Concrete in the Service of Mankind Appropriate concrete technology

Concrete In The Service Of Mankind

Appropriate Concrete Technology

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Appropriate Concrete Technology Proceedings of the International Conference held at the University of Dundee, Scotland, UK on 24–26 June 1996 Edited by

Ravindra K.Dhir Director, Concrete Technology Unit University of Dundee and Michael J.McCarthy Lecturer, Concrete Technology Unit University of Dundee

E & FN SPON An Imprint of Chapman & Hall London · Weinheim · New York · Tokyo · Melbourne · Madras

Published by E & FN Spon, an imprint of Chapman & Hall, 2–6 Boundary Row, London SE1 8HN, UK This edition published in the Taylor & Francis e-Library, 2006. “ To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to http://www.ebookstore.tandf.co.uk/.” Chapman & Hall, 2–6 Boundary Row, London SE1 8HN, UK Chapman & Hall, GmbH, Pappelallee 3, 69469 Weinheim, Germany Chapman & Hall USA, 115 Fifth Avenue, New York, NY 10003, USA Chapman & Hall Japan, ITP-Japan, Kyowa Building, 3F, 2–2–1 Hirakawacho, Chiyoda-ku, Tokyo 102, Japan Chapman & Hall Australia, 102 Dodds Street, South Melbourne, Victoria 3205, Australia Chapman & Hall India, R.Seshadri, 32 Second Main Road, CIT East, Madras 600 035 First edition 1996 © 1996 E & FN Spon ISBN 0-203-36239-X Master e-book ISBN

ISBN 0-203-37917-9 (Adobe e-Reader Format) ISBN 0 419 21470 4 (Print Edition) 0 419 21500 X (Print Edition) (5 volume set) 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 the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the London 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 Publisher’s Note This book has been prepared from camera ready copy provided by the individual contributors in order to make the book available for the Conference. Printed on acid-free paper, manufactured in accordance with ANSI/NISO Z39.48–1992 (Permanence of Paper) The cover illustration shows the Glendevon Reservoir spillway, constructed using GGBS concrete. Photograph courtesy Castle Cement Ltd.

PREFACE Concrete is ubiquitous and unique. Indeed, there are no alternatives to concrete as a volume construction material. This raises important questions of how concrete should be designed and constructed for cost effective use in the short and long-term, and yet encourage further radical development. Equally, it must also be environmentally-friendly during manufacture and in its aesthetic presentation in structures. The Concrete Technology Unit (CTU) of the University of Dundee has organised this major 5 day International Congress, following the conferences, Protection of Concrete in 1990 and Concrete 2000: Economic and Durable Construction Though Excellence in 1993, as part of its continuing commitment to the development of excellence in concrete construction. The central theme of the Congress was Concrete in the Service of Mankind, under which 5 self-contained conferences were organised; (i) Concrete for Environment Enhancement, (ii) Concrete for Infrastructure and Utilities, (iii) Appropriate Concrete Technology, (iv) Radical Concrete Technology and (v) Concrete Repair, Rehabilitation and Protection. In total 350 papers were presented by authors from 70 countries worldwide. The Congress Opening Addresses were given by the Lord James Douglas-Hamilton MP, Minister of State for the Construction Industry, Scotland and by Dr Ian J.GrahamBryce, Principal and Vice-Chancellor of the University of Dundee. The Opening Papers were presented by Emeritus Professors P.Kumar Metha and Ben C.Gerwick, University of California, Berkeley, USA and Professor John Morris, University of Witwatersrand and Mr Spencer S.Sephton, PPC Cement (pty), South Africa. The closing address was given by Professor Peter C.Hewlett, Director of the British Board of Agrément, UK and Visiting Industrial Professor, Department of Civil Engineering, University of Dundee. The Congress was supported by 14 major International Institutions together with 23 Sponsors and 50 Exhibitors, highlighting the importance of concrete and the close cooperation between the CTU and industry. A Congress of this size and scope was a major undertaking. The immense efforts of the Organising, International Advisory and National Technical Committees, who advised on the selection and review of papers is gratefully noted. The efforts of all the Authors and Chairmen of the various Technical Sessions and, in particular, those who travelled from afar to come to Dundee are greatly appreciated as are all the CTU staff and research students for their sterling efforts in ensuring the smooth running of the Congress. Particular thanks must be given to the two Congress joint Secretaries, Mr Neil A.Henderson and Dr Michael J.McCarthy and the Unit Secretaries Mr Steven Scott and Miss Diane Sherriff.

All the Proceedings have been prepared directly from the manuscripts provided by the authors and, therefore, there may be some errors or inaccuracies that have been inadvertently overlooked. Ravindra K Dhir Dundee February 1996

INTRODUCTION The specification of concrete has long been a major source of conflict between the engineer, contractor and supplier. Much of this conflict stems from the increasing litigious world in which modern construction takes place. Equally, it may arguably to be due to the misunderstandings arising from what is the appropriate performance that will be required from the materials used themselves and the structure manufactured. To overcome this conflicting interest, there will have to be an evolutionary approach away from the traditional method of specification and towards performance criteria. This will also facilitate the formulation of integrated, harmonised international standards. This transition will not be easy and it will almost certainly transfer responsibility for some concrete material decisions to the supplier. It can only be hoped that total quality management, which has done so much for the manufacturing sector, can also provide the same degree of confidence to clients in concrete construction. Since most international specifications bodies are, in principle, committed to this approach to specification by performance, it is important that the implications of this are debated at a major forum such as this international conference. The versatility of concrete continues to be underlined through the development of new binder technologies, alternative materials for reinforcement and novel design and construction techniques, which continues apace. The Proceeding of this Conference ‘Appropriate Concrete Technology’ deal with all of these subject areas under six clearly identified themes: (i) Criteria for Appropriateness, (ii) Implications of Harmonisation, (iii) Versatility of Concrete, (iv) Binder Technology, (v) Non-Ferrous Reinforcement and (vi) Design and Construction. Each theme started with a Leader Paper presented by the foremost exponents in their respective fields. In total, 65 paper were presented during the 3 day International Conference and compiled into these Proceedings. Ravindra K Dhir Michael J McCarthy Dundee February 1996

ORGANISING COMMITTEE Concrete Technology Unit Professor Ravindra K Dhir (Chairman) Dr Michael J McCarthy (Joint Secretary) Mr Neil A Henderson (Joint Secretary) Professor Peter C Hewlett Director, British Board of Agrément Professor Vasilia K Rigopoulou National Technical University of Athens Professor Sammy Y N Chan Hong Kong Polytechnic University Dr Nyok Y Ho Director, L&M Structural Systems, Sinapore Dr Frederick H Hubbard Dr M Roderick Jones Dr Mukesh C Limbachiya Dr S L Daniel Ng Dr Wenzhong Zhu Mr Thomas D Dyer Mr Steven R Scott (Unit Assistant) Miss Diane H Sherriff (Unit Secretary)

INTERNATIONAL ADVISORY COMMITTEE Dr H Z Al-Abideen Assistant Deputy Minister Ministry of Public Works and Housing, Saudi Arabia Professor M S Akman Professor of Civil Engineering Istanbul Technical University, Turkey Professor M G Alexanader Professor of Civil Engineering University of Cape Town, South Africa Professor Carmen Andradé Research Professor Instituto Eduardo Tonoja of Construction Sciences, Spain Mr J A Bickley Implementation Manager Concrete Canada, Canada Professor J M J M Bijen General Manager Institute for Materials and Environmental Research, Netherlands Professor A M Brandt Head of Section Institute of Fundamental Technological Research, Poland Mr J C Caballero General Director Instituto Del Cemento Portland, Argentina Professor A Ceccotti Fornitek Laboratory, Canada Professor O E Gjørv Professor, Division of Building Materials Norwegian Institute of Technology, Norway Professor T C Hansen Professor of Building Materials Technical University of Denmark Dr G C Hoff Senior Associate Engineer Mobil Research & Development Corporation, USA Professor S Y Huang Director

Shanghai Institute of Building Materials, China Professor C Jaegermann Professor Emeritus National Building Research Institute, Israel Professor F K Kong Head of Division of Structures and Construction Nanyang Technological University, Singapore Professor I E Korish Professor of Reinforced Concrete Structures University of Alexandria, Egypt Professor S Nagataki Professor, Department of Civil Engineering Tokyo Institute of Technology, Japan Dr A M Paillere Technical Director Laboratoire Central des Ponts et Chaussées, France Mr W G Ryan Chief Executive Officer Cement and Concrete Association, Sydney, Australia Professor A E Sarja Research Professor Technical Resarch Centre of Finland (VTT) Professor P Schiessl Director Technical University of Aachen, Germany Professor S P Shah Director ACBM, Northwestern University, USA Professor T P Tassios Director of Laboratory Concrete Structures National Technical University of Athens, Greece Professor D N Trikha Director Structural Engineering Research Centre, India Professor K Tuutti Skanska Teknik AB, Sweden Professor F H Wittmann Director Institute for Building Materials, Switzerland Professor A V ZaBegayev Head of Department RC Structures State University of Civil Engineering, Russia

TECHNICAL COMMITTEE (from United Kingdom) Professor A W Beeby Professor of Structural Design, University of Leeds Dr R D Browne Consultant, Roger Browne Consultancy Professor J H Bungey Professor of Civil Engineering, University of Liverpool Dr P Chana Divisional Director, CRIC, Imperial College Mr P M Deason Managing Director, Trafalgar House Technology Ltd Professor R K Dhir (Chairman) Director, Concrete Technology Unit, University of Dundee Mr C R Ecob Divisional Director, Mott MacDonald Ltd Professor F P Glasser University of Aberdeen Dr T A Harrison Technical Director, British Ready Mixed Concrete Association Professor P C Hewlett Director, British Board of Agrément Mr J Innes Chief Bridge Engineer, Scottish Office Mr K A L Johnson Director, AMEC Civil Engineering Ltd Professor A E Long Director, School of the Built Environment, Queen’s University of Belfast Mr G G T Masterton Director, Babtie Group Professor G C Mays Head, Civil Engineering Group, Cranfield University Mr L H McCurrich Technical Director, Fosroc International Ltd Dr J B Menzies Engineering Consultant, John B Menzies Professor R S Narayanan Senior Partner, S B Tietz & Partners Dr P J Nixon

Head, Inorganic Materials Division, Building Research Establishment Dr D J Pollock Director, Sir William Halcrow & Partners Ltd Professor D C Spooner Director, Materials and Standards Division, British Cement Association Dr H P J Taylor Director, Costain Building Products Ltd Professor P Waldron Director, Centre for Cement & Concrete, University of Sheffield Mr KR Wilson Technical Director, G Maunsell & Partners

SUPPORTING BODIES American Concrete Institute Concrete Association of Finland Concrete Institute of Australia Concrete Society of Southern Africa Concrete Society, UK German Concrete Association (DBV) Indian Concrete Institute Institute of Concrete Technology, UK Institution of Civil Engineers, UK Instituto Brasileiro Do Concreto, Brazil Japan Concrete Institute Netherlands Concrete Society Norwegian Concrete Association (NB) RILEM, France

SPONSORING ORGANISATIONS AMEC Civil Engineering Ash Resources Ltd Blue Circle Cement Boral Pozzolan Ltd British Board of Agrément British Cement Association Building Research Establishment Castle Cement Ltd City of Dundee District Council Du Pont de Nemours International SA ECC International (Europe) Ltd Elkem Materials Fosroc International Ltd Grace-Cormix Lafarge Aluminates Mott MacDonald Special Services National Ash, National Power plc PowerGen plc Ready Mixed Concrete (United Kingdom) Ltd Rugby Cement Scottish Enterprise Tayside Scottish Power plc—Ash Sales Transport Research Laboratory

EXHIBITORS Advantage Precast Allied Bar Coaters AMEC Civil Engineering Ash Resources Ltd Babtie Group Blue Circle Cement Boral Pozzolan Ltd British Board of Agrément British Cement Association Building Research Establishment Capco Test Equipment Castle Cement Ltd Cementitious Slag Maker’s Association Cem-FIL International Ltd CFPI City of Dundee District Council Colebrand Ltd Du Pont de Nemours Internatioanl SA E & FN Spon ECC International (Europe) Ltd Elkem Materials Fibraflex Fosroc International Ltd Germann Instruments A/S GOMACO International Ltd Grace-Cormix Harris Speciality Chemicals I W Farmer & Partners Ltd John Fyfe Ltd Kerner Greenwood (UK) Ltd Lafarge Aluminates Minelco Ltd Mott MacDonald Special Services National Ash, National Power plc PowerGen plc Protovale (Oxford) Ltd Ready Mixed Concrete (United Kingdom) Ltd Rugby Cement Scottish Enterprise Tayside

Scottish Power plc—Ash Sales Tarmac Topmix Ltd TBV Stanger Thomas Telford Publishing Transport Research Laboratory VNC Association of the Netherlands Cement Industry Wexham Developments

CONTENTS Preface

v

Introduction

vii

Organising Committee

viii

International Advisory Committee

ix

Technical Committee (from United Kingdom)

xi

Supporting Bodies

xiii

Sponsoring Organisations

xiv

Exhibitors

xv

Contents

xviii

OPENING ADDRESSES Chairman Professor R K Dhir, University of Dundee, United Kingdom Opening of the Congress Lord James Douglas Hamilton MP, Minister of State for the Construction Industry, Scotland Welcoming the Delegates to the University Dr I J Graham-Bryce, Principal and Vice Chancellor, University of Dundee

xxiv

THEME 1 CRITERIA FOR APPROPRIATENESS Chairmen Professor P C Hewlett, British Board of Agrément, United Kingdom Professor A V ZaBegayev, State University of Civil Engineering, Russia Leader Paper Performance criteria for structural concrete Professor G Somerville, British Cement Association, United Kingdom Who likes concrete? S MacCraith Perfomance criteria: The pains and strains of change C Oltean-Dumbrava Application of a statistical methodology for the evaluation of the potential market of new concrete products on the construction industry

2 13 22 28

C C Videla, H de T Solminihac, J de D S Ortúzar and J P Retamal Appropriate concrete design J Wang, D Knight and L Swann Assuring performance of concrete structures through a durability audit B K Marsh and P J Nixon Realistic prediction of time-dependent response of concrete structures J Lopatic, and F Saje

36 47 57

THEME 2 IMPLICATIONS OF HARMONISATION Chairmen Professor A Samarin, University of Wollongong, Australia Dr N K Subedi, University of Dundee, United Kingdom Leader Paper Implication of harmonisation Mr R S Narayanan, SB Teitz Partners, Consulting Engineers, United Kingdom Application of European concrete standards D Stoelhorst and G P L den Boer Implications of structural Eurocodes S B Desai Fracture mechanics parameters of concrete: Test methods development and harmonization of standards S N Leonovich Effects of concrete creep on the ultimate compressive strength of concrete columns A F L Wong, C Arnaouti and N K Raji Health and safety in construction in Nepal R P Adhikari Foundations for low rise buildings in Romania and UK: Comparisons and effects C Oltean-Dumbrava and W G Carter Site workers—the challenge D P Barnard Computer-based concrete specification A Osborne, A D Pullen and J B Newman

67 72 81 90

99

108 115

121 132

THEME 3 VERSATILITY OF CONCRETE Chairmen Professor M G Alexander, University of Cape Town, South Africa Professor N P Barbosa, Universidade Federal da Paraiba, Brazil Mr B V Brown, Ready Mixed Conrete (United Kingdom) Ltd, United Kingdom Leader Paper The versatility of concrete Professor F Wittmann Institute for Building Materials and Dr J Gebauer and Dr

142

Professor F Wittmann, Institute for Building Materials and Dr J Gebauer and Dr R Torrent, Holderbank Management & Consulting Limited Switzerland Concrete masonry: A different dimension for housing in developing countries. The 40 years experience in Colombia G G Madrid and L G Pelaez Material matters in affordable housing J Morris and R A Kruger Cement stabilisation of soil for the production of building blocks J Morris and G F Blight An innovative labour-intensive method for construction of arch bridges using uncut stone and mortar R G D Rankine and G J Krige Manpower motivation improves quality in construction M S Chishty and M A Choudhry Appreciating low-strength concrete M A Abdul-Salam Behaviour in extreme climates of concrete made with different types of cement C C Videla, P T Covarrubias and J M D Pascual Problems about optimization of porosity and properties of aerated concrete R Cabrillac and Z Malou The use of foamcrete for affordable development in third world countries E P Kearsley Some aspects of the design and production of foamed concrete D E Wimpenny Building underground: The concrete contribution M A Clarke

154

169 177 186

194 202 209 223 232 243 253

THEME 4 BINDER TECHNOLOGY Chairmen Mr T Jones, ECC International Ltd, United Kingdom Professor P Lenkei, Janus Pannonius Polytechnic, Hungary Professor M A Thomas, University of Toronto, Canada Leader Paper Hydraulic cements—New types and raw materials and radically new manufacturing methods Professor A Samarin, University of Wollongong, Australia Hydraulic behaviour of non-expansive sulfoaluminate cement Ch Malami, Th Philippou, T Tsakiridis and V K Rigopulou Phase equilibria in the CaO-Al2O3-SiO2-H2O system in relation to blended HAC cements K C Quillin High performance concrete containing modified rice husk ash B Chatveera and P Nimityongskul

262

274 281

291

Slag alkaline polymer cement concretes P V Krivenko, V A Raksha and L V Raksha RHA-cement as a replacement for Portland cement in rural Tanzanian villages P Stroeven and E I Sabuni Effect of the binary admixtures of fly ash and shale ash on the fluidity and compressive strength of cement concrete N-Q Feng, Q-F Zhuang and D-H Wang A study of carbonation in binding system with cement and hydraulic admixtures I Robu Application of the cement hydration equation to concrete K K Sideris, M S Konsta and C G Karayannis Properties of high temperature-humidity cured OPC-GGBS fibre concrete roofing tiles H C Uzoegbo Micropore structure variances during hydration of cement pastes Ch Ftikos, A Georgiades and J Marinos Improving the properties of adobe by pozzolanic materials B Baradan

298 307 321

328 335 344

355 363

THEME 5 NON-FERROUS REINFORCEMENT Chairmen Mr W E Brewer, Brewer & Associates, USA Mr S B Desai, Department of the Environment, United Kingdom Professor J Morris, University of Witwatersrand, South Africa Leader Paper Tailoring the properties of concrete structures with appropriate non-ferrous reinforcements Professor A E Sarja, Technical Research Centre of Finland, Finland Development of cover meters for stainless reinforcement—Two successful approaches J C Alldred Structural design using epoxy coated reinforcement J Cairns Supercover concrete: A new method of preventing reinforcement corrosion in concrete structures using GFRP rebars C Arya and G Pirathapan Cracking of carbon fibre reinforced mortars L Kucharska and A M Brandt Low cost fibre reinforced cement products by using inexpensive additives I Papayianni, N Economou, D Leventis and G Xanthakos Biaxial fracture behaviour of fibre reinforced concrete E K Tschegg, M Elser and S E Tschegg-Stanzl Designing structures using non-ferrous reinforcement J L Clarke and P O’Regan

369

385

395 408

420 430 441 453

J L Clarke and P O’Regan A preliminary investigation into the comparative performance of FRP and steel reinforcement in medium and high strength concrete C Ellis and E M Ulas Structural behaviour of bamboo reinforced concrete beams and slabs K Ghavami, A J S Mina, H C L Junior and N P Barbosa

462

472

THEME 6 DESIGN AND CONSTRUCTION Chairmen Professor H C Chan, Hong Kong University, Hong Kong Professor B Teply, Technical University of Brno, Czech Republic Professor P R Vassie, Transport Research Laboratory, United Kingdom Leader Paper Design and construction Professor T P Tassios, National Technical University of Athens, Greece The design of framed structures—A proposal for change A W Beeby and F Fathibitaraf Development of moment continuity connection for simply supported precast concrete bridges G Davies, K S Elliott and A A H Arshad Evaluation of honeycomb concrete G W Seegebrecht, S H Gebler and B G Stejskal Flexible reinforced concrete beams on elastic rubber foundation model A Hassani and D W Cox Portal A-frame vs portal H-frame structures: A choice based on total costs D R Lemelin Preliminary design rules for structural steel shearheads in concrete slabs P S Chana Shear resistance of reinforced concrete members at high temperatures S B Desai, N K Subedi and K S Virdi Repeated and cyclic loading tests on precast concrete beam-to-column connections Y C Loo, B Z Yao and S Takheklambam SISMO-building technology: Plain concrete in high rise buildings E van Rensbergen, R Bellers and D van Gemert Factory & site production—A comparison H P J Taylor Development of self-cure concrete R K Dhir, P Hewlett and T D Dyer Vibrators for compacting concrete—A radical look P G F Banfill The planning and design of concrete mixes for transporting, placing and finishing

483 495 506

518 525 536 544 551 563

574 588 596 609 616

G G T Masterton and R A Wilson Roller compacted concrete: Development and use in Queensland, Australia H Reid

629

CLOSING ADDRESS Chairman Dr T A Harrison British Ready Mixed Concrete Association, United Kingdom Presented by Professor P C Hewlett, Director British Board of Agrément, United Kingdom Index of Authors

638

Subject Index

642

OPENING ADDRESS Lord James Douglas Hamilton MP Minister of State for the Construction Industry, Scotland WELCOMING ADDRESS Dr I J Graham-Bryce Principal and Vice-Chancellor University of Dundee Chairman Professor R K Dhir University of Dundee United Kingdom

Theme 1 CRITERIA FOR APPROPRIATENESS Chairmen Professor P C Hewlett British Board of Agrément United Kingdom Professor A V ZaBegayev State University of Civil Engineering Russia

Leader Paper Performance Criteria for Structural Concrete Professor G Somerville British Cement Association United Kingdom

PERFORMANCE CRITERIA FOR STRUCTURAL CONCRETE G Somerville British Cement Association UK Appropriate Concrete Technology. Edited by R K Dhir and M J McCarthy. Published in 1996 by E & FN Spon, 2–6 Boundary Row, London SE1 8HN, UK. ISBN 0 419 21470 4. ABSTRACT. A proposal is made for a framework for durability design, which is potentially numerate and compatible with conventional structural design. It is strongly suggested that the definition of limiting performance is an essential first step, to permit sensible economic/technical decisions to be taken, when designing with life cycle costing in mind. Follow up action is then required to similarly evaluate the available resistance options on a common basis. Keywords: Durability, Performance criteria, Concrete, Design, Construction, Materials. Professor George Somerville is Director of Engineering at the British Cement Association. He is also a Visiting Professor, both at Imperial College, London, and at Kingston University. He is a structural engineer, with strong research interests in service life performance, including durability design and assessment. INTRODUCTION As a student in the 1950s, the author was taught the rudiments of structural design in terms of using numerical methods to provide adequate strength, stiffness, stability and serviceability—with some guidance on how to do that at least first cost. The performance criteria, margins, and factors of safety were given in Codes, and accepted without question. These were assumed to prevail as soon as the structure was built, as well as during its entire useful life (although this was never specified). This was not checked in any numerical sense, but assumed to be so, if material and workmanship specifications were satisfied during the construction phase. In short, the provision of durability i.e. the maintenance of the required margins and factors, was on a purely prescriptive basis. In the 1990s, that basic scenario has not really changed. To be sure, the prescriptions, specifications and factors of safety have altered, but the overall design approach is fundamentally the same.

Performance criteria for structural concrete

3

Feedback from performance in service has indicated that durability is a major problem, and is therefore the principal reason for the changes made in concrete specifications. Specific aggressive actions have been identified and quantified, with provision made to deal with these on a prescriptive basis. A simplistic summary of these developments is given in Table 1. For those actions which predominantly affect the concrete, the prescriptive approach is perhaps best; problems only really arise when several aggressive actions occur simultaneously. For corrosion—the major durability issue—the matter is not so straightforward. Much work has been done in increasing the understanding of the corrosion process, and many proposals made for improving durability, which fall into one of two categories: (a) increasing cover and/or changing the concrete mix, in terms of ingredients or proportions, or (b) introducing protective systems in the form of coatings, sealers, penetrants or cathodic protection. There is little doubt that these proposals give better durability. How much better may still be in question in some cases, since field experience is relatively short; how they might complement each other is yet another question. Some 10 years ago, the author [1] made a distinction between the production and placing of durable concrete and the design and construction of structures that will be durable. The essence of the argument was that the industry tried to solve all its durability problems via a prescriptive materials approach, and yet standards of design, detailing and construction were at least as significant. The trend of introducing protective systems tends to move durability considerations out of the materials court into the design arena. Another major factor is the growing awareness of the need to consider management and maintenance even at the design stage and of the need to attempt this via life cycle costing [2]. For any quantitative durability design approach to work, it is essential to define performance requirements, both in terms of time and of minimum technical performance.

Table 1 Conditions requiring special attention in durability terms CATEGORY (1) Those prodominantly affecting the concrete

COMMENTS (a) Freezing and thawing

Usually dealt with by: - suitable choice of materials, mix proportions and concrete grade - designing to minimise exposure to moisture - air-entrainment; air content depends primarily on aggregate size - adequate curing and compaction Note that the use of deicing salts can aggravate the problem.

(b)

(i) Sulfate

Fairly well understood.

Appropriate concrete technology

Aggressive chemical exposure

4

attack

Specific material and mix proportions are recommended for clearly defined ranges of sulfate concentration.

(ii) Acid attack

Can come from various sources, e.g. ground water, sewage, farms, industrial processes. pH value is a guide to severity (below pH=4.5 special protective measures usually necessary). Low permeability concrete will provide acceptable protection against mild attack.

(d) Chemical (i) e.g. Alkali- Unusual, in arising from the basic materials in reaction of silica reaction concrete, rather than from ecternal attack. The aggregates basic reaction is fairly well understood and provisions exist to minimise the risk of damage due to the reaction—although all potentially reactive aggregates have probably not yet been identified at a European level. (2) Those predominantly affecting the reinforcement

(a) Corrosion

(i) Due to carbonation of the concrete

Corrosion is a consequence of the penetration of liquids and gases through concrete to reach the reinforcement: the processes involved are now well understood. Resistance to these actions depends fundamentally on the permeability of the concrete, and hence on the four ‘Cs’ [Constituents (of the mix), Cover Compaction, Curing].

(ii) Due to diffusion of chlorides

There are two distinct phases in the mechanism of attack—the time taken for the deleterious substances to reach the steel, and then the rate of corrosion. Both periods require estimation in assessing loss of serviceability and hence design life. These may be different for different forms of attack, and hence the need to distinguish between, say, carbonation and chloride penetration. Current design approaches, under development, are bases fundamentally on this 2phase mechanism.

(iii) Other potential harmful gasses or liquids

There are various options available to the designer in providing adequate resistance, including surfact protection of the structure, direct coating of the reinforcement, cathodic protection, adjustment to the 4 ‘Cs’, etc. The option chosen depends on the severity of the attack and on economic factors.

This is no different from establishing minimum requirements for safety and (say) crack width, in structural design; without such metre-sticks, it is not possible to compare alternative options in whole life cost/benefit terms.

Performance criteria for structural concrete

5

In performance criteria terms, durability is not the only issue. At present in the UK, the construction industry is itself undergoing change, in the procurement process. For some time now, concrete technology has had to cope with large continuous pours, with pumping, and with round-the-clock production in a precast factor, and with delivery in a ready-mix truck. However, demand for increased productivity and quality, linked to speed of construction, is imposing increased pressure on technology for the construction phase. Design is becoming more closely related to the construction process, and therefore we have to strike a balance between buildability and satisfactory performance in service. This means that performance criteria must be derived to permit that to happen, i.e. to balance the needs both of buildability and durability; the merits of alternative design options can then be judged on a common basis. In brief, the time has come when durability should be considered as an integral part of structural design—ideally based on the same principle of establishing margins or factors of safety, in providing resistance against known loads, while satisfying established performance criteria. The purpose of this paper is to propose a framework for such a design method, before going on to suggest some limiting performance criteria. WHY AN ENGINEERING APPROACH TO DURABILITY? Data of the type provided by Paterson [3] and Wallbank [4] clearly demonstrate that the level of deterioration in individual cases is dictated by a combination of factors, in which design and construction issues are significant. The provision of durable concrete is important, but it is possible to have ‘failure’ even with the best materials, if design and construction standards are poor. Moreover, the spectre of obsolescence also enters the arena. Many buildings and bridges have had to be upgraded or replaced, because their functional needs have changed—quite apart from any decrease in technical performance. In addition, different components in individual artifacts (eg. cladding in buildings; expansion joints in bridges) have been shown to have useful lives much less that those for the basic structures. Growing recognition of this situation has led to the development of a performance profile approach to design, eg. by White [5], for buildings, and by BSI [6] in a formalised general approach. It is not always possible to precisely define the useful life of a structure at the design stage or to second-guess the need for future upgrading. However, in many cases an informed decision can be taken; for example, in the UK, much of the motorway network is being upgraded within 30–40 years of construction. This leads to a basic proportion as follows:- durability should be an integral part of design: the essential requirement is to ensure fitness for purpose, while taking account, as far as possible, of future functional and financial needs, in whole life costing terms. ELEMENTS IN A DESIGN FRAMEWORK Table 2 shows the five essential elements which make up the detailed process of structural design. To gain acceptability, durability design has to be seen alongside these,

Appropriate concrete technology

6

and parallel proposals are also made in Table 2. Currently we concentrate on item 5, while trying to improve, via research mainly associated with items 1 and 3. Missing is any serious consideration of items 2 and 4, and yet both are fundamental to a quantitative approach; we need to know what we are trying to achieve, in what will never be an exact science, and we need to have some confidence in the predictions we make. To understand better what is intended here, Figure 1 is proposed as a possible relationship between the elements in Table 2. Each aspect of Figure 1 will now be considered in more detail.

Figure 1 Suggested outline relationship between the elements in a durability design framework LOADS AND LOAD EFFECTS In designing for durability, a knowledge of the ‘loads’ is more important than in structural design. How the effects of these loads are treated will depend on the level of calculation proposed in the design strategy. The situation is summarised in Table 3. As a minimum, Zone A in this Table will always be necessary, particularly if going for a prescriptive type of solution. However, it is strongly suggested that, to be truly effective, the definition of exposure conditions has to be orientated towards specific deterioration mechanisms: this is contrary to the present system in the UK, but consistent with the proposals in the European Standard for concrete, ENV206.

Table 2 Elements in a design framework ITEM

ACTUAL FOR STRUCTURAL DESIGN

PARALLEL POSSIBILITIES DURABILITY DESIGN

1. Loads

Imposed loads taken from Codes.

Classification of environments.

Performance criteria for structural concrete

7

Identification and quantification of aggressive actions. 2. Performance Criteria

Adequate strength, stiffness and A statement of required life in qualitative serviceability. Deflection and crack of quantitative terms. Some account of width limits. criticality (risk analysis). A definition of a performance profile including any strategy for maintenance. Specific limits to ‘damage’ or effects of deterioration (e.g. cracking or loss of section due to corrosion; expansion due to ASR; internal damage due to freezethaw.)

3. Modelling Analysis

Methods of analysis used to determine action effects due to the applied loads. Design equations used to provide resistance to the action effects (bending, shear, etc.). Recommendations on detailing.

Predictive models to determine the effects of the aggressive actions. Models/equations used to calculate the effects of deterioration on conventional action effects. Evaluation of alternative options in providing the required resistance for the required time— usually a combination of material, design and construction options.

4. Factors of Partial factors which are generally Safety, Margins applied both to the loading and resistance sides of the design condition S