THE ICT The The Institute of Concrete Technology was formed in 1972 from the Association of Concrete Technologists. Full membership is open to all those INSTITUTE OF who have obtained the Diploma in Advanced Concrete Technology. The Institute is internationally recognised and the Diploma has world-wide CONCRETE TECHNOLOGY acceptance as the leading qualification in concrete technology. The Institute sets high educational standards and requires its members to abide by a Code of Professional Conduct, thus enhancing the profession of concrete technology. The Institute is a Professional Affiliate body of the UK Engineering Council.
AIMS The Institute aims to promote concrete technology as a recognised engineering discipline and to consolidate the professional status of practising concrete technologists.
PROFESSIONAL ACTIVITIES It is the Institute's policy to stimulate research and encourage the publication of findings and to promote communication between academic and commercial organisations. The ICT Annual Convention includes a Technical Symposium on a subject of topical interest and these symposia are well attended both by members and non- members. Many other technical meetings are held. The Institute is represented on a number of committees formulating National and International Standards and dealing with policy matters at the highest level. The Institute is also actively involved in the education and training of personnel in the concrete industry and those entering the profession of concrete technologist. The INSTITUTE OF CONCRETE TECHNOLOGY - Yearbook: 2003-2004 - Yearbook: TECHNOLOGY CONCRETE OF INSTITUTE The
The INSTITUTE OF CONCRETE TECHNOLOGY P.O.BOX 7827, Crowthorne, Berks, RG45 6FR Tel/Fax: (01344) 752096 Email: [email protected] Website: www.ictech.org Yearbook: 2003-2004 ICT YEARBOOK 2003-2004 ICT RELATED INSTITUTIONS & ORGANISATIONS
ASSOCIATION OF CONCRETE ADVISORY SERVICE INSTITUTION OF HIGHWAYS CONSULTING ENGINEERS Century House & TRANSPORTATION EDITORIAL COMMITTEE Alliance House Telford Avenue 6 Endsleigh Street 12 Caxton Street Crowthorne London WC1H 0DZ London SW1H 0QL Berkshire RG45 6YS Tel: 020 7387 2525 Professor Peter C. Hewlett (Chairman) Tel: 020 7222 6557 Tel: 01344 466007 www.iht.org www.acenet.co.uk www.concrete.org.uk BRITISH BOARD OF AGRÉMENT INSTITUTION OF & UNIVERSITY OF DUNDEE ASSOCIATION OF INDUSTRIAL CONCRETE BRIDGE ROYAL ENGINEERS FLOORING CONTRACTORS DEVELOPMENT GROUP Brompton Barracks 33 Oxford Street Century House Chatham Peter C. Oldham Leamington Spa Telford Avenue Kent ME4 4UG CHRISTEYNS UK LIMITED CV32 4RA Crowthorne Tel: 01634 842669 Tel: 01926 833 633 Berks RG45 6YS www.acifc.org.uk Tel: 01344 762676 INSTITUTION OF www.cbdg.org.uk STRUCTURAL ENGINEERS Dr. Philip J. Nixon ASSOCIATION OF LIGHTWEIGHT 11 Upper Belgrave Street BUILDING RESEARCH ESTABLISHMENT AGGREGATE MANUFACTURERS CONCRETE INFORMATION LTD London SW1X 8BH Wellington St Telford Avenue Tel: 020 7235 4535 Ripley Crowthorne www.istructe.org.uk Graham Taylor Derbyshire DE5 3DZ Berks RG45 6YS INSTITUTE OF CONCRETE TECHNOLOGY Tel: 01773 746111 Tel: 01344 725700 INTERPAVE www.concrete-info.com Concrete Block Paving Association BRE (BUILDING RESEARCH 60 Charles Street ESTABLISHMENT) LTD Laurence E. Perkis CONCRETE REPAIR ASSOCIATION Leicester LE1 1FB Bucknalls Lane Association House Tel: 0116 253 6161 INITIAL CONTACTS Garston 99 West St www.paving.org.uk Watford WD25 9XX Farnham Tel: 01923 664000 Surrey GU9 7EN MORTAR INDUSTRY ASSOCIATION www.bre.co.uk Tel: 01252 739145 156 Buckingham Palace Road www.concreterepair.org.uk London SW1W 9TR BRITISH BOARD OF AGRÉMENT Tel: 020 7730 8194 P.O.Box 195 THE CONCRETE CENTRE www.mortar.org.uk Bucknalls Lane Century House Garston Telford Avenue QSRMC Watford Crowthorne Quality Scheme for Ready Herts WD25 9BA Berkshire RG45 6YS Mixed Concrete Tel: 01923 665300 Tel: 01344 762676 3 High Street www.bbacerts.co.uk www.concretecentre.com Hampton Middlesex TW12 2SQ BRITISH CEMENT ASSOCIATION THE CONCRETE SOCIETY Tel: 020 8941 0273 Telford Avenue Century House www.qsrmc.co.uk Crowthorne Telford Avenue Berks RG45 6YS Crowthorne QUARRY PRODUCTS ASSOCIATION Tel: 01344 762676 Berkshire RG45 6YS 156 Buckingham Palace Road www.bca.org.uk Tel: 01344 466007 London SW1W 9TR www.concrete.org.uk Tel: 020 7730 8194 BRITISH PRECAST www.qpa.org CONCRETE FEDERATION CIRIA 60 Charles Street Construction Industry Research RIBA Leicester LE1 1FB & Information Association Royal Institute of British Architects Tel: 0116 253 6161 6 Storey's Gate 66 Portland Place www.britishprecast.org.uk Westminster London W1B 1AD London SW1P 3AU Tel: 020 7580 5533 BSI STANDARDS Tel: 020 7222 8891 www.architecture.com British Standards House www.ciria.org.uk 389 Chiswick High Road SOCIETY OF CHEMICAL INDUSTRY London W4 4AL CORROSION PREVENTION 14/15 Belgrave Square Tel: 020 8996 9000 ASSOCIATION London SW1X 8PS www.bsi.org.uk Association House Tel: 020 7598 1500 99 West St www.sci.mond.org BRITPAVE Farnham Professional Affiliate UNITED KINGDOM British In-Situ Concrete Surrey GU9 7EN ACCREDITATION SERVICE Paving Association Tel: 01252 739145 21-47 High Street Century House www.corrosionprevention.org.uk Telford Avenue Feltham Crowthorne INSTITUTE OF CORROSION Middlesex TW13 4UN Published by: Berks RG45 6YS Corrosion House Tel: 020 8917 8400 www.ukas.org.uk THE INSTITUTE OF Tel: 01344 725731 Vimy Court www.britpave.org.uk Leighton Buzzard UNITED KINGDOM CONCRETE TECHNOLOGY Beds LU7 1FG CAST STONE ASSOCIATION P.O.Box 7827 CEMENT ADMIXTURES ASSOCIATION Tel: 01525 851771 Century House Crowthorne 38a Tilehouse Green Lane www.icorr.org Knowle Telford Avenue Berks RG45 6FR West Midlands INSTITUTE OF MATERIALS Crowthorne Tel/Fax: 01344 752096 B93 9EY MINERALS & MINING Berks RG45 6YS Email: [email protected] Tel: 01564 776362 1 Carlton House Terrace Tel: 01344 762676 www.ukcsa.co.uk Website: www.ictech.org London SW1Y 5DB CEMENTITIOUS SLAG Tel: 020 7451 7300 UNITED KINGDOM MAKERS ASSOCIATION www.materials.org.uk Croudace House QUALITY ASH ASSOCIATION Rights reserved. No part of this publication may Goldstone Road INSTITUTION OF CIVIL ENGINEERS Regent House be reproduced or transmitted in any form Caterham One Great George Street Bath Avenue without the prior written consent of the Surrey CR3 6XQ London SW1P 3AA Wolverhampton publisher. The comments expressed in this Tel: 01883 331071 Tel: 020 7222 7722 WV1 4EG publication are those of the Author and not Tel: 01902 576 586 necessarily those of the ICT. www.ukcsma.co.uk www.ice.org.uk www.ukqaa.org.uk
97 The INSTITUTE OF CONCRETE TECHNOLOGY
CONTENTS PAGE
FOREWORD 5 By Dr Bill Price, President, INSTITUTE OF CONCRETE TECHNOLOGY
THE INSTITUTE 6
COUNCIL, OFFICERS AND COMMITTEES 7
FACE TO FACE 9 - 11 A personal interview with Philip Owens
MILESTONES IN THE HISTORY OF CONCRETE TECHNOLOGY 13 - 23 THE DEVELOPMENT AND USAGE OF HIGH ALUMINA CEMENT: By John Bensted
ANNUAL CONVENTION SYMPOSIUM: 25 - 86 PAPERS PRESENTED 2003
ADVANCED CONCRETE TECHNOLOGY DIPLOMA: 87 - 96 SUMMARIES OF PROJECT REPORTS 2002 - 2003
RELATED INSTITUTIONS & ORGANISATIONS 97
Yearbook: 2003-2004
3 4 FOREWORD
t gives me great pleasure to welcome you to 2003 also sees the launch of ‘The Concrete the 2003-2004 ICT Yearbook, ably and Centre’ the new central market development Iprofessionally produced by the editorial board. organisation for the UK concrete industry. The ICT The high standard of the Yearbook continues to welcomes the establishment of this new reflect creditably on the Institute as a whole. organisation and will work closely with it, particularly in the fields of education and training. The past year has been a particularly active one The Institute recognises the need for all for the Institute and I have tried to illustrate some organisations within the concrete industry to form of the highlights in this foreword. closer links and alliances in order to strengthen the The annual Convention and Technical message that concrete is the construction material Symposium was, yet again, a tremendous success. of choice. The past proliferation of organisations It was well attended and a number of interesting claiming to represent the concrete industry has only papers were presented. There also seemed to me succeeded in diluting this message and a more to be a more relaxed atmosphere than usual, with coherent approach is greatly to be desired. networking and the social side of the event playing I would like to end by thanking all those who a major role in the overall success of the have contributed to the ongoing success of the ICT Convention. over the past year, through membership of Council Despite many production difficulties along the or other committees or through supporting various way, the excellent new ICT promotional CD was ICT events. The Institute relies heavily on the also unveiled at Convention. This is a powerful voluntary efforts of our members to maintain and marketing tool for the Institute and any member develop our various activities and their efforts are who can make use of it to attract more members greatly appreciated. or enhance the awareness of the Institute, is This is my final year as President of the Institute encouraged to obtain a copy from the Executive of Concrete Technology and I wish to thank the Officer. We always need new members! membership for indulging me and trust that Rob During the past year the Institute finally Gaimster will enjoy his term as President as much succeeded in establishing a route for our members as I have. to achieve registration with the Engineering Council EC(UK). It had initially been hoped that ICT would progress towards becoming a Licensed Member (Nominated Body) of EC(UK) and registering ICT members directly. However, the resources required both to achieve this status and to administer the registration process were too great to be sustained by such a small body as the ICT. Consequently, whilst ICT remains as a Dr BILL PRICE Professional Affiliate of EC(UK), the Institute has PRESIDENT entered a partnership with the Society of INSTITUTE OF CONCRETE TECHNOLOGY Environmental Engineers, who are a Licensed Member of EC(UK), which enables us to achieve this objective without the same impact on the Institute’s resources. Registration as MICT, C.Eng (or as I.Eng or Eng.Tech) is now possible via two routes. Firstly, by the standard route of obtaining the formal qualifications required by EC(UK) combined with suitable professional experience and secondly, via a ‘Mature Candidate’ route. This has been a long standing aim of the Institute and one which surveys of the membership suggested was also supported by our members. It is a little disappointing therefore, that so few ICT members have taken this opportunity to seek registration. I would urge all of you to explore the benefits of becoming registered with EC(UK) both as a means of enhancing your individual professional status and the status of the ICT itself.
5 THE INSTITUTE
INTRODUCTION A GRADUATE shall hold a relevant university degree containing a significant concrete The Institute of Concrete Technology was technology component. All candidates for formed in 1972. Full membership is open to all Graduate membership will be invited to nominate those who have obtained the Diploma in a corporate member to act as Superintending Advanced Concrete Technology. The Institute is Technologist. There is no minimum age limit in this internationally recognised and the Diploma has grade. world-wide acceptance as the leading qualification The STUDENT grade is intended to suit two in concrete technology. The Institute sets high types of applicant. educational standards and requires its members to abide by a Code of Professional Conduct, thus i) The school leaver working in the concrete enhancing the profession of concrete technology. industry working towards the Technician The Institute is a Professional Affiliate body of the grade of membership. UK Engineering Council. ii) The undergraduate working towards an appropriate university degree containing a MEMBERSHIP STRUCTURE significant concrete technology component. A guide on ‘Routes to Membership’ has been All candidates for Student membership will be published and contains full details on the invited to nominate a corporate member to act as qualifications required for entry to each grade of Superintending Technologist. There is no minimum membership, which are summarised below: age limit in this grade. There is a limit of 4 years in this grade. A FELLOW shall have been a Corporate Member of the Institute for at least 10 years, have a minimum of 15 years appropriate experience, Candidates are not obliged to attend any including CPD records from the date of course (including the ACT course) prior to sitting introduction, and be at least 40 years old. an examination at any level. A MEMBER (Corporate) shall hold the Academic qualifications and relevant experience Diploma in Advanced Concrete Technology and can be gained in any order for any grade of will have a minimum of 5 years appropriate membership. experience (including CPD). This will have been Corporate members will need to be competent demonstrated in a written ‘Technical and in the science of concrete technology and have Managerial/Supervisory Experience Report’. An such commercial, legal and financial awareness as alternative route exists for those not holding the is deemed necessary to discharge their duties in ACT Diploma but is deliberately more onerous. accordance with the Institute’s Code of A Member shall be at least 25 years old. Professional Conduct. AN ASSOCIATE shall hold the City and Guilds Continuing Professional Development (CPD) is CGLI 6290 Certificate in Concrete Technology and common to most professions to keep their Construction (General Principles and Practical members up to date. All members except Applications) and have a minimum of 3 years students, are obliged to spend a minimum of 25 appropriate experience demonstrated in a written hours per annum on CPD; approximately 75% on report. An appropriate university degree exempts a technical development and 25% on personal Graduate member from the requirement to hold development. The Institute’s guide on ‘Continuing CGLI 6290 qualifications. Those who have passed Professional Development’ includes a record sheet the written papers of the ACT course but have yet for use by members. This is included in the to complete their Diploma may also become Membership Handbook. Annual random checks Associate members. All candidates for Associate are conducted in addition to inspection at times of membership will be invited to nominate a application for upgraded membership. corporate member to act as Superintending Technologist. There is no minimum age limit in this grade. ACT DIPLOMA A TECHNICIAN holding the CGLI 5800 The Institute is the examining body for the Certificate in Concrete Practice must also submit a Diploma in Advanced Concrete Technology. written report demonstrating 12 months Courses for the Diploma are currently held in the experience in a technician role in the concrete United Kingdom, Ireland and South Africa. A web- industry. An alternative route exists for those who based distance learning package is scheduled for can demonstrate a minimum of 3 years 2004. Details are available from the Institute. appropriate experience in a technician role. All candidates for Technician membership will be invited to nominate a corporate member to act as Superintending Technologist. There is no minimum age limit in this grade.
6 COUNCIL, OFFICERS AND COMMITTEES COUNCIL
EXAMINATIONS Dr. W.F. PRICE TECHNICAL AND COMMITTEE President EDUCATION R. Gaimster COMMITTEE R. RYLE Vice President Chairman C.D. Nessfield Dr. B.K. MARSH Chairman G. Taylor Hon Secretary Secretary J.C. Gibbs J.V. Taylor Secretary Dr. Ban Seng Choo Hon Treasurer Dr. P.L.J. Domone M.D. Connell L.K. Abbey R. Gaimster I.F. Ferguson R.A. Binns J. Lay R.E.T. Hall M.W. Burton Dr. J.B. Newman Dr. B.K. Marsh G.W. David H.T.R. du Preez P.C. Oldham R. Hutton (corresponding) B.F. Perry J. Lay R.V. Watson H.T.R. du Preez C.B. Richards J.D. Wootten (corresponding) A.T. Wilson A.R. Price W. Wild
FINANCE MARKETING ADMISSIONS AND COMMITTEE COMMITTEE MEMBERSHIP COMMITTEE J.C. GIBBS A.M. HARTLEY Chairman Chairman M.D. CONNELL C.D. Nessfield D.G. King Chairman Dr. W.F. Price (corresponding) G. Taylor R.J. Majek Secretary W. Wild P.L. Mallory Dr. W.F. Price C.D. Nessfield J.D. Wootten M.S. Norton G.Taylor
SCOTTISH CLUB EVENTS SOUTHERN AFRICA COMMITTEE COMMITTEE CLUB COMMITTEE
J. WILSON P.M. LATHAM H.T.R. DU PREEZ Chairman Chairman Chairman J.C. Gibbs G. Taylor R. Page Secretary & Treasurer Secretary Y. Staples L.R. Baker R.G. Boult R. Tomes R.C. Brown I.F. Ferguson H.T. Cowan I.E. Forder G. Prior P.L. Mallory EXECUTIVE K.W. Head P.C. Oldham OFFICER R.A. Wilson B.C. Patel G. TAYLOR G. Prior (corresponding)
7 8 FACE TO FACE A personal interview with Philip Owens
Philip Owens is seen by many as a rebel but his 50- year career in concrete has been guided by questioning authority and his strong Christian principles. His career has been varied but he has always viewed it as a quest. He joined the Institute in 1972 after taking the ACT course at Fulmer Grange and became Fellow number 8 some 14 years ago.
Q: Philip, how did you get into concrete? capstone – a waste material which couldn’t be A: As a schoolboy I had terrible problems used in conventional architectural masonry but is reading due to dyslexia (which I didn’t realise until there in high performance concrete in that bridge. 1980) but when, in 1949, I did National Service, At the Ministry of Works we did the basement for they suggested that I join the Intelligence Corps the Fleet Telephone Exchange in 1957, with 20% because I was good at logics; however, there were fly ash and then, 20 years later, the Thames no vacancies so I went into the Military Police. Barrier which was designed with 20% fly ash but ended up with 30%. After National Service I went back to the Borough Engineer’s office in Colchester for two The moment you question the status quo you years before joining Wimpey’s Central Laboratory are in for a tough ride. You have to break down in Southall in 1953. Tony Harman was deputy the barrier of the people who have authority. If head of the concrete section and Len Murdoch the authority doesn’t respect you for what you the Laboratory Director; both of them were are and what you are saying, it is hard to return passionate about concrete. that respect.
Q: How did your early career develop? Q: How has concrete technology changed? A: Dyslexia meant that I couldn’t read and understand properly but I could get a clue and A: It’s the expression, the word. Look how had to go away and do it practically. The joy at simply concrete was described in CP114 and discovering something new on the way means compare it with EN206. You begin to wonder. that you have to tell others about it. A classic The principles haven’t changed over that time – or was when we made concrete boil at the C&CA’s even from when the Coliseum was built in Rome. Training Centre, where I was on the lecturing staff The only difference between then and now is that for seven years. I was told you couldn’t do that. we can measure what we do to a higher degree It set and we tested it for strength – it was 40 and when you think about it, once you start to
N/mm2 at 21/2 hours. This taught me about the measure things you want higher performance out energy that is locked up in cement and you can of it. Strength is the measurement of something use that if you want to increase production. we don’t really understand because it’s done at a standard temperature but when you use it in a I have always been of a questioning nature. If structure the temperature, due to the exothermic someone says ‘you can’t do that’ I say ‘why not?’ reaction, can be considerably greater than 20ºC! I always have to have that hands-on experience. The expression to the technology has changed One structure which delights me is the footbridge because our understanding has changed. in St James’s Park, on which I worked in 1957 – Concrete is mainly sold by strength, which is a because it defies all the rules. It’s made with
9 disappointment, and that hasn’t changed in the humorous, his wife’s reaction was ‘Oh, a man last fifty years. If you want performance from in with a proper job’. So, there is recognition as situ concrete then you have to know how in situ long as we remain challenging. concrete performs.
If there were more enquiring minds, we might Q: Do you have any views on the ICT? get over some of the problems. Take ASR, for A: I wouldn’t be a member if I didn’t respect example; In 1979 I tried to persuade the UK it. Whilst I’m working, and I’ve no intention of industry that putting 25% fly ash into concrete retiring, I shall remain a Fellow. There is a value would solve the problem but the smoke screen there whilst ICT has active members. I haven’t and shenanigans that were raised put a lot of viewed the ICT as a social club but as I passed the concrete at risk unnecessarily. I have no problem ACT exams I treat the Institute as a worthwhile with commercial interests but I have no time for technical body. Whether it survives in the long some of the intellectual nonsense that can go term depends on members’ interest but I still with them. believe we need a discipline called Concrete When I went to Pozzolanic in 1974 it was Technology. Where does our technology go if we viewed as me changing sides but I was mystified. I can’t transmit to those who will be taking action was only working in the interests of the on it? We only dream up the conditions. construction industry. At the time, demand for cement couldn’t be met and I saw the use of all Q: Do you have any interest outside that surplus ash as being the logical, and work? technically beneficial, way out. Taking a radical route, we got progress. I found myself putting A: Anything goes if I have time to do it. I am the extreme view, knowing that there would be a a Christian and that means, when you get to the compromise, and that has been a cross to bear. point, what other challenges are there? A Christian has to get on with people, things and Concrete technology does change conditions that are. He can’t live a life that fundamentally but it will always change for the doesn’t rely on other people. Part of the problem better in practice if the people taking part have a is that I have to respect everybody, and that’s ‘wash and brush up’ now and then and recognise terribly difficult! I don’t envy anybody but I am what it is telling them for the future, because disappointed with other human beings who don’t concrete is always for the future. appreciate that, for them to live, they have to live with people like me. And that’s hard. It can be Q: Does the industry appreciate concrete very lonely. technologists? I plan to do my next sky dive in three years’ A: Yes, I think so, so long as the concrete time when I’m 75 to raise money for the therapy technologist has got something to say for himself. centre at Halton for MS, from which my wife has I’m still working because I can give people suffered for the past 37 years. Sky diving is not confidence to do what I tell them will work. really extreme; you’re in the hands of a pilot. I Personal promotion is by people interacting with have also driven a racing car and I climbed up to each other and the degree of success that comes see the crater of Mount Vesuvius and spend time, from that interaction. Unfortunately some do not at least once a year, climbing peaks in the Lake have the background to understand the District. fundamentals. I’m not sure how the general population react Q: After fifty years in the industry, what to us but, recently, whilst delayed at Gatwick plans do you have for the future? Airport, I met the Master of the Rolls, Lord A: I don’t intend retiring. Why should I retire? Phillips, and his wife by accident; the man who is I see myself as a civil servant – I have a state number two in law in the country yet, on a social retirement pension and I’m paid to do nothing. I basis, I could respect him because he gave me am always challenging things. The latest respect. When his wife learned that I was ‘in challenge is - how do you qualify what is cement? concrete’, and when he and others found this
10 With John Newman we are currently drafting a paper to be presented next year at CanMet. We have identified a solution. If you specify a w/c ratio you have to specify what water and cement are. We have identified the non-reactive bits in cement, such as limestone, which is just a diluent, and this shouldn’t be included in the w/c ratio. Nustone will be on-going because its potential has not yet been realised. This year, I have been co-opted onto the main BSI Aggregates Committee, B/502. I am there not representing anyone, and I see this as an accolade.
Q: Do you have any final comments? A: Never trust authority; always question it - without being destructive but to expose any intellectual inconsistencies. We will only find the truth if we have the opportunity to do so. The truth is always there. We’re not allowed to find anything that hasn’t been invented. I don’t want anyone to think other than that I’m an ordinary working class chap who has had to work relatively hard to get anything - and that is a great privilege. In addition, I have known some great people. I also believe in natural justice. For example, those on community service should benefit the community, not the community benefit them. Life is like a piggy bank; one can never expect to get out more than you put in.
Philip, thank you. I’m sure that, having read what you have to say here, people will come to understand you better. We wish you good luck in your future endeavours and look forward to many more years of ICT membership.
11 12 MILESTONES IN THE HISTORY OF CONCRETE TECHNOLOGY
The technology of cement based materials has been developing since the first concrete mix was produced. Much of this technology was further improved with time but much was forgotten (sometimes to be later ‘reinvented’). Some developments have been accidental, such as the discovery of the benefits of air entrainment. Some have been the result of foresight and endeavour, or commercial gain, whilst some have been born of necessity such as those for military and structural reasons. This series of articles - ‘Milestones in the history of concrete technology’, will include some of the more important steps which the science of materials has taken. Later papers may include the work of pioneers such as Vicat, Hennebique and Powers; the early use of admixtures; the work of the Cement and Concrete Association; no fines concrete and the advent of precast buildings. In this, the fourth ‘Milestone Paper’ – the spotlight falls on the development and usage of high alumina cement, with the emphasis on the U.K. scene.
THE DEVELOPMENT AND USAGE OF HIGH ALUMINA CEMENT. By John Bensted
Introduction by Ebelman (1848), and Sainte-Claire Deville Originating from early experiments in the mid- (1856). Meanwhile, in Germany Winkler studied nineteenth century and commercial production the reactions of calcium aluminates with water, from 1913, the story of high alumina cement is whilst Michaëlis (1865) and Schott (1906) remarkably fascinating. The product’s scientific confirmed the setting and hardening of the less development and uses tie in strongly with socio- basic calcium aluminates. The latter showed that economic changes almost decade by decade. very high strengths are obtainable. From the defences of war to the current fashion Serious problems of concrete deterioration in for garden makeovers, high alumina cement sulphate-containing soils - particularly on the (HAC) plays its part. capital to coast PLM (Paris, Lyon & Mediterranean) High alumina cement has also not been free Railway in the South of France in 1890 and in from controversy, as the 1970s brought the shock some seawater defences - led directly to work by [2] of building collapses involving the product. With Bied . This resulted in his patenting in 1908 investigation, these three high profile cases – (France) and 1909 (UK) of the production of high widely reported in the press – established site alumina cement from heating limestone and [3] misuse as the cause. By the 1990s, since no bauxite to high temperatures . further building collapses involving HAC had occurred in the UK, the public and industry The 1910s – from peace to war perception started to become more favourable. Primarily because of demand for its resistance The Concrete Society responded by setting up a to seawater corrosion as well as general sulphate- working party in 1993 to take a fresh look at high resisting properties, commercial production of alumina cement and concrete. Their Report of HAC using a hot-blast cupola furnace (an early 1997 was well received and the product saw a type of blastfurnace) began in 1913, at the Le Teil resurgence in use and development. Today, high works in Ardèche (France) of J. and A. Pavin de alumina cement assumes its rightful place as an Lafarge. added value quality cement product in the range With its relatively long setting times and rapid- of materials available to the concrete industry. hardening properties at early ages (rather than its sulphate-resisting properties), HAC came to Early history prominence with extensive use during World War The classic 1962 text by Robson[1] charters the I (1914-1918) for the building of gun early history of high alumina cement. The origin is emplacements and shelters[1]. More general detailed from early experiments in France on marketing of HAC in France by Lafarge, after heating mixtures of lime or marble with alumina, extensive trials, began in 1918 under the name Ciment Fondu.
13 The 1920s and beginning of the The overall market for HAC developed further next decade – part one of the within the UK during the late 1920s and early interwar years 1930s for rapid-hardening and chemical resistance In 1923 Lafarge financed a company in the UK, applications, such as floors, foundations and called the Lafarge Aluminous Cement Company, pilings, and for refractory usage. A major contract with a license to sell Ciment Fondu in the UK and, at the time was for the construction of Pier B at importantly, the then British Colonies, and also the Ocean Terminals in Halifax, Nova Scotia, the later right to manufacture and to the know- Canada, during 1929-1931, using Ciment [4] how, if satisfied. The right to manufacture was Fondu , which is still in use today (see Figure 1). exercised soon after, due to the demand for During the 1920s HAC manufacture began to Fondu concrete for foundations in sulphated spread to other countries, including the United ground and also for use in refractory applications, States, Spain, Germany, Hungary, Czechoslovakia, which had developed during the 1920s[4]. the USSR and Japan. Brazil, China, India, Croatia, Consequently, the Lafarge HAC manufacturing Poland and Romania have also been plant opened at West Thurrock, Essex in 1926, manufacturing HAC. using reverberatory furnaces to produce the clinker which was ground to the cement. In the The 1930s – part two of the same year, an HAC production plant for Istra interwar years Cement was established at Pula on the Istrian Since it was not really economically viable to Peninsula, in what was then Italy. Lafarge were have two competing production plants for an the licencees of the plant, which had individual speciality cement such as HAC within reverberatory furnaces similar to those at West the then UK market, agreement was reached Thurrock. HAC produced in this factory was not between Lafarge and BPCM on resolving this marketed in the UK at this time. problem in 1932. All HAC production would be concentrated at West Thurrock, with BPCM In the meantime, competition had developed closing down their HAC manufacturing facility at in the UK. The Blue Circle Group (trading then as Magheramorne. Lafarge agreed to supply BPCM the British Portland Cement Manufacturers Ltd. (the ‘junior’ partner in terms of overall sales at the [BPCM]) started producing HAC at their time) with as much HAC under the brand name Magheramorne works in Northern Ireland in 1925 Lightning as they needed. Lafarge’s direct sales of under the name ‘Lightning Brand’ because of its the ordinary dark grey/black product would rapid early hardening. continue to be marketed as Ciment Fondu[4].
Figure 1: Pier B, Ocean Terminals, Halifax, Nova Scotia, Canada – built of HAC exported from West Thurrock.
14 The 1930s were a good period for HAC pH values above 11, so should not be used in employment in construction activity, because of alkaline environments unless they can be fully the development of the motor industry, neutralised beforehand. particularly in relation to rising refractory use During the late 1940s efforts began in earnest because of the increased demand for steel. After to broaden the use of high alumina cement by World War I, the steel industry had suffered developing low-iron HAC to extend refractory decline and it was primarily the introduction of applications at higher temperatures than had the motor car that led to more steel works – with been hitherto possible. It was realised that, since larger chimneys – and larger blastfurnaces being pure CA fused at 1608°C by itself and ordinary built. The British Standard for HAC (BS 915) was HAC did so at 1100°C or just above, the iron- being developed during this period and was containing components needed to be reduced, so actually introduced in July 1940. that higher temperature refractories could be produced. The 1940s – storms over Europe During World War II HAC production continued The 1950s – a time of with difficulty, particularly in relation to adequate reconstruction [4] bauxite supplies . Emergency measures led to the Post-war reconstruction established a demand use of waste material discarded by aluminium for higher temperature refractories in producers when bauxite became unobtainable for reconstructing the industrial scene including the HAC production. Such material included steel industry where there was a demand for aluminium dross and red mud from alumina better quality products that necessitated higher [6] production by the Bayer process . However, the production temperatures. resulting quality of the by-product alumina was The 1950s, therefore, saw the not good. commercialisation of white HAC when the first Due to the low emergency production of HAC, white HAC (containing ~70% w/w Al2O3 ) was the material was only allowed to be used where produced in France. It was named Secar 250 Portland cement was unsuitable, as in rapid repair because the first production run took place in work, so that advantage could be gained from its February 1950. It was later in 1957 that [4] ultrarapid-hardening properties at early ages . manufacture started at West Thurrock, using Consequently, the entire HAC output was used white bauxite and high grade limestone, in a by the then Ministry of Supply - established by small gas-fired rotary kiln. Subsequently this Prime Minister Winston Churchill - for important product was renamed Secar 71 because it repair jobs. Such work included emergency ship contained around 70% w/w Al2O3. repairs, where all ships were required to carry a Interestingly, this white HAC is manufactured few bags of HAC for plugging any leaks and to comply with French Standards NF P15-315 torpedo holes from conflict. Also, bombed (Hydraulic binders - melted aluminous cement) aerodrome runways needed to be repaired with and NF P15-316 (Hydraulic binders – use of HAC to render them usable again as soon as melted aluminous cement in concrete structures), possible. because there have been no British Standards nor In maintaining a number of essential industries any apparent desire to create either British or during wartime, refractory usage and repairs to European Standards for this type of special furnaces and chimneys with HAC were very cement. important. It is astonishing to note that a pure ‘cement’ of this type had been produced experimentally as The 1940s - after World War II long ago as 1856 by Sainte-Claire Deville, who After World War II, production and usage of heated together equal parts of powdered alumina this speciality cement became consolidated in its and marble. Combination to calcium aluminate niche market areas where it imparts benefits over took place at temperatures far below fusion the use of Portland cement. These areas include point, and that crucibles moulded from this chemically aggressive environments, such as pure product and corundum aggregate could waters, seawater, sulphated environments, withstand the highest temperatures which he chlorides, diluted organic or mineral acids, and could apply[1]. It took 94 years – almost a solutions of organic products like beers, wines, complete century - from Sainte-Claire Deville’s sugars, oils and hydrocarbons with a pH of 4-11. initial experiments to commercialisation! However, HAC is not resistant to alkalis at high
15 MANUFACTURE HAC was and is most commonly manufactured by fusion of a mixture of limestone and bauxite at 1500-1600˚C in reverberatory furnaces. (In some countries sintering in a kiln is employed). The liquid melt is poured out at the base into pans and solidifies as ingots. This clinker is allowed to cool slowly and is ground to a surface area of around 350 m2/kg (minimum 225 m2/kg), which is the finished cement. Gypsum addition is not necessary for Calcium Alluminate Cement (CAC) since it does not [5] contain phases leading to quick setting like C3A in OPC. HAC-gypsum mixes are inclined to set rapidly .
The 1960s – increasing product During the 1960s there was a growing interest in popularity using HAC in many structural applications, including [4] This period in the development of HAC was the production of prestressed concrete at the time . marked by considerable interest in its durability, and The capacity of HAC for producing high strength in particular with the scientific and engineering concrete in 24 hours allowed precast concrete properties associated with hydration and manufacturers to speed up production from their [4] conversion, together with growing interest in casting plants . utilising admixtures (see Table 1). Also, HAC had However, Neville had warned in the early 1960s, become increasingly popular for being a superior that there could be serious long term consequences efflorescence inhibitor on exposed surfaces and thus for the durability of structures made with HAC if maintaining a more aesthetically pleasing conversion arose at high water/cement ratios. In the appearance[8]. next decade his words turned out to be prophetic.
Use of admixtures in HAC concrete has paralleled their employment in Portland cement concrete. Some were used pre-1960, but subsequently have been more extensively utlised for improving concrete production and quality. Admixtures employed for HAC are set out in this Table.
• Accelerators – include lithium carbonate (Li2CO3), lithium chloride (LiCl), sodium hydroxide (NaOH) and potassium hydroxide (KOH). Lithium salts are very powerful accelerators, especially
the carbonate. Portland cement, lime and calcium sulphate hemihydrate (CaSO40.5H2O) also accelerate HAC setting. • Retarders – such as hydroxylic organic compounds that retard OPC setting normally also retard HAC setting, e.g. lignosulphonates, sugars, citric acid, gluconic acid and tartaric acid. Many common inorganic salts that generally accelerate OPC setting tend to retard HAC
setting, e.g. calcium chloride (CaCl2), sodium chloride (NaCl) and sodium silicate (Na2SiO3). Sugar, sodium borate and glycerine also retard HAC setting. • Superplasticisers – like the conventional type such as SMFC and SNFC tend to be less effective with HAC, for which they generally behave as mere plasticisers, than with OPC. However, with the new generation superplasticisers like the polycarboxylate and polyacrylate types, results have so far looked much more promising for HAC in terms of showing actual superplasticising behaviour. More work still needs to be done in this area to confirm the generality of interesting findings made to-date. • Waterproofing and hydrophobic additives – do not appear to have been reported for HAC for a long time[5]. Waterproofers have not been recommended for addition to HACs, since they might seriously affect the strength developed[1]. For hydrophobic agents like lauric, stearic and oleic acids in amounts 0.10-0.25% w/w the water repellant properties rise considerably, but the setting and compressive strength values up to ca. 7 days are retarded[1,8]. • Anti-settlement agents – like carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC) and carboxymethylhydroxyethylcellulose (CMHEC) also show retardation and viscosification, like Portland cements do in similar circumstances. • Latexes – such as styrene-butadiene copolymers are utilised to improve bonding to surfaces, as with surface coatings and screeds. • Air entrainers – like vinsol resins are employed to improve mix plasticity and lower any propensity to bleed. • Defoamers – like polypropylene glycols, lower sulphonate oils and lauryl alcohol are commonly used with organic retarders in small quantities (~0.01%) to avoid foaming within cement slurries that can give rise to bleeding.
Table 1: Admixtures commonly used with HAC HAC HYDRATION AND CONVERSION The main phases of ordinary HAC are calcium monoaluminate (CA) (commonly 50-70%) and
calcium aluminoferrite (C4AF) (usually 15-30%). CA hydrates quickly and ferrite at a slower rate.
Minor phases of importance are mayenite (C12A7), which hydrates rapidly, and the silicate phases
melilite (C2MS2-C2AS solid solution) and larnite (β-C2S), that hydrate slowly and give some needed later strength. They are each generally present in amounts ca. 2-5%.
White HACs contain CA as the main constituent, with calcium dialuminate (grossite) (CA2) and
α-alumina (α-A) usually being significant, and mayenite (C12A7) as a minor constituent, but with
negligible contents of dark phases like ferrite (C4AF), alkalis and sulphates. CA is the main reactant
with CA2 reacting much slower. HACs generally exhibit set times comparable or slower than ordinary Portland cement, but harden very rapidly after setting. As an example, for a concrete with water/cement ratio of 0.40, compressive strength reaches 25 MPa 2-3 hours after setting.
Early strength is given by metastable hexagonal hydrates CAH10 and C2AH8. High transient strengths of around 70 MPa or more may be obtained with these hydrates. However, this high transient strength should not be considered for design purposes since it will eventually decrease to reach a lower but stable strength. This strength evolution is due to the conversion phenomenon in
which metastable hydrates convert to the stable cubic hydrogarnet phase (C3AH6). Conversion decreases the volume of hydrates and thus raises the porosity and permeability that lowers the strength. As the temperature increases, conversion is accelerated. As an example, if temperature is maintained at 50°C, conversion will occur in 24 hours. For mass concrete, if self-heating is high enough, conversion can occur during hardening and there will be no strength loss later on. The hydration and conversion process (Figure 2) and the compressive strength development (Figure 3) are illustrated diagrammatically. Besides CA hydration, some supplementary strength is commonly apparent at greater ages
(around 28 days and later) due to formation of strätlingite (C2ASH8) (from melilite) and calcium silicate hydrate (C-S-H) (from larnite). Strength after conversion can be easily predicted by laboratory test where conversion is accelerated by curing concrete under hot water, for example during 5 days at 38°C. In refractory usage with aggregates like crushed firebrick, the hydrates start to dehydrate as the temperature rises, and the strength reduces to a minimal value at ca. 900-1100°C. Dehydration has been completed and as the temperature rises further a ceramic bond appears, which increases the strength once more. Greater details of the technology of HAC hydration and conversion are given elsewhere[5,7]. Calcium hydroxide is not formed during HAC hydration, which is advantageous in enabling HAC to resist formation of unsightly efflorescence in mortar and concrete[8].
Figure 2: Chemical reactions involved in HAC conversion.
17 Figure 3: Strength development of HAC concrete.
The 1970s – up to and including • HAC to be used at a water/cement ratio not building collapses exceeding 0.4 In 1972 a revised British Standard with metric • A minimum HAC content in the concrete of 3 units (BS 915 Part 2) was issued for HAC, to 400 kg/m to ensure suitable workability supercede the 1947 edition. But the 1970s were • To base the compressive strength to mark the end of an era in which HAC had requirements upon the predicted converted strengths rather than on the high initial increasingly played a more prominent role in new transient strengths[13] structural concrete. • Doubt was also expressed about the use of Three well publicised collapses of structures HAC in prestressed beams[14], which led to containing HAC concrete has occurred in the UK the demise of this use, as already in the period 1973-1974[9]. Each one arose in mentioned. buildings which used prestressed beams made from Ciment Fondu. It was widely reported that The 1970s – post building workmanship had been inadequate in all three collapses instances, with design in two of them being As a precautionary measure HAC was banned particularly poor. Neville’s 1975 book discussed from use in structures, because of the inadequacy the civil and structural engineering aspects of of the guidance given in the1972 Code of [9] HAC concrete including the collapses . He Practice (withdrawn 1975) for the manufacture of emphasised the dangers of overdosing HAC with durable aluminous cement concrete[13,15]. The water during construction. Building Regulations in force at the time and There was naturally considerable concern at beyond were modified accordingly. the time and this led to around 50,000 buildings At the same time extensive work was carried containing structural HAC concrete being out on HAC, particularly on the conversion appraised. Of these buildings, only 38 required process[13,17,18] to ascertain where it could be remedial action and only one of these had been utilised safely. The rate of conversion was found due to the cement. The Department of the to be a more significant factor than the extent of Environment took the step of not recommending conversion in contributing to greater strength loss HAC as a construction material (see below). As a with consequent increased permeability and result, the previous large demand for HAC in the porosity in the hardened cement. Conversion manufacture of precast and prestressed concrete particularly takes place in warm and damp [4] ceased immediately . environments. These UK collapses led to three noteworthy It was felt that where structures are designed 10-12] official reports at the time together with a to accommodate strength loss by conversion over general rethink in the use of HAC. The main a long time period then HAC concrete could be conclusions were: used safely.
18 Following the collapses and loss of the market The 1990s – a fresh look at HAC for building structures, other opportunities were In the 1990s there had been neither further sought and opened up. Applications of HAC in collapses involving HAC containing structures in the mining industry took off because rapid setting the UK since the 1970s, nor any noteworthy and hardening, but not very high strength, are problems reported for HAC concrete in use[20-23]. required. In particular efficient uses came to Confidence in the use of HAC had been include pack-binding to support tunnel roofing increasing in consequence. Following renewed and abrasion resistant flooring. interest, The Concrete Society set up a working To satisfy this demand, particularly in the late party to take a fresh look at HAC and reassess its 1970s, quantities of HAC from Pula started to be position in construction. Their Technical Report imported by suppliers to the UK mining industry. was published in 1997[24]. HAC production at Pula had previously stopped in The Report did not recommend the use of HAC World War II after which most of the Istrian in either prestressed concrete (a precautionary Peninsula including Pula had been ceded to measure, because of the risk, however small, of Yugoslavia. Production resumed in 1958 following overdosing the concrete with water) or in refurbishment of the state controlled plant. concrete pipes for the conveyance of drinking water (where the leach rate of aluminium from The 1980s – an added value HAC concrete under certain conditions can be speciality cement one hundredfold that of ordinary Portland cement This extensive work on HAC continued well concrete). The main recommendations were: into the 1980s. Although there had been no • Specifiers, users and clients should be further collapses since the early 1970s, extensive encouraged to consider applications where nervousness remained about possible use of HAC HACs would have technical and commercial in structures. For instance, in the 1985 Building benefits, either in conventional concrete Regulations the following clause was still form or as specialist proprietary products included[16]: • A change of emphasis should be considered High Alumina Cement (HAC): for the Approved Documents to the Building Regulations to reflect more fully selection on 1.8 HAC or any material which contains this the basis of the demonstration of suitability cement will meet the Requirements of the contained in the regulation itself Regulations only where it is used as a heat • To underpin 1 and 2 above, further resisting material. It should not be used in coherent, detailed and independent structural works, including foundations. guidance should be developed as a safe More investigations were undertaken to basis for determining in situ strength of HAC establish a final converted strength, over a longer concrete for particular structures period of time by being able to accommodate • Further to 3, research should be undertaken strength loss through conversion. and guidance developed, which is devoted to understanding more fully the nature and Converted HAC concrete carried on reducing in behaviour of HAC concrete in aggressive strength even when highly converted and to service conditions. In particular, the role of attain lower minimum strength than comparable the various cement hydrates and [19] concrete under dry conditions . microstructure in influencing performance It was becoming more commonly realised by should be examined further. The studies now that HAC was not a competitive product to should include examples of both good and Portland cement as such, but an added value bad performance. speciality cement that had its own niche The Concrete Society Report was well received applications (see later). overall within the construction industry and the The Ciment Fondu clinker production plant at recommendations have been or are being largely West Thurrock containing the reverbatory implemented. For example, the Recommendation furnaces was closed in June 1985. The Ciment 2 was enacted in by a Main Change in the 1999 [25] Fondu clinker has from this time been produced Edition of the Building Regulations : at the Lafarge plant at Dunkerque in Northern Materials susceptible to changes in their France and shipped to West Thurrock, for properties: grinding to give the Ciment Fondu product. 1.7 ………calcium aluminates (HAC)………can be used in works where these changes do not
19 adversely affect their performance. They will meet This importation led to competition for markets the requirements of the Regulations provided that with Ciment Fondu and Lightning Brand in the their final residual properties, including their UK. structural properties, can be estimated at the time In summary, the overall position of HAC for of their incorporation in the work. It should also many applications (see Table 2) grew or remained be shown that these residual properties will be strong during the decade. The only notable area adequate for the building to perform the function affected by a downswing was the mining industry. for which it is intended for the expected life of This was a consequence of large scale closures - the building. in particular coal mines. Recommendation 4 is being carried out, viz. the numerous technical papers in a 2001 HAC The beginning of a new Century symposium on the cement hydrates and their In 2001 Blue Circle was taken over by Lafarge. microstructure, and good performance as with fire However, Lightning Brand HAC is still available to resistance, fibre reinforcement and applications in customers from the former Blue Circle sewers for instance[26]. Also, ‘bad’ performance organisation which is now called Lafarge Cement has been studied at excessive water/cement ratios UK Ciment Fondu (the same product) is of course with ingressing sulphates, which demonstrates available as before from Lafarge Aluminates. The that delayed ettringite formation[27] and (at low white HAC Secar 71 continues to be temperatures in the presence of carbonate, manufactured by Lafarge Aluminates at West silicate and sufficient calcium ions) thaumasite Thurrock for refractory and other specialist uses. formation[28] can take place if the conditions of Castle High Alumina Cement also serves the UK usage are effectively abused. After all, HAC has HAC market as an alternative source to Ciment very good sulphate resisting properties when Fondu. All these HAC products are manufactured employed correctly. to current standards and are subjected to rigorous In 1991, Castle Cement took over the up-to-date quality assurance and quality control importation of HAC from Istra Cement of Pula, procedures. and has marketed it under the brand name Castle Current applications of HAC are very diverse[5,29] High Alumina Cement. Subsequently, both Castle and are summarised in Table 2 below. Cement and Istra Cement became part of the However, it is also important to be aware of Heidelberg Cement Group. In the meantime those areas where HAC is not recommended for Yugoslavia had broken up and Pula was now part use[5]. The primary ones are given in Table 3. of Croatia. So this one HAC manufacturing facility located in the same place for well over 70 years has, in its time, been in three different countries. Figure 4 illustrates the HAC manufacturing plant of Heidelberger Aluminates at Pula.
Figure 4: Heidelberger Aluminates HAC factory at Pula, Croatia.
20 • Corrosion Resistance - Reinforcement is protected by alkaline pH (11) of interstitial solution, plus very low solubility of aluminium hydroxide in pH range 4-11, provided total water/cement ratio does not exceed 0.40 • Chemical Resistance - High resistance to chemical attack (including sulphates) largely due to lack of calcium hydroxide liberation. Greater resistance than Portland cement concrete against aggressive agents like pure waters, water- and ground-containing sulphates, seawater, diluted organic or mineral acids, plus solutions of organic products like sugars, oils, beers, wines and hydrocarbons • Acid Resistance - Better than Portland cements in acidic environments, including sewer pipes where bacterial corrosion is present • Seawater Resistance - Good resistance to seawater is shown • Chloride Resistance - Often better than that given by Portland cements • Resistance to Temperature, Thermal Shocks and Abrasion - Good with appropriate aggregates. Better than Portland cements with fluctuating temperatures and fire resistance • Cold Weather Concreting - Early rapid heat evolution enables concreting to take place at temperatures as low as –10˚C, provided warm water is used for gauging, frozen aggregates are not employed, and the concrete is protected from freezing until it begins to harden and the temperature starts to rise • Freeze-Thaw Cycles - Good resistance like Portland cement concretes where porosity is low (below ca.13%) • Hot Weather Concreting - For success avoid risks by not exposing concrete constituents to the sun, use chilled gauging water, and carefully cure with water as cold as possible during hardening • Oilwell and Geothermal Well Cementing - Good at low, high and fluctuating temperature regimes, in deepwater well cementing. and also in special phosphate-containing cements for
resisting CO2 corrosion in critical geothermal well applications • Mining and Tunnelling - For providing support where rapid setting and hardening, but not very high strength, are required • Rapid Repair Mixes - Usually in proprietorial formulations which may contain a variety of components, including lime, and/or Portland cement, and/or gypsum and/or various admixtures • Grouts, Tile Adhesives and Flooring Compounds - As well as ordinary HAC usage, white HACs are increasingly being used here where aesthetic considerations are important • Refractory Applications - Higher temperatures require white HACs with greater alumina contents: Their advantages are resistance to temperature fluctuations, as lack of calcium hydroxide is beneficial for overcoming spalling, and good sulphate resistance militates against attack by
gases like SO2 produced • In Garden Furniture - Slow setting and rapid hardening properties are beneficial for quick turnaround of moulds during manufacture • Efflorescence Inhibition – Very effective on external surfaces of HAC concrete and mortar, due to absence of residual calcium hydroxide in the hardened cement[8].
Table 2: Applications of HAC
• In Prestressed Concrete - A precautionary measure, as overdosing with water can be harmful. • In Lining Pipes for the Conveyance of Drinking Water - A precautionary measure, since in some situations leaching of aluminium can be one hundredfold that of Portland cements. • In Alkaline Environments - Due to likelihood of destructive hydrolysis. • Use with Alkali-Releasable Aggregates - Again, due to likelihood of destructive hydrolysis. • In Encapsulation of Radioactive Waste - Because of uncertainties about very long term structural integrity where safety is required for hundreds or thousands of years, as a result of conversion causing increases in porosity and permeability. • In Encapsulation of Toxic Waste - Insufficient experimental data are as yet available for making clear recommendations. Various laboratory studies have shown promising results in fixing heavy metals but the full long term ramifications of the effects of conversion remain to be reliably ascertained. • At Total Water/Cement Ratios above 0.40 – Another precautionary measure.
Table 3: Where HAC is not recommended for use
21 Prospects for HAC in the Acknowledgements 21st Century The author wishes to thank: As a result of the greater understanding of the • Lafarge Aluminates for Figures 1,2 and 3, properties of HAC, resulting from the detailed and Tony Newton and Ron Montgomery investigative work and surveys of recent years, it is (Lafarge Aluminates, West Thurrock) for clear that HAC concrete and mortar have a very helpful discussion useful future ahead during this century: • Heidelberger Aluminates for Figure 4, and • It is increasingly becoming realised that HAC Tom McGhee (Castle Cement, UK) for is not a competitive product to Portland helpful discussion. cement per se, but an added-value speciality product that is advantageously employed over Portland cement in a wide range of References niche areas of construction • HAC is an excellent cement when properly 1. T.D. Robson: High Alumina Cement and used, but must not be abused in Concrete. Contractors Record Ltd, London (1962). construction • New generation superplasticisers, like the 2. J. Bensted: Cements: Past Present and polycarboxylate and polyacrylate types, can Future. Greenwich University Press, Dartford substantially benefit HAC concreting by (1997). permitting better workability of the mixes, where the older superplasticiser types have 3. J. Bied: British Patent 8193 (1909). generally tended only to demonstrate plasticising properties with HAC 4. L. Grice and M. Grice: Three Score Years and Ten. A Personal View of Lafarge • HAC is no longer excluded from structural Aluminous Cement Co. Ltd 1923-1993. L. & work in the Codes of Practice, but care must M. Grice, West Thurrock (1993). be taken if used in any structural application. If it doubt about any particular 5. J. Bensted: Calcium aluminate cements, in aspect of HAC concreting, seek professional Structure and Performance of Cements, 2nd Edition. (Editors: J. Bensted and P. Barnes), advice before use pp.114-139. Spon Press, London (2002). • New HAC standardisation is around. An updated version of BS 915 has been 6. A.V. Hussey: Aluminous cement as a bond issued[30], which has brought the official test for refractory concrete. Chemistry & Industry procedures more into line with those of (London) No. 3, 53-61 (1937). Portland and extended cements given in 7. J. Bensted: High alumina cement – Present EN197-1:2000. Also, a draft European state of knowledge. Zement-Kalk-Gips 46, standard prEN 14647 under the name No. 9, 560-566 (1993). calcium aluminate cement has been issued for comment at this stage[31]; the full 8. J. Bensted: The chemistry of standard, which will replace BS 915, is efflorescence./Chemia wykwitów. Cement- expected around 2005 Wapno-Beton No. 4, 133-142 (2001). • Encapsulation of Toxic Waste: Numerous 9. A.M. Neville: High Alumina Cement experiments are being carried out to assess Concrete. The Construction Press, Lancaster whether HAC can safely fix heavy toxic (1975). elements. As yet, it is too early to give definitive conclusions in this particular area 10. S.C.C. Bate: Report on the failure of roof of study. beams at Sir John Cass’s Foundation and Red Coat Church of England Secondary Since high alumina cement first entered the School, Stepney. BRE Current Paper No. 58. market place over ninety years ago there have Building Research Establishment, Watford been decades of ups and downs. Product (1974). development and usage in the UK have 11. Building Research Establishment: High unquestionably shown a fascinating interlink with alumina cement concrete in buildings. BRE the broad sweep of socio-economic and historical Current Paper No. 34 (1975). evolution over a lengthy as well as eventful time period. HAC concrete enters the 21st Century on 12. Building Regulations Advisory Committee: High alumina cement concrete. Report by an optimistic note, because of this accumulated Sub-Committee P40. Structural Engineer 54, knowledge base together with the realism and No. 9, 352-361 (1975). quality assurance prevailing today.
22 13. C.M. George: Aluminous cements: A review 25. Department of Environment, Transport and of recent literature (1974-1979). 7th the Regions: The Building Regulations 1991, International Congress on the Chemistry of Materials and Workmanship, Approved Cement, Paris, 1980. Vol. I: Principal Document to support Regulation 7, 1999 Reports, pp. V-1/1-23. Editions Septima, Edition. The Stationery Office, Norwich Paris (1980). (1999).
14. C.M. George: The structural use of high 26. R.J. Mangabhai and F.P. Glasser (Eds.): alumina cement concrete. Lafarge Fondu Calcium Aluminate Cements 2001. IOM International, Neuilly-sur-Seine (1975). Communications Ltd, London (2001).
15. British Standards Institution: The structural 27. J. Bensted and J. Munn: Formazione use of concrete. Code of Practice CP 110. ritardata dell’ettringite nell’idratazione del BSI, London (1972). cemento calcio alluminoso./Delayed ettringite formation in calcium aluminate 16. Department of the Environment and the cement hydration. L’Industria Italiana del Welsh Office: The Building Regulations Cemento No. 715, 806-812 (1996). 1985. Materials and Workmanship. Approved Document to support Resolution 28. J. Bensted and J. Munn (unpublished work). 7. Her Majesty’s Stationery Office, Norwich (1985). 29. K.L. Scrivener and A. Capmas: Calcium aluminate cements, in ‘Lea’s Chemistry of 17. H.G. Midgley and A. Midgley: The Cement and Concrete’, 4th Edition, (Ed. P.C. conversion of high alumina cement. Hewlett), pp. 709-778. Arnold Publishers, Magazine of Concrete Research 27, No. 91, London (1988). 59-77 (1975). 30. British Standards Institution: Specification 18. J. Bensted: An investigation of the for high alumina cement – Part 2: Metric conversion of high alumina cement by units, BS 915-2: 1972 (2003 version). BSI, infrared spectroscopy. World Cement 13, London (2003). 117-119 (1982). 31. Comité Européen de Normalisation: Draft 19. R.J. Collins and W. Gutt: Research on long- prEN 14647:2003 E, Calcium aluminate term properties of HAC concrete. Magazine cement – Composition, specifications and of Concrete Research 40, No. 145, 195-208 conformity criteria. CEN, Brussels, March (1988). (2003).
20. R.J. Mangabhai (Ed.): Calcium Aluminate Cements. Proceedings of the International Symposium held at Queen Mary and Westfield College, University of London, 9- 11 July 1990. E. & F.N. Spon, London (1990).
21. J. Bensted: Calcium aluminate cements: Highlights from a recent symposium. World Cement 21, 452-453 (1990).
22. C.M. George and R.J. Montgomery: Hormigon de cemento aluminoso: durabilidad y conversión. Un nuevo punto de vista sobre un terma antiguo./Calcium aluminate cement concrete: durability and conversion. A fresh look at an old subject. Materiales de Construcción 42, No. 228, 33- 50 (1992).
23. Anon.: Neville speaks up for HAC. New Civil Engineer, p. 5, 15 October (1992).
24. R. Cather, J. Bensted, A. Croft, C.M. George, P.C. Hewlett, A.J. Majumdar, P.J. Nixon, G.J. Osborne and M.J. Walker: Concrete Society Technical Report No. 46: Calcium aluminate cements in construction – a re-assessment. The Concrete Society, Slough (1997).
23 24 ANNUAL CONVENTION SYMPOSIUM: PAPERS PRESENTED 2003
A major part of the ICT Annual Convention is the Technical Symposium, where guest speakers who are eminent in their field present papers on their specialist subjects. Each year papers are linked by a theme. The title of the 2003 Symposium was:
CONCRETE AND THE INFRASTRUCTURE Chairman: Mr. D. Storrar BSc, CEng, MICE
Edited versions of the papers are given in the following pages. Some papers vary in written style notwithstanding limited editing.
PAPERS: AUTHORS:
KEYNOTE ADDRESS Mr. Paddy Tipping MP for Sherwood
CONCRETE FOR PAVEMENTS Mr. Geoffrey Griffiths BSc, MSc Ove Arup & Partners
OPPORTUNITIES FOR FIBRES Mr. Les Hodgkinson IN CONCRETE Grace Construction Products
THE BRIDGES OF IRELAND - Mr. Nigel O’Neill CURRENT PRACTICE DipEng, BSc(Eng), MSc, CEng, MIEI Roughan and O’Donovan
CONSTRUCTION OF SUBMARINE Mr. Murray Chapman SUPPORT FACILITIES – BSc(Hons), FSA, CEng, FICE, MCIWEM, MCIArb DEVONPORT ROYAL DOCKYARD Kellogg, Brown & Root
CONCRETE SUPPLY SOLUTIONS TO Mr. Andrew Bourne THE CHANNEL TUNNEL RAIL LINK BSc(Hons), MSc, AMICT Brett Concrete Ltd
MODERN SPRAYED CONCRETE Mr. Ross Dimmock FOR URBAN TUNNELS BSc(Hons) Master Builders Technologies
25 26 KEYNOTE ADDRESS Paddy Tipping MP MP for Sherwood
Ladies and Gentlemen, I’m "You know, the result was so good" said Sir sorry to be almost late and to David, "When the General Election comes, and I cause a moment or two of know it’s a couple of years away now, we’re heartache. going to throw you out of Bolsover Dennis. I’m pleased to be here and You’re gonna lose your seat and we’re gonna guess you are pleased to see have a Liberal Democrat MP." Dennis looked him me come in. Let me place the blame elsewhere. up and down again and said "That’s very Since the decision to come, the Chancellor interesting, very interesting." decided to have his budget and, despite the Sir David was rising to this he said "You know, family friendly hours of the House of Commons, I the results going to be so good Dennis, that, for was still voting at midnight on the budget and the first time for many, many years, for decades, getting from London to here has not been easy in we’re not going to have a Labour government, that time. The Chancellor calls his budget a we’re gonna have a Liberal Democrat consolidating budget. There’s been a lot of government." discussion about what’s in it or, more particularly, Again, Dennis looked him up and down and what’s not in it and, when I was talking to he said " That’s very interesting, very interesting". Gordon Brown last week, I was saying that this David was nonplussed at this and he said notion of a consolidating budget wasn’t very "Dennis, you’re talking like New Labour. You’re exciting: you ought to have an image – a fresh talking like Peter Mandelson." image, a new spin on budget and I suggested to Dennis said to him "Look, all I know about him that he ought to employ a new spin-doctor New Labour is this, that when Tony Blair won the to help him. Mohammed Sahid al Sahaf, Saddam second General Election, he called me across to Hussein’s Minister of Information, has 10 Downing Street and he said "Dennis, after 18 disappeared at the moment but I firmly expect to years of the Tories we need not two periods of see him, comically, in his green uniform on the the Labour Government, we need three, and you steps of the Treasury. This is my prediction for the can help, Dennis". future. Dennis said, "How can I help?" And Tony One of the ways that you find out what’s said" Well I just want you to do one small thing. I going on in Westminster (one of the ways that I want you to stop talking rubbish". I want you to used to find out what was going on, when I was stop saying ‘rubbish’ and say ‘very interesting’ the leader of a very large organisation) was to do instead." what I call "earwig". As I left the Houses of Now, I am confident that at the 31st Annual Parliament last night, I saw two of the Symposium you are going to have some very parliamentary greats there, having an animated interesting discussions, and it’s not just Dennis discussion and I thought, "This is my opportunity who talks in a very interesting way. There are all to find out what’s going on". And it was Sir kinds of politicians at Westminster who talk in a David Steel, the ex-leader of the Liberal Party, very interesting way. My favourite is John now Lord Steel, talking to my old and good Prescott, the Deputy Prime Minister. Now, I’ve friend Dennis Skinner, the Beast of Bolsover, in known John a long time and I have to say, I still whose constituency you are today and I have to don’t understand what he’s talking about. John’s say, if you don’t listen to the Chairman and come problem is this, he once said it to me, he said back on time after lunch, they’ll set Dennis on "Paddy, I talk so quickly that when I get to the you. He’s more ferocious than armed guards are. end of a sentence, I can’t remember how I The discussion was going like this. David Steel started it." And, the other famous example for said to Dennis "Dennis, we had a by election up John was that when he became in charge of local your way last Thursday. A council by election, in government finance. Many of you will know that North East Derbyshire, and we the Liberal this is a very difficult area, it’s a kind of fixed Democrats won". Dennis looked him up and game sum. If somebody wins, another local down and said. "That’s very interesting, very council loses and I kind of gave him a seminar on interesting."
27 this and he seemed to understand and he went to hear what people are saying and thinking away and came back some weeks later and he about public services. The truism is that voters said "Paddy, you’re right, it’s highly competitive, and residents are interested in the bread and it’s dog eat dog, or vice versa." butter services, the NHS and Education. If you Now, of course John was in charge of examine, in fact, our recent polling, you’ll see our transport policy for four years. I’ll resist the second focus from Labour links into crime, temptation to say that’s why Labour’s in a mess perception of crime, anti-social behaviour, on this but, what John would say is that this is a streetscapes, litter and that whole area of public difficult policy area. First of all, it’s plagued by concern about anti-social behaviour has come decades of under-investment, and, secondly, in way up the agenda. You’re interested in where more recent years, under the last Conservative transport stands and, again, in our own private government (the back end) and during the period polling and our own discussions, in the eyes of of the Labour government, that under-investment the public, transport lies about 5th, 6th, or 7th, has been compounded by fairly rapid economic and I wouldn’t be too alarmed about that growth and that puts additional strain on a weak because things can change. The notion of crime infrastructure. Thirdly, as John would argue, I has gone right to the top of the agenda and, at think it’s fairly clear that in the first four years of one point, during the period of the last the New Labour government, that transport government, before the General Election, hadn’t been a very high priority for Labour and transport did come to the top of the agenda. If that sufficient investment hadn’t gone into it. you remember the fuel protests during the last Now, currently, all the political discussion is on parliament, the only time that Labour was behind the international agenda on Iraq and Syria and in the polls was during the fuel/transport crisis, the Gulf, on the Middle East, on our relationship and it was a crisis, and it did have effects. Some with Europe, on our relationship with the United of the effects were reflected in the budget but States. Let me make my second prediction. I think going back a bit further to a previous budget, the we will rapidly get back to the domestic agenda notion of the fuel tax escalator was knocked out and what runs the domestic agenda is the notion, because of the protests, so I do think transport is as the Prime Minister would put it, of world class, important in political terms. One of the things high quality public services. If you think back to that I think of Gordon Brown is that he’s Labour’s first General Election victory, that’s what interested in investment today for gains in the won it for Labour. The campaign about years of future. If you look at the transport sector, you’ll under-investment in public services, particularly in see that, historically, it’s been under-invested but, Education and Health, but also in Transport. In in recent years, investment is beginning to come the last General Election again the argument was in. One of the issues around transport and the about public services. The phrase then was politics of transport is that there’s no quick fix. "We’re not complacent, this is a work in Many of you are engineers and will know the progress. We’ve achieved a lot but there’s still a planning cycle from the beginning to the end and lot more to do." I think there was some the problem is that politics is a short-term fix. We confidence that the government, after the first do things because events are happening. We’re four years, was still moving in the right direction already working on plans for the next General on public services. I think that when the next Election. A big capital project can take a decade General Election comes, whether it’s in 2 or 3 from start to finish and this is a hard issue for years time, again the political battleground will politicians to handle: the short-term political cycle be on public services and there can be no excuse alongside the long-term investment cycle. Extra for a government that then will have been in money is going in. Let me give you one example: power for 8 or 9 years, if it really hasn’t improved The ten-year transport plan brings in £180 billion public services. You’ve got to be sure that there for the railways. In real terms that’s a 40% has been real success. Now, what I’m interested increase. One of the figures that sticks in my in, and I guess what you’re interested in, is where mind, many of you who use the West Coast main transport stands in the hierarchy of public line will know the problems with improvements services. There’s no secret, and perhaps the but every day and every night £3 million of work reason I’m here is that Labour’s interested in what is being done on that main line. I could go the public thinks. The stories you hear about through a whole list of projects where big, long- private polling, about focus groups are right. I term investment is going in; Channel Tunnel Rail have focus groups for Labour and I’m very keen Link, Kings Cross, St Pancras, 72 major road
28 schemes. You will know that investment is taking intent into action on the ground. I work a lot place in the transport infrastructure. In with Civil Servants and actually help train Civil Nottinghamshire, for example, the amount of Servants. One of the issues that’s around money for highway improvements going to the government is that Senior Civil Servants are good County Council has gone from £5.3 million in on policy, they’re good at developing ideas but 1996/97 to £16.8 million in the current year and they’re not good on implementation. One of the that’s in real terms. things that we’re not good at in Government is A lot of the money is capital money and it’s revisiting the laws that we pass to see what’s easier to maintain capital spend than revenue happened and I think that we’ve got to address spend. Again, in the budget this week, the this issue of management within Government Chancellor’s had to revise his growth figures, just because we’ve got a set of well paid people who, over 2% in the current year and an optimistic in project management and delivery terms, just 3.5% next year. Can he maintain that spending don’t have the skills. One of the things that this on creating world class public services? Can he Prime Minister’s government is particularly keep the momentum of public services going? I interested in is bringing people from the private actually think he will and that he intends to sector in. People who have the notion of how because capital investment is easier than day-to- important it is to have a timetable and to achieve day revenue investment. Of course, infra-structure it, to help us do just that. I think, if you were investment alongside pays dividends, it brings looking at changes in the government, you’d see new jobs, but it develops a base now for long more focus on that. One of the things that I think term improvements. So, I expect that the you need to listen to when the Prime Minister or Chancellor will stick with his current spending the Chancellor is talking is the notion of plans. If you want a third prediction, I think that investment. Both of them talk about investment in the budget next year he will not meet his and reform on the same side. What they mean growth targets and he will need to borrow even about reform is that we’ve got to look at the way more. But, having said that, he will still be within that we develop policy but, more particularly, the fiscal rule that he set himself about reform the way that we deliver policy. I think borrowing over a long period of time. I’m not that’s a problem that only 6 years into worried about a cut in investment. What worries government, we’re just beginning to address me more is about whether this investment can be properly. achieved. Whether what’s been promised in terms Perhaps I ought to say a word about the of transport infrastructure can be delivered. Put Private Finance Initiative (PFI). PFI is a creation of another way: what is promised can be produced. John Prescott’s. I’ll always remember the day that Can we really build these big road, rail, and he came in, when we were in opposition, to see airport projects? I have some doubts. One of the Margaret Beckett who was then the Chief things that worries me fundamentally is that, if I Secretary. He wanted a load of money to develop look at departmental spending targets on their transport policies. In opposition we were very capital programme, the slippage is immense. The timid and Margaret told him that it wasn't money’s in the budget but it’s not being spent. It possible. John came back and said, "If I can seems to be a crazy situation that you have borrow off the private market to deliver these addressed money to deliver things after a period things, is that acceptable?" In a sense that’s of sustained under-investment and you’re not where the notion of PFI has come from. PFI has spending it. A large number of projects, as you been fairly controversial within the Labour will know, are being committed but not yet Government and remains controversial within the achieved. Government. In a sense it does two things for us. That brings me onto a set of issues that I’m Firstly it brings in capital which is off balance concerned about and the Prime Minister is sheet and that’s important in the big view of fundamentally concerned about which is about government financing but, secondly, it transfers management. In a sense it’s easy to govern, it’s the risk of delivery from the government to the easy to run the cabinet, it’s easy to get what you private sector and that’s why I think we’ll stick want through the House of Commons, but, in with PFI. I actually think that, in the long term, delivery terms, actually achieving things on the PFI will cost the government and the public more ground can be very difficult. I think one of the money. I’m very simple: I know that if you buy things that surprised the Labour Government is things on HP it does, in the long term, cost you how far and how difficult it’s been to create more but in the short term what it delivers is
29 private companies coming in, taking the project going to reduce the number of people who travel and the risks, then delivering on timetable. That's by car. In real terms I’m going achieve that." why I’m confident that PFI will stay. What I’m not Promises are now far more modest and I think confident about is around a separate agenda, perhaps are achievable. The promise now is that which is a skills training agenda. I think the we’re going to reduce the increase in car Institute has been addressing this. We have a ownership so car travel will go up but not as plethora of training schemes. Let me be quick as what it might have done. I think we confessional for a moment and say I simply don’t know from our own experience that that is understand our vocational education training achievable. Now, how are we going to do that? system and I think that there are major gaps and People say to me that the environment isn’t major skills shortages. I think there is loads of important to the government. That it’s never money going into further education that we’re been high on the agenda. That the European not getting the best from. One of the things that Elections before last when the Green Party and we’ve got to be more sophisticated about is Environmental Party made a big way forward, has setting up bridges between the public sector, the now ceased. If I were looking in my crystal ball I government and the private sector to make sure think a defining moment for the government and that those skill shortages are, first of all, the environment is the Energy White Paper that identified and, secondly, met. was just published. It had a lot of criticism but I think that a third constraint on delivery is the important thing is what it says and what around the planning system. Joy of joys, I have people are saying about it. The PM hails it as a been a member of a group of MPs that has been significant milestone and, if it can be achieved, considering the planning and compulsory it’s going to make a significant difference because purchase bill to become law later this year. It what it’s saying is that by 2020, 20% of our fuel springs from a desire, from the PM, to speed up is going to come from renewable sources, that the planning system. I think the jury’s out on this. we’re going to go on and meet the Royal I’m fairly jaundiced, having dealt with this bill for Commission’s targets but reducing the CO2 by some time, that it’s going to make a great deal of 60% and, fundamentally, we’re going to move to difference. What I am clear about is that people a low carbon economy. Now transport figures in won’t invest in the long term unless they’re the White Paper, in a low-key kind of way. We secure in the knowledge that they’re going to get have made enormous gains on climate change planning consent in a relatively fixed timetable. but they’ve been easy gains. The gains, really, Extra resources are going in to planning have been on the back of closing down the coal authorities to try and ensure that we hit planning industry and closing down coal generation. If we timetables. I think there’s a wider issue. I know want a hard target to try and reduce carbon planners, I love planners, I moan about planners, emissions, the next frontier must be transport and but one things that impresses me about planners I don’t think this is going to be easy. I think there is that they always tell you how difficult things are some short-term solutions. I think there are are, i.e. what the reasons are for refusing things some short-term fixes. I’m running a campaign at and I think we just need to change the the moment, which we’re beginning to win, and perspective and perception in the planning we’ll win fundamentally in perhaps 18 months system from a group of people who tell us how time, to move towards the notion of bio-fuels; difficult it is to a group of people who say, "This bio-diesel and bio-ethanol. You’ll notice that in investment is important to us. This investment is the last two budgets, the rate of duty on bio- going to bring new jobs and new future to this fuels has been reduced by 20p. That won’t make area. What we’re going to do is determine a way the industry take off but I think that if we got to to make it happen rather than reasons for a situation where the rate of duty was 26, 28, making it difficult." I hope that what we’re doing even 30%, then we’d see the bio-fuel industry with planning schools at the moment, will mean take off. The significance of bio-fuels is straight that we can do some work on that. forward. You can just mix it and put it in your tanks, so I think that is an early, short-term fix. I Finally, one of the constraints on the way think, more significantly, we need to look at forward is about the environment. I can’t come to bigger policy issues and the one that’s on the a conference like this without talking about the table at the moment is congestion charging. environment. The big promises have gone. Do People are anxious about this in London. you remember the Prescott big promise? "I’m Congestion charging, before it was introduced,
30 was all the responsibility of the Mayor, Ken wider political issues. Let me put it in a nutshell. Livingston. If it messes up, it’s all his fault. Well, it The government is presently reviewing airport isn’t messed up and everybody is now trying to policy. There will be a White Paper at the end of get in on the act. Research is still unclear on this the year and the notion of environment and but congestion charging in London has, basically, economic growth will run through that White reduced traffic flows by about 30%. That’s a Paper. Let me give you some examples. There’s significant gain. I think we can go on with the talk of a new airport in the South East. Go to London experiment when we look at the M6 toll Ladbrokes and say it won’t be Cliffe in Kent road. That coming on board gives us another because of environmental concerns. Secondly, we opportunity to play with it and then there are need to have a think about aviation fuel. Aviation smaller experiments. Those of you who know fuel isn’t dutiable at the moment but the Durham will know that to use the street along to significant thing that’s happening at the moment the cathedral, you’ve got to pay. That’s a clear is that, because of the low budget airlines, 50% environment and streetscape gain. Just down the of all people, 50% of all residents travel abroad road in the Peak District, the National Park is by air at least once a year. We have this notion going, I think, to introduce congestion charging that airlines pollute the atmosphere, are not good at weekends. This gives us an area to play with to live with, are bad for wildlife, but people, and I think that congestion charging is back on because they are more prosperous and there is the agenda. I think it’s been shown that the still economic growth in the system, have now technology can work, I think it’s been shown that the opportunity to travel abroad each year. That’s the public can live with it although, maybe, they the dilemma: how we can have growth and don’t like it. Thirdly, I think there’s an issue about prosperity and maintain the environment at the what happens to the revenue from congestion same time? charging. One of the things that’s not been When I was a University Lecturer, my students readily understood is that Ken Livingston expects used to say to me "You never tell us anything". I to gain, in rough terms, £120 million of free used to say, "My job is to ask the questions, not money after costs through congestion charging in give the answer." The question for all of us, those Central London. If you look at the long-term of us in government, those of us who actually budget for the London authority you will see build and develop things, is that question. Can that, over the next three years, his grant from we have growth, can we have prosperity and can government is going to go down by £150 million we protect the environment? I think we can but I a year so, on the one hand, Transport for London think we’ve got to be clear about how we sell are, over a period of years, gaining nothing from that idea to the general public. If the private and congestion charging. That’s a crazy situation. I public sectors work together, we can ensure that think we can sell congestion charging to people if the demands and the constraints put by the charges are held locally and used to develop government on the private sector are realistic and new transport initiatives because it’s clear to me respectable. that people will only swap from cars to public transport if it’s high quality, reliable and decent. Thanks very much. You’ll switch from your cars if it’s good for you in those terms. I think this issue around the proceeds from congestion charging remains to be resolved but the way forward must be to allow it to remain locally. Edinburgh City council is looking at congestion charging and they’ve set up an "arms length" company so that the money from congestion charging will go, not to the council, but to the "arms length" company. If the Scottish Executive are then minded to say "You’re getting all this money from congestion charging, we’re going to cut your grant", it will be more transparent. I’m conscious that I’m on time and conscious that I haven’t mentioned the word "concrete" at all but, what I’ve tried to do is talk about some
31 32 CONCRETE FOR PAVEMENTS Mr Geoffrey Griffiths BSc, MSc Ove Arup & Partners
Geoffrey Griffiths is an • Diesel spillage or other chemical spills may Associate of Ove Arup & attack alternative materials Partners based in their • Low subgrade strengths are expected Nottingham office. He is a civil • Heavy axle loads can be anticipated. engineer with specialist The systems are also particularly useful in knowledge of pavement providing cost-effective pavement solutions to engineering and has extensive experience of the projects where large quantities of site-won sands design, construction and specification of and gravels can be found. pavements for infrastructure projects. He is currently the pavement engineer responsible for STANDARD PAVEMENT TYPES the design work associated with M6 Toll on behalf of CAMBBA’s designer Atkins/Arup. External trafficked cement bound pavements fall into three distinct groups: ABSTRACT • High quality surface slab systems; the conventional 40N, wet laid concretes used This paper presents a practising engineer’s for URC (unreinforced concrete), JRC (jointed views on some standard solutions to concrete reinforced concrete) and CRCP pavements pavements. The paper also examines some of the problems that are regularly found in undertaking • Flexible composite pavements. Pavements the design, specification and construction of which rely on a combination of the tensile cement bound pavement materials. Some strength of the CBM and a thin bituminous examples of current UK construction methods are surface to carry a significant proportion of described. The views expressed within the paper the pavement load. The CBM is a high are the views of the author and should not be quality material produced from good quality considered to be either a Code of Practice or aggregate that is batched and paver laid design advice. • Cement bound sub-base systems. CBM materials produced from lower quality KEYWORDS aggregates that may be site won and can be CBM (cement bound material), CRCP produced by in situ stabilisation techniques. (continuously reinforced concrete pavement), The CBM is simply used as a construction pavement quality concrete, specifications and platform to support the bituminous construction problems pavement, which carries the majority of the pavement load. INTRODUCTION The boundaries between the three groups of materials are not precise; each type of Concrete surface slab systems have many construction is in some way interchangeable. advantages when compared with bituminous pavements; a concrete pavement consists of a This paper describes some recent interesting system of stiff plates connected together to form projects and is intended to share some of the a continuous, hinged slab system. common engineering problems that can occur in producing cement bound pavements. Cement bound materials are a particularly useful form of construction, which can be used in UNREINFORCED CONCRETE (URC) situations where pavements are subjected to FOR LOW TRAFFICKED considerable point loads and aggressive INDUSTRIAL PAVEMENTS environments. Concrete pavements have a Jointed URC construction has been extensively number of advantages that make them beneficial used on major highway projects; the system is when compared with alternative bituminous currently out of favour in UK highway schemes designs. Concrete pavements are useful when: but is extensively used on general infrastructure. • High point loads are expected The pavement consists of a patchwork of
33 concrete slabs joined together with dowel and tie EXAMPLE OF URC SLAB bars or crack induced joints. Each slab will consist CONSTRUCTION IN AN of approximately square units. The detailing of INDUSTRIAL PROJECT the joint layout is crucial to the successful design, A simple, cheap but effective form of URC execution and operation of the pavement. pavement can be constructed for low trafficked The system relies on the tensile capacity and industrial sites by simply laying a 200mm mass flexural strength of the concrete to resist cracking concrete slab across a crushed rock sub-base. The and successfully carry a load. When the pavement mass concrete is then sawn into 4.5m panels that is built, the size of the concrete panels is crack as the concrete shrinks. Figure 2 illustrates controlled by the shrinkage strain generated by the construction of a slab, Figure 3 shows sawn the hardening process. As the concrete sets, gains joints, Figure 4 shows the action of a crack strength and cools, shrinkage strains generate a inducer and Figure 5 shows the completed loaded tensile force in the pavement. The size of the pavement. concrete slab controls the magnitude of the The precise specification for the system can be force. If the tensile capacity of concrete is summarised as: exceeded, the slab cracks. • 200mm, 40N/mm2, air-entrained concrete, A number of rules govern pavement detailing. which can be wet laid in approximately The most important feature is to ensure that the 25m bays joints are detailed, designed and, most • The joints are sawn in 4.5m bays using crack importantly, spaced correctly. Pavement joints inducing techniques must be arranged to produce a patchwork of roughly square panels; the longitudinal joints • The slab is constructed over a 250mm thick running in one direction, with the transverse crushed rock sub-base system joints arranged at 90 degrees. Joint spacing is • No reinforcement, dowels, ties, expansion controlled by standard practice and is a function joints or debonding plastic membrane of pavement thickness: thicker pavement slabs is used. can have greater joint spacing. It is noted that the This system is a simple, effective method of recommended maximum ratio of longitudinal to providing industrial hard standings. The transverse joint spacing is 1.25. Pavement joints construction process is simply described as: may be constructed as dowelled or undowelled: • Lay the crushed rock sub-base current practice is to construct most pavements • Shutter the intended slab with road forms with dowelled tie bars. Removing the steel and pour the concrete dowels reduces the efficiency of the joints and gives a small increase in pavement thickness. • 12 hours later cut the pavement joints • Complete construction by installing a sealant in the joints.
Figure 1: A typical URC pavement.
34 Figure 2: Constructing a URC industrial pavement.
Figure 4: The action of a crack inducer on a URC pavement.
Figure 3: Newly sawn crack-induced joints.
CONTINUOUSLY REINFORCED CONCRETE PAVEMENT (CRCP) A continuously reinforced concrete slab consists of a regular section of cracked, square Figure 5: The completed pavement. concrete plates connected together by the steel reinforcement. CRCP pavements are an excellent spacing is essential to the efficient operation of form of construction for major highway projects; the pavement. Transverse cracks must be spaced the system has been developed from reinforced between 1.5 m and 4 m centres; if the cracks are concrete pavements. Continuously reinforced too closely spaced the blocks of concrete can fail concrete pavements are constructed as long slabs in shear as punch-outs. Cracks can also be spaced with longitudinal reinforcement fixed at the too greatly; if the cracks are spaced too far apart centre depth of the slab. The longitudinal aggregate interlock is lost across the joint. Crack reinforcement is intended to control shrinkage spacing is controlled by the longitudinal cracking. A nominal amount of transverse reinforcement content that is currently fixed at reinforcement is also provided to hold the 0.6% of the section area using 16mm diameter longitudinal reinforcement in place. The system is high yield bars. very similar to a mass and reinforced concrete pavement except that the cracks are formed in a EXAMPLE OF CRCP random fashion and remain unsealed. A second CONSTRUCTION; M6 TOLL feature of a continuously reinforced concrete M6 Toll near Birmingham is the most notable system is that ground anchors are required at CRCP pavement that is currently under terminations. construction in the UK. Approximately 50% of A CRCP slab will move extensively under the the 3-lane motorway is being constructed as a influence of changing environmental CRCP system over a CBM sub-base. All of the temperatures. The ends of the slab are therefore aggregates are site won and processed. anchored to prevent massive movement. Crack
35 The system is summarised as: • 35mm of 14mm aggregate, open, negative textures thin wearing course with a 1.5mm minimum surface texture • A bituminous emulsion, sprayed bond coat typically 0.8 litres per m2 • 220mm, CRCP, 40N/mm2 concrete, with longitudinal reinforcement as 0.6% by section area using 16 mm diameter Grade 460, deformed bar and nominal secondary reinforcement of 12 mm bars Figure 7: The completed reinforcement • A bituminous sprayed de-bonding mat membrane • 230mm CBM using 10N/mm2 mean 7-day compressive cube strength concrete with a smooth, regular even surface • 3% CBR subgrade • The pavement ends are anchored into ground beams with movement joints. The pavement is constructed progressively using a number of carefully planned construction processes which consist of: • Paver laying sub-base • Fixing the rebar and crack inducers • Slipform the pavement slab Figure 8: The slipform paver • Complete the system with a bituminous wearing course These processes are illustrated in Figures 6 to 10.
Figure 9: The completed pavement
Figure 6: The completed CBM Figure 10: The completed, cracked construction platform and the pavement. reinforcement laying system.
36 CBM SUB-BASE SYSTEMS, SUPPORTING A CONVENTIONAL BITUMINOUS PAVEMENT CBM sub-base systems are a very practical form of construction that is becoming popular within the UK and Design and Build projects. The CBM sub-base is formed by adding cement to a site won granular material. The process can be either undertaken in situ or batched and then paver-laid. The UK specifications are described within the Highways Agency’s Specification (1) as CBM1, 1A, 2 and 2A. The CBM material has a 7- Figure 12: The CBM sub-base surface complete with the bituminous curing day compressive cube strength of between 6 MPa membrane. and 10 MPa and is laid semi-dry. Cement bound sub-base systems are in many SURFACE SLAB CONSTRUCTION ways similar to flexible composite pavements; the PROBLEMS essential difference is that the CBM layer acts in a UK surface slab pavements require a high manner similar to a granular sub-base. The strength, 40N/mm2, air-entrained concrete to material can be heavily cracked; the pavement successfully operate without premature design will not rely on the tensile capacity of the deterioration. Many readymix companies are cement bound layer. reluctant to supply 40 N/mm2 air-entrained EXAMPLE OF CBM SUB-BASE concrete and often request a misguided CONSTRUCTION; M6 TOLL instruction to change the specification to a lower strength or an air entrained concrete mix. The recently constructed M6 Toll motorway has extensive areas of paver-laid CBM material. LACK OF AIR ENTRAINMENT IN Wherever possible the material is used to replace CONCRETE quarried crushed rock sub-base. M6 Toll uses a Air entrainment is essential for the durability of standard CBM1A material that has an average 7- surface slab concretes. day compressive cube strength of approximately 13 MPa. The standard pavement construction Much debate has occurred around this issue. consists of: Some frost resistant high strength concretes can be produced, but the technique is not accepted • 285mm HMB 35pen bituminous material in the UK. Frost damage is a major problem in • 200mm CBM1A, paver laid in one layer concrete pavements. If the pavement is • 250mm conventional capping constructed in normal un-air-entrained concrete • 3% CBR (California Bearing Ratio) at the surface will be quickly removed by the formation. weathering action of frost. The concrete must be The CBM sub-base layer is deliberately air entrained. A number of researchers have thickened when compared to an alternative suggested that if concrete achieves 50N/mm2 crushed rock system to ensure the sub-base is able strength the material will not be susceptible to to carry the heavy construction traffic loading. frost but UK specifications are unable to define when a material will be able to work without adding air. A typical standard of frost-protected concrete will be achieved with 5 % ±1.5 % air content. The air-entraining agent acts as a cracking agent, reducing the size of any bubbles to a point where the formation of ice lenses within the pores will not cause damage to the concrete matrix. In a conventional concrete, ice lenses are formed in the voids contained within the structure of the concrete. The ice is then able to crack the concrete thus resulting in the formation of Figure 11: Paver laying CBM sub-base surface scaling.
37 Figure 13 illustrates a section of frost-damaged specifications permit the construction of a concrete. 150mm thick low strength slab which, when construction tolerances are considered, can be just 100mm thick. If a thin CBM slab is excessively trafficked the surface can simply fail. Figure 14 illustrates a failed pavement. A CBM failed pavement must be reconstructed. The surface of a CBM sub-base is weak and can be easily eroded. Figure 15 illustrates a typical problem. Surface trafficking is not a particularly serious problem but can require some re-profiling using a regulating material before the pavement is completed.
Figure 13: Air entrained concrete compared to non air entrained concrete
SUB STANDARD LOW STRENGTH CONCRETE Many materials suppliers are in the misguided belief that a 35 MPa concrete mix will be of equal value to the standard 40 MPa mix in producing a durable pavement design. Regrettably this is not the case. Reducing the concrete strength will directly lead to a reduction in the pavement load Figure 14: A section of failed pavement carrying capacity. A reduction in the design mix strength from 40 to 35 MPa will require an increase in the pavement thickness of 20%. A reduced concrete strength will also lead to pavement surface durability problems. A lower surface strength material will produce a pavement surface which is susceptible to surface abrasion. Surface abrasion is an important design consideration. The surface of a heavily trafficked pavement will quickly scrub and abrade away under the action of traffic if the concrete is of an inadequate strength.
CBM SUB-BASE CONSTRUCTION Figure 15: Surface scaling resulting from PROBLEMS traffic abrasion CBM sub-base systems have a number of construction problems that are not immediately obvious when one initially considers using the POOR LEVEL CONTROL materials. The sub-base can offer significant CBM materials must be laid correctly in one financial advantages but must be used with care. construction operation. The actions of The following problems are noted as important compaction and rolling, combined with poor site issues that must be considered. level control, can lead to difficult problems. Figure 16 illustrates a typical problem where the CONSTRUCTION TRAFFICKING material has been incorrectly laid too high. The THE CBM pavement is being corrected using a motor CBM is a brittle material that is very grader. susceptible to construction damage. The material must not be excessively trafficked. The UK
38 REFERENCES
1. HIGHWAYS AGENCY, Manual of Contract Documents for Highway Works, Volume 1, Specification for Highway Works, August 2001.
Figure 16: CBM sub-base level control problem
IMPORTANT CBM DESIGN REQUIREMENTS The author suggests that design engineers should consider the following issues in producing a pavement design using cement bound materials: • Keep CBM layers thick! Typically 200mm for CBM and mass concrete • CRCP pavements are a very successful alternative to bituminous materials in large construction projects • CBM sub-base can be a very successful alternative to crushed rock systems • Simple URC slabs may be successfully used in many industrial applications • Always use 40N/mm2 air entrained concrete in surface slab systems.
39 40 OPPORTUNITIES FOR FIBRES IN CONCRETE Mr. Les Hodgkinson Grace Construction Products
Les Hodgkinson is the UK reason for the inclusion of the straw may have Technical Services Manager of had nothing to do with the control of cracking. Grace Construction Products The above practical problem highlights the Limited. He has spent the last difficulty in dealing with composite materials and, thirty years in the development particularly, in understanding what processes are of admixture systems, at play. admixture standards and the associated concrete Most concrete technologists are very familiar technology involved in the successful transition of with the properties of the various Portland new technology from laboratory to the field. cements, ground granulated blastfurnace slags and pulverised fuel ashes, and of their mechanical ABSTRACT influence upon concrete. Introduce novel Fibres are already used in significant quantities materials like micro-silica, metakaolin, or poly- in numerous concretes used in the infrastructure, ether based superplasticisers, then there is a but often their prescence goes unnoticed and period of uncertainty and learning. But within a unappreciated. For example, internal, industrial short period, the new materials are incorporated slabs now commonly contain steel fibres. Tunnel into the technology because all the new segments may often contain two types of fibre, properties can be quantified in terms that are both fulfilling differing roles. This paper familiar and readily understood, such as summarises the role played by the various types compressive strength, permeability or porosity. of fibres in concrete. It describes the types of But include any reinforcement, in the form of fibres avaliable, and compares their properties steel bars or fibres, then the propeties of the and performance. The paper then attempts to composite become difficult to explain to a describe, in simple terms, the opportunities concrete technologist because the terms of available to the materials technologist, and to the explanation require a knowledge of another engineer, by the inclusion of the various types of technology; that of mechanical or structural fibres in concrete. engineering. On the other hand, the engineers who do have the engineering skills to calculate KEYWORDS the mechanical and structural requirements of the Fibres, Alignment, Fibre loading, Fibre length, end product, often do not understand the basic Modulus of elasticity, Crack control, Freeze/thaw properties of the materials. This problem of the protection, Fire protection, Impact resistance, bridging of disciplines is at the root of explaining Toughness, Residual strength factor. why there is so much difficulty in quantifying the benefits of fibres and why there is so much INTRODUCTION misunderstanding about fibres in concrete. Fibres have been included in construction Speaking as a concrete technologist, I am very products since Biblical times, and the first familiar much a victim of the problem and have great reference to most of us would be that one in the difficulty in understanding the mechanical Bible where the Israelites were having great behaviour of composites other than in the most difficulty making bricks without straw. basic terms. This paper is an attempt to try and We have all seen how mud cracks on drying, explain, in simple terms, the fundamental and the straw was presumably required to stop properties and benefits of the most commonly the mud-bricks from cracking when they dried encountered fibres and how they affect the out. As I was not there at the time, have never mechanical properties of the composite. In made a mud-brick, and have never met anyone addition, the paper tries to explain how the who has made a mud brick, this is an assumption inclusion of fibres could lead to new opportunites based on a reasonable degree of the knowledge in the use of fibre-concrete composites. of the materials and a prediction of what is likely to be happening. On that basis, the aforesaid Fibres in Concrete analysis could be a load of nonsense and the true Fibres cannot replace primary, structural steel
41 reinforcement. This steel is designed to transfer Alignment high loads, over significant distances, once the Because of the random, three-dimensional concrete has cracked. Most technologists, and orientation of the fibres in concrete, only one- even some engineers, do not realise that the sixth are effectively aligned in the direction of reinforcement does nothing unless the concrete stress. This limitation only applies to normally does crack. Only when the concrete cracks, does batched concretes, and this explains why some the load transfer onto the bar and the steel then glass reinforced concretes are produced in sheets, controls the width of the crack. This means that with chopped, glass-fibre being sprayed onto every concrete bridge must have thousands of their surface. These fibres are thus aligned in two cracks all over it, but they are so small that you dimensions, improving the efficiency of the fibre. cannot see them. If this were not so, then the design engineers would not be spending a small Fibre Loading fortune on all those steel bars to hold it together. Fibre loading is also an important Fibres cannot be used to reinforce in the consideration. In normally batched concretes, it is conventional sense for other reasons, and their not practical to incorporate more than behaviour is dictated by the following properties. approximately 1% volume of any fibre into concrete. This limitation may not theoretically
1) Grain bridging traction 4a) Micro-cracking in the matrix 2) Ductile matrix bridging 4b) Intragranular micro-cracking 3) Grain delamination from the matrix 5) Plastic deformation
Figure 1: Mechanisms involved in the process of crack propagation
1 Damage of the matrix
2 Fibre/matrix debonding
3 Fibre bridging
4 Fibre failure
5 Fibre pull-out
Figure 2: Mechanisms of fibre failure
42 apply to sprayed, chopped glass-fibre but there is the behaviour of any fibre is dictated by the also the consideration of cost. For example, 1% previously described properties, it should be volume of steel fibre represents a loading of 70kg possible to predict the behaviour of any natural per cubic metre, which in most situations would or synthetic fibre in concrete. not be economically viable. Polypropylene Micro-fibres Fibre Length These are typically 6-12mm long, mono- In most practical situations, the primary mode filament but, at 24 micron in diameter, they are of failure of fibres is pull-out. (see Figure 2). For extremely fine, and very numerous for a given this reason, the longer the fibre, then the better weight of fibre. ( See Figure 6). They are normally will be its performance in respect of this type of marketed in 0.5–1.0 kg small bags and, as the failure. However, in practice, the ability to achieve fibre loading is relatively low, this is sufficient to a sufficiently high fibre-loading requires a major dose 1m2 of concrete. As pointed out previously, compromise on the length of the fibre because of fibre loading, fibre length and surface area are the problems of physically incorporating the fibres important in modifying the failure mode of into the mix. This compromise on maximum hardened concrete. For these reasons, length is also related to the stiffness of the fibre, polypropylene micro-fibres have only a limited as the incorporation of fibres into plastic concrete effect on mechanical failure. Their main is a very important consideration. Flatter fibres application is described below: offer the advantage that they have increased surface area in contact with the cement matrix. Cohesion They also have reduced stiffness, which eases Micro-fibres are helpful in the prevention of handling, particularly with respect to the segregation, as they play a role in physically incorporation of the fibre into the mix. holding the mix together. They can be used in any concrete that is prone to bleeding. They can Modulus of Elasticity also be used in self-compacting concrete to assist Steel has a very high modulus of elasticity and in the achievement of high flow without it is easy to understand why steel fibres perform segregation. well in any performance test involving the pull- out of fibres. Equally, it is also easy to accept that Plastic Shrinkage Cracking polypropylene micro-fibres, with a low modulus When concrete udergoes the transition from a of elasticity, can perform the task of prevention of plastic state to a hardened concrete, it is very plastic cracking, as the loads involved in the vulnerable to the effects of moisture loss, and control of plastic shrinkage are very small. exhibits significant shrinkage. (See Fig 3.) So how do polypropylene macro-fibres control At this transition point, if the plastic shrinkage cracking in the same manner as their steel exceeds the strain capacity of the concrete, then counterparts? The answer is that the fibre only a plastic crack will result. (See Figure 4). The has to have a modulus of eleasticity similar to, or surface tension of the water, effectively tears slightly greater than, the concrete matrix. Steel open the immature concrete, just like mud has a modular ratio of 15 times that of concrete drying. Plastic shrinkage cracks always occur at a and thus its performance is never challenged. The very early age and resemble tears. These features steel fibre pulls out when the cement matrix fails, distinguish plastic shrinkage cracks from drying well below that required to induce the steel to shrinkage cracks, which occur much later in the stretch. Polypropylene fibres are now produced life of a concrete. with a modular ratio just in excess of 1. Failure by The inclusion of 0.5–1.0 kg per m3 of micro- pull-out will occur at the same loading, as the fibre has a significant beneficial effect in reducing cement matrix still fails at the same loading. the incidence of plastic-shrinkage cracking in concrete slabs. Small fibres are able to prevent The Role of Fibres any plastic cracks propagating, as the loads This paper is mainly concerned with the three involved are very small. This is the most common types of fibre that are normally used in site- and application of micro–fibre. ready-mixed concretes: steel fibre, polypropylene Micro-fibres are particularly useful in external micro-fibre, and polypropylene macro-fibre renders, as renders have a very large surface area (synthetic structural fibre). However, given that for a given volume of mortar. For this reason,
43 Figure 3: Early shrinkage of cement and concrete
Figure 4: Early shrinkage strain and cracking
they are prone to plastic-cracking, caused by that micro-fibres did, in fact, have some benefit moisture loss from evaporation due to exposure in the prevention of freeze-thaw damage. to wind. It is probable that air-entrainment is technically superior in the prevention of freeze-thaw attack Freeze/Thaw Protection than the use of micro-fibre, and air entrainment As part of a British Board of Agrément (BBA) would probably outperform micro-fibre in most test programme designed to ensure that micro- discerning freeze thaw tests. This has not been fibres had no deleterious effects upon the freeze- conclusively proved, and such a comparison thaw resistance of concrete, it was discovered would make an excellent ICT project.
44 It was initially thought that the fibre coating the inclusion of micro-fibres for many years. was entraining air into the concrete but it would When furnaces are being relined, the new liner appear that the micro-fibres do confer protection has to be cast, cured and control-fired prior to in their own right. The mechanism for this is not being put into service. The fibres allow the clear, but the most logical and simple explanation moisture, incorporated during casting, to be would be that the fine-fibres act as crack- driven off, without physically disrupting the stoppers. That is, any micro-crack stops at the furnace lining. nearest fibre. There are photo-micrographs that The inclusion of micro-fibres into appear to support this mechanism but the theory conventional concrete significantly reduces the is not really proven. effects of fire damage. The same principals seem to apply as with refractory furnace technology. It Fire Protection is possible that the voids resulting from the This is a very important benefit of micro-fibre melting of the polypropylene offer a large and one that illustrates the importance of number of voids for the expanding steam to vent technology transfer. Refractory furnace into, reducing the tendency of the concrete to technologists have been aware of the benefits of spall.
Method Effectiveness Comments Polypropylene fibres Very effective, even in Low-cost solution but may not prevent spalling high-strength concrete in expansive ultra-high-strength concrete. Does not reduce temperatures, only pore pressures Air-entraining agent Effective, if low moisture content Can reduce strength Thermal barrier Very effective Reduces concrete temperatures and increases fire resistance Moisture content control Reduces vapour pressure Moisture content in tunnels is normally higher than in buildings and more difficult to control Compressive stress control Reduces explosive pressure Not economical with larger section sizes Choice of aggregate Most effective to use low If low-moisture lightweight concrete used, additional expansion and small size aggregate fire resistance is possible. In high-moisture conditions, violent spalling is promoted Reinforcement Reduces spalling damage Limited spread of spalling in Channel Tunnel fire Supplementary reinforcement Reduces spalling damage Difficult to use in small, narrow sections Steel fibres Reduces spalling damage Explosive spalling may be more violent due to extra strain energy stored by steel fibres Choice of section type Thicker sections reduce spalling damage Important for I-beams and ribbed sections
Table 1: Preventive measures to avoid spalling of concrete exposed to fire
Figure 5: Pore pressure profiles in heated concretes
45 A number of major fires, including one in the High strength, low permeability concretes are Channel Tunnel, clearly illustrated the vulnerability more likely to spall explosively and to experience of high strength concrete to fire damage. multiple spalling than normal concretes. This is Exposed to high temperature, the evaporation of because greater pore pressures build up during moisture in the concrete causes major spalling of heating, as the moisture is unable to diffuse. concrete. In addition, as illustrated in Figure 5, the peak The main factors influencing the degree of pore pressure in high strength concretes occurs spalling of concrete exposed to fire are heating nearer to the surface than it does for normal rate, permeability of the material, pore saturation concretes.This explains why even thin sections of level, presence of reinforcement and level of high strength concrete can spall in the presence external applied load. [1] of fire.
Figure 6: Variation of fibre number with fibre diameter
Figure 7: Variation of fibre surface area with fibre diameter
46 Impact Resistance respect, as the number of fibres per unit weight, Micro-fibres are normally dosed at a low fibre is far higher than that for steel. loading of 0.5–1.0 kg/m3 and, for this reason, No macro-fibre shows any benefit with respect have only has a limited benefit on impact to freeze/thaw protection. resistance. Not only is the fibre loading small, but Because of the relatively coarse nature of the fibre length is also small. Steel fibres and macro-fibres, it is unlikely that these will have any polypropylene macro-fibres are much longer, and significant benefit in terms of fire-protection. It is dosed at much higher dosages, and for this quite normal for concrete to contain both micro reason, are much more effective in this and macro fibre, where the micro-fibre is application. incorporated specifically for fire protection and the macro-fibre for structural purposes. Steel and Macro-fibres (Structural fibres) Toughness (Flexural toughness) Most macro-fibres or structural fibres used in Toughness is the key property in understanding site- or ready-mixed concrete are mainly based on the benefits of the inclusion of macro-fibre in steel or polypropylene. The use of glass-fibre concrete. Essentially, toughness is the ability of tends to be restricted to specialist precasters. concrete to retain structural integrity after it has Long, glass fibres tend to be handled in a unique nominally failed by being exposed to a load manner, whereby they are handled as a rove; which exceeds its flexural strength. chopped and co-sprayed with a cementitious Plain,unreinforced concrete, when subjected to slurry, using a gun, onto a horizontal mould. a bending load, will withstand that load with very There are a number of types of steel fibre, little movement until the load exceeds its flexural with a large variety of profiles. Similarly, there are strength. At this point, the concrete will fail a mumber of synthetic structural fibres in the suddenly and catastrophically and fall to pieces. market, again distinguished by their length and This is the classic behaviour of a brittle material aspect ratio. This paper will not attempt to possessing no toughness. That is, it has no differentiate between any of them, but will try residual mechanical strength after a sudden, and highlight their general behaviour and brittle failure. performance. In most circumstances, the inclusion of fibres In general, steel and polypropylene structural does not improve the flexural strength of fibres perform a similar role. The weight of steel concrete. When subjected to the same load as a fibre used is typically 10–40 kg/m3. Polypropylene, plain concrete, the concrete will fail at the same macro-fibres are dosed at a much lower weight, loading. This is because the flexural strength is typically 2-8kg/m3, but because polypropylene has still a function of the concrete and is also related a much lower specific gravity, the fibre-loading to the dimensions of the unit as expressed in the expressed in volume terms is similar to that of equation below. steel fibres at 0.2–0.6% volume of concrete. W x L The number of fibres, for a given weight, is Flexural strength = B x D2 low compared with micro-fibre. ( See Figure 7). Because of the coarse nature of both steel fibres Where W is the applied load and synthetic macro-fibres, they do not improve L is the length of span the cohesion of a concrete mix. On the contrary, B is the breadth of the specimen they deprive the mix of paste and, for this reason, the fines content of concretes containing macro- D is the depth of the specimen fibres needs to be increased to preserve cohesion. Steel fibres and most synthetic structural fibres But in the prescence of macro-fibre, the confer no benefit in terms of the prevention of differences become apparent immediately after plastic shrinkage cracking. For a given fibre failure. (See Figure 9). At failure, the concrete loading, there are too few fibres available to fulfill cracks, but the crack width is initially so small this role.(See Figure 6). The steel fibres are too far that it cannot be seen. The load has been apart to arrest, deflect or modify the behaviour in transferred to the fibre. If the concrete unit any significant way at typical dosage rates. Some continues to be loaded, then the fibres start to of the flat polypropylene macro-fibres, with a pull out, and the crack starts to widen. At this high aspect ratio, do have some benefit in this stage the unit is broken but is still able to
47 Figure 8: Load deflection diagram- South African Test Panels
withstand a large proportion of its maximum Toughness Index load. This ability to carry load after failure is Toughness indices identify the mode of called toughness. material failure. These are determined by dividing In the above test ( See Figure 8), a plain panel the total area under the load-deflection curve up without structural-fibre would have shown no to a selected deflection value by the area under load bearing capacity after first-crack deflection. the curve at the deflection at which the first crack When steel or synthetic fibres are added, the is deemed to have occurred. concrete shows significant flexural toughness.
Figure 9: Characteristics of the load deflection curve
48 In the above diagram, the concrete unit has Definition of Toughness Indices failed at point A. Without fibre, it would have Toughness Index I5 – the number obtained broken into pieces and arrived at point B, having by dividing the area up to a deflection of 3.0 no ability to retain any load and having exhibited times the first-crack deflection by the area up to no flexural toughness. first crack. The same concrete, but containing structural- Toughness Index I10 – the number obtained fibre, still fails at point A but the fibre now takes by dividing the area up to a deflection of 5.5 the load, and even though the crack-width times the first-crack deflection by the area up to increases to 3 times the original deflection up to first crack. point D, the concrete still shows considerable Toughness Index I20 – the number obtained residual load bearing capacity at point C. by dividing the area up to a deflection of 10.5 Values of I5, I10, I20 and I30 respectively, are times the first-crack deflection by the area up to defined below. All the concretes show near linear first crack. elastic behaviour up to first-crack, both with and Toughness Index I30 – the number obtained without fibres. Plain concretes show instant by dividing the area up to a deflection of 15.5 failure at first-crack with zero residual strength times the first-crack deflection by the area up to thereafter. first crack.
Values of Toughness Indices
Area Index Deflection Plain Elastic-Plastic Observed Range for BasisA Designation Criterion Concrete Material Fibrous Concrete
OACD I5 3δ 1.0 5.0 1 to 6
OAEF I10 5.5δ 1.0 10.5 1 to 12
OAGH I20 10.5δ 1.0 20.0 1 to 25
OAIJ I30 15.5δ 1.0 30.0 -
A indices calculated by dividing this area by the area to the first crack OAB
Table 2. Toughness Indices Calculation
49 Residual Strength Factors deflect, absorb energy and stay in one piece after The residual strength factors R5,10 and R10,20 a major impact. It would be difficult to think of a represent the average level of strength retained better example of where flexural toughness could after first crack as a percentage of the first-crack be of value, and of a better application of strength for the deflection intervals as specified in structural polypropylene fibres, which would not ASTM 1018-97. cause injury when exposed at the fractured surface. Opportunites for Fibre Concrete Septic tanks, pipes, covers, concrete ducting Many plain concretes used in the infrastructure and tunnel segments are all examples where are brittle by design but would benefit greatly secondary steel can be replaced by structural from the inclusion of fibres. Having an fibres. In addition to fulfilling the same function understanding of how the behaviour of a brittle as mesh, they are also more readily included into material can be modified by fibres immediately the unit. presents opportunites which can be readily Shotcrete is an ideal opportunity for the use of understood by a concrete technologist. polypropylene structural fibre to give the required Any thin or slender unit can be toughened to toughness but without the pumping, spraying dramatically improve its service life. and rebound difficulties, not to mention the health hazard associated with sprayed steel fibres. Concrete roof tiles, promenade tiles and many unreinforced units can all benefit from the However, the biggest commercial opportunity inclusion of structural fibres. A good example is for the use of structural fibres in the paving flags. infrastructure, lies in their use in concrete flooring and paving, where their usage can be justified by Paving flags, designed for pedestrian usage, the design of thinner and more economic regularly fail in service because of overloading concrete slabs. when trafficked by service vehicles. Such failure has become a major problem in terms of compensation paid to the general public. In Design Aspects of Fibre Leicester, in 2002, the council paid as much in Reinforced Concrete compensation as it did in actually maintaining A discussion of the principles that can lead to pavements. Toughening of paving flags laid in the design of thinner slabs containing structural public areas represents a significant opportunity fibres is a complicated topic and is worthy of a for the use of structural fibres. When overloaded paper in its own right. by service vehicles they still fail, and they still The arguments need to be presented by an crack, but because of their flexural toughness engineer, as they lead us into that area where they retain most of their load-bearing capacity. most concrete technologists, including myself, The general public do not trip on them, and are have great difficulty understanding the principles. blissfully unaware of their initial failure. Below is a summary of the basic arguments Many other simple precast items can benefit justifying the use of thinner slabs when from fibres. Very often it is difficult to place the incorporating structural fibres. steel reinforcement in the right place. Fencing The traditional code-adopted design approach posts are typical of simple units where is based on strength and no post-cracking reinforcement is included in a haphazard way. We behaviour is considered. Recognition of the post- have all seen fence posts where the corroded cracking behaviour at the design level is essential steel has caused spalling of concrete. With to transfer the technology of structural fibres to synthetic fibres this is not a problem. Take out the the industry. badly positioned bars and put in fibres. Concrete in the cracked section carries tensile Bollards are an example of where toughness load in fibre reinforced concrete (FRC), while would be an added benefit. A bollard should be concrete after cracking becomes ineffective in designed to be tough rather than fail plain concrete (PC), as indicated by a stress-strain catastrophically. Incorporation of fibres would diagram. The bending moment distribution after enable it to withstand minor collision without any cracking is different for FRC. Plain concrete evidence of failure, but also perform far better in exhibits a regular hinge, whereas fibre concrete the event of a major collision. exhibits a plastic hinge (with yield capacity). Concrete barriers should be designed to The final design of a plain concrete slab is
50 governed by slab stiffness and interaction with References the sub-base. The final design of a fibre reinforced concrete is governed by the interaction 1. Passive fire protection in tunnels. G.A. between the positive and negative moment as a Khoury, Concrete, Feb 2003: Vol 37 No2 function of slab stiffness and sub-base. The failure load of a FRC slab is a function of the sum 2. Concrete Society Technical Report 34 – Concrete Industrial Ground Floors, A guide of the negative and positive moment. The failure to their Design and Consruction. Third load of a PC is a function of the cracking Edition. moment. The inclusion of fibres improves flexural capacity and can significantly modify the design of structures governed by modulus of rupture. The concept of equivalent flexural strength is a measure of performance which takes into account the toughness obtained from experiment, by measuring the area under the load-deflection to a deflection of 3mm (L/150). This is commonly referred to as the Re,3 value. The third edition of Concrete Society Technical Report 34 [2] has recently been published, and the design approaches in Chapter 15 consider both the ultimate and serviceability conditions. Determination of the strength of a concrete slab based on plastic analysis (as compared to the traditional elastic analysis), requires that the slab has adequate ductility. The ductility is now specified in terms of the Re,3 value. Steel and synthetic structural fibres may be used, at a minimum dosage, sufficient to give a value of Re,3 of at least 0.3; otherwise the concrete shall be regarded as plain. In summary, fibres reduce the stresses in the reinforcing steel at service loads, reduce crack width, improve ductility and increase confinement capacity. The reduction of slab thickness, and elimination of steel mesh, has significant cost benefits in terms of material cost, material handling, storage, safety and time. In terms of the infrastructure, there are a myriad of applications where fibres are used and could be used. These include paving slabs, promenade tiles, posts, panels, bollards, concrete barriers, concrete roof tiles, concrete paviors, cover slabs, concrete ducting, septic tanks, concrete pipes, tunnel segments and internal flooring. In the future, the opportunities for the wider application of fibres in the infrastructure will undoubtedly spread to the use of structural fibres in external slabs and paving, and possibly to their use in thinner concrete pavements for roads and aircraft pavements and taxiways.
51 52 THE BRIDGES OF IRELAND - CURRENT PRACTICE Mr. Nigel O’Neill Dip Eng, BSc(Eng), MSc, CEng, MIEI Roughan and O’Donovan
Nigel O’Neill is an Associate of later than the "advanced" countries of Europe Roughan and O’Donovan and North America. However, this has turned into Consulting Engineers and is an unexpected advantage as Irish bridge one of their senior bridge engineers have benefited from the experiences engineers. He has participated (both successes and mistakes) of others. The in many of Roughan and principal lessons that we have learnt from others’ O’Donovan’s bridge projects. experience is the importance of good design and of designing for durability. Thankfully, Irish bridge ABSTRACT engineers have not in general inflicted on the general public a "brutalist" or utilitarian design This paper presents some of the design and philosophy and we are hopeful that our bridge technical aspects of current practice in bridge designs will both last and be a lasting engineering in Ireland. Bridge engineering in contribution to the built environment. Ireland is in the middle of an exciting period of large-scale expansion of the country’s In comparison with other countries the scale of infrastructure assets. An opportunity to create a almost all bridges in Ireland would be classified as whole new species (the modern bridge) within "small" to "medium" in scale with the vast the built environment exists and the role of majority falling into the "small" category. Most of engineers in accomplishing this is explored. Most our motorway overbridges and underbridges fall new bridges in Ireland are constructed from into this "small" category and occasionally, as in concrete and the materiality of this plastic and the case of the cable stayed Boyne Bridge, we organic medium and its influence on design is make it into the "medium" category. The examined. The design of both commonly approach in Ireland to the design of "small" occurring and larger bridges is presented with bridges is perhaps something that our fellow examples from the work of Roughan and bridge engineers in Europe could benefit from. O’Donovan. DESIGN KEYWORDS Bridges, Ireland, Design, Aesthetics. Aesthetics The term "aesthetics" has gained some INTRODUCTION currency in the language used by bridge engineers and I think that this is unfortunate Since the 1980s a large number of new because it tends to convey the impression that bridges have been built in Ireland as part of the aesthetics is just another criterion along with construction programme to develop the country’s durability, function, economy and safety, so that transport infrastructure. This process received a when money is short, aesthetics is first to get cut boost with the founding in 1993 of the National from the list. I prefer to think of "design" as Roads Authority (NRA); the government body being more or less equivalent to what people with responsibility for developing and maintaining mean when they say "aesthetics". There is the National Primary and National Secondary road something forced about isolating those factors in network (5429 km long, roughly evenly divided bridge design as belonging to "aesthetics" when between Primary and Secondary). The NRA in fact what makes a bridge a pleasure to provides the centralised planning and funding for perceive is, in many cases, difficult to express in national road schemes and is also the technical words. And after all, we have no problem saying approval authority in matters of national whether something like a coffee cup is either of standards and specifications. It is anticipated that good design or of bad design – let’s use the same the founding in 2002 of the Railway Procurement language about bridges. I suppose this slippage in Agency will provide a similar boost to the railway language has occurred because engineers use the network. term "design" when what is really meant is In simple terms, Ireland is building her something like "section design" or "structural motorways and main roads about a generation scheme design".
53 Materiality Concrete dominates the materiality of Irish bridges. Most modern bridges in Ireland (approximately 98%) are constructed from concrete – reinforced concrete, precast pre- tensioned concrete and post-tensioned concrete are all commonly used. Steel is an imported material while cement is natively produced, thereby making concrete generally more economical to use. A major fraction of the Irish landmass sits on top of limestone bedrock Figure 2: Grange Newbrook Bridge making clinker and aggregates readily available for cement and concrete production. Ireland with just ordinary Portland cement are Aside from its default material status, bridge dark grey in colour, which, combined with our engineers are attracted to concrete because of its generally overcast grey skies, adds to the overall plastic nature. The ability of concrete to take on depressive effect unless relieved by lightening the virtually any shape, to be in effect moulded, colour. Most bridges in Ireland constructed in the permits organic and sculptural designs. Piers last fifteen years or so have surface impregnation provide the most striking examples of freedom of concrete with siloxane and an acrylate-based with the materiality of concrete: the variety and coating. In the last few years we have been expression to be found on motorway overbridges experimenting with the use of controlled clearly exhibit this possibility. permeability formwork and cement replacement In response to the brutalists who would have with 50% ground granulated blastfurnace slag us build dumb, expressionless rectangular walls, it (ggbs) with a view to eliminating the requirement is worth remembering that piers make up to surface impregnate and coat the surfaces of something like only 7% of the cost of a bridge. concrete. The lighter colour concrete achieved when ggbs is used is encouraging, although the fact that ggbs is an imported material means that its use is likely to be restricted to specialist applications such as in bridges and other large civil engineering structures. Light and shade are powerful determinants of the quality of surface. Shadow lines can be made using chases. (Example: chases in abutments and deck on Rowan’s Road Bridge –Figure 3: Rowan’s Road Bridge).
Figure 1: Killarney Road Bridge Piers
Surface Complementary with the bridge engineer’s freedom with the materiality of concrete is his freedom to decide on its surface and full use is made of it to give further expression to the design – smooth, patterned, coloured coatings, are all used to effect. Large bland areas of plain Figure 3: Rowan’s Road Bridge concrete walls, whether on abutments or retaining walls, are thankfully rare. Texture can be formed by the use of form Typology and Form liners (relatively inexpensive two- or three-use Bridge typology provides immediate access, liners are preferred for large pours). based on experience, to a wide range of forms and span arrangements that "work": motorway Colour can be chosen by application of a overbridges, motorway underbridges, railway and coating. (Examples: Figures 1 and 2). Concretes in
54 canal bridges, are types where a form has converged to an almost standard solution. In the case of motorway overbridges the two span arrangement is dominant. (Figure 4: Killarney Road Bridge.) However, typology can trap the unwary when atypical site conditions assert themselves. For example, take a motorway overbridge where the deck has to have a steep longitudinal fall because of the road alignment – Figure 6: Ballycahill Road Bridge a typical two-span arrangement could look deck following the road profile, this type unbalanced and out of proportion because the becomes visually distorted as the lack of abutments might tend to be of different sizes and symmetry causes unequal pier heights and the deck could look visually unstable as it slopes problems with either unbalanced areas of off to one side. Now look at Killarney Road abutments or unequal end spans – the overall Bridge: the fascia is curved to express the span impression can be one of visual instability. A way and the abutments have rounded corners and are of solving this problem is to break away from the inclined so as to balance the visible areas of the typology and to design a form that can two abutments and to visually anchor the bridge harmonise with the constraints: Ballycahill Bridge ends into the sideslopes. The solution is still a on the N7 Nenagh Bypass achieves this ambition two-span arrangement but careful detailing of by virtue of an asymmetric form that expresses the form integrates it into a difficult geometry. It the longitudinal fall of the deck instead of is also worth noting that the deck comprises ignoring it. The soffit of the deck was made precast U-beams and the deck erected during horizontal to create a plane of stability for the short possessions of the busy N11 National observer; the "downside" abutment by its mass Primary, which was upgraded to dual appears to anchor or brace the deck; the short carriageway. end-span and inclined pier almost look like the fingers and thumb of a hand placed against a surface. An overall impression of balance is achieved. The utility of typology breaks down again when it comes to larger bridges and unusual situations where the form must evolve from a more fundamental consideration of the design constraints. For instance, take the Boyne Bridge that carries the M1 motorway over the River Boyne west of Drogheda. This bridge is both a river bridge and an underbridge; a viaduct could Figure 4: Killarney Road Bridge easily carry out its function. However, the history and archaeology present on the site of Yellow Significant lengths of the National Network Island (directly underneath the bridge), one of the comprise single carriageways and when an crossing points of the Battle of the Boyne (a not overbridge is required, the type of bridge insignificant event in Irish history), make it emerging almost as a standard is a three span arrangement. However, in particular situations with difficult geometry, such as a steep longitudinal fall in the
Figure 5: Claremorris Bridge Figure 7: Boyne Bridge
55 imperative that the bridge form must span over ENVIRONMENT this area and not require support off it during construction. A cable stayed form with a Heritage cantilever form of construction gradually emerged Bridge engineering in Ireland is characterised as the most appropriate solution. In a different, by a modernist approach to design. However, in urban, context Taney Luas Bridge, built to carry cases where a bridge is required to be inserted the Luas Light Rail, in the Dublin suburb of into an existing heritage, such as at canals and Dundrum demonstrates the similar use of a cable railways, it sometimes becomes necessary to stayed bridge constructed by the cantilever adopt an almost "arts and crafts" approach to method over one of Dublin’s busies traffic design if one is to respect the vernacular of the junctions. existing built environment. For example, Moran’s Bridge in Mullingar, carrying a road over the Royal Canal, is in fact a reinforced concrete box but it is clad in stone with the full complement of the mason’s art expressed: pilasters, quoins, voussoirs and the like. A similar example is Shaw Bridge,
Figure 8: Taney Luas Bridge
Occasionally one gets to use a rare form because it particularly suits the constraints of a particular site and the client also wishes to make a bold statement with a landmark bridge. Such is Figure 10: Moran’s Bridge the case with Kilmacanogue Footbridge – Ireland’s only stressed ribbon bridge. Six bearer Kilcock, which combines replacement bridges for tendons are stretched between the abutments a railway bridge and a canal bridge in quick and stressed and these support the precast deck succession – the respect for heritage went so far panels. Four post-tensioning tendons are placed as to carefully remove a stone plaque from the in the deck and in situ concrete topping added – parapet wall of the existing canal bridge and re- the deck is then stressed. The bridge was erected set it into the replacement bridge. Honesty is a over the live N11 National Primary – police halted key modernist design principal and one can feel road traffic for about 15 minutes at a time while uneasy about hiding concrete instead of each of the bearer cables was lifted into place. expressing it. However, I feel that when it comes The deck panels were lifted up at one end and, to replacement bridges, some compromise with using pulleys, were slid into position over the live the existing fabric of the area must be made. road, thereby keeping traffic disruption to a minimum. The deck is extremely slender: 270mm Landscaping thick for a span of 48m. One of the pleasures about driving on motorways in Ireland is enjoyment of the landscaping: wide grassed central reserves (sometimes planted with daffodils), sideslopes planted with low woodland mixed planting and somewhere along the scheme a commissioned piece of sculpture (the "one per cent for art" initiative). Integrating bridges with the landscaping requires careful design. Regrettably, some landscape designers take the view that when it comes to bridges "the taller and thicker Figure 9: Kilmacanogue Footbridge
56 the planting the better". Tall trees and shrubs making small bridges integral with their placed adjacent to wingwalls and piers mean that supporting soil, Irish bridge engineers are also the abutments and piers are completely trying out other ideas, such as the use of obstructed and all that is visible is a short length controlled permeability formwork (CPF) combined of deck furtively running from one clump of trees with ggbs cement replacement (example: Rowan’s to the next. Such tactics are justified if bridges Road Bridge and Airport Bridges – use of CPF). are ugly but when it comes to elegant bridges The use of stainless steel rebar is also becoming such camouflage tactics border on vandalism. common in selected highly susceptible concrete Fortunately, communication within design teams elements such as parapet edge beams, piers and has improved and a truce exists between bridge bearing shelves. engineers and landscape designers so that planting is now kept low next to bridges and one Procurement can actually see them. In the past, a road would have been designed directly by the Local Authority and procured in TECHNICAL relatively short lengths (say 10km) and if there were six bridges on the scheme three separate NRA Standards and Specifications consulting engineers would each get two to In 1999 the National Roads Authority formally design. The merit of this approach was that it adopted the Highways Agency’s Design Manual generated great variety in design and when the for Roads and Bridges (DMRB). Bridge engineers designs were good (and thankfully they generally in Ireland were already familiar with the DMRB were) the resulting collection of bridges provided and its formal implementation regularised this immediate interest and genuine experience. Now usage. The Roughan and O’Donovan - that vastly greater sums of money are being FaberMaunsell Alliance was appointed to invested in infrastructure, the length of schemes implement the DMRB through the use of NRA has grown considerably and a single design Addenda to the standards and, especially in the organisation (a joint venture of two or more firms area of road and junction design, to prepare new of consulting engineers is common) undertake NRA Standards. the design of both the road and the bridges. No longer designing a couple of bridges on a The NRA also maintains a Manual of Contract scheme, bridge teams are now designing whole Documents, encompassing the Specification for families of bridges. This might be no bad thing – Road Works, The Method of Measurement for too much variety can be discordant – but the Road Works and their associated notes for pressure to standardise where the constraints are guidance. As with the DMRB, the Manual of not standard has to be resisted. The pace of Contract Documents is similar to the equivalent development is increasing, putting pressure on Highways Agency documents but with many the capacity of bridge design teams: between variations to suit Irish conditions. 1997 and 2002 about 200 bridges were added to Durability the NRA’s stock; from 2003 to 2010 approximately 500 more bridges on National Bridge engineers are mindful of the Roads will be constructed. Another pressure on considerable durability problems that have beset the quality of design is the design and build a considerable fraction of the developed world’s (D&B) and public private partnership (PPP) bridge stock. Mistakes made by an earlier procurement strategies being adopted. In a generation of engineers in other countries have competitive tendering situation the rational been noted, e.g., inadequate provision of response of bridge engineers is to make their drainage, overprovision of expansion joints (that designs as cheap as possible within the subsequently very often leak), poor weathering parameters set by the Employer’s Requirements. details (lack of drippers and the like), inadequate Fortunately the NRA has adopted an approach deck waterproofing, inadequate site supervision whereby the design (i.e., the aesthetic quality) of (e.g., lack of grout in post-tensioning tendon bridges is an explicit construction requirement ducts). Considerable effort is being made to and must be matched by tenderer’s proposals. design for durability and to avoid mistakes even though there is a considerable rush to create a Research sizeable bridge stock in a relatively brief time. With the volume of bridge design going on in Apart from taking obvious measures such as Ireland at the moment its not surprising that
57 there is considerable research interest in the field. 6. Ballycahill Road Bridge, Roughan and In 1999 the Bridge Engineering Research Group O’Donovan with Grafton Architects (N7 Nenagh Bypass, County Tipperary). was founded in University College Dublin and in 2002 plans were set in motion to create an All- 7. Boyne Bridge, Roughan and O’Donovan Ireland Bridge Engineering Research Network with Grafton Architects (M1 Northern involving both academics and practitioners. Motorway: Drogheda Bypass, County Louth).
CONCLUDING REMARKS 8. Taney Luas Bridge, Roughan and O’Donovan (Luas Light Rail Transit, Saint Fritz Leonhardt sums it up well: Stephen’s Green to Sandyford, Dublin). "Bridges have always fascinated people, be it a primitive bridge over torrent or deep gorge or 9. Kilmacanogue Footbridge, Roughan and one of the magnificent modern bridges whose O’Donovan with Grafton Architects (N11, Kilmacanogue, County Wicklow). immense spans almost defy the imagination. A variety of qualities are called for to build a 10. Moran’s Bridge, Roughan and O’Donovan modern bridge; a considerable amount of (Royal Canal, Mullingar, County knowledge, the courage to take daring decisions Westmeath). and the ability to lead a large team of fellow workers to the successful completion of the project. Bridge building is one of those difficult constructional endeavours that both attract and challenge the energetic and self-confident engineer. The importance of bridge building gives rise to a correspondingly intense joy and satisfaction when successfully completed. Bridge building can grow into a passion that never loses its freshness and stimulus throughout a man’s life." [1]
REFERENCES
1. Leonhardt, F. Brücken Bridges, Architectural Press, 1982, pp308.
Figure Credits
1. Killarney Road Bridge Piers, Roughan and O’Donovan with Grafton Architects (N11 Bray Bypass, County Wicklow).
2. Grange Newbrook Bridge, Roughan and O’Donovan (Grange to Newbrook Link Road, Mullingar, County Westmeath).
3. Rowan’s Road Bridge, Roughan and O’Donovan with Grafton Architects (M1 Northern Motorway: Balbriggan Bypass, County Dublin).
4. Killarney Road Bridge, Roughan and O’Donovan with Grafton Architects (N11 Bray Bypass, County Wicklow).
5. Claremorris Bridge, Roughan and O’Donovan (Knock Claremorris Bypass, County Mayo).
58 CONSTRUCTION OF SUBMARINE SUPPORT FACILITIES - DEVONPORT ROYAL DOCKYARD Mr. Murray Chapman BSc(Hons), FSA, CEng, FICE, MCIWEM, MCIArb Kellogg, Brown & Root
Murray Chapman has spent a to support the Royal Navy’s nuclear submarine large percentage of his fleet at Devonport Royal Dockyard. In particular, working life with Gibbs, the to satisfy nuclear regulatory requirements the Consulting Engineers, working structures, amongst other requirements, had to on docks. He started in 1971 be designed for extreme loading conditions with the design of the during which their behaviour had to be Submarine Refit complex at Devonport and, in predictable. 1991, worked on the Trident refit contract for the same dockyard. After carrying out an KEYWORDS assessment of damaged facilities of the Kuwait Safety Case, Nuclear, Dock Structures, Shear Naval Base following the First Gulf War, he was Friction Dowels, Surface Preparation, Caissons, seconded to Devonport Management Ltd to Ductile Concrete. prepare designs and safety cases for the upgrade of facilities to accommodate the Royal Navy’s INTRODUCTION nuclear submarine fleet. He is presently involved in examining further upgrade works relating to The Dockyard low-level refuelling of submarines. Devonport Royal Dockyard is situated to the west of Plymouth on the east bank of the River ABSTRACT Tamar (also known as the Hamoaze at this point). The paper presents an overview of the design It covers an area of some 120 hectares with over and construction of the reinforced concrete 5km of deep water berths, 5 fitting out basins ground works that were undertaken during the and 14 dry docks. period 1997-2002, to provide upgraded facilities
Figure 1: View of Dockyard looking south
59 It is the single largest naval support complex in agreed in March 1997 between the MoD and Western Europe and offers a wide range of skills DML. The works essentially comprised the and a level of back-up services which are upgrading of: fundamental to the continuation of the Royal • 14 and 15 Docks within the Submarine Navy as an effective fighting force. Devonport Refit Complex (which were originally Royal Dockyard has played a vital role in constructed in the early 1970s) to supporting the Royal Navy’s nuclear submarine accommodate the Swiftsure and Trafalgar fleet through repair and refit of the vessels since classes of submarines without precluding the early 1970s following construction of the the future Astute class of submarines Submarine Refit Complex (SRC). • 9 Dock, which was originally constructed In 1993, the Secretary of State for Defence during the period 1896-1904, to announced that Devonport would be the single accommodate the Vanguard class of UK site that would carry out future maintenance, submarines refitting and refuelling of the UK submarine fleet • Provision of a new low level refuelling including the Vanguard class submarines. To facility to accommodate new and used provide the facilities for the Vanguard class nuclear fuel submarines and to enable continuation of use of • Ancillary buildings the submarine docks in the Submarine Refit Complex it was necessary for the existing docks • A new seismically qualified railway system. and ancillary facilities to be upgraded and enhanced. The upgrade of 9 Dock had to be completed It should be recognised that the Devonport site to accommodate HMS Vanguard by February is unique within the UK in that it accommodates 2002. 15 Dock’s upgrade had to be completed both a privately owned commercial dockyard, by June 1999 to accommodate HMS Trenchant. owned by Devonport Management Ltd (DML) 14 Dock’s upgrade had to be completed for the involved in the refit, repair and maintenance of defuel of HMS Valiant in May 2002. All of these nuclear powered submarines as well as an targets were achieved. operational submarine base, owned by the Whilst 15 Dock was being upgraded, refitting Ministry of Defence (MoD). of a nuclear submarine in 14 Dock was undertaken and similarly, when 14 Dock was Award of contract being upgraded, 15 Dock was occupied by a The contract for the facility redevelopment nuclear submarine undergoing refit. programme, known as the D154 Project, was
Figure 2: Plan of 5 Basin
60 To ensure the timely success of the project dock effectively supported a nuclear reactor. required the mobilisation of diverse UK The site was subject to regulation by two engineering skills and this was achieved by DML organisations: creating an alliance partnership with: • HM Nuclear Installations Inspectorate (Civil • Kellogg, Brown & Root (KBR) Regulator) (management services and design of • Chairman, Naval Nuclear Regulatory Panel buildings and infrastructures) (MoD Regulator). • Rolls Royce (nuclear fuel handling The consequences of failure were viewed from equipment and nuclear power process) the perspective of any design being inadequately • Strachan & Henshaw Ltd (reactor access conceived and executed. The level of scrutiny of house to facilitate refuelling, and designs and construction methods were, seismically qualified submarine support therefore, commensurate with the consequences cradles) of failure. • BNFL Engineering Ltd (safety case The dock structures thus fell into the highest production and design of low level safety category and their designs had to be refuelling facility) robust against extreme loading conditions, of • Babtie Group Ltd (civil design and building which seismic loading generally proved to be the services design). most onerous. The docks had to withstand a seismic design basis event (DBE) with a return At its peak, in August 2001, the D154 project period of 10,000 years. A site-specific seismic employed 2865 personnel on site. It is estimated hazard assessment was undertaken which that, at various stages, more than 100 separate determined that the magnitude of such a return contractors and 40,000 people were involved in period seismic event would have a peak turning the facility proposal into timely reality. horizontal ground acceleration of 0.25g with a The upgrade works had to be carried out in the vertical component of two-thirds of this value. It confines of an operational dockyard where was also a requirement to check that there would nuclear safety remained paramount. be no cliff-edge effects immediately beyond the DBE and to satisfy this, the designs were checked SAFETY CASE REQUIREMENT at DBE + 40% ie, 0.35g earthquake. To provide the necessary ductility in the The design and construction of the upgraded concrete structures significant amounts of docks were subject to rigorous reviews and reinforcing steel had to be utilised. checking due to their safety significance - each
Figure 3: 14 Dock, showing floor construction
61 Facility Concrete Rebar Dowels m3 tonnes No.
9 Dock 73,000 15,000 600
14 Dock 28,885 5,000 6,000
15 Dock 27,174 5,000 6,000
Table 1
PRINCIPAL QUANTITIES qualified railway in the UK. Some 8,100 m3 of concrete were used in its construction. Overall, some 195,000 m3 of concrete has been used within the various facilities of which 150,000 m3 were supplied from a dedicated on- site batching plant operated by RMC Readymix South West. The volumes of concrete and reinforcing steel used in each of the dock structures were as Table 1. The low level refuelling facility which accommodates the new and used nuclear fuel was constructed on an island site within 5 Basin. The island, 47m x 26m in plan, was constructed from the rock surface of the basin floor using mass concrete, which was placed under water Figure 5: Nuclear transfer route using tremie tubes to form a platform 10m above (railway) under construction the basin floor. 11,000 m3 of mass concrete were required to be placed in this way. Placing CODES AND STANDARDS concrete under water is not new but is unusual The principal code used for the design of the on such a large scale and where quality standards reinforced concrete structures was ACI 349-85 are so demanding. A paper describing this work "Code Requirements for Nuclear Safety Related was published in Concrete Engineering, Summer Concrete Structures", including amendment of 2001 [1]. March 1st 1990. During the design and construction period, the code underwent a significant revision and was re- issued as ACI 349-97 in 1998 with an additional chapter (Chapter 21) which addressed ductility requirements. In particular, it defined additional confinement reinforcement to be provided in the form of ties and links. 15 Dock had already been designed to ACI 349-85 and its construction was nearing completion by the time the new code became available. 9 Dock’s construction had commenced but had Figure 4: Low level refuelling base to have additional reinforcement fixed to meet constructed using tremie concrete the requirements of ACI 349-97. 14 Dock’s design fully embodied the The new railway system (1.8km long) was requirements of ACI 349-97. constructed comprising tram lines at standard gauge set into a 0.5m thick reinforced concrete slab overlying a 0.5m thick mass concrete The change of the Code ensures ductility foundation. Because it is used to transfer fissile beyond the design basis earthquake (DBE). The material between the nuclear facilities it, too, had designs for the 9, 14 and 15 Dock structures have to be seismically qualified; the first seismically been undertaken and detailed so that they will
62 behave elastically to DBE plus a 40 percent As noted earlier, the majority of the concrete margin. The effect of the code change means was supplied from a dedicated concrete batching that beyond DBE plus 40 percent 9 and 14 dock plant operated by RMC Readymix South West, structures will behave in a ductile manner which was established at Weston Mill Lake within whereas this is not assured for 15 Dock. the dockyard. On occasions, it was necessary to Early age thermal cracking was checked undertaken large pours of the order of 1,000m3 against BS 8007 used in conjunction with in one day. To ensure the timely supply of Department of Transport Publication BD 28/89 concrete, as well as ensuring back-up, concrete "Early Thermal Cracking of Concrete", 1987. was also provided by RMC’s Saltash and Plymouth depots. Although an American code was used for the design, the concrete materials used were to British Standards: Ground granulated blastfurnace slag BS 6699 Portland Cement BS 146 or BS 4246 Concrete Testing BS 1881 Statistical monitoring of cubes BS 5328. The design of reinforced concrete was based on 50N/mm2 concrete.
CONCRETE MIX DESIGN AND BATCHING Due to restricted working areas and to avoid significant drop heights (9 Dock is about 14.25m deep and 14 and 15 Docks are each about 13.75m deep), pumped concrete was generally adopted A typical C50 concrete mix comprised:
Figure 6: 15 Dock under construction
Materials Dry batch weights (kg/m3)
Portland Cement Blue Circle - Hope P C-RM 235 GGBS Civil & Marine - Western 235
Sand Bardon Aggregates, Moorcroft 790 10mm limestone Bardon Aggregates, Moorcroft 285 20mm limestone Bardon Aggregates, Moorcroft 665 Water reducing agent Grace WRDA 2820(ml) Water Free water/cement ratio 0.42
Note: Air entrainment was not beneficial for C50 mixes. Table 2
63 MONITORING OF CONCRETE Quality sampling of concrete was undertaken in accordance with the requirements of BS1881: Part 101 at the following rates with a minimum of three cubes per set:
Size of Pour (m3) Rate of Sampling No. of sets of cubes Less than 50 1 per 18 m3 Greater than 50 1 per 30 m3 Figure 8: 9 Dock before commencement Each load of concrete was subjected to a of construction workability test. The rejection rate was 1%. such as nuclear safety, buildability, ease of design Figure 9 indicates a typical graph for monitoring justification, programme and cost. 7 and 28 day cube strengths. None of the test results fell below the minimum strength 9 DOCK requirements. The existing mass concrete dock floor and During the progress of the works, there was a upper sections of the mass concrete dock walls period in mid 2001 when there was a noticeable (which were lined with granite sets) were reduction in concrete strength, albeit that the demolished and a new reinforced concrete minimum specified acceptable strength was structure provided. The floor of the dock was always achieved. The problem was traced to the provided with an extensive underfloor drainage use of weak cement. system which is fully accessible. The design of Monitoring of concrete temperatures was the dock, and hence its safety case, is reliant on required when the thickness of the concrete this underfloor drainage system to avoid the sections was greater than one metre or the build-up of uplifting hydrostatic pressure acting volume of concrete placed was greater than on the dock structure. 9 Dock was upgraded 3 20m . A typical temperature-time graph (Figure during the period 1998-2001. 10) is shown for 14 Dock floor slab (2.20m thickness) which indicates that the temperature differential across the section was below the specified maximum differential of 25°C.
THE DOCK STRUCTURES Figures 11, 12 and 13 show typical cross sections through 9, 14 and 15 Docks respectively. The design philosophy for each was different and determined from detailed value engineering studies which considered a range of attributes
Figure 7: On-site batching plant sited at Weston Mill Lake
64 Figure 9: 14 Dock upgrade – C50/20, 15mm slump concrete. 7 & 28 day cube strengths
Figure 10: 14 Dock upgrade. Dock floor G/L 4.2-7 concrete pour thermocouple readings
65 Figure 11: Section through 9 Dock
Figure 12: Section through 14 Dock
66 Figure 13: Section through 15 Dock
15 DOCK This was the first dock to be upgraded (1997- 1999). It was not feasible to provide an accessible underfloor drainage system and so the dock structure was designed for full hydrostatic and hydrodynamic uplift forces. A total of 206 number 75mm Macalloy bar anchorages were installed in the dock floor. Any beneficial effects of the existing rock anchorages and underfloor drainage system installed in the 1970s construction were ignored. The west and east walls were tied to the new Figure 14: 9 Dock during construction reinforced concrete lining of the dock by means of dowels which were grouted in place. Cement grout was found to be better than epoxy since it was less problematic to mix, more user-friendly and equally reliable, whilst the epoxy appeared to soak into the concrete leaving little available to bond to the dowel itself. The design took account of the mass of the original west wall and for the east wall it was conservatively assumed that 50 percent of the existing reinforcement was effective. The design of the dowels was undertaken in accordance with the requirements of ACI 349 for calculating shear friction resistance. In shear friction, the applied shear is resisted by friction between the interfaces of old and new concrete Figure 15: 9 Dock near end of and the dowel action of the reinforcement across construction the interface.
67 Figure 16: Reinforcement in 15 Dock floor slab (note pockets for rock anchorages)
The existing concrete surfaces were required to been both time consuming and expensive. After be roughened to ensure that the necessary shear many trials, the roughness was achieved by friction component between the concrete providing grooves in both directions on a 100mm interfaces would be attained. The code required x 100mm grid using grit blasting. the surface to have an amplitude of 5mm but did not indicate at what wave length. Discussions 14 DOCK with the authors of the code indicated the wave 14 Dock was the last of the three docks to be length was typically 100mm. upgraded. Work commenced in November 2000 When trial panels were produced it was found and was completed by December 2001. The that shot blasting and water jetting did not design principle for this dock was very similar to produce the desired roughness and, instead, that for 15 Dock, saving that the majority of rock ended up polishing the surface due to the anchorages were installed in the east dock wall aggregates and cement matrix having the same (94 No.) with only 50 No. installed in the floor to hardness. Scabbling also proved not to be ensure that there would be no uplift and entirely satisfactory and due to the large surfaces consequent "chatter" of the floor during a to be prepared (some 2,500 m2) it would have design basis earthquake. An optimisation study was undertaken with the Building Research Establishment to re- examine the shear friction dowel arrangement which concluded (and quantified) that the roughening of the concrete surface need only be local to the dowels. With the improvement in jetting equipment and technology between the start of 15 Dock in 1997 and 14 Dock in late 2000, further trials of water jetting were undertaken and by careful adjustment of pressure and flow through the water jetting nozzles it was possible to achieve Figure 17: 15 Dock, showing drilling for the specified roughness of the existing concrete dowels on the prepared surface surface within 14 Dock without the need to
68 Checking that the required roughness profiles were achieved was done by comb survey; see Figure 19.
Figure 18: 14 Dock, showing drilling for dowels on the prepared surface provide a grid of grooves. The specification required a clean, rough, uniform face which, when measured over a representative portion of the prepared face, a profile drawn on a pair of 1200mm long straight lines, forming a horizontal/vertical cross, showed one of the Figure 19: Comb survey following characteristics: • that there exists a minimum of 24 CAISSONS individual indentations (measured peak to The design of the dock closures (concrete valley) of amplitude 5mm or greater caissons) proved to be particularly challenging • or that over the same distance there are a since they had to: minimum of 40 individual indentations of i) Resist a drop load of 10t from a height of amplitude 4mm or greater +25.0m AOD. (ie, a total drop height to • or that the sum of individual indentations bottom of caisson of about 34m); 3.5mm or greater in amplitude over the ii) Remain stable and maintain the seal to 1200mm length totals at least 150mm. the dock when subject to an impact of a 20,000t vessel travelling at 0.4 knots;
Figure 20: 14 Dock at completion of construction
69 Overall Wall Thickness Base Dock Number Width Length Height External Internal thickness of cells m m m mm mm mm 9 12 26.7 18.0 14.9 700 550 900 14/15 9 20.5 18.0 14.9 700 550 900
Table 3: Dock dimensions
iii) Maintain the seal to the dock when width of the caisson is provided. The shear key is subject to a reverse hydrostatic head of 2.5m in width and 300mm high. 6.1m in conjunction with a seismic event Figure 22 shows typical details of the caisson which had a return period of 100 years. for 14 Dock. The construction of the caissons The co-efficient of friction between the was carried out in an available dry dock using underside of the caisson and the cill was conventional formwork techniques. It was the taken as zero to cater for mollusc original intention to construct the new 14 and 15 infestation. Dock caissons together in 9 Docks prior to its upgrade works commencing. Site investigations of the dock indicated that its floor was sound. Problems were, however, encountered for the 14 Dock caisson which was sited further into the dock than the 15 Dock caisson, which was close to the entrance. Investigations revealed that the granite floor sets embedded into the mass concrete of the dock had separated and arched upwards from the underlying mass concrete by some 75mm due to hydrostatic uplift (see Figure 23). The casting of the 950mm thick base slab of the caisson provided sufficient mass to depress this, resulting in a bow shaped base slab. The Figure 21: General view of caisson base slab had to be scrapped and, due to Value engineering studies identified the best programming requirements, arrangements had to option to be a multicellular reinforced concrete be made to use another dry dock for its structure, the principal dimensions of which are construction. The construction of 15 Dock as follows for each of the docks. caisson proceeded as there was no separation of To counteract a reverse head with zero friction, the granite floor sets from the underlying mass a spigot/socket shear key running across the concrete.
Figure 22: 14 Dock caisson
70 Figure 23: 9 Dock before start of construction
Figure 24: 15 Dock caisson under construction in 9 Dock and 14 Dock Figure 25: HMS Vanguard in 9 Dock caisson being demolished in the foreground.
CONCLUDING COMMENTS REFERENCE The construction of the upgraded facilities to 1 Concrete Engineering, Summer 2001. support the Royal Navy’s nuclear submarine fleet Construction Beneath the Waves. Dave within the confines of a working dockyard proved Cullen, Rob Williams and Jon Knights. to be challenging within the timescales set to ensure minimal disruption to the submarine refit programme and the need to maintain the fleet in an operational state. Although concrete, in itself, is a brittle material, extensive use throughout the upgrade works in conjunction with carefully detailed reinforcement provides robust structures which can behave predictably when subjected to seismic loading.
71 72 CONCRETE SUPPLY SOLUTIONS TO THE CHANNEL TUNNEL RAIL LINK Mr. Andrew Bourne BSc(Hons), MSc, AMICT Brett Concrete Ltd
Andrew Bourne, over the past INTRODUCTION 21 years, has been responsible for the concrete for many The Channel Tunnel Rail Link has been a very major projects, including the visible feature of construction in the South East of M25, Thanet Way, Bluewater England since 1998. Since that time it has been Park and now the Channel one of the major if not the major construction Tunnel Rail Link, as Technical Manager for Brett project in Europe. Concrete Limited. He has a first degree in The whole project is due for completion in geology and a masters in environmental earth 2007 although Phase 1 is due to open to rail science. traffic in September of this year. The scale of the project has posed many ABSTRACT challenges to suppliers and contractors alike, This paper discusses various aspects of particularly in terms of resource provision from concrete supply to the Channel Tunnel Rail Link. It the skills, personnel and materials perspectives. concentrates on the contracts supplied in part or The ready-mixed concrete industry has whole by Brett Concrete, however the comments sometimes been accused of being inflexible and are also applicable to other Projects. Supply unable to respond to changing circumstances, solutions in terms of concrete mix design, as well however the range of concrete types that have as plant and equipment options are examined. been supplied to the Channel Tunnel Rail Link proves the opposite and highlights that suppliers KEYWORDS are able to work in conjunction with contractors and clients to satisfy the most demanding of Channel Tunnel Rail Link, Concrete requirements. Specification, Oxygen and Chloride Diffusion, Ground Granulated Blastfurnace Slag (GGBS), Brett Concrete has now supplied concrete to Shotcrete Concrete, Polypropylene Fibres, Steel four major contracts and has worked in Fibres, Concrete Segments, Partnership, partnership with contractors and client Rail Link Teamwork, Communication Engineering (RLE), as well as being suppliers
Figure 1: The route of the Channel Tunnel Rail Link
73 Phase 1 Phase2 Channel Tunnel to Fawkham Junction Fawkham Junction to St Pancras 1998 Critical design work complete Critical contracts let or firm bids received Construction commences 2001 Track laying commences Critical design work complete Critical contracts let or firm bids received Construction commences 2002 Track work and most fixed equipment Boring of London and Thames installation completed Tunnels commences Testing and commissioning commences 2003 Testing and commissioning complete Boring of London and Thames Permit to use issued Tunnels commences Railway Open 2004 Track laying commences Tunnel boring complete 2006 Track work complete Testing and commissioning commences St Pancras station completed Fixed equipment installation complete 2007 Testing and commissioning complete Permit to use issued Railway Open
Table 1: The CTRL Work Programme - some dates, overall statistics & interesting facts
either solely on contracts or in conjunction with Ultimately 8 Eurostar trains per hour will use other suppliers as part of a joint venture the Rail Link travelling at speeds of up to operation. 300km/hour. At the present time Brett Concrete Ltd has The travel time for passengers travelling to supplied in excess of 600,000m3 since Paris from London will be cut by 45 minutes from commencing supply in the autumn of 1998 with 3 hours to 2 hours 15 minutes. the prospect of approximately another The budget cost for construction of the link is 100,000m3 to be supplied to complete current £5.2 billion. commitments. Phase 1 of the link contained 6 major civil The approach of Brett Concrete to supply on engineering contracts and is at the current time this overall project has encompassed several some 95% complete and due to open to fare- fundamental tenets namely: exploring paying customers in September 2003. partnerships, engendering a positive proactive To date, in excess of 25million man-hours have approach, utilising teamwork and clearly been worked on the project. Some 11,500 piles communicating in a consistent manner with all have been placed together with in excess of involved in the supply chain. 550,000m3 of structural concrete. The overall length of the link is 113km of The total volume of concrete supplied is which 25% will be in tunnel. difficult to estimate but can safely said to be in Phase 1: Channel Tunnel Terminal to Fawkham excess of 800,000m3 Junction is 74km long and Construction of phase 2 began in July 2001. In construction commenced in 1998. excess of 50% (20km) of this phase is in tunnel; Phase 2: Ebbsfleet to St Pancras Station is nominally twin bored tunnels of 7.15m internal 39km long and construction diameter. commenced in 2001.
74 The first tunnel drive on Contract 320 greater knowledge as a result of testing enabled (Thames Tunnels) is now complete. us to significantly improve our understanding of This phase also includes the construction of these parameters and to refine mix designs two new international stations, at Stratford and accordingly. Ebbsfleet. Concrete Supplies to Phase 1 Contract 310 at Thurrock takes the railway over the Dartford Crossing approaches and under Brett Concrete was involved in two major the Queen Elizabeth Bridge, between two of the contracts with differing supply characteristics. piers. Contract 430 THE CONCRETE SPECIFICATION On Contract 430 (Ashford town centre to Lenham Heath) Brett Concrete entered a formal The concrete specification is extensively based partnership arrangement with the contractor on the Department of Transport Specification for (Skanska Construction UK Ltd) and the project Highway Works with contract-specific manager (Rail Link Engineering). This amendments as appropriate and required. arrangement meant that we were fully involved in Structural and piling concrete is essentially developments on the supply front and were able Grade 40 with specific durability requirements to contribute fully to the decision making depending on the contract conditions. Concrete process. The partnership also meant the in the ground has had a range of Class 1 to Class development of a pricing formula based on 4 sulfate conditions to be met. material price and production cost declarations. Compliance is based on means of 4 analysis In relation to this contract, the initial with the familiar moving margin depending on considerations concerning supply concentrated on the standard deviation of the previous 40 results. the provision of sustainable sources of materials. The overriding requirement within the The initial tender volumes of approximately specification is for all concrete in contact with 285,000m3 meant that the supply of marine ground or air to be in compliance with the gravel aggregate concrete was not feasible due to oxygen and chloride diffusion characteristics constraints on the availability of coarse detailed below and in reality it is this requirement aggregates. The company sourced a sustainable that has been the main driver in terms of mix source of Glensanda granite coarse aggregate design characterisation. from Foster Yeoman at the Isle of Grain, which The parameters within the structural concrete was used in conjunction with marine sand landed specification were as follows: at wharves in Kent. • Chloride diffusion coefficient shall be less Concrete mixes were optimised for than 1x10-12m2/s performance in conjunction with Skanska. • Oxygen diffusion coefficient shall be less As a means of getting away from the usual than 5x10-8m2/s. discussions about the workability of concrete, all At the commencement of the contract only structural concrete was designed with a target limited knowledge was available to us about the workability of 100mm and as pump mixes; a mix parameters that would satisfy the philosophy that was readily embraced by Skanska requirements of the specification; however, and RLE. All concerned with the supply of concrete appreciated the costs of unnecessarily rejected concrete and the difficulty of disposing of such material on site. To overcome this, a comprehensive water addition procedure was developed and used with the assistance of the project manager and contractor for both piling and structural concrete options. This procedure detailed the process for initial testing at site and the exact methodology to be followed if water was to be added, including the compulsory taking of extra cubes for strength Figure 2: The Ashford Viaduct
75 testing. The procedure was distributed to all cabin. Control of concrete produced through the drivers, plant staff and representatives of the dry batch process was controlled visually and by independent test house employed to carry out the use of truck-based workability meters. These the compliance testing on site. Similar proved to be extremely successful. procedures, fundamentally based on the original All of the structural and piling concrete generic procedure, have been used on all of our contained admixtures and these were stored on supply contracts since. site in bulk double-bunded storage tanks in A range of mix design options were developed volumes of up to 10,000 litres; delivery was and offered to the contractor and RLE to optimise typically via tanker direct to site. the commercial benefits available. In respect of Haulage for the project was provided by a the piling concrete, four options of GGBS contract haulier who provided a truck-base fleet replacement level were offered, with a range of with additional support depending on the 50%-80% GGBS being available. Each of the programmed quantity of concrete to be delivered different mixes attracted a different price and the in any period. contractor was able to take advantage of the All trucks were equipped with regularly price differences to suit particular circumstances. calibrated (every 3 months) water meters, so that In cases where piles were to be in the ground if water needed to be added on site then the for a number of months before further work, exact amount discharged was known and could higher replacement levels of GGBS were used; in be recorded easily. fact almost all of the piling concrete was At the end of 2002 the project was awarded ultimately placed with 70% or 80% replacement. the accolade of Major Project of the Year at the All of the mix options were trialed through Annual British Construction Industry Awards. The the formal trial mix procedure prior to being New Civil Engineer and the Daily Telegraph accepted as available approved options for use on sponsor these awards. site. A letter received in recognition from the Structural concrete was similarly offered with a Project Director noted… range of GGBS options at 50%, 60% and 70%. "To win this award is a real achievement and This range of options had the benefit of allowing as such recognises the hard work carried out by large pours, e.g. bases and pile caps, to be placed everyone on the contract. It is also recognition of with a low heat option to minimise heat the quality of the work carried out and the team- generation and limit the possibility of thermal working that helped the project to be completed cracking and permitted the placement of slender on time. elements or elements where a rapid formwork Brett Concrete played a major role in this turnaround was required to be placed with the achievement, producing and supplying quality 50% option. concrete throughout the project to enable the This approach to mix design has had the works to be completed on programme, benefit of maximising the returns available to the supported by a first class team who worked contractor and project manager and has enabled extremely closely with Skanska…" the most economic options to be assessed and used for each particular situation. Contract 420 Consideration of the batching plant to supply On Contract 420 (Boxley to Lenham Heath) such contracts is also of prime importance; in this the company led a consortium that was put case two site plants were commissioned: a together to supply both the aggregate and 3 Steelfields Major 60 wide-line plant with a 3m concrete requirements of the project. The capacity pan mixer, which was supplemented company - KCML (Kent Construction Materials 3 with an Elba 60 Plant with a 1m capacity pan Ltd) was a joint venture between Brett, Hanson mixer. In addition, the local static plant in Ashford and RMC. was upgraded so that it could support the Brett Concrete project managed the supply supplies of concrete to the project. All plants and as the liaison and contact point between the supplying the project were equipped with the contractor and supply consortium; taking the lead latest computer controlled batching system, in regular progress meetings on site as required, supplied by Command Alkon. we were then able to liaise with the other Workability control through the pan mixer suppliers as appropriate. was achieved via an ammeter fitted in the batch
76 The consortium appointed a project manager as the stabiliser has a pH value of 2. and shipper who were based on site in the main Haulage was supplied under a contract project office. They formed the primary day-to- between the contractor and the site-based day link with the contract and were able to bring haulage subcontractor; this enabled the in specialist support as required. contractor to have trucks available for 24 hours Up to 7 supply plants were made available by per day. the consortium. All of the plants used marine Steel fibres were imported from Germany in aggregates and we were able to justify that the 20 kg boxes and transferred into a dispenser, sources of aggregate available were all which then "blew" them into the truck-mixer. demonstrably similar to QSRMC requirements. Other plant constraints meant that the concrete Part of our approach was to ensure that all plants had to be dry batched with an extended mixing carried the same admixtures and cementitious time of 30-45 minutes to ensure the elimination materials and, where necessary, supply sources of cement or fibre balls. Workability control was wee changed to meet this requirement. also critical with a target of 175mm slump All of the plants were able to use a single ± 25mm. consistent mix design for each of the mix options Yet again the importance of understanding a developed. Formal plant trials were carried out on contractor’s needs and discussing all details of the each plant for the piling and structural mix supply on a regular basis cannot be options. overemphasised. The project benefited from having the resources of three major suppliers at their Segment Concrete disposal with a single point of contact to ensure The volume of segment concrete on Contract consistency of approach. 320 for the Thames Tunnels Contract is approximately 45,000m3. Concrete Supplies to Phase 2 Hochtief Murphy has constructed a purpose- Supplies to the second phase of the project built factory on site solely for the purpose of have, in may ways, been more challenging than supplying this element of the contract. It consists on Phase1, essentially due to the different nature of a single carousel system, which is capable of of the concrete mixes required, over and above producing up to 140 segments per day. the more normal structural and piling options; The specification for the segment concrete these include, steel fibre-reinforced shotcrete contains requirements in respect of the following supplies and segment concrete. parameters: compressive strength, tensile strength, first-crack flexural strength and residual Steel Fibre-reinforced Shotcrete flexural strength. Additionally a measurement of Supplies were required for temporary works to the distribution of steel fibres was also included. allow construction of the foundations associated In addition to steel fibres the mix also was with a major bridge slide on the North Kent railway line forming part of the Ebbsfleet Contract 342 works. Initial indications were that a total volume of 400m3-500m3 was required. To date in excess of 1500m3 has been supplied, essentially due to the ground conditions encountered in the chalk spine that has been excavated. The mix design was essentially "Prescribed" with 430kg/m3 CEM I, approximately 60%fines content (marine sand), a maximum aggregate size of 10mm and the use of crushed rock (granite) aggregate. The mix had to be set-retarded for in excess of 12hours with Delvocrete stabiliser and was required to contain 40kg/m3 of steel fibres. The supply required the installation of a stainless steel admixture pump and special lines Figure 3: Concrete segment for use in the Thames Tunnel
77 designed to contain monofilament polypropylene CONCLUSIONS fibres for fire protection purposes. The Channel Tunnel Rail Link has been a major As ever with a precast operation, efficiency in feature on the construction landscape since 1998. the turnaround of moulds is paramount and the de-moulding strength of 18N/mm2 was required The project has been demanding for concrete to be achieved at 6-hours or earlier age (albeit suppliers and the approach that has been after steam curing). The use of hot water at employed to meet the challenges has required 55°C, when necessary, has facilitated stripping of the application of a flexible approach to moulds at 5 hours age; the strength being traditional and new methods of work, embracing assessed from cubes passed through the curing teamwork and partnering principles and process alongside the segment moulds. techniques as well as continued close-knit communication between supplier, contractor and Target workability for the mix was required to client. be in the range of 20-30mm slump, this being to facilitate finishing of the extrados of the ACKNOWLEDGEMENTS segments prior to steam curing, which typically commences at approximately 1 hour after the The author would like to express his mould is filled with concrete and vibrated. appreciation to members of the Rail Link Engineering staff in particular Peter Shuttleworth Ground conditions necessitated compliance for his helpful and thoughtful assistance with Class 4 sulfate conditions and hence the use throughout the length of the contract. of a PFA blended cement to achieve the early strength, stripping times and specification In addition, he also thanks the publicity durability requirements. department of Union Railways for permission to see the information included in this paper. Brett Concrete invested in fibre handling and transfer devices to facilitate the loading of the steel and polypropylene fibres; both devices were FURTHER READING linked to the plant’s batch computer to ensure consistent accuracy of weighing and autographic 1. BOURNE, A. Precast segments on the recording of all materials in each batch of Thames tunnels, CONCRETE, April 2002 Vol.36 No.4, pp.32-33. concrete. We further arranged for bulk deliveries of steel fibres in 24 tonne containerised deliveries from Germany in 400kg bags and for the bulk delivery of polypropylene fibres to be in 250kg size boxes to facilitate loading into the bulk dispenser. The whole supply operation depends greatly on a proactive approach with suppliers, customer and project manager alike. There is no doubt that the process has been time consuming and often frustrating; however, the successful placement of segments in the tunnel certainly brings sufficient reward to those involved. The compliance requirements for this mix are onerous and influenced by many factors beyond the control of the concrete producer. These factors have been discussed in two recent papers published in Concrete magazine. By developing an understanding of the difficulties involved in the production of the concrete for this critical phase of the project we were able to negotiate a position whereby the risk for the factors beyond the control of the concrete producer were accepted by the contractor; another example of a close working relationship.
78 MODERN SPRAYED CONCRETE FOR URBAN TUNNELS Mr. Ross Dimmock BSc(Hons) Master Builders Technologies
Ross Dimmock is Technical environmentally safe sprayed concrete via the Director of Master Builders adoption of the wet-mix process using robotic Technologies’ International spraying techniques coupled with advances in Underground Construction sprayed concrete mixture proportions, particularly Division. His main activities are operator- and structure-friendly liquid the development of permanent accelerators. sprayed concrete linings for use in underground As highlighted in the paper, emphasis within structures. The focus of his company’s business is the industry now needs to be given to a more on providing the industry with the whole system holistic approach to creating durable sprayed from equipment to waterproofing and fire concrete structures using the modern application protection systems. Ross is also the Technical systems described. With a construction method Chairman of the EFNARC (European Federation of whose success is fully dependent on human Producers and Applicators of Specialist Products influence, the paper provides an overview of for Structures) European Technical Committee for critical elements such as contractor and designer Sprayed Concrete and is involved in the EFNARC experience and site control systems. Furthermore, Fire Protection for Tunnel Linings team. the need for modern, up-to-date specifications to reflect current technology are suggested, coupled ABSTRACT with the industry-wide need for relevant The paper gives an overview of the nozzleman training and recognised certification improvements in sprayed concrete technology schemes. that have occurred rapidly over the last 10 years, allowing the industry to consider sprayed KEYWORDS concrete as a "permanent" structural support for Alkali-free accelerators, Durability, Fibre urban tunnels. Consequently, its implementation reinforcement, Fire protection, Permanent, as a support system has increased dramatically Specifications, Sprayed concrete, Waterproofing. worldwide. The developments have been focused on attaining high quality, homogeneous,
Figure 1: Factors that significantly determine the durability of a sprayed concrete structure
79 INTRODUCTION "buildability" of tunnels using sprayed concrete. Designing "buildability" ensures that safety and The durability of a tunnel lining should be such durability critical elements are either designed that the lining remains safe and serviceable for out, or simplified for ease of construction on the the designed life, without the need for a high job site. degree of maintenance expenditure. To attain To facilitate this goal, design teams should be durability, the designer needs to assess the aware of the limitations of modern sprayed exposure environment of the structure during concrete construction processes and be familiar both construction and operation, as structural with the likely material performance. They also degradation normally occurs with unforeseen should have a strong site presence to ensure that environmental changes. the critical safety and durability features are With this in mind, the term durability may be constructed in accordance with their design. related to structures that are designed to resist loads during a construction period before a SPECIFICATIONS AND GUIDANCE secondary lining is placed. However, more often, Unfortunately, too often in the sprayed with the use of sprayed concrete for permanent concrete industry, specifications and guidance single shell linings, the durability of the concrete documents tend to be "cut and pasted" into new should consider a design life of 100 years or contracts year after year, without much in depth more. It is this latter case that is the focus of the research as to the current advanced state of the presentation and paper. sprayed concrete industry. The recent increase in As can be seen from Figure 1, the durability of wet-mix sprayed concrete has provided an a sprayed concrete structure is established via a opportunity to re-examine the "old" total of many possible parameters. In sprayed specifications and now new documents are concrete construction, not only correct concrete emerging which reflect the current state-of-the- mixture proportions and cover to reinforcement art in sprayed concrete technology. as with traditional cast concrete is sufficient. The These modern sprayed concrete specifications main reason behind this is that the material is now specify permanent, durable sprayed concrete spray applied, and consequently the quality is for the first time as a construction material. They significantly reliant on human skills and spray address the issues of achieving a quality equipment performance. Some of the main controlled modern mixture proportions, providing durability issues listed in Figure 1 are briefly guidance on promoting and testing for durability discussed in this paper. and effective execution of the spraying processes. BUILDABLE DESIGNS As an example, the new European Specification for Sprayed Concrete (1996) produced by With respect to existing concrete tunnel EFNARC, provides comprehensive systems to structures, the major durability problems are not attain permanent sprayed concrete. This directly related to the concrete itself, but more specification has been the basis for new project- often to the corrosion of steel reinforcement specific specifications worldwide and for the new elements that have been insufficiently protected European Norm Sprayed Concrete Specification. against water ingress or humidity. Tunnels Furthermore, the EFNARC Sprayed Concrete constructed with permanent sprayed concrete Specification is the first document to address create other durability concerns, particularly in issues such as national nozzleman training and terms of providing the required material accreditation for high capacity, mechanised properties such as compaction, and with the robotic spraying. The Specification also sets out unknown stability concerns associated with the systems for contractors and specifiers/designers to necessary amount of admixtures used for modern consider, prior to construction, the sprayed wet-mix sprayed concrete application methods. concrete structures they are to build, so as to To address the durability requirements, a adapt the sprayed concrete system and mixture holistic approach to the design and construction proportions accordingly. of durable sprayed concrete tunnel linings is required. In essence, the sprayed concrete lining CONSTRUCTION COMPETENCE method is heavily reliant on human competence The construction team should be made aware during construction and therefore the design of the design elements that are key factors in should reflect this by considering the determining the safety and durability of the
80 tunnel structure. To ensure that the quality of the • Use of pozzolanic materials such as silica concrete lining is achieved, quality review systems fume and fly ash. Silica fume has a should be adequate to control the production. It definite filler effect in that it is believed to is of paramount importance that the distribute the hydration products in a communication link between design and more homogeneous fashion in the construction teams should be maintained from available space. This leads to a concrete pre-design stage to project completion so that with reduced permeability, increased the above processes are promoted. sulphate resistance and improved freezing Nozzlemen should have previous experience in and thawing durability the application of sprayed concrete and have • Control of micro-cracking to 0.2mm by knowledge of the sprayed concrete process to be fibre reinforcement instead of mesh, adopted on the specific project. It is thereby allowing autogenous healing recommended that an operator be able to • Controlled, low dosages of alkali-free demonstrate his experience either as a holder of a accelerators for reduced reduction in final certificate from previous work, or required to strength compared to the base mixture, demonstrate his competence in a non-works significantly reduced leachates, reduced location. rebound and dust, and most importantly, Prevailing regulations place added to provide safe working conditions requirements on the people doing the spraying • Hydration control admixtures to prevent work to have technical knowledge of concrete, premature hydration of the concrete particularly with sprayed concrete. Present mixture before it is applied to the requirements have led to better training of the substrate. Pre-hydration may cause personnel involved. The result of this is an significant deleterious effects to the improved quality of work. The number of special hardened physical properties of the contractors who are working with sprayed sprayed concrete, such as low strengths concrete has increased over the last few years, and densities, and increased permeability. which has globally raised the quality of application. NEW "ALKALI-FREE" ACCELERATING ADMIXTURES SPRAYED CONCRETE MIXTURE PROPORTIONS Of late, safety and ecological concerns have become dominant in the sprayed concrete The main factor that determines the durability of accelerator market, and applicators have started a concrete structure is achieving a low permeability, to be reluctant to apply aggressive products. In which reduces the ingress of potentially deleterious addition, requirements for strength and durability substances, thereby inhibiting chemical reactions of concrete structures are increasing. Strength such as those involving the cement and thereby loss or leaching effects suspected to be caused by preventing chemical changes. Low permeability is strong alkaline accelerators (aluminates) has achieved in sprayed concrete applications by the forced our industry to provide answers and to following means: develop products with better performances. • A well graded material suitable for the Due to their complex chemistry, alkali-free sprayed concrete application system in accelerators are legitimately more expensive than terms of pumpability, workability, rebound traditional accelerators. However, accelerator reduction and good compaction. All prices have very little influence on the total cost aggregates should be checked for alkali- of in-place sprayed concrete. Of much larger silica reaction consequence are the time and rebound savings • Adequate cementitious content, typically achieved, the enhancement of the quality, 400 to 500kg/m3. The cement content durability and, most importantly, the provision of should not be less than 350kg/m3 a safe working environment. • Low, pre-defined W/C less than 0.45, The increasing demand for accelerators for achieved using water reducing agents / sprayed concrete termed alkali-free always superplasticisers. Modern superplasticisers, contains one or more of the following issues: referred to as "hyperplasticisers", can • Reduction of risk of alkali-aggregate provide W/C between 0.35 and 0.4, whilst reaction, by removing the alkali content maintaining a slump of 200mm
81 arising from the use of the common A number of comments can be made caustic aluminate based accelerators regarding these results: • Improvement of working safety by • Alkali-free accelerators can be used to reduced aggressiveness of the accelerator produce sulphate resisting sprayed in order to avoid skin burns, loss of concrete up to dosages of 10% eyesight and respiratory health problems. • Alkali-free accelerators perform better The typical pH of alkali-free accelerators is than modified sodium silicate accelerators between 2.5 and 4 (skin is pH5.5) with normal Portland cements • Environmental protection by reducing the • The use of 6% silica fume provides amount of aggressive leachates to the comparable sulphate resistance with ground water, from both the in situ normal Portland cement as with sulphate sprayed concrete and rebound material resisting cement (SR). This is important as deposited as landfill it is preferential to use normal Portland • Reduced difference between the base cement rather than SR cement in sprayed concrete mixture and sprayed concrete concrete due to the faster setting and final strength compared to older style early strength development aluminate and waterglass accelerators that • The lower the water-cement ratio, the typically varied between 15 and 50% higher the sulphate resisting performance. dosage. It is recommended to have a W/C below The focus within different markets, regarding 0.45, and preferably with the aid of new the above points, is variable. Where most sprayed hyperplasticisers, attain a W/C of less concrete is used for primary lining (in design than 0.4. considered temporary and not load bearing), the second and third points are the most important. APPLICATION REQUIREMENTS When sprayed concrete is used for permanent Quite often, the benefits of well-engineered structures, the first and last items become equally mixture proportions to achieve the durability important. requirements of the structure are negated by As a result of the above demands, in excess of poor application processes. 25,000 tonnes of alkali-free accelerator has been It is strongly recommended that only the wet- used worldwide since 1995. From MBT’s mix sprayed concrete process be used for the perspective, this accelerator type is considered construction of durable linings. The wet-mix state-of-the-art, and as a result is currently process is currently the only viable method to producing it in 18 countries. achieve quality, particularly with respect to In terms of sulphate resistance, a number of controlling the water cement ratio that is vital for tests have been carried out by SINTEF, Norway concrete durability and long term strength. and the results are summarised in Table 1, with Additionally, the wet-mix process has also "High" denoting excellent sulphate resistance. demonstrated significant economical benefits over the dry-mix process.
Cement Type OPC OPC OPC OPC SR Aggregates: alkali-silica reactivity reactive reactive non-reactive non-reactive slightly reactive Microsilica 0% 6% 0% 6% 0% and 6% w/c ratio 0.45 0.47 0.52 0.48 0.45 to 0.48 Accelerator & Dosage Modified sodium silicate 5% moderate high none high high Modified sodium silicate 10% none high none high high alkali-free 5% high high none high high alkali-free 10% moderate high none high high
none (no resistance) : greater than 0.1% expansion moderate resistance : between 0.05% and 0.1% expansion high resistance : less than 0.05% expansion
Table 1: Sulphate resistance of sprayed concrete (SINTEF, 1999)
82 Figure 2: MEYCO Robojet spraying manipultor - correct angle and distance for reduction in rebound and enhanced quality
Many of the factors that cause high rebound quantity of steel reinforcement by: values, poor compaction, loss in structural • Optimisation of the tunnel cross-sectional performance and hence increased project costs profile to reduce moment influences are attributed to the performance of the • Increasing the thickness of the tunnel nozzleman, particularly that of the hand held lining to maintain the line of thrust to the nozzle systems using the dry-mix process. middle third of the concrete section The advent of modern admixtures applied to • Where structurally possible, using the wet-mix sprayed concrete has reduced these more favourable option of fibre problems significantly by enabling the placed reinforcement. concrete to be initially plastic in nature. For some Steel fibres have been used successfully in minutes after application, new sprayed concrete permanent sprayed concrete tunnel projects to can be absorbed and compacted more readily reduce cracking widths to 0.2mm to produce than very fast, or flash setting materials. This watertight, durable tunnel linings. The advantage approach reduces rebound significantly and over conventional anti-crack reinforcement is that allows steel encapsulation to be achieved more the fibres are randomly distributed and readily. discontinuous throughout the entire tunnel lining Problems relating to nozzle angle, nozzle structure, allowing uniform reinforcement that distance and achieving the correct compaction evenly re-distributes tensile loads, producing a with the required air volume and pressure have greater quantity of uniformly distributed been facilitated by the use of robotic spraying microcracks of limited depth. Steel fibres also manipulators, particularly in large diameter transforms the concrete from a brittle into a tunnels. The MEYCO Robojet spraying highly ductile material, giving the lining a higher manipulator is controlled by a remote-control load bearing capacity, post initial cracking joystick by the nozzleman to allow the nozzle to through the effective redistribution of load, be spraying at the correct distance and angle at thereby increasing the safety of the structure all times (Figure 2). This, coupled with the during construction. More recently, HPP fibres required air volume and pressure, ensures low have been introduced, having the added benefit rebound and well-compacted sprayed concrete. of being corrosion resistant, whilst offering similar Good surface finishes can be achieved by performance to steel fibres. selecting the automatic oscillating movement of With all fibre-based concrete mixtures, care the nozzle mode as indicated in Figure 2. should be taken to match the fibre strength to STEEL AND HIGH PERFORMANCE the tensile strength of the concrete, as high POLYMER FIBRE REINFORCEMENT strength concrete with normal tensile strength fibres may still produce a brittle material. As From experience, water ingress is associated fibres are added during the batching process, this with sections of the sprayed concrete lining that removes the timely operation of welded mesh contain large diameter steel reinforcement, such installation from the construction cycle. as lattice girders, lattice girder connection bars, If conventional reinforcement is required for and excessive overlaps of steel reinforcement. structural purposes, then the reinforcement Therefore the emphasis should be to minimise the
83 should be designed with the installation method and tunnel geometry, particularly at junctions. in mind, and be evenly distributed. The Furthermore, when sheet membranes have been reinforcement arrangement should be such that installed with an inner lining of sprayed concrete, the nozzleman can facilitate full encapsulation of the following adverse conditions can occur: the bars, and the construction sequence can • As the sheet membranes are point fixed, allow sequential installation of the reinforcement. sprayed inner linings may not to be in Under no circumstances should sprayed concrete intimate contact via the membrane to the be applied through full reinforcement cages or substrate. This may lead to asymmetrical excessive overlaps of mesh. Attention should also loading of the tunnel lining be paid to avoiding flash sets from high dosages • To aid the build of sprayed concrete onto of accelerating admixtures, as this inhibits the sheet membranes, a layer of welded mesh fresh concrete from behaving plastically and is used. Due to the sheet membrane being moving around reinforcement immediately after point fixed, the quality of sprayed spraying. concrete between the mesh and the sheet membrane is often inferior and may lead ACHIEVING WATERTIGHTNESS VIA SPRAYABLE MEMBRANES to durability concerns • The bond strength between sprayed With the advent of permanent sprayed concrete inner lining and sheet membrane concrete linings, there has also been a request by is inadequate and leads to potential de- the industry to provide watertight sprayed bonding, particularly in the crown sections concrete. This is of particular importance with of the tunnel profile. This is a detrimental public access tunnels and highway tunnels that effect when constructing monolithic are exposed to freezing conditions during winter structures months, and also electrified rail tunnels. It has • As there is little bond strength at the been shown that most permanent sprayed concrete/sheet membrane interface, any concrete exhibits an extremely low permeability ground water will migrate in an unlimited (typically 1 x 10-14 m/s), however, water ingress manner. Should the membrane be tends to still occur at construction joints, at breached, the ground water will inevitably locations of embedded steel and rockbolts. seep into the inside tunnel surface at any Traditionally, polymer sheet membranes have lining construction joint or crack over a been used, where the system has been shown to considerable length of tunnel lining. be sensitive to the quality of heat sealed joints
Figure 3: Spray applied waterproofing membrane for complex underground structures
84 To combat these problems, MBT have drainage, the second layer of sprayed concrete developed a water based polymer sprayable must be designed to resist any potential membrane, Masterseal® 340F. hydrostatic load over the life of the structure. This sprayable membrane has excellent double- sided bond strength (0.8 to 1.3 MPa), allowing it PROVISION OF FIRE PROTECTION to be used in composite structures, and thereby In recent years, the tunnelling industry has effectively preventing any potential ground water been shocked by the rapid devastation, and in paths on both membrane/concrete interfaces some cases loss of life, caused by very notable being created. Masterseal® 340F also has an fires, such as the Channel Tunnel, Mont Blanc elasticity of 80 to 140% over a wide range of and more recently, tunnels in Austria. temperatures allowing it to bridge any cracks that Whilst systems are being developed to further may occur in the concrete structure. Being a secure the safety arrangements of passengers and water-based dispersion with no hazardous operatives of tunnels during tunnel fires, clients components, it is safe to handle and apply in are increasingly requesting that structural tunnel confined spaces. The product can be sprayed linings remain fire damage resistant. using a screw pump and requires two operatives Currently, a common form of fire protection in to apply up to 50m2/h, particularly in the most new-build concrete lined tunnels is through complex of tunnel geometries, where sheet modification of the concrete mixture proportions membranes have always demonstrated their with the addition of monofilament polypropylene limitation, as shown in Figure 3. fibres in both precast and in situ concrete linings. As presented in Figure 3, in single shell lining This approach offers defences against explosive applications, Masterseal® 340F is applied after the spalling but may not offer adequate thermal first layer of permanent fibre-reinforced sprayed protection in high energy fire scenarios, such as concrete, where the sprayed surface should be as with petrol tanker fires, and, consequently, steel regular as possible to allow an economical reinforced concrete sections will have limited, if application of membrane 5 to 8mm thick (all not no, tensile strength during such fires, leading fibres are covered also). A second layer of to collapse. permanent steel fibre reinforced sprayed concrete Master Builders Technologies has addressed can then be applied to the inside. As the bond the issue by developing a relatively thin (30 to strength between the Masterseal® 340F and the 50mm) thermal barrier system referred to as two layers of permanent sprayed concrete is MEYCO® Fix Fireshield 1350. The philosophy about 1MPa, the structure can act monolithically, behind MEYCO® Fix Fireshield 1350 is to provide with the sprayable membrane resisting up to a passive fire-protective layer to any underground 15bar. As this application considers no water
Figure 4: Sprayed application of passive fire protection layer to structural sprayed or cast concrete tunnel lining
85 structure using a rapid robotic spray application construction process has become highly process, as indicated in Figure 4. Furthermore, the automated thereby significantly reducing the protective layer should be as thin as possible to degree of human influence that has, in the past, reduce effects on the required operating prevented clients from considering sprayed structural envelope. If attacked by fire, the concrete as a permanent support. underlying structural concrete would be protected Modern sprayed concrete specifications now for temperatures up to 1350ºC. Repair is simply address the issues of achieving quality controlled completed by local removal of the damaged modern mixture proportions, providing guidance protection layer and re-sprayed with a new on promoting durability and effective execution application. of the spraying processes. As an example, the The performance of such passive fire new European Specification for Sprayed Concrete protection systems is currently evaluated at the (1996) produced by EFNARC, provides TNO Test Centre for Fire Research, Delft, comprehensive systems to attain permanent Netherlands. To simulate a petrol tanker fire in a sprayed concrete. tunnel, the Dutch RWS fire curve is currently With the increased use of durable sprayed specified for testing fire protection systems for concrete linings, new technologies to promote underground structures. Apart from the and maintain their use have entered the market temperature being above 1200ºC for two hours recently. These systems enhance watertightness and a maximum temperature of 1350ºC, the test and provide high performance fire resistance. also puts the system under immediate thermal Further implementation of durable sprayed shock. See Figure 5 for time-temperature curve of concrete for tunnels and other civil engineering furnace temperature and corresponding curve for structures is increasing, with a marked change interface temperature between fire protection during the mid 1990s. This trend is set to increase and structural concrete sample. further as design and construction teams become Testing of MEYCO® Fix Fireshield 1350 at the more familiar with modern sprayed concrete TNO Centre has shown excellent results with a technology, and the durable concrete that can be layer thickness of between 40 and 55mm, produced. producing very low interface temperatures of below 225ºC at 50mm thickness and below FURTHER READING 400ºC at 40mm thickness. No spalling was observed on any of the test panels. TNO consider 1. ALDRIAN, W., MELBYE, T. & DIMMOCK, R. a temperature of 225ºC as the most onerous 2000. "Wet sprayed concrete – maximum permissible interface temperature Achievements and further work"; Felsbau requirement to date. Publication. Vol 18, No.6 Novr 2000. Pp16- 23.
CONCLUSIONS 2. DIMMOCK, R. & GARSHOL, K.F. 2002. To achieve durable sprayed concrete linings, "Robotic application of high performance thermal barriers in tunnel linings"; Concrete the development of the concrete mixture journal published by the Concrete Society, proportions is but one facet that needs to be UK. April 2002, Vol 36, No4, pp12-13. accomplished. The production of durable sprayed concrete is significantly reliant on human skills 3. EFNARC. 1996. The European Specification for sprayed concrete. Published by EFNARC, during spraying and on equipment that is fit for Hampshire, UK. the purpose. The designer also has a key role to play. The 4. MELBYE, T.A., DIMMOCK, R. & GARSHOL, K.F. 2001. Sprayed Concrete for Rock important issues in this case are to understand Support. 9th edition. Published by MBT the sprayed concrete application process and not UGC International. Switzerland, December to over-specify material properties. The key to 2001. achieving durability is through "buildable" by 5. KORTEKAAS & VAN DEN BERG 2001. keeping details as simple as possible. "Determination of the contribution of a Wet-mix sprayed concrete applied using coating MEYCOFix Fireshield 1350 to the fire resistance of tunnels". Published by modern, high performance, environmentally safe TNO Building and Concrete Research, admixtures and equipment equips the tunnel Centre for Fire Research. Report No 2001- industry with an economical tool to construct CVB-R03026, March 2001. permanent, durable single-shell linings. The
86 The Concrete Centre has been established to champion the benefits of concrete construction. Formed by the major UK cement and concrete companies, with the aim of helping designers and constructors to get the best out of this unique material, The Concrete Centre provides a vital new resource to the £5 billion concrete sector.
Working closely with industry partners, specifiers, contractors, clients and the Government, The Concrete Centre’s prime goals are to communicate the benefits of concrete across all sectors and to make its business case in new and robust ways.
For more information on The Concrete Centre, and to find out how it can help you to better design and construct in concrete, visit www.concretecentre.com or call 01344 762986
INFORMATION • EDUCATION • TRAINING • RESEARCH MANAGEMENT • MARKET DEVELOPMENT • PRODUCT INNOVATION THE INSTITUTE OF CONCRETE TECHNOLOGY
ADVANCED CONCRETE TECHNOLOGY DIPLOMA COURSES The ACT Diploma is the principal entry qualification for Membership of the Institute. Residential courses are held in the UK, Ireland and South Africa.
For further details contact: ICT Secretariat, P.O. Box 7827, Crowthorne, Berks. RG45 6FR Tel: +44(0)1344 752 096 E-mail [email protected]
A web-based course is due to be available from June 2004. For details, contact Dr J B Newman, Imperial College, London, SW7 2BU E-mail: [email protected]
The OSCRETE • range of admixtures for concrete and mortar
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THE INSTITUTE OF MG Associates CONCRETE TECHNOLOGY WOULD LIKE TO THANK ALL THE COMPANIES MG Associates is a small consultancy dealing AND ORGANISATIONS with the investigation and testing of buildings and structures, advice and project management WHO HAVE ADVERTISED and supervision of repairs. IN THIS YEARBOOK Non Destructive Testing Forensic Investigations PLEASE SUPPORT THEM. Laboratory Testing Fire Damage Appraisal Abseiling Surveys DATE FOR YOUR DIARY Core Drilling and sampling Training in Concrete, Inspection and Repair. THE ICT 2004 CONVENTION MG Associates Construction Consultancy Ltd. will be held at the 11 The Quadrant, Manor Park Crescent Edgware, Middlesex. HA8 7LU RENAISSANCE HOTEL Tel: +44 (0)20 8381 1429 DERBY/NOTTINGHAM Fax: +44 (0)20 8381 1425 E-Mail: [email protected] ON 22-24 MARCH 2004 Web: www.concrete-testing.com Ready Mixed Concrete Which third party scheme will you rely on for EN206-1 certification? One which has the experience considered essential by the European Standards organisation? * * An essential element in maintaining the confidence and credibility of the concrete family system is that the system, the relationship between members of the family and the functioning of the system are approved and regularly audited by a third party certification body that has expertise in concrete technology and production." (CEN REPORT CR 13901 – ‘The use of the concept of concrete families for the production and conformity control of concrete’) • QSRMC is the only UK certification body for ready mixed concrete which has a dedicated full time team of field assessors with a combined experience of more than 100 man-years with the scheme.
One designed specifically to meet the requirements of concrete producers, purchasers and specifiers?
• The QSRMC Quality and Product Conformity Regulations were written by concrete specifiers, purchasers and producers to bring together industry best practice and customer requirements in a scheme designed to meet the needs of all sectors of the construction industry.
Demonstrate product conformity with the most widely specified and the only UK Certification Body dedicated to the supply of ready mixed concrete
To find out more about the benefits of QSRMC certification contact:
The Quality Scheme for Ready Mixed Concrete, 3 High Street, Hampton. TW12 2SQ Telephone: 020 8941 0273. Facsimile: 020 8979 4558. E-mail: [email protected]
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Our daily challenge is to push the limits to find unusual solutions. We do it by applying our innovation potential and our understanding of the market. Using this combination, we get more out of concrete. We are constantly creating new and better properties for concrete, expanding its field of application. That means added value for everyone in the project.
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ADVANCED CONCRETE TECHNOLOGY DIPLOMA: SUMMARIES OF PROJECT REPORTS 2002
The project reports are an integral and important part of the ACT Diploma. The purpose of the projects is to show that the candidates can think about a topic or problem in a logical and disciplined way. The project normally spans some six months. Significant advances can be made and several of the projects have evolved into research programmes in their own right. Summaries of a selection of projects submitted during the 2002 - 2003 course are given in the following pages.
PROJECT TITLE: AUTHOR:
NON-DESTRUCTIVE TESTING FOR CRACKING AND DE-BONDING Jannes Bester OF SURFACE REPAIRS ON CONCRETE STRUCTURES
THE EFFECT THAT MANUFACTURED SAND AND COREX SLAG HAS ON THE Jaco Cokart WORKABILITY, WATER DEMAND, COMPRESSIVE STRENGTH AND THE COST OF READYMIX CONCRETE
THE INFLUENCE OF SAND GRADING ON THE AIR VOID SYSTEM OF Harry Corporaal FRESH MASONRY MORTAR
THE SENSITIVITY OF THE MICRO-CONCRETE HALF-SLUMP TEST, Santie Gouws AS INFLUENCED BY CEMENT CHARACTERISTICS
THE SALT SCALING RESISTANCE OF SELF-COMPACTING CONCRETE Esa Heikkilä
INFLUENCE OF TEST AGGREGATE ON THE COMPRESSIVE STRENGTH OF Kevin Macleod PORTLAND AND PORTLAND FLYASH CEMENTS
ALKALI-SILICA REACTION IN KWA ZULU NATAL Wayne Milligan
THE EFFECTS OF FINER GROUND SLAG ON WORKABILITY Robin Page
A PRELIMINARY INVESTIGATION INTO THE EFFECT OF DRUM COLOUR Zoë Perks ON CERTAIN FRESH AND HARDENED PROPERTIES OF CONCRETE
THE FEASIBILITY OF USING RHEOLOGICAL TEST METHODS TO DEVELOP Christopher Rigby MIX DESIGNS FOR FLOWING SELF-COMPACTING CONCRETE
SELF-COMPACTING CONCRETE AT REDUCED LEVELS OF POWDER CONTENT Andrew Rogers
THE INFLUENCE OF BINDER TYPE ON EARLY AGE CRACKING IN CONCRETE Ebrahim Yusuf Seedat
THE EVALUATION OF NEW GENERATION SOUTH AFRICAN CEMENT Clive Sofianos EXTENDERS: A CONTRACTORS VIEWPOINT
BOND STRENGTH ACROSS JOINTS IN A ROLLER COMPACTED Yvette Staples CONCRETE DAM
POTENTIAL USE OF SANDSTONE AND/OR NATURAL SAND AS SOURCE OF Tente Tente FINE AGGREGATES FOR CONCRETE PRODUCTION AT FUTURE MASHAI DAM
A full list of earlier ACT projects, dating back to 1971 when the individual project was introduced as a requirement for the Advanced Concrete Technology Diploma examination, was published in the 2000 - 2001 edition of the ICT yearbook.
Copies of the reports (except those that are confidential) are held in the Concrete Information Ltd (CIL) Library and these can be made available on loan. Subscribers to the CIL’s information service, Concquest, may obtain copies on loan, free of charge. Requests should be addressed to: Concrete Information Ltd, Century House, Telford Avenue, Crowthorne, Berkshire RG45 6YS.
ICT members may address their requests to: The Executive Officer, Institute of Concrete Technology, P.O. Box 7827, Crowthorne, Berkshire RG45 6FR. Copies can then be obtained from CIL free of charge.
87 NON-DESTRUCTIVE TESTING FOR THE EFFECT THAT MANUFACTURED RACKING AND DE-BONDING SAND AND COREX SLAG HAS ON THE OF SURFACE REPAIRS ON CONCRETE WORKABILITY, WATER DEMAND, STRUCTURES COMPRESSIVE STRENGTH AND THE By: Jannes Bester COST OF READYMIX CONCRETE By: Jaco Cokart SUMMARY This project was concerned with repairs to SUMMARY concrete and was aimed at determining whether In South Africa a shortage of good quality the incidents of follow-up repairs could be avoided. sand, stockpiling of crusher fines and concerns The problems associated with concrete repair at about alkali silica reaction have led ready mix the Rand Afrikaans University (RAU) stimulated the companies to consider ways of incorporating the work. Inadequate concrete cover (12 mm against a required 25 mm) was regarded as the cause of crusher fines into their mixes and finding new deterioration. ways to combat ASR. In this investigation the It would seem that concrete repair is a very performance of concrete mixes containing crusher competitive market with low profit margins. As a sand and Corex Slagment were evaluated against result there is a reluctance to perform re-hash cost and durability requirements. The parameters repairs and therefore some means of determining investigated included: workability, water demand, the quality and effectiveness of patch repairs to compressive strength and cost. The concretes begin with is desirable. investigated had a water/binder ratio of 0.70 and Two techniques were used namely: a constant water content of 180 litres. • Ultrasonic pulse velocity - (TICO) It was found that the fines content, quantity • Rebound Hammer (DIGI - Schmidt 2). and shape play a large role in determining water The two techniques were used together with content, workability, density and strength. When ultrasonic pulse velocity determining cracking and fines (<0.075mm) are increased above set limits debonding and the rebound hammer to determine uniformity of the repair. there is a detrimental effect on water content that necessitates an increase in cementitious The background to concrete deterioration is given, together with details on both techniques. content leading to increased costs and, for 70% Particular reference is made to Rilem Publication: slag mixes, increased bleeding. For 70% slag Materials and Structures, 1993, pp43-49. mixes longer curing periods should be used. The aims of the laboratory work were: On the other hand, if fines are increased from • To determine the effect of concrete strength 5.70% to 11.20% the density of the concrete on pulse velocity increases from 2450kg/m3 to 2550kg/m3. This • To determine the effect of moisture content could mean the difference between passing or on pulse velocity failing on compressive strength and/or durability • To determine the effect of path length on pulse velocity indices. • To determine the effect of reinforcement on Even though the best densities and strength pulse velocity performance were achieved with the highest • To determine the effect of reinforcement diameter on pulse velocity amount of slag replacement, the achieved setting • To establish the conditions of debonding of times and demand by contractors mean that the the repair material from the substrate slag replacement should be kept between 20% • To establish the cause of cracking of the and 50%. repair material. Overall it was found that concrete stability: It was found that cracking of the repair was not workability, surface finishing, permeability and normally preceded by debonding. The ultrasonic pulse velocity method did indicate when hydration compressive strength can be increased by was poor. inclusion of optimal amount of fines in the The laboratory work was not extended to concrete. evaluate actual fuelled repair situations so it is not possible to judge the potential capability of the two techniques when used together in a field application. Five appendices are given covering: • Corrosion inhibiting reinforcement primer • Reprofiling polymer modified mortar • Rapid setting mortar • Digi-Schmidt 2 • TICO UPV equipment.
88 THE INFLUENCE OF SAND GRADING ON THE SENSITIVITY OF THE MICRO- THE AIR VOID SYSTEM OF FRESH CONCRETE HALF-SLUMP TEST, AS MASONRY MORTAR INFLUENCED BY CEMENT By: Harry Corporaal CHARACTERISTICS By: Santie Gouws SUMMARY SUMMARY Masonry mortar is important in contributing to strength as well as durability. The workability of The objective of this work was to establish a masonry mortar is equally important if the method of determining the effect of a number of bricklayer is to make good masonry brickwork. parameters on the workability of concrete Good workability is achieved by a combination of without having to use concrete as the test mix design, flow characteristics and a stable air material. Such tests are regarded as costly. void system. A simple ‘micro-concrete’ or mortar was used The air content in masonry mortar has always with a half-slump cone test. A link between the been an important parameter because the air mini-slump test and changes to concrete gives the mortar its cohesiveness and consistency. composition was determined. The use of air-entrainment means that less water Such changes as cement fineness, gypsum is needed for the same flow capability. Less water content and its chemical form, together with free leads to better stability in that there is less lime content was studied. bleeding. In order to limit the number of samples to be Up to now only total air content has been tested, two levels of the above variables were measured. With the availability of new measuring used in the programme. A half-factorial techniques such as the Air Void Analyser it experimental design was used. becomes possible to explore the complete air void The outcome can be expressed as: system of the mortar. The size of the formed air • the micro-concrete half-slump shows good bubbles becomes pertinent because the more potential to be used as a tool to predict smaller air bubbles (less than 300 microns) acting behaviour of cement in concrete like fine sand will give a better workability of the • the micro-concrete half-slump test mortar. performed on a modified EN 196 mortar In this project the influence of sand grading on shows good potential to be used as a the air void system in masonry mortar has been control test in cement factory laboratories, studied. Three sand gradings are defined as – and gives a better indication of cement low, mean and high. The difference between performance in fresh concrete than other these gradings is the amount of fines (less than routine cement control tests used in these 250 microns) in the sand. It can be concluded laboratories that the sand grading does have a significant • the micro-concrete half-slump test should influence on the resulting air void system in only be used to assess the performance of masonry mortar. That categorised as mean cement in well-proportioned concrete produces the most small air bubbles, which result mixes. Harsh, stony mixes do not give in a good workability for the mortar. More or less good correlation with concrete slump fines in the sand (low or high) leads to fewer • the micro-concrete half-slump test gives a small air bubbles. good indication of slump retention A knowledge of the air void system rather • concrete slump of cement from the same than total air content may be a better indicator of source is only significantly affected by performance. The Air Void Analyser would allow changing the gypsum from dihydrate to such a measure at early ages and permits the hemi-hydrate. assessment of air-entrainer efficiency. Changes in specific surface area of cement and Optimising mix design and in particular fines increasing temperature up to 70˚C as well as addition, content and shape, including cement increasing the SO3 content up to 3% and free content is desirable. lime to 2.7% had no significant effect. Other factors such as type of mixer, mixing It is recommended that repeatability and time and temperature all affect the air void reproducability tests be performed together with system. factory produced cements using a wider range of slump rather than the 25-85 mm used in this work.
89 THE SALT SCALING RESISTANCE OF INFLUENCE OF TEST AGGREGATE ON SELF-COMPACTING CONCRETE THE COMPRESSIVE STRENGTH OF By: Esa Heikkilä PORTLAND AND PORTLAND FLYASH CEMENTS SUMMARY By: Kevin Macleod The aim of this work was to establish the role of air entrainment in self-compacting concrete SUMMARY and its effectiveness in resisting freeze-thaw This investigation was prompted by the attack. unexpectedly high compressive strengths given by The durability of concrete against repeated Portland flyash cements when tested in laboratory freezing and thawing cycles is one of the major gravel concrete. These results were not factors affecting the durability and service life of consistent with feedback from the field an outdoors concrete structure in Finland and concerning the relative performance of plain Portland and Portland flyash cement. other northern countries. The project investigated the 28-day To make freeze-thaw durable concrete, air compressive strength achieved in laboratory entraining admixtures are used. Their pedigree concretes and mortar made with 3 Portland has been well established in normal concretes. cements and 3 Portland flyash cements from the However, their role in self-compacting concrete is same 3 cement plants. The concrete mixes less clear since this concept is also relatively new. contained granite, flint gravel, and quartzitic Self-compacting concrete moves and compacts gravel aggregate. The strengths achieved in EN without vibration, under its own weight. The self- 196 mortar were also tested. compactivity is achieved using polycarboxylate- It was found that the main factor affecting the type superplasticisers in conjunction with viscosity strength ranking of the cements is the amount of modifying agents based on polymerized entrained/entrapped air within the concrete melamine sulphate. In addition, a high fines mixes. Therefore concrete manufacturers who use materials content is used. The superplasticiser and aggregates that have a tendency to retain air workability of concrete have a large effect on the should find that Portland flyash cement performs stable air entrainment of concrete. relatively well compared with PC. Concrete Three different mixes were tested containing manufacturers who use aggregate that does not granulated blastfurnace slag, limestone filler and have a tendency to retain air within the mix microsilica. The cement used was rapid hardening should find relatively poorer performance with CEM II/A-LL 42.5R. The aggregate was granite- Portland flyash cement. based sand and gravel covering the range from A key aspect affecting the amount of filler to 16 mm. entrained air in the gravel concrete is the large In this study four different self-compacting quantity of the sand particles in the size range concrete mixes were tested. It was found that air- 300 – 600 μm. entrainment has the greatest effect on the salt- scaling resistance of self-compacting concrete. Air entrained self-compacting concrete with slag, limestone filler and micro-silica additions will resist against surface scaling in salt water. The effect of air content is similar to the effect on concrete with normal workability. However, the loss of entrained air is greater in self- compacting concrete than in normal workability mixes. This effect has to be taken into account when measuring the air content of air-entrained SCC at the mixing plant. Making durable self-compacting concrete seems to be a prospect when using slag, limestone filler or silica-fume additions together with an air-entraining admixture.
90 ALKALI-SILICA REACTION IN THE INFLUENCE OF SAND GRADING KWA ZULU NATAL ON THE AIR VOID SYSTEM OF FRESH By: Wayne Milligan MASONRY MORTAR By: Robin Page SUMMARY The aim of this Project was to compile a SUMMARY comprehensive survey of the alkali reactivity of In South Africa, the fineness of ground aggregates from commercial quarries in Kwa Zulu granulated blastfurnace slag (GGBS or SL) is Natal by petrographic examination and an typically 3600 cm2/g (Blaine). The producers are accelerated mortar test programme to identify the now looking at finer ground slags, 5000 cm2/g. potentially reactive aggregates. Once these had to improve the strength performance. been identified, to ascertain their alkali reactivity In this investigation, the strengths of concrete with two cements (CEMI 42.5N) with different mixes of similar workability made with various alkali levels, and then determine at what level of binder contents and binder proportions were ground granulated blastfurnace slag (GGBS) compared. Various methods of measuring replacement this reaction could be controlled. workability were used, including rheology testing. In the initial survey 23 aggregates were tested, Four binder types were investigated; Portland 22 local and a known reactive aggregate from the Cement (CEMI), GGBS (3600), GGBS (5000) and Cape Province (hornfels). The test method used pulverized fuel ash (PFA). To eliminate the effects was the accelerated mortar bar method (SABS of aggregates on workability, it was decided to 1245:1994) in which mortar bars are stored in 1N use only binder pastes, where possible, for NaOH at 80˚C. Initial tests used a CEMI 42.5 testing. The blending proportions adopted are cement with a Na2Oeq of 0.52%. These tests common ratios used in practice. The PFA was were repeated on selected aggregates using a included in the programme to provide another CEMI 42.5N cement with a Na2Oeq of 0.86% and reference and an indication of the sensitivity of with replacement levels of 15, 20, 30 and 50% the test methods. slag. The comparative tests carried out on the It was found that alkali-silica reaction could be binder pastes were: a potential problem in Kwa Zulu Natal with nine of the aggregates being classified as "slowly • Standard Consistency reactive" and five being classified as • Flow Table "deleteriously reactive or rapidly expansive". • Viscosity over Time (Single Speed) The adverse effect of the increase of the alkali • Rheology of Mortar - Variable Speed content of the cement from 0.52% to 0.86% Viscometer.
Na2Oeq was confirmed although the increase in The results showed that the use of GGBS expansion was relatively small. (3600) improved the workability of the mix, but The addition of ground granulated not as much as PFA. However, the finer GGBS blastfurnace slag significantly reduced the (5000) resulted in a similar or worse workability reaction and at the 30% replacement the compared with CEMI mixes. expansion cased by alkali-silica reaction fell below The variation in water demand for the the 0.1% which is accepted as innocuous. concrete mixes correlated well with the yield stress of the relevant pastes (determined with the variable speed viscometer). A large percentage drop in yield stress (47%) for the PFA pastes related to a high water reduction (18 litre). On the other hand the percentage change in yield stresses with the GGBS pastes were a lot less (10%), whilst the yield stress and the viscosity of the pastes with the finer ground slag increased when compared with the CEMI mix. Therefore, overall, it is concluded that the increased water requirement will have a negative impact on the initial idea to improve the early strengths of concrete by using a finer ground slag.
91 A PRELIMINARY INVESTIGATION INTO THE FEASIBILITY OF USING THE EFFECT OF DRUM COLOUR ON RHEOLOGICAL TEST METHODS TO CERTAIN FRESH AND HARDENED DEVELOP MIX DESIGNS FOR FLOWING PROPERTIES OF CONCRETE SELF-COMPACTING CONCRETE By: Zoë Perks By: Christopher Rigby
SUMMARY SUMMARY Temperature rise during mixing and making This project consisted of: can affect compressive strength at later stages • A review of literature on rheology, mortar, and also cause slump loss. Long journey times self-compacting concrete and admixtures and high ambient temperatures can exacerbate • An investigation into admixtures these effects. However, there appears to be no developed by the RMC Group for use in definite literature quantifying the effect of drum self-compacting concrete colour on fresh and hardened concrete properties. • An investigation of the relation between The work concentrated on what effect dark fine mortar viscometry tests and concrete drum colour has on the temperature within the rheology measurements. drum and any resulting changes of the concrete. Seven different admixtures were assessed using A water reducing admixture was used viscometry and workability tests and the most throughout the test. suitable admixture and dosage for use in the Durability assessment was also incorporated RMC branded self-compacting concrete into the programme, covering oxygen established. Using this admixture and dosage, a permeability, water absorbtivity and chloride comparison was made between the Haake VT500 conductivity. viscometer and the Tattersall two point Good correlation was obtained between workability machine. concrete mixing temperature and differences in It was found that mortar trials do not predict compressive strengths. The effect on durability the behaviour of fresh concrete well. However, it parameters was less conclusive. was possible to confirm the optimum dosage Changing drum colour to white could not be level from the viscometry results. This was justified at this stage. confirmed by the Tattersall machine, which gave good correlation with the viscometry data. The data from both tests show that the mortar and concrete conform to the Casson and Bingham mathematical models. Overall the project showed that proposed mix designs in flowing, self-compacting concrete can be assessed using fine mortar tests to predict plastic viscosity.
92 SELF-COMPACTING CONCRETE AT THE INFLUENCE OF BINDER TYPE ON REDUCED LEVELS OF POWDER CONTENT EARLY AGE CRACKING IN CONCRETE By: Andrew Rogers By: Ebrahim Yusuf Seedat
SUMMARY SUMMARY The potential benefits in using self- This investigation explores the influence of compacting concrete (SCC) are many. Recent binder composition on early age cracking in developments in admixtures have resulted in a concrete, with particular reference to conditions in potential for reducing the high powder contents commonly regarded as necessary for satisfactory the Middle East. It also investigates the effect of SCC. This report examines that potential by the different binders on the engineering properties assessing changes in SCC as powder content is of concrete made at elevated temperatures. reduced and admixtures are used to maintain the Four binder compositions were assessed: OPC desired properties. SCC is characterised by: (100%), OPC/GGBS (50:50), OPC/FA (70:30) and • filling ability – the property of flow permitting OPS/FA/SP (70:25:5), with total cementitious the complete filling of spaces within contents of 380kg/m3. Concrete specimens were formwork by the concrete’s own weight • passing ability – flow through gaps between cast and temperature-matched cured to a profile reinforcement and formwork without previously determined for these mixes. blocking Compressive and tensile strengths, shrinkage and • resistance to segregation – retaining uniform expansion were measured. composition during the placing stage. The results confirmed the beneficial effects of An impediment to using the SCC is the added cement extenders on long term strength gain and cost and that in turn is due to the higher cement reduced temperature rise. The FA and FA/SP mixes contents used and added admixture costs relating to higher cement contents. had higher early tensile strengths and lower early A series of trials have been carried out at the shrinkage strains, suggesting that that these mixes RMC Readymix Central Laboratory in Chertsey to would be less prone to early age cracking. The investigate the feasibility of producing SCC with GGBS mixes had moderate shrinkage values but characteristic compressive strengths in the range low early age tensile strengths, indicating a lower 30 MPa to 50 MPa. The work involved the use of ability to withstand early age thermal stresses. The aggregates representative of those readily OPC mixes had higher early age strengths but the available in the UK with partial cement replacement materials, limestone flour and PFA. higher temperatures reached by these mixes An iterative approach to gradually reducing produced lower long term strengths. These high powder content was adopted, initially without early strengths and high modulus of elasticity are viscosity modifying admixture and then repeated likely to result in temperature-related cracking. with them. It was found that: • production of true self-compacting concrete was possible using gravel and limestone aggregates incorporating partial replacement with limestone flour • incorporation of a viscosity modifying agent as well as a superplasticiser was essential at the lower powder contents, in order to stabilise the concrete, to which additional water was added • the sensitivity of the lower powder content mixes to small changes in water content is likely to give difficulties. Full-scale conditions cannot exercise the same level of control used in these trials. For practical reasons therefore target powder contents should be no lower than 400 kg/m2 unless close control of aggregate moisture contents can be guaranteed • the use of PFA as cement replacement caused ‘frothing’ of the fresh concrete • formwork design needs consideration but design on full hydrostatic head is thought to be pessimistic.
Trials showed that satisfactory SCC could indeed be produced in the laboratory at total powder contents of 350-400 kg/m3.
93 THE EVALUATION OF NEW GENERATION BOND STRENGTH ACROSS JOINTS IN A SOUTH AFRICAN CEMENT EXTENDERS: ROLLER COMPACTED CONCRETE DAM A CONTRACTORS VIEWPOINT By: Yvette Staples By: Clive Sofianos SUMMARY SUMMARY This investigation sets out to provide The effects on concrete of the new generation conclusive evidence of the most effective method cement extenders available in South Africa were of preparing the surfaces formed at cold investigated. horizontal joints in Roller Compacted Concrete "Fly Ash", "Superpozz", "Condensed Silica (RCC) dams. Roller compaction became accepted Fume" and "Ground Granulated Corex Slag" as a sound and cost-effective method of dam blends with a standard CEMI; 42.5 cement and a construction during the latter half of the 20th water reducing admixture were assessed using century. An ongoing debate, however, has been mixes typically specified for aggressive how to prepare the horizontal surfaces formed at environments. cold joints to ensure adequate bond across the Both plastic and hardened properties were joints. measured in terms of practicality of batching and Five test scenarios: no preparation, severe compacting as well as the short to medium term engineering properties. Slump retention, setting greencutting, greencutting to laitance removal time and floor finishing (floating and cutting) and only, mechanical brooming and sandblasting, all the effects of curing were evaluated. commonly-used methods of surface preparation, The assessment was carried out both under were investigated on a RCC dam currently under laboratory conditions and in the field for practical construction. Each of the scenarios tested were applications. also modelled in cubes prepared in the site This investigation has shown that there are laboratory. Cores were drilled from the in situ test definite technical and economic benefits in using sections as well as from the laboratory cubes. these extenders. These were used to compare the effectiveness of Fly ash can be used at large replacement levels each type of surface preparation by subjecting (up to 65% in dam construction), and still produce the samples to direct tensile tests and water sound, fit-for-purpose concrete. It is practical to permeability tests. work with and the relatively large replacement The investigation showed that some form of levels are easy to measure, batch and mix into the surface preparation definitely improves the bond fresh concrete. strength across horizontal cold joints in RCC Condensed silica fume is expensive to transport dams. The smooth failure plane across the joint over a long distances because of its relatively low seen in the tensile tests of in situ cores supports bulk density and requires a greater degree of this conclusion. This finding supports a recurring control regarding weighing, batching and observation in the literature study that laitance thorough mixing to ensure a homogeneous end remaining on the surface has a weakening effect product. The engineering benefits obtained using on the bond. However, the method of surface blends of condensed silica fume are well preparation applied does not have a significant documented, but are obtainable at a premium influence on the performance of the joint and the price. choice of method can safely be left to the Ground granulated corex slag is practical to contractor. work with and has all round technical benefit in concrete, particularly with regard to compressive strength development. However, it is important to ensure that minimum cementitious contents are adopted where durable concrete is required. Superpozz is used at small replacement levels (between 5 and 15%), which requires a greater degree of control. It is likely that superpozz will be used for special applications and mining projects, competing with condensed silica fume. Overall, this investigation highlights the importance of selecting an extender, not only on its technical benefits, but also on its merits with regard to practicality of storing, weighing, mixing, placing and finishing. Proper curing techniques cannot be overemphasised.
94 POTENTIAL USE OF SANDSTONE AND/OR NATURAL SAND AS SOURCE OF FINE AGGREGATES FOR CONCRETE PRODUCTION AT FUTURE MASHAI DAM By: Tente Tente
SUMMARY The work concerned obtaining a suitable sand for concrete production. In particular with determining whether replacing crushed basalt by crushed sandstone was feasible in order to give economic benefit on the Mashai Dam project (phase 2 of the Lesotho Highland Water Project). The concrete specification was used as a guideline in judging the performance of concrete produced from these sands. Acceptance criteria for concrete aggregates addressed 14 characteristics. The only research variables were the type and source of fine aggregates. A total of 11 trial mixes were cast and their compliance with the specification requirements for fresh properties were assessed. Out of 11 mixes, 8 were tested for compliance with hardened concrete requirements. The results were satisfactory and indicated that substantial savings could be made by eliminating the need to crush basalt to sizes passing a 7 mm sieve. Crushing of the sandstone could also be achieved using a simple driven roller and passing through the requisite sieves. It was concluded from the performance of the concrete produced from both crushed sandstone and natural aggregates that, despite their shortcomings, these sands have a strong potential for replacing crushed basalt sand during construction of the Mashai Dam with substantial benefits to the overall project. Further work is recommended on also using these derived sands as fine fillers.
95 96 ICT YEARBOOK 2003-2004 ICT RELATED INSTITUTIONS & ORGANISATIONS
ASSOCIATION OF CONCRETE ADVISORY SERVICE INSTITUTION OF HIGHWAYS CONSULTING ENGINEERS Century House & TRANSPORTATION EDITORIAL COMMITTEE Alliance House Telford Avenue 6 Endsleigh Street 12 Caxton Street Crowthorne London WC1H 0DZ London SW1H 0QL Berkshire RG45 6YS Tel: 020 7387 2525 Professor Peter C. Hewlett (Chairman) Tel: 020 7222 6557 Tel: 01344 466007 www.iht.org www.acenet.co.uk www.concrete.org.uk BRITISH BOARD OF AGRÉMENT INSTITUTION OF & UNIVERSITY OF DUNDEE ASSOCIATION OF INDUSTRIAL CONCRETE BRIDGE ROYAL ENGINEERS FLOORING CONTRACTORS DEVELOPMENT GROUP Brompton Barracks 33 Oxford Street Century House Chatham Peter C. Oldham Leamington Spa Telford Avenue Kent ME4 4UG CHRISTEYNS UK LIMITED CV32 4RA Crowthorne Tel: 01634 842669 Tel: 01926 833 633 Berks RG45 6YS www.acifc.org.uk Tel: 01344 762676 INSTITUTION OF www.cbdg.org.uk STRUCTURAL ENGINEERS Dr. Philip J. Nixon ASSOCIATION OF LIGHTWEIGHT 11 Upper Belgrave Street BUILDING RESEARCH ESTABLISHMENT AGGREGATE MANUFACTURERS CONCRETE INFORMATION LTD London SW1X 8BH Wellington St Telford Avenue Tel: 020 7235 4535 Ripley Crowthorne www.istructe.org.uk Graham Taylor Derbyshire DE5 3DZ Berks RG45 6YS INSTITUTE OF CONCRETE TECHNOLOGY Tel: 01773 746111 Tel: 01344 725700 INTERPAVE www.concrete-info.com Concrete Block Paving Association BRE (BUILDING RESEARCH 60 Charles Street ESTABLISHMENT) LTD Laurence E. Perkis CONCRETE REPAIR ASSOCIATION Leicester LE1 1FB Bucknalls Lane Association House Tel: 0116 253 6161 INITIAL CONTACTS Garston 99 West St www.paving.org.uk Watford WD25 9XX Farnham Tel: 01923 664000 Surrey GU9 7EN MORTAR INDUSTRY ASSOCIATION www.bre.co.uk Tel: 01252 739145 156 Buckingham Palace Road www.concreterepair.org.uk London SW1W 9TR BRITISH BOARD OF AGRÉMENT Tel: 020 7730 8194 P.O.Box 195 THE CONCRETE CENTRE www.mortar.org.uk Bucknalls Lane Century House Garston Telford Avenue QSRMC Watford Crowthorne Quality Scheme for Ready Herts WD25 9BA Berkshire RG45 6YS Mixed Concrete Tel: 01923 665300 Tel: 01344 762676 3 High Street www.bbacerts.co.uk www.concretecentre.com Hampton Middlesex TW12 2SQ BRITISH CEMENT ASSOCIATION THE CONCRETE SOCIETY Tel: 020 8941 0273 Telford Avenue Century House www.qsrmc.co.uk Crowthorne Telford Avenue Berks RG45 6YS Crowthorne QUARRY PRODUCTS ASSOCIATION Tel: 01344 762676 Berkshire RG45 6YS 156 Buckingham Palace Road www.bca.org.uk Tel: 01344 466007 London SW1W 9TR www.concrete.org.uk Tel: 020 7730 8194 BRITISH PRECAST www.qpa.org CONCRETE FEDERATION CIRIA 60 Charles Street Construction Industry Research RIBA Leicester LE1 1FB & Information Association Royal Institute of British Architects Tel: 0116 253 6161 6 Storey's Gate 66 Portland Place www.britishprecast.org.uk Westminster London W1B 1AD London SW1P 3AU Tel: 020 7580 5533 BSI STANDARDS Tel: 020 7222 8891 www.architecture.com British Standards House www.ciria.org.uk 389 Chiswick High Road SOCIETY OF CHEMICAL INDUSTRY London W4 4AL CORROSION PREVENTION 14/15 Belgrave Square Tel: 020 8996 9000 ASSOCIATION London SW1X 8PS www.bsi.org.uk Association House Tel: 020 7598 1500 99 West St www.sci.mond.org BRITPAVE Farnham Professional Affiliate UNITED KINGDOM British In-Situ Concrete Surrey GU9 7EN ACCREDITATION SERVICE Paving Association Tel: 01252 739145 21-47 High Street Century House www.corrosionprevention.org.uk Telford Avenue Feltham Crowthorne INSTITUTE OF CORROSION Middlesex TW13 4UN Published by: Berks RG45 6YS Corrosion House Tel: 020 8917 8400 www.ukas.org.uk THE INSTITUTE OF Tel: 01344 725731 Vimy Court www.britpave.org.uk Leighton Buzzard UNITED KINGDOM CONCRETE TECHNOLOGY Beds LU7 1FG CAST STONE ASSOCIATION P.O.Box 7827 CEMENT ADMIXTURES ASSOCIATION Tel: 01525 851771 Century House Crowthorne 38a Tilehouse Green Lane www.icorr.org Knowle Telford Avenue Berks RG45 6FR West Midlands INSTITUTE OF MATERIALS Crowthorne Tel/Fax: 01344 752096 B93 9EY MINERALS & MINING Berks RG45 6YS Email: [email protected] Tel: 01564 776362 1 Carlton House Terrace Tel: 01344 762676 www.ukcsa.co.uk Website: www.ictech.org London SW1Y 5DB CEMENTITIOUS SLAG Tel: 020 7451 7300 UNITED KINGDOM MAKERS ASSOCIATION www.materials.org.uk Croudace House QUALITY ASH ASSOCIATION Rights reserved. No part of this publication may Goldstone Road INSTITUTION OF CIVIL ENGINEERS Regent House be reproduced or transmitted in any form Caterham One Great George Street Bath Avenue without the prior written consent of the Surrey CR3 6XQ London SW1P 3AA Wolverhampton publisher. The comments expressed in this Tel: 01883 331071 Tel: 020 7222 7722 WV1 4EG publication are those of the Author and not Tel: 01902 576 586 necessarily those of the ICT. www.ukcsma.co.uk www.ice.org.uk www.ukqaa.org.uk
97 THE ICT The The Institute of Concrete Technology was formed in 1972 from the Association of Concrete Technologists. Full membership is open to all those INSTITUTE OF who have obtained the Diploma in Advanced Concrete Technology. The Institute is internationally recognised and the Diploma has world-wide CONCRETE TECHNOLOGY acceptance as the leading qualification in concrete technology. The Institute sets high educational standards and requires its members to abide by a Code of Professional Conduct, thus enhancing the profession of concrete technology. The Institute is a Professional Affiliate body of the UK Engineering Council.
AIMS The Institute aims to promote concrete technology as a recognised engineering discipline and to consolidate the professional status of practising concrete technologists.
PROFESSIONAL ACTIVITIES It is the Institute's policy to stimulate research and encourage the publication of findings and to promote communication between academic and commercial organisations. The ICT Annual Convention includes a Technical Symposium on a subject of topical interest and these symposia are well attended both by members and non- members. Many other technical meetings are held. The Institute is represented on a number of committees formulating National and International Standards and dealing with policy matters at the highest level. The Institute is also actively involved in the education and training of personnel in the concrete industry and those entering the profession of concrete technologist. The INSTITUTE OF CONCRETE TECHNOLOGY - Yearbook: 2003-2004 The INSTITUTE OF CONCRETE TECHNOLOGY - Yearbook:
The INSTITUTE OF CONCRETE TECHNOLOGY P.O.BOX 7827, Crowthorne, Berks, RG45 6FR Tel/Fax: (01344) 752096 Email: [email protected] Website: www.ictech.org Yearbook: 2003-2004