how fully saturated recycled aggregate will affect freeze-thaw resistance of new concrete. Because the density is lower and the water absorption is higher, and because the range of densities and water absorption is higher for recycled concrete aggregates than for conventional aggregates, it is imperative that density and water absorption of recycled concrete aggregates be carefully determined before it is attempted to design a mix of recycled aggregate concrete. Moreover, it is important that the two properties be carefully monitored during concrete production. This must be done in order to avoid large variations in properties of hardened concrete as well as in yield of fresh concrete. This is fairly easy when coarse recycled concrete aggregate is used with natural sand, but difficult when fine recycled concrete aggregate is used. It is very difficult to determine the free water content of fine recycled aggregates. That is one of many reasons why it is not recommended to use fine recycled concrete aggregate for production of new concrete. It is very difficult to determine the free water content of fine recycled aggregates. 9. Recycled concrete aggregates, produced from all but the poorest quality of concrete, can be expected to pass ASTM and BS requirements to LA abrasion loss percentage, BS crushing value as well as BS 10% fines value, even for production of concrete wearing surfaces, but probably not for granolithic floor finishes. 10. American results indicate that the sulfate soundness of recycled concrete aggregates generally is lower than ASTM maximum allowable limits. Japanese results indicate that the opposite is true. Further research is required in order to determine whether the sulfate soundness test is suitable for evaluation of the durability of recycled concrete aggregates, and in order to explain the large discrepancy between American and Japanese results.


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11. In standard specifications on recycled concrete aggregates it is recommended to impose maximum allowable limits on the content of contaminants such as bitumen, gypsum, organic substances, soil, chlorides, metals, and glass. See Section 7.7. 12. In the laboratory it is found that compressive, tensile, and flexural strength of recycled aggregate concrete can be equal to or higher than that of original concrete when the recycled aggregate concrete is made with the same or lower water-cement ratio than the original concrete. However, in practice and often in the laboratory, strengths of recycled aggregate concretes are found to be lower than those of corresponding original concretes. This is particularly important when it is attempted to produce structural-grade or high-strength recycled aggregate concrete from original low strength concrete or when recycled fine aggregate is used with recycled coarse aggregate. In such cases the compressive strengths of conventional structural concrete and corresponding recycled aggregate concrete made with the same water-cement ratio may vary by as much as 50% or more depending on the quality of the recycled concrete from which the recycled aggregate is derived. More commonly the compressive strength of recycled aggregate concretes is found to be 5–10% lower than that of corresponding concretes made with conventional aggregates. Differences in strength between the two types of concrete are smaller and less important when lower strength foundation grade-recycled aggregate concretes are produced. However, it is recommended always to make trial mixes in order to determine the strength potential of any recycled aggregate before it is used in production. 13. When a recycled concrete aggregate of uniform quality is used, the coefficient of variation of compressive strength between mixes of recycled aggregate concrete is no different from that of original concrete. When recycled aggregates of non-uniform quality are used, the coefficient of variation of compressive strength between mixes may be very high for structural grade concretes, but lower for foundation grade concretes. This may be the case when recycled aggregate is delivered from a central crushing plant in an urban area which accepts concrete rubble from many different demolition sites simultaneously. Considering that acceptance criteria for structural concrete in modern concrete codes frequently are based on the standard deviation or the coefficient of variation of compressive strength test results, it may not be economical, though technically feasible, to produce structural grade concrete from recycled aggregate of nonuniform quality. Thus, in the future such recycled aggregates may be limited to production of lower grade concretes, if only for economic reasons. 14. There is some evidence that coarse recycled aggregates can be used in reinforced concrete without any inconveniences at all. Use of both coarse and fine recycled aggregate may lower bond strength between concrete and reinforcing bars by 15% and ultimate flexural strength of reinforced concrete by as much as 30% due to bond failure, when compared to bond and flexural strength of corresponding reinforced concrete made with conventional aggregates. Further investigations into this matter are recommended. 15. Due to the large amount of old mortar which is attached to original aggregate particles in recycled aggregates, the modulus of elasticity of recycled aggregate


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concretes is always lower than that of corresponding control concretes. Values from 15% to 40% lower are reported. Comparatively high values of elastic modulus are reported for recycled aggregate concretes produced with coarse recycled aggregate and conventional sand. Comparatively low values of elastic modulus are reported when both coarse and fine recycled aggregates are used. 16. Due to the large amount of old mortar which is attached to original aggregate particles in recycled aggregates, drying shrinkage and creep of recycled aggregate concrete are always from 40% to 80% higher than for corresponding control concretes which are made with conventional aggregates. Comparatively low drying shrinkage is reported for recycled aggregate concretes produced with coarse recycled aggregate and conventional sand. Comparatively high drying shrinkage is reported when both coarse and fine recycled aggregates are used. As the effects of high drying shrinkage and high creep tend to cancel out in restrained structural members which are made from recycled aggregate concrete, such members appear to be no more prone to cracking due to drying shrinkage than members which are made from conventional concrete. 17. It is generally accepted that when natural sand is used, up to 30% of natural crushed aggregate can be replaced with coarse recycled aggregate without significant changes in the mechanical properties of concrete. 18. When new concrete is produced from coarse recycled aggregate, the presence of plasticizing, retarding, and air entraining admixtures in the old concrete has no significant effect on the properties of the new concrete. However, when calcium chloride has been added to the old concrete as an accelerating admixture, approximately 30% of the original chloride content can be traced as free chlorides in the new concrete. This may significantly accelerate strength development of the recycled concrete. Also, when parking or bridge structures have been submitted to deicing chloride containing salts, or when marine structures have been exposed to sea water for long periods of time, fairly large amounts of chlorides can be traced in recycled concrete aggregates. Considering the fact that specification limits on chloride content in concrete for the purpose of protecting reinforced structures against corrosion tend to become even more strict, chloride contamination may eventually turn out to be a serious obstacle towards more widespread use of recycled aggregates in concrete production. 19. On a more positive side it appears that small amounts, up to 1% by weight, of bitumen from asphaltic concrete surfacing which remains in coarse recycled aggregate will not seriously affect the properties of recycled aggregate concrete. 20. Surprisingly perhaps, there is evidence to support the fact that when recycled aggregate concrete is produced with coarse recycled aggregate which originates from structural grade concrete, frost resistance of the recycled aggregate concrete will be as good as, or better than the frost resistance of the original concrete. There is also some evidence that repeated recycling of such concrete may continue to improve frost resistance. Therefore, one may project that existing concrete structures, in addition to providing an aggregate source for the immediate future, may continue to generate an adequate supply of aggregates for concrete construction in the more distant future after once being recycled.


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However, when both coarse and fine recycled aggregates are used, or when lowgrade recycled aggregates are used, frost resistance of a recycled aggregate concrete may be lower than that of corresponding control concretes made with conventional aggregates. Frost resistance of recycled aggregate concrete is reported to be improved when 16– 19 mm maximum size coarse recycled aggregate is used rather than 32–38 mm maximum size. Further studies of the frost resistance of recycled aggregate concretes are urgently recommended, particularly the use of air entrained recycled aggregate concrete made with recycled aggregates which originate from original concretes of different qualities and which have not been air entrained. 21. No studies have been reported on the susceptibility to alkali reactions of recycled aggregate concrete produced from recycled aggregates which originate from original concrete that has been damaged by alkali reactions. Such studies are also urgently needed. 22. For equal water-cement ratio, the water permeability, the rate of carbonation and therefore the risk of reinforcement corrosion seems to be somewhat higher for recycled aggregate concretes compared to conventional concretes. However, it appears that such undesirable effects can be offset if recycled aggregate concretes are produced with slightly lower water-cement ratios than corresponding conventional concretes. 23. No attempts have been made to compare rates of chloride penetration into recycled aggregate concretes and corresponding conventional concretes. Such studies are urgently needed. 24. In principle, mix design of recycled aggregate concrete is no different from mix design of conventional concrete, and the same mix design procedures can be used. In practice, slight modifications are required as shown in Section 10.6. Slightly more water and cement may be required for recycled aggregate concretes than for corresponding concretes made with conventional aggregates in order to obtain same workability and strength. There is one major difficulty though. It is not possible to determine water adsorption, free water content or density in saturated surface dry condition of fine recycled concrete aggregate sufficiently accurately by any existing testing method. This is due to high water absorption and high cohesion of such materials. Thus, it is very difficult to control the quality of concrete produced with such aggregate, and it is not possible to know with any degree of certainty what is the free water-cement ratio of such concrete. Therefore, it is not recommended to use fine recycled concrete aggregate for production of new concrete. 25. For technical as well as economical reasons it is recommended to produce recycled aggregate concretes with coarse recycled aggregate down to no less than perhaps 4 mm, or definitely not less than 2 mm, and conventional sand for what concerns the rest. Use of crushed concrete fines below 2 mm appears to have a detrimental effect on economy as well as on many techncial properties of new concrete. Fortunately, when there is a shortage of aggregate in a region, shortage of coarse aggregate is more common than shortage of fine aggregate. 26. Practical experience has shown that recycled aggregate concrete is as easy to batch,


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mix, transport, place, compact, and finish as conventional concrete. However, because of the relatively high water absorption of recycled aggregate, it is generally recommended to batch recycled aggregates in a pre-soaked condition, and in a state which is as close to saturated and surface dry as possible. 27. Susceptibility to plastic shrinkage cracking of fresh recycled aggregate concretes remains to be studied. 28. Crushed concrete fines contain so little unhydrated cement that such fines do not qualify as hydraulic cements. When mixed with water, a slight setting, but no real hardening of the concrete is observed. This is so, even when pastes are cured in water at 50°C for prolonged periods of time. On the other hand, crusher fines below 4 mm may contain up to 4% by weight of calcium hydroxide which is formed by hydration of original cement in the old concrete. When mixed with water and left to dry in the laboratory, the product will gradually harden much like a weak lime mortar would do. Such hardening is probably due to formation of calcium carbonate when calcium hydroxide in the fines reacts with atmospheric carbon dioxide. It may give rise to caking in stockpiles. 29. When mixtures of crusher fines, water, and pulverized fly ash, or condensed silica fume are prepared and autoclaved, calcium hydroxide from the fines can be brought to react with mineral particles in the crusher fines, with fly ash or with silica fume to form reaction products of considerable compressive strength, much like calcium silicate bricks. 30. In principle, crusher fines may also be used for soil stabilization or soil modification purposes. Other possible uses include trickling filters for waste water treatment, poultry grit, cat litter, acid soil or waste water neutralization, substitution for ground limestone in SO2 scrubber filters in coal burning power plants, stabilization of sewage sludge, or as a source of available silica in highly leached lateritic soils. However, because the concentration of calcium hydroxide in the crusher fines is very low, use of crusher fines for most of these purposes may be uneconomical, even if it can be shown that beneficial effects do exist. 31. Recycling of alkaline waste water and waste aggregate from ready-mixed concrete plants is possible. For environmental reasons this will probably be required in many countries in the future. Recycling of rebound from shotcrete is also possible, but probably not economical. 32. Codes, standards, and testing methods for recycled aggregates and recycled aggregate concretes have been prepared in the United States, Japan, the Netherlands, the United Kingdom and Denmark. See Section 13. 33. At the time when this document was prepared, practical experience had shown that the use of recycled concrete aggregate is economical for pavement reconstruction purposes under all but extreme circumstances, when compared with the use of conventional aggregates. However, use of recycled concrete aggregate for general construction purposes still remained more costly than the use of conventional aggregate even in a country like Holland, where there is a shortage of conventional aggregate. In most countries this situation is expected gradually to change in favour of recycled aggregates. For one thing, it is expected that the extra cost which is now commonly charged for the


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processing of old concrete and mixed demolition rubble can be lowered once the initial developing phase is over. Also, the price of conventional aggregates will probably continue to rise in the future as raw materials get scarcer and transportation costs continue to rise. Moreover, dumping charges are certain to rise steeply over the next decades as the quantities of demolition debris continue to increase, at the same time as the number of accessible dumping sites continues to decrease. 34. This state-of-the-art report spells a bright future for the recycling of concrete, provided that all parties involved proceed with reasonable prudence in order to avoid set-backs which may reflect in unfavourable ways on the reputation of recycled aggregate concrete.

19. Acknowledgments The author wants to express his thanks to all members of RILEM Technical Committee 37-DRC, without the help of whom it would not have been possible to prepare this document. In particular, the author is indebted to Dr. Stamatis Frondistou-Yannas of Newton, Massachusetts, for her contribution to Section 14 on economic aspects of concrete recycling, to Mr. Gordon K.Ray, Concrete Pavement Consultant, Arlington Heights, Illinois, and Mr. Alan D.Buck, Research Geologist, US Army Engineering Waterways Experiment Station, Vicksburg, Mississippi, for keeping me informed about developments in the United States; to Dr. Ch. F.Hendriks of Rijkswaterstaat, Delft, The Netherlands, for his assistance with Dutch documents, and to Professor Y.Kasai of Nihon University, Japan for valuable material from Japan which he and his co-workers have reviewed and translated in order to facilitate preparation of this state-of-the-art report.


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(120) Henrichsen, A., Jensen, B. and Thorsen, T., Styrkeegenskaber for beton med genanvendelsesmaterialer, (internal report) Danmarks Ingenior Akademi, Bygningsafdelingen, Afdelingen for Fysik og Materialer, Bygning 373, DK 2800 Lyngby (in Danish). (121) Schwartz, D.R., (1987) D-cracking of concrete pavements, National Cooperative Highway Research Program, Syntheses of Highway Practice 134 . Transportation Research Board, National Research Council, Washington DC. (122) Krejcirik, M., (1986) Recycling von Betonschwellen bei der Tsechoslowakischen Staatsbahn’, Eisenbahningenieur , 37. No. 2. pp. 69–71. (123) Hurd, M.K., (1986) What happens to left over ready mix. Concrete Construction , 31, No. 3. pp. 299–305. (124) Grelk, B., Genbrug af frisk betonspild—State-of-the-art-report, available from Byggeteknik , Teknologisk Institut, Gregersensvej, Taastrup, Denmark. Technical Report 1988–09–06, bg/ema 89/63 (in Danish). (125) Grelk, B. and Jensen, P., Genbrug af frisk betonspild—Projektrapport, available from Byggeteknik , Teknologisk Institut, Gregersensvej, Taastrup, Denmark, Technical Report beg/bir 64/1 (in Danish). (126) Kuhlman, R.H., (1989) Soil cement from recycled pavement, Concrete International . pp. 35–38. (127) Ivanyi, G., Lardi, R. and Esser, A., (1985) Recycling beton. Forschungsbericht aus dem Fachbereich Bauwesen No. 33, Universität-Gesamthochschule, Essen. (128) Gütegemeinschaft Recycling Baustoff e.V., Recycling-Baustoffe für den Strassenbau, Gütesicherung. RAL-RG 501–1 , Beuth Verlag, Berlin. (129) Anon, (1985) Merkblatt über die Verwendung von industriellen Nebenprodukten im Strassenbau, Teil: Wiederverwendung von Baustoffen Forschungsgesellshaft für den Strassen und Verkehrswesen, Bonn. (130) Dohmann, M., Gefahren durch Bauschuttrecycling, Entsorgungs-Praxis , 10/87. (131) Anon, (1986) An innovating solution for the demolition material treatment of all kinds in the Gennevilliers Port, Chantiers de France No. 187, pp. 24–29 (in French). (132) Anon, (1985) Une installation-pilote de bergeaud pour le traitement de materiaux de demolition en beton armé, Chantiers de France , No. 185, pp. 43–45. (133) Laure, D., Pelletier, J.L. and Stotzel, J., (1985) Reinforcement de la RN6 en Seineet-Marne: recyclage des produits de demolition de structures de beton armes. Rev. Gen. Routes Aerodr . 59, No. 615 pp. 113–117 (in French). (134) Anon, (1975) Dechets et sous-produits industriels: elimination-recyclagevalorisation, Journees d’Information , Institut National des Sciences Appliquees, Villeurbanne. Available from CSTB Library. (135) Proceedings of the Second International RILEM Symposium on demolition and reuse of concrete and masonry . 2: Reuse of demolition waste. (ed. Y.Kasai), Nihon Daigaku Kaikan, Tokyo, Japan, Chapman & Hall, London. 135a Puckman, K. and Henrichsen, A., Reuse of concrete pavements, Ibid, Ref, 135, pp. 746–755. 135b Yoda, K., Yoshikane, T., Nakashima, Y. and Soshiroda, T., Recycled cement and recycled concrete in Japan, Ibid. Ref. 135, pp. 527–536. 135c Yoshikane, T., The instances of concrete recycled for base course material in Japan. Ibid. Ref. 135 , pp. 756–765. 135d Schulz, R.R., Concrete with recycled rubble-development in West Germany. Ibid. Ref. 135 , pp. 550–509. 135e Kashino, N. And Takahashi, Y., Experimental studies on placement of recycled


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aggregate concrete. Ibid. Ref. 135 , pp. 557–564. 135f Kakizaki, M., Harada, M., Soshiroda et al. Strength and elastic modulus of recycled aggregate concrete, Ibid, 135 , pp. 565–74. 135g Kawamura, M. and Torii, K., Reuse of recycled concrete aggregate for pavement. Ibid. 135 , pp. 726–35. 135h Mulheron, M., The recycling of demolition debris: current practice, products and standards in the United Kingdom. Ibid. Ref. 135 , pp. 510–519. 135i Goerle, D. and Sayes, L., Reuse of crushed concrete as a road base material, Ibid. Ref. 135 , pp. 736–745. 135j Busch, J., Crushed concrete used as base course material on runway 04r-221 at Copenhagen Airport. Ibid. Ref. 135 , pp. 766–774. 135k Jakobsen, J.B., Elle, M. and Lauritzen, E.K., On-site use of regenerated demolition debris, Ibid. Ref. 135 pp. 537–46. 135l Bauchard, M., The use on roads of aggregates made from demolition materials, Ibid, 135 , pp. 719–725. 135m Kaga, H., Kasai, Y., Takeda, K. and Kemi, T., Properties of recycled aggregate from concrete, Ibid. 135 , pp. 690–698. 135n Ikeda, T., Yamane, S. and Sakamoto, A., Strengths of concrete containing recycled aggregate, Ibid. 135 , pp. 585–594. 135p Nishibayashi, S. and Yamura, K., Mechanical properties and durability of concrete from recycled coarse aggregate prepared by crushing concrete, Ibid. 135 , pp. 652–659. 135q Kawai, T., Watanabe, M. and Nagataki, S., Preplaced aggregate concrete made from demolished concrete aggregates, Ibid. 135 , pp. 680–689. 135r Trevorrow, A., Joynes, H. and Wainwright, P.J., Recycling of concrete and demolition waste in the UK, Ibid. 135 , pp. 520–524. 135s Kakizaki, M., Harada, M. and Motoyasu, H.., Manufacturing of recovered aggregate through disposal and recovery of demolished concrete structures, Ibid. 135 , pp. 699– 708. 135t Morlion, D., Venstermans, J. and Vyncke, J., Demolition of the Zandvliet lock as aggregates for concrete, Ibid. Ref. 135 , pp. 709–718. 135u Mukai T. And Kikuchi M., Properties of reinforced concrete beams containing recycled aggregate. Ibid. Ref. 135 , pp. 670–679. 135v Kabayashi, S. and Kawano, H., Properties and usage of recycled aggregate concrete, Ibid. Ref. 135 , pp. 547–556. 135w Hansen, T.C. and Marga, M., Strength of recycled concrete made from coarse and fine recycled concrete aggregates. Ibid. 135 , pp., 605–612. 135x Kasai, Y., Hisaka, M., and Yanaga, K., Durability of concrete using recycled coarse aggregate, Ibid. Ref. 135 , pp. 623–632. 135y Yamato, T., Emoto, Y., Soeda, M. and Sakamoto, Y., Some properties of recycled aggregate concrete, Ibid. Ref. 135 , pp. 643–651. 135z Yanagi, K., Hisaka, M., Nakagawa, M. and Kasai, Y., Effect of impurities in recycled coarse aggregate upon a few properties of the concrete produced with it. Ibid. Ref. 135 , pp. 613–620. 135aa Ravindrarajah, R.S. and Tam, C.T., Methods of improving the quality of recycled aggregate concrete, Ibid. 135 , pp. 575–584. 135bb Kikuchi, M., Mukai, T. and Kozumi, H., Properties of concrete products containing recycled aggregate, Ibid. 135 , pp. 595–604. 135cc Fujii, T., Strength and drying shrinkage behavior of concrete crushed aggregate, Ibid. 135 , pp. 660–669.


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136 Hansen, T.C., Recycled concrete aggregate and fly ash produce concrete without cement”. Accepted for publication in Cement and Concrete Research , 1989. 137 Mulheron, M. and O’Mahony, M., (1987) Recycled aggregates. Properties and performance. The Institute of Demolition Engineers, 18 Station Approach, Viginia Water. Surrey GU25 4AE. 138 Building Research Establishment, (1983) Hardcore, Digest 276 , Department of the Environment. 139 Department of Transport, (1986) Specifications for highway works. HMSO, (UK). 140 Japan Road Association, (1984) Technical guideline for utilizing work pavement materials (Draft) 141 Kleiser, K., (1986) Wiederverwendung von Bauschutt als Betonzuschlag. Vortrag in Rahmen der Fachveranstaltung: Aufbereitung und Wiederverwendung von Bauschutt, Haus der Technik , Essen, (In German). 142 Mulheron, M., (1989) Update on recycled materials in the UK. ( Private communication ).


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21. APPENDIX A. Literature reviewed in first stateof-the-art report 1945–77. Nixon (5) Nixon, P.J., (1976) The use of materials from demolition in construction, Resources Policy , pp. 276–283. Buck, A.D., (1976) Recycled concrete as a source of aggregate. Proceedings of the Symposium on Energy and Resource Conservation in the Cement and Concrete Industry , Canada Center for Mineral and Energy Technology, Ottawa. Glushge, P.L., (1946) The work of the scientific research institute, Gidrotskhnicheskoge Stroiteistvo No. 4 , pp. 27–8 (USSR). Brief English summary in Engineer’s Digest , 7, No. 10, p.330. Graf, O., (1948) Uber Ziegelsplittbeton, Sandsteinbeton und Trümmerschuttbeton, Die Bauwirtschaft , No. 2, No. 3, No. 4, (Germany). Crushed brick concrete, sandstone concrete and rubble concrete, Trans. No. 73–1 , (1973) US Army Engineer Waterways Experimental Station, C E. Vicksburg, Miss. Ploger, R.R., (1947) An investigation of the compressive strength of concrete in which concrete rubble was used as an aggregate. Unpublished thesis, Cornell University. Malhotra, V.M., (1976) The use of recycled concrete as a new aggregate. Proceedings of the Symposium on Energy and Resource Conservation in the Cement and Concrete Industry Canada Center of Mineral and Energy Technology, Ottawa. Buck, A.D., (1973) Recycled concrete. Highway Research Record No. 430 . Frondistou-Yannas, S., (1977) Waste concrete as aggregate for new concrete, ACI Journal, pp. 373–374. studies in the reuse of demolished concrete (1975) Committee for Research on the Reuse of Construction Waste , Building Contractors Society, Tokyo, ( personal communication by F. Tomasawa). Gaede, K. Deutscher Ausschuss für Stahlbeton 109, (1952) and 126, (1957). Newman, A.J. (1946) The utilization of brick rubble from demolished shelters as aggregate for concrete, Inst. Mun. Eng. J. 73, No. 2, pp. 113–121.

PART TWO RECYCLING OF MASONRY RUBBLE Dr R.R.SCHULZ Institute for Building Materials Testing, Waldkirch, Germany and Dr Ch.F.HENDRICKS Road Engineering Division, Rijkswaterstaat, Delft, The Netherlands

Recycling of masonry rubble

141

List of Abbreviations and Symbols Abbreviations cal

calculated

f

guilder (Dutch monetary unit)

g

aerated concrete

HOZ

blast furnace slag cement

HS

slag aggregate brick or block

KS

sand-lime brick or block

k-Wert

grading value (the sum of the percentage retained particles on the entire set of sieves divided by 100)

LB

lightweight concrete

M.-%

% by weight

Mio

million

Mz

sold baked clay brick

NB

normal concrete

NE-Metall

non-ferrous metal

obs

measured

PZ

Portland cement

RAL

German Insititute for Quality Assurance and Quality Marking

V

solid blocks made from lightweight rubble

Vol.-%

% by volume

Symbols B

degree of certainty

DZ

degree of crushing by compression

E

modulus of elasticity

N/mm2

Eb

modulus of elasticity of concrete

N/mm2

g

aggregate

kg/m3

mns

natural sand content

–Z

n

number

–

r

correlation coefficient

–

SE


142

standard error of estimate

*

V

volume

m3

W

water content

kg/m3

W30

water absorption after 30 minutes

% by vol

W24h

water absorption after 24 hours

% by vol

z

cement content

kg/m3

βD

compressive strength

N/mm2

βBZ

flexural strength

N/mm2

βDmz

brick or block compressive strength

N/mm2

βsz

tensile splitting strength

N/mm2

γ

aggregate/cement ratio

–

λ

thermal conductivity

W/(Km)

t’b

concrete density

kg/m3

tRg

particle density

kg/m3

(s

bulk density

kg/m3

ω

water/cement ratio * unit of associated mean value


143

1 Introduction Recycling and re-use of building rubble present interesting possibilities for economizing on waste disposal sites and conserving natural resources. RILEM Technical Committee 37-DRC has contributed to the elimination of existing technical barriers and promotion of the use of mineral materials from building rubble. To provide a basis for this work, two state-of-the-art reports have been prepared, summarizing available literature and analysing it with a view to suitable practical applications. In formulating the aim, it became obvious that a subdivision into at least two distinct groups of building materials would be necessary in order to ensure an optimum use of building rubble. Concrete rubble resulting from the breaking up of roads and other civil engineering concrete construction works contains few other building materials than concrete. But rubble from building structures contains generally many other types of materials such as masonry. The properties of concrete rubble and mixed masonry rubble are so different that they need to be treated separately. For this reason it has been necessary to present separate reports on aggregates based on recycled concrete rubble and on recycled masonry rubble. Part One of this volume contains the report on aggregates based on recycled concrete rubble. The present report on crushed masonry and recycled concrete made with crushed masonry as aggregate draws largely on knowledge acquired on the use of rubble from buildings destroyed in the Second World War. More recent research (4, 42, 40, 50) published in the Netherlands has contributed substantially to the extending and updating of this part of the report. The reader is frequently referred to literature reference (4) which summarizes the results of a major study of mixed demolition rubble which was made in the Netherlands. A brief summary of the properties of the raw materials used in this study and the results obtained on corresponding concretes are presented in Appendix A.

2 Historical survey “Concrete” (Opus Caementitium) buildings made with crushed brick have been known since Roman times (24 to 29). The concrete channels of the Eifel water supply to Cologne are an example of this type of structure in which the binder is a mixture of lime and brick-dust or other pozzolanas. Crushed brick concrete with portland cement was used in Germany from 1860 for the manufacture of concrete products. Systematic


144

investigations on the effect of the cement content, water content and grading of crushed brick have been carried out since 1928. However, the first significant applications only date back to the use of rubble from buildings destroyed (11) in the Second World War. During the period of reconstruction after the Second World War it was necessary on the one hand to satisfy an enormous demand for building materials and on the other to remove the rubble from the destroyed cities. The amount of brick rubble in German towns was about 400 to 600 million cubic metres. Using this rubble made it possible not only to reduce site clearing costs but also to contribute considerably to fulfilling the need for building materials. Rubble-recycling plants in the Federal Republic of Germany produced about 11.5 million cubic metres of crushed brick aggregate by the end of 1955, with which 175000 dwelling units were built (29). The statistics compiled by the Association of German Cities show that by the end of 1956, about 85% of all building rubble in the German Federal Republic had been cleared. In two-thirds of all municipalities clearance was complete at the beginning of 1957. Only in 15 large cities did about a million of cubic metres still remain by the end of 1955 (29). By about 1960, there was no longer any rubble recycling done in the Federal Republic. There are many technical and economical directives and guidelines dating from the period between 1945 and 1960 (the main one being DIN 4163 (1)) and also many publications. The German Society for the Use of Rubble issued a total of 437 publications listed in reference (29). In the UK also, rubble was recycled and used after the Second World War, although to a lesser extent than in Germany. It applied more particularly to redundant defence structures, mainly to brick masonry constructions (30). These were very seldom rendered so that there was hardly any presence of impurities as would be the case with other types of construction. Although other parameters apply nowadays, both as regards the composition of rubble and demolition and recycling technologies, the experience acquired during the post-war years remain interesting particularly in connection with recycling of masonry rubble for use as aggregate for production of new concrete.

3 Prospects Forecasts have been made about the use of rubble from demolitions in the coming decades (78), on the basis of existing use of materials and an average life hypothesis. According to these forecasts, the annual concrete rubble production within the European Community (EC) is expected to increase from 55 million tonnes in 1980 to 162 million tonnes in the year 2000, while that of brick rubble will remain more or less constant at about 52 million tonnes. These figures may well be too high in view of the recession in the building market and provide only a rough overall estimate (unless the newer members of the EC are included). It is very clear that the proportion of concrete rubble and


145

masonry rubble has shifted towards concrete rubble and is connected to the fact that, in the last decades, concrete manufacture has increased steadily whilst production figures for bricks have hardly changed. An example from another source is the Netherlands (4) (cf. (48)) where, at the beginning of the 1980s the annual figure was still 3 million tonnes of masonry rubble and only 2 million tonnes of concrete rubble. If the forecasts are correct, the production of concrete rubble should dominate by the middle of the 1990s.

4 Walling materials 4.1 Types of walling unit The term “masonry rubble” is a collective term for various mineral building materials resulting from the demolition of buildings and civil engineering structures (4). They include mainly: ordinary concrete (NB);

aerated concrete blocks (G);

bricks (Mz);

blastfurnace slag bricks and blocks (HS) and

sand-lime bricks (KS);

natural stone (NS).

lightweight concrete and lightweight concrete blocks (LB);

Masonry rubble often also contains mortar rendering and burnt clay materials such as roofing tiles and shingles. Concrete rubble may contain undesirable contaminants such as metals, asphalt, timber, plastics, glass and plaster.

4.2 Manufacture and composition 4.2.1 Ordinary concrete (NB) Ordinary concrete consists of a mix of sand and gravel embedded in a cement matrix. Crushed natural stone and sand is sometimes used instead of rounded gravels and sands, depending on availability. According to the German standards the particle density of normal aggregate is between 2200 and 3200 kg/m3 and the strength exceeds 100 N/mm2.


146

The properties of the concrete are determined mainly by the properties and amount of the weaker component, the cement matrix. 4.2.2 Masonry bricks (Mz) Masonry bricks are made of clay or clayey soils with or without addition of mineral fillers or foaming agents, which are formed and burnt and in which hardening occurs in normal bricks by dry sintering (changes and reactions in the hardened state) and in hard burnt clinker by sintering or fusion (bond obtained through partial melting flow). Both density and compressive strength increase with increasing burning temperatures. Bricks used for the construction of walls are classified as lightweight bricks, high strength bricks and clinkers, according to their density and strength (16). Clinkers are bricks that have been sintered at the surface and have been shown by testing to possess a good frost resistance. The water absorption capacity of bricks may be up to about 7% (DIN 105 T3, (92). 4.2.3 Sand-lime bricks (KS) Sand-lime bricks are made of lime and silica aggregates, pressed damp, and hardened in about 6 to 7 hours in an autoclave under high water vapour pressure, generally at 16 bar and at 200°C. The lime reacts with the SiO2 and produces calcium silicate hydrates (CSH) similar to the products of hydration of cement and resulting in high strength values (16). 4.2.4 Lightweight concrete and lightweight concrete blocks (LB) Lightweight concretes with dense structures are made with lightweight aggregates in total or in part. The density of the concrete depends mainly on the porosity of the aggregate particles. If the aggregate particles are bonded with only a little cement paste at the points of contact, the result will be an open textured concrete or porous concrete. No-fines concrete, i.e. concrete made with all aggregates of a very similar particle size is particularly porous. A combination of particle size and porosity gives a mixed porosity. 4.2.5 Cellular concrete (G) Cellular concrete is usually made with cement, lime, finely ground quartz sand or other aggregate with high silica content, water and a chemical agent (aluminium powder) and hardened under a pressure of about 10 bar with steam at temperatures of about 180°C (18). The reactive area of the aggregate has been increased by the grinding process and, when subjected to such high temperatures, it reacts with the CaO of the binder to form calcium silicate hydrates similar to those that occur during hardening of cement (16).


147

4.2.6 Blastfurnace slag bricks and blocks (HS) Blastfurnace bricks and blocks have slag as the main constituent (mostly in granulated form) with lime, slag cement or similar hydraulic binders and sometimes also other silica materials. They may be solid blocks or blocks with hollows and are generally steam hardened or hardened in exhaust gases containing carbon dioxide (blastfurnace gases). 4.2.7 Natural stone (NS) Natural stone for masonry work must be cut from sound stone only, but many types of stone are suitable for this purpose. Not all natural stones used for masonry work are completely resistant to weathering. Such a requirement applies only for unprotected masonry exposed to the weather.

4.3 Properties Table 1 shows the differences between various standardized materials used for masonry work and also the differences within each type as regards various densities and strength classifications or both. The range of variation is much greater when older, nonstandardized materials are included. Asphalt, which may be present in considerable quantity in building rubble, should be mentioned, although its effect on concrete is so bad that it is totally unsuitable for re-use as aggregate in concrete (3, 4).

5 Masonry rubble 5.1 Composition Since there are very different types of material used for masonry work in the different regions in Germany, it follows that the composition of rubble is also different from one region to another. As the investigations of Hoffmeister have shown (56), the rubble from North and Central Germany contains mainly brick and sand-lime brick; in the south, however, there were various amounts of natural stone as well (see Table 2). If the brick rubble varied considerably in physical properties (porosity and strength) and in chemical composition (silicic acid, clay and gypsum contents), the differences were even greater in the natural stone. This applied also to the sands used for mortars and renderings.


148

The end product of a single plant for the preparation of rubble to be used in building construction may well show considerable variations in composition. This was revealed by the results of more recent investigations (see Tables 3 and 4) made on eight different installations in the Netherlands (4). Although these results refer to prepared rubble, they give indications about the composition of the untreated original rubble. Table 3 gives the result of visual examination showing differences observed during one day’s production run and Table 4 shows the range of variation for ten days taken at random between 1980 and 1982. It may be seen that some plants show a preference for certain types of building materials. It appears also that in plants 1 to 5 there are considerable amounts of asphalt concrete rubble and on average about 20% by weight of mortar. Sand-lime brick occurs only in small amounts. A similar situation occurs in newer German recycling plants (see Tables 5 and 6). The amount of concrete rubble is particularly high in plants A and B (see Table 6), which seems to point to an initial preliminary sorting of the rubble.

Table 1. Properties of masonry bricks and blocks

Type of brick Density Compressive or block strength

kg/m3

N/mm2

Modulus Shrinkage DIN of Specification elasticity × number 1000 N/mm2

mm/m

Burnt clay bricks and blocks (Mz) Lightweight hollow bricks

500– 1,000

2–35

105 T2

Solid/hollow bricks

1,000– 2,200

4–>35 (20–25)

High-strength bricks and clinker

1,000– 2,500

36–>75

105 T3

Ceramic clinker

1,200– 2,500

>60

105 T4

500– 2,200

4–>75 (20–25)

7–18

up to 0.6

105 T1

Sand-lime bricks and blocks (KS) Solid, perforated & hollow bricks and blocks

7–17

up to 0.7

106 T1

Recycling of masonry rubble Facing bricks

149

800– 2,200

12–>75

106 T2

900– 2,000

6–>35

5–10

up to 1.0

398

300–800

2–>7.5 (4)

1.25–3

up to 0.7

4,165

Perforated bricks

500– 1,600

4–>15

(Pumice)

18,149

Hollow bricks

500– 1,400

2–7.5

up to 2.3

18, 151

Solid bricks and blocks (V)

500– 2,000

2 4 6 7.5

up to 1.0 (expanded clay)

18,152

Concrete (NB) Hollow blocks

1,000– 1,800

4–>15

Blast furnace slag bricks (HS) Solid, perforated & hollow bricks Aerated concrete bricks and blocks(G) Lightweight aggr. & nofines concretes (LB)

2.5–4 4–7 6–8.5

18,153

Table 2. Composition of original debris sampled from ruins of two German cities (from (56))

Constituent in weight %

Stuttgart

Nürnberg

Cement-bound materials > 40 mm Regular concrete

9.95

1.08

Lightweight concrete

0.08

0.02

Cement mortar

0.51

–

Blastfurnace slag concrete

0.03

–

10.57

1.10

–

1.20

Total of cement-bound materials Ceramic materials > 40 mm Hard burnt bricks

Recycling of demolished concrete and masonry Brick rubble

150

18.48

21.43

Burnt clay bricks, entire bricks

1.75

3.00

Other ceramic materials

0.95

0.23

21.18

25.86

Sandstone rubble

11.23

16.69

Sandstone, entire units

15.27

–

0.07

–

–

0.75

26.57

17.44

Gypsum plaster

0.07

0.01

Lime mortar

0.65

1.00

Blastfurnace slag

0.03

–

Glass

0.19

0.03

Non-ferrous metals

0.17

0.01

Steel

2.28

0.33

Wood

0.18

0.01

–

0.01

3.57

1.40

Total grains > 40 mm

61.89

45.80

Total grains < 40 mm

38.11

54.20

100.00

100.00

Total of ceramic materials Natural stone > 40 mm

Slate Granitic stone Total of natural stone Contaminants > 40 mm

Textiles Total contaminants

Total of all components

Table 3. Variation in composition of processed building waste sampled during one particular day in 8 different processing plants. Figures are in weight % (from (4))

Processing plant N° Constituent

1

2

3

4

5

6

7

8

Cement-bound Regular concrete

2–75 97–100 16–38 18–70 5–6

31–34 4–18

2–4

Lightweight concrete

0–2

–

0–1

–

–

–

1–6

–

Recycling of masonry rubble Cement mortar

0–4

Lime mortar

–

151

–

–

–

–

0–3

–

3–12 –

0–2

4–12

6–14

3–11

7–28

7–24

Hard burnt bricks

9–79 –

0–1

–

–

12–26 0–34

7–26

Brick rubble

9–45 –

1–2

9–30

71–81 12–22 34–70 56–65

Roofing tiles

–

–

–

–

–

2–10

0–2

–

Ceramic tiles

–

–

–

–

Recycling of Demolished Concrete and Masonry (Rilem Report, No 6)

Durability Design of Concrete Structures (Rilem Report)

Concrete and Masonry Databook

Masonry and Concrete

Performance Criteria for Concrete Durability (Rilem Report, No 12)

Disaster Planning, Structural Assessment, Demolition and Recycling (Rilem Report, 9)

Fly Ash in Concrete: Properties and performance (Rilem Report)

Demolition and reuse of concrete and masonry: guidelines for demolition and reuse of concrete and masonry: proceedings of the Third international RILEM symposium on demolition and reuse of concrete and masonry held in Odense, Denmark, 24-27 October 1993

Ice and Construction (Rilem Report, 13)

Reinforced Masonry Engineering Handbook: Clay and Concrete Masonry, Sixth Edition

RILEM - Connections Between Steel and Concrete 2001

Concrete Masonry Homes: Recommended Practices

Bituminous Binders and Mixes (Rilem Report)

Seismic Design of Reinforced Concrete and Masonry Buildings

Eurocode 6 - Design Of Masonry Structures

Admixtures for Concrete - Improvement of Properties: Proceedings of the International RILEM Symposium (RILEM Proceedings 5)

No Report

Masonry

Demolished Man

Recycling

Demolished Man

Demolished Man

Durable Bonded Post-Tensioned Concrete Bridges (Concrete Society Technical Report)

The Meaning of Masonry

The Meaning of Masonry

Mozart and Masonry

The Meaning of Masonry

Masonry Design and Detailing

Masonry Design and Detailing

Recycling of Demolished Concrete and Masonry (Rilem Report, No 6)

Durability Design of Concrete Structures (Rilem Report)

Concrete and Masonry Databook

Masonry and Concrete

Performance Criteria for Concrete Durability (Rilem Report, No 12)

Disaster Planning, Structural Assessment, Demolition and Recycling (Rilem Report, 9)

Fly Ash in Concrete: Properties and performance (Rilem Report)

Demolition and reuse of concrete and masonry: guidelines for demolition and reuse of concrete and masonry: proceedings of the Third international RILEM symposium on demolition and reuse of concrete and masonry held in Odense, Denmark, 24-27 October 1993

Ice and Construction (Rilem Report, 13)

Reinforced Masonry Engineering Handbook: Clay and Concrete Masonry, Sixth Edition

RILEM - Connections Between Steel and Concrete 2001

Concrete Masonry Homes: Recommended Practices

Bituminous Binders and Mixes (Rilem Report)

Seismic Design of Reinforced Concrete and Masonry Buildings

Eurocode 6 - Design Of Masonry Structures

Admixtures for Concrete - Improvement of Properties: Proceedings of the International RILEM Symposium (RILEM Proceedings 5)

No Report

Masonry

Demolished Man

Recycling

Demolished Man

Demolished Man

Durable Bonded Post-Tensioned Concrete Bridges (Concrete Society Technical Report)

The Meaning of Masonry

The Meaning of Masonry

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