aims professional activities - the concrete...
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Yearbook: 2001-2002
CONCRETE TECHNOLOGYINSTITUTE OF
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INSTITUTE OF CONCRETE TECHNOLOGYP.O.BOX 7827, Crowthorne, Berks, RG45 6FR
Tel/Fax: (01344) 752096Email: [email protected]
Website: www.ictech.org
THE ICTThe Institute of Concrete Technology was
formed in 1972 from the Association ofConcrete Technologists. Full membership isopen to all those who have obtained theDiploma in Advanced Concrete Technology.The Institute is internationally recognised andthe Diploma has world-wide acceptance asthe leading qualification in concretetechnology. The Institute sets higheducational standards and requires itsmembers to abide by a Code of ProfessionalConduct, thus enhancing the profession ofconcrete technology. The Institute is aProfessional Affiliate body of the UKEngineering Council.
AIMSThe Institute aims to promote concrete
technology as a recognised engineeringdiscipline and to consolidate the professionalstatus of practising concrete technologists.
PROFESSIONAL ACTIVITIESIt is the Institute's policy to stimulate
research and encourage the publication offindings and to promote communicationbetween academic and commercialorganisations. The ICT Annual Conventionincludes a Technical Symposium on a subject oftopical interest and these symposia are wellattended both by members and non-members. Many other technical meetings areheld. The Institute is represented on a numberof committees formulating National andInternational Standards and dealing with policymatters at the highest level. The Institute isalso actively involved in the education andtraining of personnel in the concrete industryand those entering the profession of concretetechnologist.
ICT RELATED INSTITUTIONS & ORGANISATIONS
ASSOCIATION OF INDUSTRIALFLOORING CONTRACTORS33 Oxford StreetLeamington SpaCV32 4RATel: 01926 833 633www.concrete.org.uk/acifc
ASSOCIATION OFCONSULTING ENGINEERSAlliance House12 Caxton StreetLondon SW1H 0QLTel: 020 7222 6557www.acenet.co.uk
ASSOCIATION OF LIGHTWEIGHTAGGREGATE MANUFACTURERSC/O: East Coast Slag Products LtdStantonScunthorpeN.Lincs DN16 1XYTel: 01724 856444
BRE (BUILDING RESEARCHESTABLISHMENT) LTDBucknalls LaneGarstonWatford WD2 7JRTel: 01923 664000www.bre.co.uk
BRITISH BOARD OF AGRÉMENTP.O.Box 195Bucknalls LaneGarstonWatfordHerts WD25 9BATel: 01923 665341www.bbacerts.co.uk
BRITISH CEMENT ASSOCIATIONTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 762676www.bca.org.uk
BRITISH PRECASTCONCRETE FEDERATION60 Charles StreetLeicester LE1 1FBTel: 0116 253 6161www.britishprecast.org.uk
BSI STANDARDSBritish Standards House389 Chiswick High RoadLondon W4 4ALTel: 020 8996 7000www.bsi.org.uk
BRITPAVEBritish In-Situ ConcretePaving AssociationTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 725731www.britpave.org.uk
CEMENT ADMIXTURESASSOCIATION38a Tilehouse Green LaneKnowleWest MidlandsB93 9EYTel: 01564 776362
CONCRETE ADVISORY SERVICE37 Cowbridge RoadPontyclunNr. CardiffWales CF72 9EBTel: 01443 237210www.concrete.org.uk
CONCRETE BRIDGEDEVELOPMENT GROUPTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 762676www.cbdg.org.uk
CONCRETE REPAIR ASSOCIATIONAssociation House235 Ash RoadAldershotHants GU12 4DDTel: 01252 321302www.concreterepair.org.uk
THE CONCRETE SOCIETYTelford AvenueCrowthorneBerkshireRG45 6YSTel: 01344 466007www.concrete.org.uk
CIRIAConstruction Industry Research
& Information Association6 Storey's GateWestminsterLondon SW1P 3AUTel: 020 7222 8891www.ciria.org.uk
CORROSION PREVENTION ASSOCIATIONAssociation House235 Ash RoadAldershotHants GU12 4DDTel: 01252 321302www.corrosionprevention.org.uk
INSTITUTE OF CORROSION4 Leck HouseLake StreetLeighton BuzzardBeds LU7 7TQTel: 01525 851771www.icorr.demon.uk
INSTITUTION OF CIVILENGINEERSGreat George StreetLondon SW1P 3AATel: 020 7222 7722www.ice.org.uk
INSTITUTION OF HIGHWAYS& TRANSPORTATION6 Endsleigh StreetLondon SW1H 0DZTel: 020 7387 2525www.iht.org
INSTITUTE OF MATERIALS1 Carlton House TerraceLondon SW1Y 5DBTel: 020 7839 4071www.materials.org.uk
INSTITUTION OFROYAL ENGINEERSBrompton BarracksChathamKent ME4 4UGTel: 01634 842669
INSTITUTION OFSTRUCTURAL ENGINEERS11 Upper Belgrave StreetLondon SW1X 8BHTel: 020 7235 4535www.istructe.org.uk
INTERPAVEConcrete Block Paving Association60 Charles StreetLeicester LE1 1FBTel: 0116 253 6161www.paving.org.uk
MORTAR INDUSTRYASSOCIATION156 Buckingham Palace RoadLondonSW1W 9TRTel: 020 7730 8194www.mortar.org.uk
QUARRY PRODUCTSASSOCIATION156 Buckingham Palace RoadLondon SW1W 9TRTel: 020 7730 8194www.qpa.org
QSRMCQuality Scheme for ReadyMixed Concrete3 High StreetHamptonMiddlesex TW12 2SQTel: 020 8941 0273
RIBARoyal Institute of British Architects66 Portland PlaceLondon W1N 4ADTel: 020 7580 5533www.architecture.com
CEMENTITIOUS SLAGMANUFACTURERS ASSOCIATIONCroudace HouseGoldstone RoadCaterhamSurrey CR3 6XQTel: 01883 331071www.ukcsma.co.uk
SOCIETY OF CHEMICALINDUSTRY14/15 Belgrave SquareLondon SW1X 8PSTel: 020 7235 3681www.sci.mond.org
UNITED KINGDOMACCREDITATION SERVICE21-47 High StreetFelthamMiddlesexTel: 020 8917 8400www.ukas.org.uk
UNITED KINGDOM CAST STONE ASSOCIATIONCentury HouseTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 762676www.ukcsa.co.uk
UNITED KINGDOM QUALITY ASH ASSOCIATIONRegent HouseBath AvenueWolverhamptonWV1 4EGTel: 0102 576 586www.ukqaa.org.uk
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ICT YEARBOOK 2001-2002
EDITORIAL COMMITTEE
Professor Peter C. Hewlett (Chairman)BRITISH BOARD OF AGRÉMENT
& UNIVERSITY OF DUNDEE
Peter C. OldhamCHRISTEYNS UK LIMITED
Dr. Bill PriceSANDBERG
Graham TaylorINSTITUTE OF CONCRETE TECHNOLOGY
Laurence E. PerkisINITIAL CONTACTS
Published by:THE INSTITUTE OF
CONCRETE TECHNOLOGYP.O.Box 7827Crowthorne
Berks RG45 6FREmail: [email protected]
Website: www.ictech.org
£50.00
ISSN 1366 - 4824
1
Yearbook: 2001-2002
CONCRETE TECHNOLOGYINSTITUTE OF
The
CONTENTS PAGE
FOREWORD 5By Mike Connell, President, INSTITUTE OF CONCRETE TECHNOLOGY
THE INSTITUTE 6
COUNCIL, OFFICERS AND COMMITTEES 7
FACE TO FACE 9 - 12A personal interview with Jim Wootten
MILESTONES IN THE HISTORY OF CONCRETE TECHNOLOGY. 13 - 23BROOKLANDS SPEED TRACK. By Professor Peter C. Hewlett
ANNUAL CONVENTION SYMPOSIUM: 25 - 106PAPERS PRESENTED 2001
ADVANCED CONCRETE TECHNOLOGY DIPLOMA: 107 - 123SUMMARIES OF PROJECT REPORTS 2000
RELATED INSTITUTIONS & ORGANISATIONS 125
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FOREWORD
gives me great delight once again towelcome members and readers to this,the 6th edition of the ICT Yearbook.
At the time of writing it looks as if thedust is settling after a year of upheaval formany of our members, following the majorreorganisations and mergers of some of thelarger organisations within the industrial sector,many of which are household names. It isalways unfortunate that in such circumstancespeople are affected by periods of uncertaintyand speculation whilst staff structures aremade to fit the resultant new bodies. On thefortunate side it seems that there have been alimited number of staff losses and mostmembers and others affected have been giveneither existing or new positions. It is also aninevitable sad fact that some companies, notonly in Great Britain but also in South Africa,Ireland and elsewhere, continue to downsize,rightsize and even capsize, and this has adeleterious effect on people’s jobs and lives.This reduction of companies and personnel hasa consequential effect on the number ofmembers changing posts and even leavingtheir industry and this, in turn, with a naturallevel of retirements shows, in a reduction in thenumber of our members. The Council of theInstitute recognises this situation and hasaccordingly established a target to increase thetotal number of members by 5% per annumover the forthcoming years. As individualmembers, we can all help to publicise thebenefits of ICT membership and introduce newmembers to our ranks.
As in previous years I think that thepapers presented at this year’s Symposium andwhich form a major part of the contents of thisYearbook, are illustrative of the work that isgoing on in some of the industries which areconnected by concrete and materials. It isapparent that not only are the academicboundaries continually being pushed back butthe environment, which affects each and all ofus, is not only being protected but positivelyimproved by working practices and selection ofmaterials which may previously have beenthought too expensive or impractical. Therelentless march towards a standardised andharmonised Europe, whatever one’s politicalbeliefs and aspirations, is evident in the newgeneration of concrete and material standards:it is expected that this will remove many of theproblems caused by different national rules
and make life easier for those with businessconnections across Europe. However, it ishoped that this does not result in‘Eurobuildings’ or loss of regional and nationalarchitectural identity.
The Council of the Institute has, over thepast year, continued discussions with theEngineering Council, and I am pleased toannounce that we are now a ProfessionalAffiliate of the Engineering Council, a statuswhich maintains and increases the value ofindividual membership of the Institute. Bothmyself and the Council continue to be gratefulfor the help and generosity shown bysupporting organisations and thanks are duefor this.
It
MIKE CONNELL PRESIDENTINSTITUTE OF CONCRETE TECHNOLOGY
4
INTRODUCTIONThe Institute of Concrete Technology
was formed in 1972 from the Association ofConcrete Technologists. Full membership isopen to all those who have obtained theDiploma in Advanced Concrete Technology. TheInstitute is internationally recognised and theDiploma has world-wide acceptance as theleading qualification in concrete technology.The Institute sets high educational standardsand requires its members to abide by a Code ofProfessional Conduct, thus enhancing theprofession of concrete technology. The Instituteis a Professional Affiliate body of the UKEngineering Council.
MEMBERSHIP STRUCTUREA guide on ‘Routes to Membership’ has
been published and circulated to all members aspart of the Membership Handbook. The guidecontains full details on the qualificationsrequired for entry to each grade of membership.
A FELLOW shall have been a CorporateMember of the Institute for at least 10 years,have a minimum of 15 years relevantexperience, including CPD records from the dateof introduction, and be at least 40 years old.
A MEMBER shall hold the Diploma inAdvanced Concrete Technology and will have aminimum of 5 years relevant experienceincluding CPD. This will have beendemonstrated in a written ‘Technical andManagerial/Supervisory Experience Report’. Analternative route does exist for those notholding the ACT Diploma but is deliberatelymore onerous. Details are contained within theguide on ‘Routes to Membership’. A Membershall be at least 25 years old.
AN ASSOCIATE shall hold the City andGuilds CGLI 6290 Certificate in ConcreteTechnology and Construction, General Principlesand Practical Applications. They shall also have aminimum of 3 years relevant experiencedemonstrated in a written report. Alternativeroutes exist for Graduate members where anappropriate university degree will exempt themfrom the requirement to hold CGLI 6290qualifications. In addition those who havepassed the written papers of the ACT coursebut have yet to complete their Diploma mayalso become Associate members. All candidatesfor Associate membership will be invited tonominate a corporate member to act asSuperintending Technologist. There is nominimum age limit in this grade.
A TECHNICIAN shall hold the CGLI5800 Certificate in Concrete Practice and submita written report demonstrating 12 monthsexperience in a technician role in the concreteindustry. An alternative route exists for thosenot holding the CGLI 5800 Certificate but whocan demonstrate a minimum of 3 years relevantexperience in a technician role. All candidates for
Technician membership will be invited tonominate a corporate member to act asSuperintending Technologist. There is nominimum age limit in this grade.
A GRADUATE shall hold a relevantuniversity degree containing a significantconcrete technology component. All candidatesfor Graduate membership will be invited tonominate a corporate member to act asSuperintending Technologist. There is nominimum age limit in this grade.
The STUDENT grade is intended to suittwo types of applicant.
i) The school leaver working in theconcrete industry working towards theTechnician grade of membership.
ii) The undergraduate working towards arelevant university degree containing asignificant concrete technologycomponent.
All candidates for Student membership willbe invited to nominate a corporate member toact as Superintending Technologist. There is nominimum age limit in this grade. There is a limitof 4 years in this grade.
Candidates are not obliged to attend anycourse (including the ACT course) prior to sittingan examination at any level.
It is no longer necessary for a candidate tohave relevant experience prior to being admittedto the ACT course. Academic qualifications andrelevant experience can be gained in any orderfor any grade of membership.
Corporate members will need to becompetent in the science of concretetechnology and have such commercial, legaland financial awareness as is deemed necessaryto discharge their duties in accordance with theInstitute’s Code of Professional Conduct.
Continuing Professional Development(CPD) is common to most professions to keeptheir members up to date. The Institute’s CPDscheme came into effect from April 1999. Allcorporate members are obliged to spend aminimum of 25 hours per annum on CPD;approximately 75% on technical developmentand 25% on personal development. TheInstitute has published a guide on ‘ContinuingProfessional Development’, which includes arecord card for each member. This is included inthe Membership Handbook. Annual randomchecks will be conducted in addition toinspection at times of application for upgradedmembership.
ACT DIPLOMAThe Institute is the examining body for
the Diploma in Advanced Concrete Technology.Courses for the Diploma are currently held in theUnited Kingdom, Ireland and South Africa.Details are available from the Institute.
THE INSTITUTE
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H.T.R. DU PREEZChairman
K. KotolaTreasurer
R. Tomes
R. Raw
P.M. LATHAMChairman
G. TaylorSecretary
R.G. Boult
I.F. Ferguson
P.L. Mallory
P.C. Oldham
B. Patel
G. Prior(corresponding)
A.R. Rogers
K.W. HEADChairman
J.C. GibbsSecretary and Treasurer
L.R. Baker
R.C. Brown
H.T. Cowan
G. Prior
J. Wilson
R.A. Wilson
A.R. PRICEChairman
G. TaylorSecretary
M.D. Connell
C.D. Nessfield
J.D. Wootten
A.M. HARTLEYChairman
P.L. Mallory
C.D. Nessfield
G. Taylor
EXECUTIVEOFFICER
G. TAYLORJ.C. GIBBSChairman
G. TaylorSecretary
M.D. Connell
A.M. Hartley
P.M. Latham
Dr. W.F. Price
Dr. W.F. PRICEChairman
J.V. TaylorSecretary
L.K. Abbey
R.A. Binns
M.W. Burton
G.W. David
R. Hutton
J. Lay
A.R. Price
Dr. P.J. Wainwright(corresponding)
A.T. Wilson
M.D. CONNELLPresident
Dr. W.F. PriceVice President
R. GaimsterHon.Secretary
J.C. GibbsHon.Treasurer
I.F. Ferguson
R.E.T. Hall
Dr. B.K. Marsh
C.D. Nessfield
P.C. Oldham
B.F. Perry
H.T.R. du Preez(corresponding)
A.R. Price
W. Wild
Mr. R. RYLEChairman
G. TaylorSecretary
Dr. Ban Seng Choo
S. Mac Craith
Dr. P.L.J. Domone
R. Gaimster
Dr. J.B. Newman
H.T.R. du Preez(corresponding)
R.V. Watson
J.D. Wootten
EXAMINATIONSCOMMITTEE
COUNCILTECHNICAL AND
EDUCATIONCOMMITTEE
FINANCECOMMITTEE
ADMISSIONS ANDMEMBERSHIPCOMMITTEE
SCOTTISH CLUBCOMMITTEE
EVENTSCOMMITTEE
SOUTHERNAFRICA CLUBCOMMITTEE
MARKETINGCOMMITTEE
COUNCIL, OFFICERS AND COMMITTEES
6
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Jim recently retired from Rugby Cement afterparticipating in the absorption of thatcompany into the RMC Group. This Face toFace interview was held at his old works,Rochester, which has recently ceasedproduction and is now closed.
Q: Jim, perhaps you could tell us how yougot into the cement industry - what gotyou going on such an illustrious career?
A: Well I wouldn’t necessarily describe it asillustrious but for some strange reason as ayoungster I fancied being a chemist and thisidea seemed to survive through my early yearsand in this part of the world, the southeast,this either meant being in paper,pharmaceuticals or cement. I didn’t fancy thefirst two so I opted for cement. There are orwere only two manufacturers in Kent so Iapplied to both of them; in 1955 Rugby offeredme a post about 3 weeks before the other, soI started and began a relationship which haslasted for 46 years.
Q: So going into cement was a positivedecision, rather than just drifting into it?
A: Yes it was, but the selection had beenlimited! I think it was a good choice, I still makethe comment that I joined on April 1st, AllFools Day! I think that quite significant,however I have survived, apart from a coupleof years with Her Majesty (in the RAF, doingNational Service).
Q: How do you look back over yourcareer?
A: Since I agreed to work on a couple of daysa week as a consultant I must have got someenjoyment from the job. I guess when you lookback over 46 years, which is in effect a full
working lifetime, there have been some veryhappy moments and some sad ones. I tend tothink more of the happy moments, I havefound the work interesting and consider myselfto have been very lucky, to have worked withand met some many different characters. Ibelieve it’s not just work that needs to beinteresting but people make it pleasurable orotherwise.
Q: Apart from some of the changes in thecement industry, can you comment onsome of the changes in cement itself thatyou have seen?
A: Yes, there have been changes of course; inthe very early days we were looking more forquantity rather than quality - we were trying tocontrol quality as much as was possible but theconstruction industry wasn’t so muchconcerned about high performance as gettingenough material to do the jobs. Not everyonewill remember the days of cement rationing,the material was in very short supply with thepost-war reconstruction boom. Having saidthat, in that period some very differentcements were developed, such as hydrophobiccement designed for better storage in humidclimates overseas, we looked at many coatingsbefore settling on particular stearates.Generally, development of this cement andseveral others was carried out at Rochester, soopportunities arose to get involved with andperhaps understand the basics of cementchemistry.
As times went on, and the readymixedindustry grew at the expense of site mixedconcrete, the emphasis changed inasmuch asthere was pressure to get higher strengthswith economic cement contents. The volume
FACE TO FACE
A personal interview with Jim Wootten
Members of the Institute and others in the cementand concrete industries will undoubtedly have met orheard of Jim Wootten. Jim was a founder member of theAssociation of Concrete Technologists, and was a keyfigure in its evolution into the Institute as it now stands.President of the Institute for many years, Chairman ofmany symposia and technical meetings and member ofnumerous committees, he has always been extremelyactive on behalf of the ICT and has made many friendswith his usual good humour. When the grade of Fellowwas inaugurated Jim was the first and received themembership number of Fl, although he cannot be classedas a hybrid.
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race then turned into a quality race, with theachievement of strength performance as amain goal, and that’s probably when thecompetitive element came in. Chemistry wasmodified and fineness increased, with anincrease in the heat evolved and so we thendeveloped Low Heat Cement for massiveconcrete - this was long before the days ofadding slag or ash. Durability was beginning tobe talked about.
Q: So you have reacted to a changingsituation, from where the site usagerequirement was the most importantfactor to one where specific characteristicswere measured?
A: Yes- construction began to move fromtypically a 4:2:1 mix with plenty of water to“designed” mixes such as 3,000 3/4 (nowadays21N, 20mm) and 4,500 3/4 (28N, 20mm), usingguidance on mix design in the technical bibleof the day, Road Note 4! Around this time Ibegan to take quite an interest in concrete asa material, rather than just cement, so apartfrom being involved in the production of thecement I started to become involved in theapplication of cements and how they werebeing used, and how we could make them “fitthe bill” a little better. Technical aspects camemore to the fore, and the role of the cementchemist started to change significantly.
Q: Meanwhile BS12 was still the relevantstandard for ordinary cement?
A: Yes, this had already stood the test of time,originating in 1904, was based on soundknowledge and was a good yardstick ofminimum quality etc. Of course, we have adifferent set of quality standards today andthese are precise with upper as well as lowerlimits and I believe the requirements laid downare pretty sound. Deep down I am, to use yourdescription, more of a “crusher” than a“snapper”, but now I accept that prism resultscorrelate well with the old BS concrete cubetest. It took a lot of work and many, manyresults to convince me (and many other prism-sceptics!) and there is also of course the addedbonus of saving in cube tank space!
Q: If Aspdin returned, what would hemake of it all?
A: I don’t think he would be able to makemuch of it because he didn’t know that muchabout cement technology. I know some regardhim as the Father of cement, but I rather saythat was Isaac Johnson - I believe heunderstood more about cement making,
demonstrated by the introduction of the rotarykiln. Aspdin was obviously a shrewd businessman who saw the opportunity and took it,winning the grant of the patent, but therewere others working in the field. All credit tohim, but I do think Johnson’s contribution wasmore influential.
Q: Jim, at some time in your working lifeyou saw the lack of, and the need for, anacademic qualification in concretetechnology?
A: Indeed, but I must say that others saw itbefore me. We do talk of the need for a centreof excellence today, but I believe we had thatin the Cement and Concrete Associationtraining centre at Fulmer Grange, which manyin the construction industry didn’t alwaysappreciate at the time. It was at C&CA, wherethey conceived and ran the first higher levelconcrete technology course, to see how itwould go, involving some advanced thinkerssuch as Philip Gooding, Adam Neville, NormanGrant and others who recognised that therewas very little concrete technology taught oncivil engineering courses of the day, often amatter of only a few hours tuition in a degreecourse rather than days or weeks. That wasone of the reasons why it was considered thatthere ought to be an Advanced ConcreteTechnology course. This first course wasconsidered to be successful and a second,which I attended, was held. Out of these twocourses, and a subsequent refresher, grew astrong camaraderie and lead to the formationof the Association of Concrete Technologists,with an entry exam regulated by the City andGuilds of London Institute, who issued aDiploma.
Q: You have therefore attended nearly allthe annual conventions, could you tell ussomething of the early ones?
A: The first meeting, which later became theannual convention, was a bit “vague” inarrangement, the second one was marginallybetter but we still had some organisationalproblems and I found myself on the committeeof the ACT trying to help out - after that Ifound myself manoeuvred or out-manoeuvredinto the Chair and my involvement starts there!The Institute grew out of those socio/technicalget-togethers, evolving into what it is today.The concrete industry was now getting betterinformed, you had people from readymix,precast, cement and aggregate suppliers andmany others, mixing and freely exchangingideas. At the same time, courses being run by
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the C&CA and at Bircham Newton for concreteproducers, operatives, site engineers andmanagers etc, meant that concrete wasbecoming more recognised as an importanttechnical material and product performancewas subsequently improving.
Q: During your 16 years as President and25 years on the Council there must havebeen some notable moments which standout in your memory?
A: Yes, quite a few, the time we took over thesupervision of our own Diploma course andexaminations. When the Institute wasestablished and registered at Company Housewith learned society status. The establishmentof the Scottish and Southern Africa Clubs.
On a very personal note, I remember howhonoured I felt when I was given the SilverMedal at the end of my time as President andto be made the first Fellow(F1) really touchedme. Despite my rude jokes about MikeConnell’s “glass jar” I was also touched by thekind remarks he made and the very friendlyreaction by the Convention audience, verymuch the ICT “family” feeling.
Q: I believe that some of the earlyconventions were held in universities, withaccommodation in halls of residence?
A: Certainly, some places were what wewould now regard as very spartan, sometimeswith fairly basic facilities. The technical side hasimproved but still the social side, with itsfriendly and informal exchange of information,has always been very important to me, morelike a family gathering. The early meetings Iremember as happy events but often asChairman I was too active in the domesticorganisation and the minor problems thatalways seemed to keep cropping up. On oneoccasion the catering staff were on the vergeof going on strike and shutting the wholeconvention down, so I spent most of the daypleading and begging with the unionrepresentative to allow us to keep going.Other committee members, notably RichardHall, later took over planning and running theevent and it became much more professionalin organisation.
Q: Once a member gains the Diploma andjoins the Institute, and continues in his jobfor a couple of years, technology hasmoved on - how does he or she keep upto date?
A: We all owe it to ourselves, our employersand the public to keep informed. In recognitionof this need to maintain a good level of
development the Institute recently instigatedthe Continuing Personal Development scheme- very necessary (but I would comment that inmy present position I’m glad I’m past it!). Ibelieve that in common with other learnedsocieties it is very important we keep up todate. As I see it, the idea of having such anInstitute is to provide the public at large with afund of qualified people, professionaltechnologists. If you qualified some years ago,as I did, unless you keep up to date yourtechnology can still be in the days of RoadNote 4. So I see CPD as vitally important, it maytake a little while for it to become routine andI know some members are reluctant, but itshould become a habit and will work.
Q: Some say that ICT seems to be at acrossroads in its development; either tostay relatively small and independent or tomerge with some other body which isactive in a related field, what do you feel?
A: I think we have been at the crossroads forsome time, perhaps always. There was anargument in the early years that to surviveperhaps we should become the academicwing of the Concrete Society or some othergroup. This went hand in hand with theconcern over small numbers that the Institutehas always attracted, but there was and is theviewpoint that we should not be worried overthe number of people in our organisation, weshould continue to concentrate more on thequality. A smaller number of keen anddedicated people may be better than a largermass. Another early view was that we shouldget under the protective wing of a largerorganisation. Twenty-odd years on, we’rehaving the same discussions! My view is thatwe should co-operate with, and have mutualsupport of, other learned societies but I don’tbelieve we want to lose our identity. Thefeeling of a sense of family and camaraderie,even between competitors, that has enabledmembers to exchange technical advice andhelps the exchange of information andfriendship which is extremely important. Ibelieve we have all benefited from this morethan we might have done from a much largerorganisation. I feel proud of the ICT, and I thinkI can say that I feel I have made many friendswithin and because of the Institute.
Q: On aspects of membership, how canthe ICT maintain the interest of members?
A: As with the last topic, this has been underdiscussion for a long time. I must say that theservices offered: facility of convention, bulletin,Yearbook, availability of project reports, and a
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valuable qualification with usable letters toone’s name, are certainly not less than anyother learned body. Many intangibles, such asthe contacts and friendships, now callednetworking, are invaluable. As with manyother things in life, what you get out dependson what you put in. To those who ask whatthe ICT can do for them, I would ask what theycan do for the ICT.
Q: Should more use be made of theinformation contained in project reports?
A: Absolutely. I feel it should be used where itscontribution is likely to improve commonknowledge. Bearing in mind that one of theaims of the Institute is to promote concretetechnology it is important that thatinformation is not just passed to members butto the concrete world generally, provided thatthe information is accurate and not outdated.It may be that for future years the Instituteshould suggest topics for research tocandidates, on the basis of industrial need.
Q: You are leaving the industry at a timeof great change both for your industryand your company. Do you see theindustry going forward, and are you sorryto leave it?
A: Yes, I am sorry to be leaving the industry fortwo reasons. Firstly, it is a challenging time,although the industry has met challengesbefore. Up to recent times cementmanufacturers have always stood alone, andvertical integration was something whichhappened in other countries - it is happeninghere now and I only hope the cement industrydoesn’t lose its identity, there is a risk thatcould happen. Secondly, I have made so manyfriends, and met so many interesting people.The friendships will last well into retirementand the memories of some of the characterswill remain with me for all time.
Q: Now you have more free time on yourhands, apart from consulting work, howwill you occupy your time?
A: What free time? I am not actively pursuingconsultancy work, unless it’s very interesting!Cora and myself will certainly do moretravelling, although nothing too adventurous. Ihaven’t been fishing for years and I want to getinto watercolour painting, I have been doingsome dabbling but need to go on a course tolearn how. I am also involved with the localhospice, representing the Rugby CementBenevolent fund in the building of anextension.
Q: Will you be doing a watercolour ofRochester works?
A: Not Likely! A cement factory is not the mostattractive thing in the world! Also, I feel thatthe most important part of any factory ororganisation is its people- take out the peopletake out the soul.
Jim, thank you for your time andcomments. The Editorial Committee andthe Institute wish you a long and happyretirement, and we hope that you andCora reap the rewards of an active career.
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Brooklands in the parish of Weybridge atthe turn of the 20th Century was a quietbackwater of Surrey with 6,000 inhabitantswhere little was heard but for summersongbirds and the chink of fine china as teawas served on the lawns.
This idyll was changed when HughFortescue Locke King, a wealthy landowner,architect and civil engineer, decided in the earlypart of 1906 to build a motor track on part of hisestate, south west of Weybridge. Indeed thiswas to be the premier speed trial track in theworld. Up to that time automotive developmentwas dominated by French, German and Italiancars. Locke King was to provide the wherewithal
to change that and at his own cost - anescalating fortune as it turned out.
He lived in a mansion at Heath Road inWeybridge that was called Brooklands, hencethe name given to the track (Photo 1).
At the heart of all this endeavour was amaterial that made this vision a reality and thatmaterial was concrete. In the main it was plainunreinforced concrete, although as part of thecircuit, both material and radical design cametogether under the names of Hennebique andMouchel. Brooklands became the crucible ofengineering innovation for cars and flyingmachines as well as construction and buildingpractices. An age of radical and rapid
MILESTONES IN THE HISTORY OF CONCRETE TECHNOLOGY
The technology of cement based materials has been developing since the firstconcrete mix was produced. Much of this technology was further improved with time butmuch was forgotten (sometimes to be later ‘reinvented’). Some developments have beenaccidental, such as the discovery of the benefits of air entrainment. Some have been theresult of foresight and endeavour, or for commercial gain, whilst some have been born ofnecessity such as those for military and structural reasons.
This series of articles - ‘Milestones in the history of concrete technology’, will includesome of the more important steps which the science of materials has taken. Later papersmay include the work of pioneers such as Vicat, Hennebique and Powers; the early useof admixtures; Roman, Victorian and Portland cements; the work of the Cement andConcrete Association; no fines concrete and the advent of precast buildings.
This second paper in the series details the construction of Brooklands speed track in Surrey, England.
BROOKLANDS SPEED TRACK. By Professor Peter C Hewlett
Note: Units of money and measurement that pertained in the 1906-1946 period have been retained. Post 1946 metric units are used where appropriate.
For conversion, £1(1906/1907) = £60(2001) 1 mph = 1.61 km/h 1 ton = 20 cwt =1,018 kg1inch = 2.54 centimetres 1 cu yd = 0.765m3
Photo 1
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development from which we are benefitingtoday - all made possible with concrete, visionand missionary zeal. A re-estimate of cost, inAugust 1906, to cover the preparation of theground, lay the track, build three bridges anderect eight miles of fencing was £22,004 (atpresent day prices £1,276,000). Sounds like asnip, taking regard of the potential forspectator indulgence. It has to be rememberedthat a new era was being created, an erapreviously dominated by horse transportation.
However, this was only the beginning ofa financial escapade resulting in near ruin forLocke King.
The track was a pear shape runningapproximately south-west to north-east and inpart running alongside the London and SouthWestern Railway Line to the north and StGeorge’s Hill and the Itala Motor Works to thesouth, with the high speed embankments atByfleet and Weybridge at each end. Figure 1shows an outline map at around 1933.
The outer circuit was 2.7 miles long butincluding the finishing straight it rose to 3.25miles. Track width was 100 ft and themaximum height of the banking was 28 ft 8 in.Notwithstanding the rigours of time andopportunistic development about 80% of thetrack still exists to this day and bears testimonyafter 94 years to the function and hardiness ofconcrete.
Back to the finances, and there are somemodern parallels in relation to price escalation,for instance the British Library. On closerexamination the costs rose temporarily to£60,750 (£3,500,000) and methods of
payment became a matter of concern for thecontractors, Willis and Reeves. It would seemthat the people involved in this venture madesome very brave if, by the conditions ofmeasures of today, questionable decisions.Such adventurism is absent these days.People’s private fortunes were at stake here.Even so, extensive estimates of numbers likelyto attend Brooklands events were put at100,000 to 200,000 per meeting and neitherwas it going to be cheap. The cheapestadmission in 1914 was 2s 6d when wagesaveraged 24 shillings a week. It is difficult, at atime when transportation was not as readilyavailable as today, to imagine that such amigration of people from London and itssurroundings was close to hopeful kiteflying.However, as later events showed, theestimates were pretty close with 30,000 in thegrandstand and standing room for 150,000.
Estimates now climbed steadily andstood at £96,904 (£5,600,000).
Instead of getting cold feet Locke Kingforged ahead with missionary zeal. The recordsshow the final cost was somewhere between£100,000 and £150,000 (£5,700,000 -£8,550,000).
The track opened on the 17th June 1907.It should have opened on the 18th March1907 but was put off due to winter frostsdelaying the laying of the concrete surface. Ittook only seven months to build fromscrubland to finished track. By any standardsthis was a remarkable outcome. Some wouldsay the track was opened too soon and beforethe concrete had fully cured, since at the
Figure 1
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inaugural drive around the circuit, bits ofconcrete surfacing were thrown up, hittingthose taking part in the procession. Indeed justbefore the public opening, the pioneeringmotorist S F Edge drove around the track for 24hours at 65 miles an hour in a six cylinder 7.72litre Napier to show that a human being couldwithstand such treatment. I suppose a faircomparison for achievement for us todaywould be the first man into space circling theearth.
Concrete was chosen both as the baseand surfacing material because it was judgedto be durable, easy to repair and had good skidresistance. This was more a hope thantechnological prognosis.
The specification called for 200,000 tonsof gravel and cement to be laid to a depth of 6inches over the whole surface notwithstandingthe contract with Willis and Reeves requiredthat gravel to be overlaid with 4 inches of ‘tarconcrete’ well rammed on the slopes androlled on the flat sections. The ‘tar concrete’was to be overlaid by 1/2 inch of an ‘approvedmaterial’. What was laid and is there for all tosee is plain concrete. Photo 2 shows thefinishing straight where it meets the WeybridgeBanking, along with the Club House.
Why such a change? Cost saving is thelikely answer. Not the first time a contractorexercised discretion over a specification tomeet the realities of the job.
Brooklands is unique and came intobeing when the motor car, motor cycle andaeroplane had only just been invented. Copieswere soon to follow with Indianapolis (USA) in1909, Monza (Italy) in 1923 and Montlhery(France) in 1924.
For instance, the first motor car ran in1885 and the first aeroplane flew at Brooklandsin 1908. This coming together of opportunityand one-man’s vision often precedes majorprogressive steps. They are accompanied byimpatience and that was certainly so for LockeKing and Brooklands. Seven months in whichto carry out groundworks that meantremoving 30 acres of woodland, theredirection of the River Wey, cutting through ahill, create a gorge 110 ft wide, 28 ft deep anda quarter of a mile long, build two bridges, oneof which being the first of its kind, build aclubhouse, not to mention shaping andcreating the track itself, involving thedemolition of two farmhouses. In addition toall of this, seven miles of branch railway linehad to be built to bring in materials such aschalk from Reigate to create the bankings atWeybridge and Byfleet.
Some 200 carpenters, sawmen andwoodmen were involved in timber felling andmaking sleepers, benches, stands and oakfencing. The site resembled something fromthe pioneering days of railway track laying inthe wild west of North America (Photo 3).
Photo 2: Concrete finishing straight and Club House (Weybridge Banking) - 1907
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To do all this required planning,politicking and the influx of 2000 navvies,including labourers from Sussex, Yorkshire andIreland. This influx came into a very ruralcommunity and I leave it to your imaginationto think of some of the problems that wouldhave resulted. The navvies lived on the site in avariety of makeshift homes and it was verythirsty work!. It should be remembered thatLocke King had previously sold substantial plotsof land on which elegant houses had beenbuilt by people seeking an elegant life. Theconstruction of Brooklands must have beenlike an exploding bomb in the heart of ruralSurrey. Not a recipe for co-operation and goodrelationships. But still he pressed on and stillthe costs escalated.
Brooklands from 1907 to 1939 playedhost to famous names and makes of machinein the embryo field of mechanisedtransportation. To mention but a few, becausethere were so many. For car enthusiasts therewas Parry Thomas, Malcolm Campbell, JohnCobb, Tim Birkin, Count Louis Zborowski (doyou remember his machine called Chitty ChittyBang Bang that finished a 100 mile race at anaverage speed of 100.7 miles per hour in1921?), Kenelm Lee Guiness (famous for theKLG spark plugs), Henry Segrave, Kaye Don,George Eyston, Raymond Mays, Prince Bira ofSiam and not least of all the band leader BillyCotton. As to cars, AC, Alvis, Aston Martin,Austin, Bentley, Lagonda, MG, Riley, Sunbeam,Napier, Talbot, Vauxhall and Wolseley andmany, many more.
Photo 4: Section through banking showing compacted underlay and 6” concrete overlay.
Photo 3: Land clearing and tree felling - ground preparation for Brooklands in 1906.Horses and carts dominate the scene.
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If that was not enough, Brooklands washome to early aviation. Located towards thesouth west Byfleet end and close to a sewagefarm, activity in the air was as rampant as on thetrack. Several pilots had close encounters withthe sewage farm, including A V Roe himself,indeed the pilots were sometimes referred to as‘bog rats’.
Taking a selection of players in the field ofaviation we have Louis Paulhan (the first publicflight in Britain in a Henry Farman biplane) T. O.M. Sopwith and I have to say Hilda Hewlett whoran one of the first flying schools called Hewlettand Blondeau, Adolphe Pegoud performed thefirst aerobatics display, Sidney Camm (Hurricane
designer) and Allcock and Brown who flew theAtlantic in a Vickers Vimy built at Brooklands.
In 1930 the Brooklands Aeroclub wasformed and its headquarters exists to this dayand was used as a pattern for future flightcontrol buildings.
During World War II the track was closedand made over to aircraft production with theVickers (located on what was previously the siteof Itala Motorworks), Bristol and Hawkercompanies being the dominant makers. Again itis a roll-call of history with the VickersWellington, Varsity, Viking and Vanguard, not tomention the nuclear bomber the Valiant and
Photos 5a and 5b: Then and now! The Weybridge banking and members’ bridge in1907 and May 2001. Note the railway track that delivered materials to various pointsaround the newly formed track.
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more recently the VC10, TSR2, BAC One-elevenand even parts of Concorde. As for Hawkers,the Hurricane and the Hunter were built atKingston and assembled and test flown atBrooklands. The famous inventor/developer,Barnes Wallis (designer of the Wellington, DamBusters Bombs, including the so-called Tall BoyBomb) worked at Brooklands. Whatever youtouch or wherever you turn you bump intoachievement and endeavour. Even when flyinghad all but finished there was research atextreme temperatures and pressures thatsubjected air frames to the effects of highaltitudes and the rigours of fire, in thestratospheric chamber.
The record is breathtaking but thenBrooklands has always stood for records andprogress. In an article really dealing withconcrete why mention all of this? Rememberconcrete used for roadmaking and specialisedsurfacing was also relatively new and madesuch developments possible. Throughinnovation we obtained other innovations.Concrete enabled such a development to bepossible. Concrete was the midwife, the enablerof these innovations.
In 1946 the track was sold to Vickers andsince then gradual building development hastaken place, mainly within the track boundariesbut occasionally slashing through it, exposingthe banking profile (Photo 4). It has to be saidconcrete has played its part in such changesalso. But for 32 years Brooklands was the hub,
the pacesetter, the benchmark and its legacy isthere for all to see and to appreciate (Photos 5aand 5b). If you have any imagination the ghostsstill linger with a whiff of Castrol R in the air. Isthat pine I can smell? is that the roar of 250,000spectators? - no it was a gentle breeze but ...........
The Land and the TrackThe land earmarked for the motordrome
was of no great value being part of the floodplain of the River Wey.
Whilst the river was diverted no attemptwas made to include flood protectionmeasures and nature has caused floodingproblems on a fairly regular basis and asrecently as last winter (2000/2001).
Most of the track could be described as aconcrete carpet. The two embankments atWeybridge (short bend) and Byfleet (long bend)had inclinations of 1 in 2 and 1 in 21/8
respectively with radiuses of 1,000 ft and 1,550ft. Such dimensions permitted speeds of up to120 miles per hour although occasionallypeople were known to go over the top with adrop of about 18 ft. Jean Chassagne crashedover the edge of the banking in his 11/2 litreTalbot-Darracq as a result of a deflating tyreduring the 1922 two hundred mile race.
Bearing in mind the normal vehicle speedlimit in 1906/7 was raised from 12 mph to 20mph, it was in fact only 4 months into the lifeof the track when 115 mph was recorded.
Photo 6: the Brooklands Weybridge Banking just beyond the Members’ Bridge lookingtowards the River Wey (anti-clockwise) - taken May 2001.
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Track repairs to the concrete were numerous.Some reports say annually. The granite basedwearing layer was tested severely by bothnature and motors alike. Even by 1930questions were raised over the viability of thetrack but this was a steep learning curve forcars, aeroplanes and concrete itself (Photo 6).
Before letting the contract, threematerials were considered, namely,tarmacadam (tar and slag), asphalt andconcrete. Tarmacadam was in its infancy andrequired rolling and this was not possible onthe embankments.
Asphalt had similar problems totarmacadam and had to be laid on concrete.
Concrete had never been used as awearing surface for high speed heavy vehicles.In fact the first concrete road was at St Marks,Chester and was laid in 1912, five years afterthe track had opened and there were notmany road-racers at St Marks!
The concrete used was quite dry (referlater) and was easy to lay on the lower slopes,using shutters. The upper slopes were laidonce the lower adjacent one had set. Since thebanking at the Weybridge end was 1 in 2, selfcompacting concrete would not have helped.A stiff mix, wheelbarrows and hard work werethe order of the day, occasionally assisted bypowered winches to get to the top of thebankings (Photo 7).
Some 200,000 cubic yards of concretewere mixed by hand in 8 hour shifts (8 on and8 off) for 6 days a week. Notwithstanding theexistence of traction engines it was horse andcart that provided the means of movingmaterials.
It was concrete’s adaptability that actedin its favour, although the records show whatwas specified and what the contractor usedmay well have been somewhat different.
The aggregate used was flint gravel fromthe Thames and Wey gravel beds.
The cement was ordinary Portlandcement of 1907 grade - somewhat morecoarsely ground than today. Supplied underthe name of J B White and Bros brand.
A sample taken in later years from theMembers Banking (Weybridge) indicated thefollowing composition,
Aggregrate 72%
Cement 18%
Water 5%
Total 95%
The remaining 5% was thought to besoluble material in the aggregate but notidentified. We have to assume from thesefigures that the aggregate included coarse andfine, in which case we have a 4 : 1 aggregateto cement mix as opposed to a moreconventional 4 : 2 : 1 mix. In this regard the mix
Photo 7: The Byfleet Banking takes shape. The moulds for the concrete surface of thetrack are being put in position.
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was rich with respect to cement and with awater : cement ratio of 5 : 18 (approximately0.3). No wonder the mix was stiff; it may alsohave shrunk considerably.
Granite was also found in the mix -probably the remains of the wearing surface.Remember speed of construction was of theessence and rapid set and early strength apremium, so the forms could be moved andthe laying progressed.
By way of comparison, in 1980 a 24metre section of the track that had beenremoved during the war, was reinstated to its30 metre width (readers will note the subtlechange in units whilst reflecting the change intime!). The work was carried out by KyleStewart Ltd and references were made to theoriginal concrete.
The bank reinstatement consisted oframmed sand topped with 150 mm of grade30 pavement quality concrete, using 40 mmcoarse aggregate. A minimum cement contentof 300 kg /m3 and whilst the original concretehad no reinforcement the reinstatementconcrete had an expanded metalreinforcement and the new section of trackincluded mesh reinforcement.
Perhaps the most technically challengingand at the same time innovative work was thecrossing over the River Wey.
Bridge Construction ProblemThere was a problem on the section
coming out from the Members Bankingtowards the River Wey, the river had to becrossed, notwithstanding its previousdiversion.
Photo 8: John Cobb in the 23 litre Napier-Railton at the Bump in 1933. It won its firstrace with an average speed of 122.33mph and is the forever lap record holder.
* The continuous line denotes the centre of the track and the upper dotted line the safety limit. Cobb holds the trackrecord at 143.44 mph in the 23 litre Aero engined Railton. It was not uncommon for the faster drivers to go beyond the dotted line.
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This task was easily carriedout with the railway line some 69years earlier because it was in oneplane using a seven arch brickbridge. However, the track had tobe curved in two planes, verticallycoming off the banking andhorizontally to follow the railwaystraight. Consultant LG Mouchelwas to design a new type ofbridge using the Hennebiqueconstruction system, itself usingferro-concrete principles thatwere invented and patented in1892.
The span was 180 ft inlength and 100 ft wide.Calculations were based onmotor cars weighing up to 4tons, with anticipated vibrationsdue to high speeds, the steelreinforcement of the decking wasincreased by 30%.
A static load ofapproximately 1lb per sq inch or arolling load of 2 tons per sq ftwere assumed to apply. TheNapier Railton track record holder(Photo 8 shows John Cobb at thefamous Bump off the MembersBanking) weighed about 10 tonsand would have crossed thebridge in about 1 second whenmoving at 118 mph.
Photo 9: Rear or non trackside view of Hennebique Bridge across the River Wey.
Figure 2: Cross-sections of the Hennebique Bridge attwo locations.
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Concrete and steel were favoured oversteel alone which was judged difficult to adjustto the curves and would have flexed too muchand vibrations would have stressed the thinshell of the surface.
Other factors were concrete’s lower costthan steel or stone alone and steel had alegacy of costly maintenance. Would a differentstory be told today? The concept of a shellsupported by a concrete and steel frame wasvery radical indeed. In fact it had never beenused before - yet another courageous andinnovative first.
Forty-two piles were constructed to adepth of 19 ft with 10 of them in the river beditself. On top of the piles, columns of between18 and 26 ft were built and the columns tiedtogether by horizontal beams of reinforcedconcrete. Across the top of the columns werelongitudinal arched beams. A diagrammaticrepresentation is shown in Figure 2. Photo 9shows the back of the bridge and Photo 10erecting the track surface on the reinforcedconcrete sub-frame.
Over this sub-frame of columns andbeams was a decking of 32 bays each. Eachbay contained 7 panels and over that a slab offerro-concrete 41/2 inches thick was cast andover that a finishing coat of concrete 1 inchthick containing granite chippings as a wearingsurface. By the standards of the day a radical
and innovative structure - just like the conceptof the track in its entirety. Edwardianentrepreneurship at its best.
Work began on the bridge in December1907 and was finished in 5 months. There is norecord of whether cold weather workingaffected the concrete or what steps weretaken to offset slow setting and hardening.Remember there was no readymix that couldbe pumped or moved around with cranes anddumper trucks - without such assistance it wasa quite remarkable feat.
Brooklands, the great concrete saucer, isa monument to human courage, vision,innovation, endeavour and to the materialconcrete.
Innovation extended to state-of-the-artcommunication with 50 miles of telephonicwiring so that race marshalls in sentry boxesaround the track could report instantly toheadquarters in case of accident orbreakdown.
It is there to see, to touch and toimagine. The last Brooklands race meeting wason August 7th 1939 but the spirit lives on,both as a place with regular events and as aliving museum and an active supportmembership through The Friends ofBrooklands and the Brooklands Society.
If some wealthy and very brave persondecided to create another Brooklands, I am
Photo 10: Track laying construction on the reinforced concrete sub-structure- the Hennebique Bridge.
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sure concrete would be the chosenconstruction material. How concrete haschanged since 1907 and what opportunities itcould offer - a useless dream no doubtbecause entrepreneurial flare and grittycourage have sadly been replaced by clinicalanalysis and early returns on capital outlay. DidI hear a small clear voice say what aboutRockingham?
Acknowledgements
I first contacted the Director ofBrooklands, Morag E Barton, on the 23rd May2000 and have obtained unfailing help since. Iwish to mention John Pulford (Curator) and inparticular Tony Hutchings (Research Assistant)whose infectious enthusiasm and generoushelp are greatly appreciated. What began as atask became a pleasure in personal andtechnical terms and has left a lastingimpression. I am indebted to the BrooklandsMuseum and Library for providing the historicalvisual material and access to much writtenwork mentioned in the Bibliography.
Bibliography
Noted below is a selection of publicationsreferred to in writing this article. The availableliterature is substantial and readily available.Knowing where to stop is the problem.Because much of the written material overlapsone with the other specific references have notbeen given in the text. However, I am indebtedfor all the written material that was madeavailable to me.
1 ‘Automobile Racing in England’, The Car No218, July 25th 1906 (early map of the circuit)
2 ‘25 Years of Brooklands Track’ R H Beauchamp(2nd Edition) 1995. R A Smith Ltd pp 104(detailed automobile record up to 1949).
3 ‘The Story of Brooklands’ (audio visualpresentation to Gallagher Ltd (1st November1983) available from the Brooklands Library.
4 ‘The Locke Kings of Brooklands Weybridge’ byJ S L Pulford, Paper No 31 1996, Autumn andWeybridge Local History Society 52-66, 67-69.
5 ‘The Theory Behind Brooklands - A Study inEdwardian Engineering’, the Cyril Posthumusessay A J Hutchings, March 1993, pp15,Brooklands Society Gazette Vol 19 No 1 1994.
6 ‘Brooklands’ Motorsport, March 2001, pp 72-80.
7 ‘The Car - A Journal of Travel by Land, Sea andAir’ Edited by Lord Montague, October 1906,No 229.
8 ‘The Automotor Journal’ December22nd 1906.
9 ‘Brooklands Motoring History’ 1906-1939(available from Brooklands Library).
10 ‘Why and How I Built the Brooklands Course’H F Locke King, The Spirit (The BrooklandsMagazine), Spring 1997 pp 10. Reproducedfrom the Souvenir Programme of the First RaceMeeting on July 6th 1907.
11 ‘Brooklands and the Environment’ S Flower,27th June 1991 (available through BrooklandsMuseum Library).
12 ‘The History of Brooklands Motorcourse’(archive photocopy) 1979, W. Boddy.
13 ‘A Brief History of Concrete’, C Stanley(reprinted from Building Technology andManagement, October 1974) pp 20-23.
14 ‘The Hennebique Bridge’ by A J Hutchings.Brooklands Society Gazette, March 1981, pp 11-15.
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25
ANNUAL CONVENTION SYMPOSIUM: PAPERS PRESENTED 2001
PAPER BY:
ISO 9001: 2000 Mr. R.E.T. HallA Quality Standard for the New Millennium BA, FIAT, FICT, MIHT, AIQA, MCS
QSRMC
Conformity to EN206 Mr. S.J. CromptonBEng(Hons), MICTRMC Readymix Ltd
Environmental Issues - Water Mr. A.J. Dowson BA, MICTMarshalls
New European Standards for Admixtures Mr. J. BuekettBSc, CChem, MRSC, MIQACEN Observer for EFCA
New BRE Guidance on Use of Concrete Dr. P.J. NixonIn Aggressive Ground BSc, DIC, PhD, HonFICT
Building Research Establishment Ltd.
A Review of the Use and Abuse of Mortar Mr. S.E. BellDip Arch, RIBA, MIMMarshalls
The Future of Recycled and Mr. J. BarrittSecondary Aggregates Tarmac Recycling Ltd
Examples of Efficient Mechanical Mr. M. ProbstHandling of Precast Materials Dipl. Engineer
Probst Handling & Laying Systems GmbH
Recycling London’s Waste - A blueprint Dr. J.B. Newmanfor manufacturing construction products BSc(Eng), ACGI, CIC, PhD, CEng, MIStructE, FICE, MICT
Imperial Collegeand Mr. P.L. OwensHNC, MPhil, FICT, MInstWMPhilip L Owens and Partners Ltd
A major part of the ICT Annual Convention is the Technical Symposium, where guest speakerswho are eminent in their field present papers on their specialist subjects. Each year papers arelinked by a theme. The title of the 2001 Symposium was:
CONCRETE IN A CHANGING WORLD
Chairman: Dr. John B Newman, Imperial College BSc(Eng), ACGI, CIC, PhD, CEng, MIStructE, FICE, MICT
Edited versions of the papers are given in the following pages. Some papers vary in writtenstyle notwithstanding limited editing.
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27
Richard E T Hall is the SchemeManager for the QualityScheme for Ready MixedConcrete and has beenactively involved in preparinga revision of the QSRMC
Regulations to meet the new ISO 9001Standard. He specialises in quality and productconformity matters associated with the UnitedKingdom Ready Mixed Concrete Industry. Priorto joining QSRMC in 1991 he had over 20 yearsexperience of identifying, testing, manufactureand utilisation of construction materialsassociated with civil engineering and buildingboth in the UK and overseas.
ABSTRACTThis paper deals with the BS EN ISO 9000:
2000 family of quality standards andconcentrates in particular on BS EN ISO 9001:2000 “Quality Management Systems -Requirements”, and the changes comparedwith the previous 1994 edition. The underlyingquality management principles are consideredtogether with the use of a process approach toquality management. Consideration is alsogiven to the application of the new standard tothe ready mixed concrete industry.
KEYWORDSISO 9001, ISO 9004, Quality, Quality
Management, Quality Management Systems,Quality Management Principles, ProcessApproach to Quality.
INTRODUCTION & HISTORYQuality by definition is the degree to
which a set of inherent characteristics fulfilsrequirements and represents meeting theneeds and expectations of a customer.
A need for quality systems was identifiedin specific industrial manufacturing industriessuch as defence and aerospace. The lessonslearnt from the establishment of such specificschemes led to the development of the firstBritish Standard relating to Quality, this beingintroduced in 1979 as the BS 5750 series ofdocuments, entitled “Quality Systems”.
During the subsequent review of this
series of standards it was recognised by ISO, theInternational Standards Organisation, that theBritish Standard represented a model for anInternational Standard and in 1987, the BS5750, ISO 9001 series of documents waspublished, again entitled “Quality Systems”.
In the light of users’ experiences in the useof this family of standards they were againsubject to review and revision. Account wasalso taken of the Vision 2000 strategy for thelonger-term development of the ISO 9000family of quality standards, adopted by the ISOTechnical Committee ISO/TC 176 in 1990. Atthe same time the European Committee forStandardization (CEN) accepted the revisionand in 1994 the BS EN ISO 9000 series ofdocuments was published, entitled “QualityManagement and Quality AssuranceStandards”.
A further review of the 1994 Qualitystandards culminated in the publication of threeprimary Quality standards, BS EN ISO 9000,9001 and 9004, during December 2000,entitled “Quality Management Systems”.
BS EN ISO 9000addresses fundamentals and vocabulary.
BS EN ISO 9001 addresses requirements.BS EN ISO 9004addresses guidelines for improvements.
With the publication of the year 2000quality management standards, it is theintention that the other standards anddocuments in the ISO 9000 family will either bewithdrawn, transferred to other technicalcommittees, or replaced by technical reports,specifications or brochures. The exception isISO 10012 “Quality Assurance for MeasuringEquipment”, which will remain as aninternational standard.
This paper concentrates on BS EN ISO9001: 2000 Quality Management Systems -Requirements.
THE NEED FOR REVISIONISO directives require standards to be
periodically revised to ensure that they are bothcurrent and satisfy the needs of the globalcommunity.
ISO 9001: 2000
Mr. R.E.T. Hall BA, FIAT, FICT, MIHT, AIQA, MCS
QSRMC
28
The main reason for revising the 1994-year quality standards was the recognition ofproviding users with the opportunity to addvalue to their activities and to improve theirperformance continually by focusing on majorprocesses within their organisation.
There was also recognition of a need toemphasise the monitoring of customersatisfaction, the production of more user-friendly documents, assuring consistencybetween quality management systemrequirements and guidelines, promoting theuse of generic quality management principles,and enhancement of their compatibility withBS EN ISO 14001 “Environmental ManagementSystems”.
During the revision stage several factorswere considered and taken into account, theseincluded:
• Evolving customer and user needs
• The use of process basedmanagement
• Meeting the needs of customers andinterested parties
• Previous standards appear biasedtowards large manufacturingcompanies
• Small business difficulties in applyingprevious standards
• A need for compatibility with othermanagement system standards.
NEW EMPHASISThe new standard is more customer-
orientated than the previous edition with agreater emphasis on identifying customerneeds and meeting their expectations, with arequirement to communicate with customersand to monitor and measure customersatisfaction.
It now explicitly requires organisations toevaluate the effectiveness and suitability oftheir quality management system and toidentify and implement system improvementson a continued basis.
The aim of continual improvement of aquality management system is to increase theprobability of enhancing the satisfaction ofcustomers and other interested parties.Actions for improvement include:
• Analysing and evaluating the existingsituation to identify areas forimprovement
• Establishing improvement objectives
• Identifying solutions in achieving theobjectives
• Implementation of the solution
• Measuring, verifying, analysing andevaluating the results ofimplementation to determine thatobjectives have been met
• Formalising changes.
MAIN CHANGES TO THE STANDARDS
The main changes that have beenintroduced in the consistent pair of qualitymanagement system standards are:
• A new process-oriented structure anda more logical sequence of thecontent
• A continual improvement process toenhance the quality managementsystem
• An increased emphasis on the role oftop management, which includes acommitment to the development andimprovement of the qualitymanagement system, consideration oflegal and regulatory requirements andestablishment of measurable objectivesat relevant functions and levels
• The concept of “Application” of thestandard has been introduced to copewith a wide spectrum of organisationsand activities
• A requirement for the organisation tomonitor information on customersatisfaction as a measure of thesystem’s performance
• A reduction in the amount of requireddocumentation
• Changes/improvements in terminologyfor easier interpretation
• Specific reference to qualitymanagement principles
• Consideration of the benefits andneeds of all interested parties
• Increased attention to resourceavailability
• Determination of the effectiveness oftraining
• Measurement requirements extendedto include system, processes andproduct
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• Analysis of collected data on thequality management system’sperformance
• Addition of the concept oforganisational self-assessment as acatalyst for improvement (BS EN ISO9004).
THE QUALITY MANAGEMENTPRINCIPLES
Eight quality management principlesprovide the basis for the revised standards andfacilitate the achievement of quality objectives.A quality management principle is acomprehensive and fundamental rule or belieffor leading and operating an organisation,aimed at continually improving performanceover the long term by focusing on customerswhile addressing the needs of all stakeholders.These principles are:
• Customer-focused organisations
• Leadership
• Involvement of people
• Process approach
• System approach to management
• Continual improvement
• Factual approach to decision making
• Mutually beneficial supplierrelationships.
Customer-Focused OrganisationsOrganisations depend on their customers
and therefore should understand current andfuture customer needs, meet customerrequirements and strive to exceed customerexpectations.
LeadershipLeaders establish unity of purpose anddirection of the organisation. They shouldcreate and maintain the internal environmentin which people can become fully involved inachieving the organisation’s objectives.
Involvement of PeoplePeople at all levels are the essence of the
organisation and their full involvement enablestheir abilities to be used for the organisation’sbenefit.
Process ApproachA desired result is achieved more
efficiently when related resources and activitiesare managed as a process.
System Approach to ManagementIdentifying, understanding and managing
a system of interrelated processes for a givenobjective improve the organisation’seffectiveness and efficiency.
Continual ImprovementContinual improvement should be a
permanent objective of an organisation.
Factual Approach to DecisionMaking
Effective decisions are based upon theanalysis of data and information.
Mutually Beneficial SupplierRelationships
An organisation and its suppliers areinterdependent, and a mutually beneficialrelationship enhances the ability of both tocreate value.
THE PROCESS APPROACHThe new standard promotes the adoption
of a process approach when developing,implementing and improving a qualitymanagement system.
Any activity, or set of activities, that usesresources to transform inputs to outputs can beconsidered as a process.
For organisations to function effectively,they have to identify and manage numerousinterrelated and interacting processes. Often, theoutput from one process will directly form theinput into the next process. The systematicidentification and management of the processesemployed within an organisation, and particularlythe interactions between such processes, arereferred to as the “process approach”.
The process approach aims at achieving adynamic cycle of continual improvementsproviding gains to the organisation, typically interms of product and business performance,effectiveness, efficiency and costs.
Within ISO 9001: 2000 the processapproach requires an organisation to identify,implement, manage and continually improve theeffectiveness of the processes that are necessaryfor the quality management system, and tomanage the interactions of these processes inorder to achieve the organisation’s objectives.This includes top management, productrealization and relevant support processes, and inaddition monitoring and measurementprocesses.
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This concept is essentially a variant on thewell-known “Plan - Do - Check - Act” cycle,which is known as the Shewart, Deming, orhuman activity cycle.
“Plan” establish the objectives andprocesses necessary to deliverresults in accordance withcustomer requirements and theorganisation’s policies.
“Do” implement the processes.
“Check” monitor and measure processesand product against policies,objectives and requirements forthe product and report theresults.
“Act” take actions to continually improve process performance.
The P-D-C-A cycle can be used within theorganisation’s processes, it being directly linkedwith the planning, implementation, controland continual improvement of productrealization and other quality managementsystem processes.
By applying the P-D-C-A concept at alllevels the process capability of an organisationcan be maintained and improved. Such anapproach applies equally at all levels from high-level strategic processes, such as qualitymanagement system planning or managementreview, and to simple operational activitieswithin product realization.
CONSISTENT PAIRThe idea of a consistent pair of standards,
namely BS EN ISO 9001: 2000 and BS EN ISO9004: 2000, was central to the revision process,with both documents having the same layout,identical numbering and headings.
BS EN ISO 9004: 2000 provides guidanceon a wider range of the objectives of a qualitymanagement system to improve anorganisation’s overall performance, with anemphasis to perform self-evaluation. It doesnot represent a guideline for implementing BSEN ISO 9001: 2000 and it is not intended forthird party certification or contractual use.
BS EN ISO 9004: 2000 contains norequirements and the text within each clause isnot intended to represent an interpretation ofthe requirements within the same clausenumber of BS EN ISO 9001: 2000.
NEW DEFINITIONS/CONCEPTSWith the publication of the new series of
standards a number of newdefinitions/concepts have been introduced.
Organisation/SupplierIn the previous standard certified
organisations were termed suppliers, becausethey supplied products and provided servicesto customers; the term organisation is nowused.
The term supplier now refers to theorganisation’s supplier and replaces the oldterm sub-contractor.
ProductPreviously ISO appeared to recognise four
kinds of products:
• Software
• Hardware
• Services
• Processed materials.
These are now deemed to be genericelements, not types of products; ISO nowconsider that most products are made up of allfour elements.
Product RealizationThis represents a rather abstract concept
and refers to the interconnected processes thatare used to bring products into being.
TOP MANAGEMENTThe new standard has a greater emphasis
on the role of Top Management within aCompany Quality System, by definition this isconsidered to be the person or group of peoplewho directs and controls an organisation.Section five of the standard identifies thefollowing key areas of managementresponsibility:
• Management commitment
• Customer focus
• Quality policy
• Planning
• Responsibility, authority andcommunication
• Management review
• Provision of resources.
As part of the review process there is arequirement to review process performance
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and product conformity, this including theoutput from process monitoring andmeasurement activities. Of equal importanceis the review of customer feedback, with a keyrequirement the monitoring of customersatisfaction.
To satisfy the requirement for continualimprovement the review should includeexamination of corrective and preventiveactions. The key differences between thesetwo activities are:
• Corrective actions eliminate the causeof a detected nonconformity
• Preventive actions eliminate the causeof a potential nonconformity.
DOCUMENTATIONThe new standard is far less prescriptive
than the previous and provides flexibility to anorganisation in the way that it documents itsquality management system. This enableseach individual organisation to identify andestablish the amount of documentationneeded to demonstrate the effective planning,operation and control of its processes and theimplementation of its quality managementsystem.
BS EN ISO 9001: 2000 requires, as haveprevious versions, a documented qualitysystem and not a system of documents.
Of all the activities within a qualitymanagement system, the standard onlyrequires six procedures to be formallydocumented. These are:
• Control of documents
• Control of quality records
• Internal audits
• Control of nonconformity
• Corrective action
• Preventive action.
It is recognised that for the administrationof the quality system other documentedprocedures will almost certainly be required inorder to manage the processes, which arenecessary for its effective operation. Indetermining which other elements or processesshould be documented the organisation couldconsider some or all of the following factors:
• Effect on quality
• Risk of customer dissatisfaction
• Regulatory requirements
• Economic risk
• Effectiveness and efficiency.
EXCLUSIONSThe previous 1994 standard was in
three parts:
• BS EN ISO 9001: 1994 Model for qualityassurance in design, development,production, installation and servicing
• BS EN ISO 9002: 1994 Model forquality assurance in production,installation and servicing
• BS EN ISO 9003: 1994 Model forquality assurance in final inspectionand test.
This provided a mechanism for anorganisation to elect which part best reflectedthe quality system associated with theirbusiness, this in turn forming the criterion forcertification. For example a company notproviding design services would be certificatedto BS EN ISO 9002.
As a consequence of BS EN ISO 9001:2000 replacing all three parts of the 1994standard, the new standard recognises andpermits an organisation to make a statementof exclusion. However where such exclusionsare made, claims of conformity to the standardare not acceptable unless such exclusions arelimited to any of the requirements withinClause 7. Such exclusions not affecting theorganisation’s ability, or responsibility, toprovide a product that meets customer andapplicable regulatory requirements.
Clause 7 addresses Product Realizationand covers the following requirements:
• Planning
• Customer related processes
• Design and development
• Purchasing
• Production and service provision
• Control of monitoring and measuringdevices.
BS EN ISO 9001 AND THE READY MIXED CONCRETE INDUSTRY
When QSRMC developed the 1995edition of the Quality and Product ConformityRegulations to reflect the requirements of BSEN ISO 9001: 1994 the opportunity was takento identify the key processes involved in
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producing ready mixed concrete (as shownbelow). This approach led to the documentbeing produced in six parts:
• Part 1 Quality System Requirements
• Part 2 Order Processing
• Part 3 Purchase and Control ofMaterials
• Part 4 Concrete Mix Design
• Part 5 Shipping Production andDelivery
• Part 6 Control of Concrete.
The structure of each individual part wasset out to follow that of the 1994 standard.
With the publication of the new standard itwas recognised that such a part structure to theRegulations would be inappropriate, particularlyas significant elements of Parts 2, 3, 4 and 5 fallwithin the “Product Realization” and Part 6within the “Measurement, Analysis andImprovement” sections of BS EN ISO 9001:2000.
As a consequence the QSRMC Regulationsrevised to meet the new standard have aseamless structure, this following that within the9001: 2000 document.
It should be recognised that theterminology in the standard is generic andapplies to any application, whether this is amanufacturing or service industry. Where theapplication is sector specific it is quite normal forthe terminology commonly used to be atvariance with the standard. In such cases it is
appropriate to use alternative wording as longas this is clearly stated and defined in anydocumentation.
To illustrate this concept the contents pageof the QSRMC Quality and Product ConformityRegulations (BS EN ISO 9001: 2000) is as follows:
1. Scope
1.1 General
1.2 Application
2. Normative References
3. Terms and Definitions
4. Quality Management System
4.1 General Requirements
4.2 Documentation Requirements
4.2.1 General
4.2.2 Quality Manual
4.2.3 Control of Documents
4.2.4 Control of Quality Records
5. Management Responsibility
5.1 Management Commitment
5.2 Customer Focus
5.3 Quality Policy
5.4 Planning
5.4.1 Quality Objectives
5.4.2 Quality Management SystemPlanning
5.5 Responsibility, Authority andCommunication
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5.5.1 Responsibility and Authority
5.5.2 Management Representative
5.5.3 Internal Communication
5.6 Management Review
5.6.1 General
5.6.2 Review Input
5.6.3 Review Output
6. Resource Management
6.1 Provision of Resources
6.2 Human Resources
6.2.1 General
6.2.2 Competence, Awareness andTraining
6.3 Infrastructure
6.4 Work Environment
7. Product Realization
7.1 Planning
7.2 Order Processing
7.2.1 Review of Enquiries
7.2.2 Review of Orders
7.2.3 Customer Communication
7.3 Mix Design
7.3.1 Mix Design Planning
7.3.2 Mix Design Inputs
7.3.3 Mix Design Outputs
7.3.4 Mix Design Review
7.3.5 Mix Design Verification
7.3.6 Mix Design Revalidation
7.3.7 Control of Mix Design Changes
7.4 Purchasing including Control ofMaterials
7.4.1 Purchasing Process
7.4.2 Purchasing Information
7.4.3 Verification of PurchasedProducts
7.5 Production and Supply
7.5.1 Operations Control
7.5.2 Validation of Concrete andService Provision Processes
7.5.3 Identification and Traceability
7.5.4 Customer Property
7.5.5 Concrete Delivery
7.6 Calibration
8 Measurement, Analysis andImprovement
8.1 General
8.2 Monitoring and Measurement
8.2.1 Customer Satisfaction
8.2.2 Internal Audit
8.2.3 Monitoring and Measurement ofProcesses
8.2.4 Control of Concrete
8.3 Control of NonconformingProduct
8.4 Analysis of Data
8.5 Improvement
8.5.1 Continual Improvement
8.5.2 Corrective Action
8.5.3 Preventive Action.
AppendicesA Definitions
B Quality Management SystemsInterpretations
C References
D Certification and AdministrativeProcedures.
IndexAppendix B includes Quality
Management Systems Interpretations asfollows:
In preparing these Regulations to meetthe requirements of ISO 9001: 2000 QSRMChas recognised that some of the terminologyand vocabulary used within the standard doesnot represent that used commonly within theready mixed concrete industry. The following isa list that shall apply and identifies thesespecific interpretations.
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In producing the revised Regulations itwas recognised that many of the requirementsof the new standard were non-specific. Theclauses set out general requirements, which acompany is required to address, but with nodetailed guidance on how this would beachieved or deem to satisfy.
In producing the revised set ofRegulations QSRMC have consciouslyrecognised that it would be wrong to produceprescriptive requirements over qualitymanagement issues, it being down to thecompany how they manage and run theirbusiness. This will, by necessity, result in anyassessment process of a quality managementsystem relying on the assessment team havinga full understanding of an individual companysystem and them making specific judgementson whether such a system satisfies thestandard.
One key issue for a company is therequirement for continuous improvement.Since 1991, QSRMC has been compilingperformance statistics on the ready mixedconcrete industry. These statistics haveprovided the means for establishing nationalbenchmarks, which on an annual basis allowthe Governing Board to monitor theperformance of QSRMC certificatedcompanies. In addition for many years QSRMC
staff have held meetings with seniormanagement of companies to discuss theirindividual performance. During thesemeetings comparisons are made between theindividual company’s performance and thenational data. This provides a mechanism tohelp companies make judgements on“continuous improvement”.
CONCLUSIONA quality management system
established to satisfy the requirements of BSEN ISO 9001: 2000 and, if appropriate, BS ENISO 9004, provides the basis for such a systemto fully recognise and react to customerrequirements, ensuring that customersatisfaction is achieved. The establishment ofappropriate monitoring and measurementprocesses enables an organisation to identifyareas for change within a quality system toenable the objective of continual improvementto be fulfilled.
For sector specific operations such asready mixed concrete, it is important thatwhere appropriate the generic quality standardterms are interpreted and redefined torepresent the specific industry terminology.
ISO 9001: 2000 TERMINOLOGY QSRMC TERMINOLOGYControl of Design and Development Changes Control of Mix Design ChangesControl of Monitoring and Measuring Devices CalibrationControl of Nonconforming Product Control of Nonconforming ConcreteControl of Production and Service Provision Operations ControlCustomer-Related Processes Order ProcessingDesign and Development Mix DesignDesign and Development Inputs Mix Design InputsDesign and Development Outputs Mix Design OutputsDesign and Development Planning Mix Design PlanningDesign and Development Review Mix Design ReviewDesign and Development Validation Mix Design RevalidationDesign and Development Verification Mix Design VerificationDetermination of Requirements Related Review of Enquiriesto the ProductMonitoring and Measurement of Product Control of ConcreteOrganisation CompanyPreservation of Product Concrete DeliveryProduction and Service Provision Production and SupplyPurchasing Purchasing including Control of MaterialsReview of Requirements Related to the Product Review of OrdersTop Management Company Senior ManagementValidation of Processes for Production Validation of Concrete and Service and Service Provision Provision Processes
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Steve Crompton is theTechnology and MarketingDirector for RMC Readymix Ltda wholly owned subsidiary ofRMC Group plc who are theworld’s largest producer of
readymixed concrete. He is Secretary toB/517/1-WG20, the British Standard Committeeresponsible for the production of BS8500, andthe convenor of CEN/TC104/TG8 the EuropeanCommittee responsible for concrete testmethods.
ABSTRACTBS EN 206-1: 2000 introduces the concept
of conformity assessment into the production ofconcrete. Conformity rules for strength,consistence, density, minimum cement content,maximum water/cement ratio, air content andchloride content are discussed in the paper. TheBS EN 206-1: 2000 rules for conformity are notstraightforward and there are many practicalissues which the standard does not address.This paper examines the implications of newrules for both suppliers and specifiers of concreteand gives recommendations on what actionscan be taken by the Producer in a number ofpractical situations. The paper also provides ananalysis of the risk of non-compliance withstrength requirements at a range of designmargins and examines the practical implicationsof the new rules on the readymixed concreteproducer. An overview of the conformity rulesfor properties other than strength is given andactions in the case of non-conformity are alsodiscussed.
KEYWORDSConcrete, Ready-mixed Concrete,
Conformity, Consistence, Design margins,Strength, BS EN 206-1: 2000, BS 8500.
1. INTRODUCTIONThis paper explains and amplifies the
conformity rules given in BS EN 206-1: 2000Concrete - Part 1: Specification, performance,production and conformity[1]. Information isgiven on the margins necessary for achieving aselected probability of acceptance (Pa). Particular
emphasis is given to conformity for compressivestrength although the rules for consistence,density, minimum cement content, maximumw/c ratio, air content and chloride content arediscussed.
Only the initial analysis of test data forconformity is covered. This leads toidentification of potential non-conformities.Further analysis is necessary to confirm non-conformity. This should include:
• checking that the correct testspecimens were tested
• checking that the data did not give anyjustifiable reason for excluding themfrom the conformity assessment
• checking for non-uniform conditions ofproduction
• an in-depth analysis to determinewhich members of the family were inconformity and which members were innon-conformity and over what period.
The information and recommendations inthis paper are based on statistical theory,analysis based on simulated data and analysis ofreal production data from a range of concreteplants. Data from the following types of plantwere included in the analysis:
• busy stable plant
• busy unstable plant
• low volume, regularly sampled plant
• low volume, irregularly sampled plant.
This analysis showed that the greatest riskto producers occur in busy plants with high ratesof testing. This is simply because there will be alot of production before any problem is detectedand corrected.
Clause 9.1 of BS EN 206-1: 2000 statesthat production control includes conformity.However BS EN 206-1: 2000 also recognisesthat the producer needs a system forproduction control that is independent fromconformity control. To avoid confusion, thispaper uses the term “production control”where it refers to the actions taken to controlthe production e.g. the Cusum system. For thepurposes of this paper, the term “productioncontrol” does not include conformity control.
CONFORMITY TO EN206
Mr. S. J. Crompton BEng(Hons), MICT
RMC Readymix Ltd
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2. CONFORMITYConformity is defined as “assessment
procedures undertaken by the producer toassure the specifier that the concrete conformsto the requirements of BS EN 206-1: 2000 andBS8500”.
BS EN 206-1: 2000 requires that thefollowing properties of concrete are checkedfor conformity:
• strength (compressive and tensile ifspecified)
• consistence (formerly known asworkability)
• density
• minimum cement content
• maximum water/cement ratio
• air content
• chloride content.
This standard uses two statisticalmethods for assessing conformity. Strengthconformity is assessed by variables whilst allother properties are assessed by the method ofattributes.
3. RESPONSIBILITY FOR CONFORMITY CONTROL
Clause 9.1 of BS EN 206-1: 2000 clearlyrequires the producer of concrete to beresponsible for verifying that all the concretesthey place on the market conform to theirspecifications. This is demonstrated byapplication of the conformity rules given in BSEN 206-1: 2000. There is also a generalprinciple in the European Union that non-conforming products should be prevented fromreaching the market. With fresh concrete this isclearly not possible for all properties and a
compromise had to be reached. For example,the European Standardisation Body (CEN)wanted strength to be a requirement ofdesigned concrete, but this is not a property ofconcrete as it is placed on the market.Excluding this requirement from specificationswas not acceptable. The compromise was thatconcrete could be placed on the market with adeclared strength class and the producer isrequired to inform the specifier if subsequenttesting shows that this claim is not correct. Toavoid unnecessary bureaucracy, it isunnecessary for producers to issue statementssaying that the claims made on the deliverytickets have been subsequently proven to becorrect. This should be assumed unless toldotherwise.
The conformity rules in BS EN 206-1:2000 were formulated on the basis that onlythe producer exercises conformity control. Anychange to this approach will requirefundamental and significant changes to theconformity rules. However, in recognition thatsome specifiers may wish to occasionallysample and test the delivered concrete, BS EN206-1: 2000 provides for identity testing.
4. CONFORMITY CRITERIA FOR STRENGTH
4.1 Initial ProductionWhere there are less than 35 results and
the standard deviation of the plant is unknownthe conformity criteria is based on the mean of3 results fcm ≥ (fck+4). Brown & Gibb[2] analysedthe risks of non-conformity with the BS EN206-1: 2000 requirements for initial production.These risks are presented in Table 1 for non-overlapping results.
Table 1: Probability (%) of non-conformity with the strength requirements for initialproduction.
Design Normal distribution Castellated distribution
margin Standard deviation, N/mm2 Standard deviation, N/mm2
3 4 5 3 4 5
1.64σ 28.41 11.11 6.25 33.34 16.17 10.11
2.00σ 10.45 3.81 1.62 20.71 8.74 3.99
2.33σ 4.08 1.01 0.25 10.8 3.01 1.11
Data from Brown & Gibb[3]
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The castellated distribution of data isconsidered to reflect more accurately the stepchanges in quality that occur with concreteproduction[3]. These data show that even witha margin of 2.33σ, there is a significant risk ofnon-conformity if the standard deviation is verylow.
The producer may adopt the samplingand testing plan and the criteria for initialproduction for continuous production (see8.2.1.1 of BS EN 206-1: 2000). The analysisgiven in Table 1 indicates that this approachposes high risks to the producer of having non-conforming concrete. It is recommended thatwhere conditions for continuous productionexist, conformity be based on the continuousproduction criteria and not on a continuationof the initial production criteria.
These high risks and high margins applyto special concretes that are continuallyassessed by the initial production criteria. Itshould be noted that the analysis used randomnumber generation without auto-correlation.Auto-correlation is likely where the initialproduction criteria are applied to specialconcretes as they tend to be producedintermittently and tested frequently duringthese periods of intermittent production. This,in theory, could increase the risk of non-conformity.
4.2 Continuous ProductionContinuous Production rules apply where
the standard deviation can be assessed from atleast 35 results, the rule is:
fcm ≥ fck + 1.48σ
The choice of number of results to assessthe mean is the producers but must be greaterthan or equal to 15.
In BS EN 206-1: 2000, the characteristicstrength has been defined as the 5% fractileand consequently the mean strength of thetotal population is required to be:
fcm ≥ fck + 1.65σ
In practice, however, only a sample fromthe total population is tested. In this case thestatistical test applied is one that gives a smallrisk that the producer will conclude that theconcrete is conforming with the specificationwhen the population is non-conforming i.e. fcm
is substantially lower than (fck + 1.65σ). In thecontext of BS EN 206-1: 2000, the populationis all the production of a single concrete orconcrete family in an assessment period.
Consequently it is possible for all the concretein a single structural element or series ofelements to contain concrete with a strengthbelow the specified characteristic strength, e.g.a single batch of concrete with strength (fck - 2)could be placed in all the columns of a smallbuilding. Such realities are not new and theformer concrete conformity requirements gavethe same situation. Current design methodsand safety factors result in concrete that israrely loaded to more than 40% of itscharacteristic strength and an upper limit of0.6fck for concrete compressive stress isrecommended in prEN 1992-1: Design ofconcrete structures - Part 1: General rules andrules for buildings[4].
4.3 Individual Criterionfci ≥ fck -4
This is an absolute criterion, which appliesto both initial and continuous production, andno individual result can fall below therequirement. This requirement influences thetarget mean strength and to ensure a highprobability of conformity a design margin of 3σabove (fck -4) will need to be adopted.
5. REQUIREMENT FOR UNIFORMCONDITIONS OF PRODUCTION
Clause 8.2.1.2 of BS EN 206-1: 2000states that sampling shall be carried out “underconditions that are deemed to be uniform”.The implication of this is that conformity onlyapplies to uniform conditions of production.What constitutes “uniform conditions” is notdefined nor is what to do when uniformconditions do not apply. A change in meanstrength or a change in standard deviationcould be taken as a change in the conditions ofproduction. However, it is not normallynecessary for such a change to trigger the endof the assessment period.
Whether a significant change in the meanstrength should ever trigger the end of anassessment period is an open question. Inpractice, once a significant change in meanstrength is detected, the mix proportions areadjusted to achieve the intended meanstrength. This will leave a short period ofproduction where a few data sets will have adifferent mean strength. If this strength wereto be lower than expected, analysis of thesefew data sets is more likely to indicate a non-conformity than if these data were part of alarger population. It is recommended that a
New σ smaller New σ largerthan old σ than old σ
Number of results obtained prior to the detection of a change in the standard deviation n≤ 6 n>6 n≤ 6 n>6
Case 1 Case 2 Case 3 Case 4
Standard deviation to be used for production control in the rest of the assessment period New σ Old σ New σ New σ
Standard deviation to be used to assess conformityin the current assessment period New σ Old σ New σ Old σ
Assess conformity using the “n” results or wait until the normal number of results are available Wait Wait Wait Use “n”
results
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change in mean strength should not be usedto determine the end of an assessment period.However, when analysing a potential non-conformity, part of the analysis should includechecking for a change in mean strength as thismay delimit the period of non-conformity.
A significant change in the standarddeviation is an indication that the productionconditions have changed. Thus a change inthe standard deviation should indicate the endof one assessment period and the start of thenext. This can create a practical problem whenthe start of a new assessment period creates aperiod with less than the expected number ofsets of compressive strength test results e.g.there are less than 15 results from the end ofthe last assessment and the time when achange in standard deviation was detected.The following procedure is recommendedwhere the normal number of results in anassessment period has been set at a value of≥ 15.
There are three decisions that have to betaken:
• whether to use the new standarddeviation or the old standard deviationfor production control in the rest ofthe assessment period
• whether to use the new standarddeviation or the old standard deviationto assess conformity in the currentassessment period
• whether to use the “n” results toassess conformity immediately or towait until the normal number of testresults are available.
Table 2 gives recommendations of whatactions should be taken and the following
comments give the basis for theserecommendations.
Case 1: When the change in σ issignalled some way into an assessment period,it is likely that the change actually took placebefore the start of the period, so the new σ willbe the correct one to use for both productioncontrol and conformity assessment.
Case 2: When the change in σ issignalled some way into an assessment period,the change may have actually taken placeduring the assessment period, and neither theold σ ?nor the new σ will be the correct one touse for conformity assessment. Using the oldσ for conformity assessment gives the smallerrisk to the specifier, so the producer shouldretain the old σ for production control until theend of the assessment period to avoidincreasing his risk.
Case 3: When an increase in σ issignalled, the new value should be adopted forproduction control immediately. As in Case 1,the new σ is likely to be the correct one to usefor both production control and conformityassessment. However, using the new ( toassess conformity will increase the producer’srisk because the “n” results will have beenobtained at a lower target average strengththat that given by the new σ. In Case 3, thisincrease in the producer’s risk is limitedbecause the “n” results will be a small part ofthe ≥ 15 results used to assess conformity.(Note that the actions as given in Table 2 arethe same for Cases 1 and 3.)
Case 4: It is not acceptable from theproducer’s point of view to use the new, larger,σ to assess conformity when most or all of theresults in an assessment period relate to
Table 2: Recommendations on actions to be taken where a change in standarddeviation has been indicated part way through an assessment period.
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concrete produced using a target averagecalculated using the old, smaller, σ.Consequently, the old σ is used to assessconformity in Case 4, and the increase in thespecifier’s risk is limited by bringing theassessment period to a close as soon as theincrease in σ is signalled, and assessingconformity using the “n” results available atthat time.
In all cases, the new value of standarddeviation is used in the next assessment periodfor both production control and conformity.
6. TEST DATAThe requirements of BS EN 206-1:
2000 are:
From 8.1 Where tests for productioncontrol are the same as those required forconformity control, they shall be permittedto be taken into account for the evaluationof conformity. The producer may also useother test data on the delivered concretein the conformity assessment.
It makes commercial sense to usestrength test data for both production andconformity control. The inclusion of other testdata e.g. that obtained from the customer byidentity testing, is the producer’s choice. Therecan be differences in data produced by adifferent organisation using different testmachines and, possibly, different specimenshapes. The producer has no control over howwell these specimens are made, cured andtested. In most cases, the sampling frequencyfor identity testing is likely to be lower than thatrequired for conformity testing. As a generalrule, the best option is to use the producer’sdata only, but there may be exceptions to thisadvice. For example, when the producer iscontrolling a single concrete and it is unlikelythat sufficient data will be obtained to qualifyfor continuous production. In this case it maybe of benefit to use identity test data.
Where there is insufficient test data fromdesigned concretes the inclusion of data fromprescribed concretes should be considered. Ifthese data are included, the individual criterionis not applicable. The actual cement content iscorrected back to those materials andproperties of the Reference Concrete and thiscorrected cement content used to determinethe target strength. This target strength isused in the assessment of conformity of themean strength.
When an assessment period containingsome data from prescribed concretes is in non-conformity, further analysis of the data shouldexclude data from prescribed concretes for theperiod of non-conformity.
For production control purposes, it isnormal to exclude statistical outliers. These arenormally defined as results that are ± 3σ fromthe target mean strength. However, if thisapproach were to be applied to conformitycontrol, the effect would be to eliminate resultsthat may fail the individual criterion. Theconformity control system should identify alloutliers and each one should be investigated.Unless there is a valid reason for rejecting theresult, low outliers should be included in theconformity assessment but excluded from thecheck on standard deviation. Producers mayeliminate high outliers from the conformityanalysis, but if the high result is caused byrequirements other than the specified strengthcontrolling the actual strength e.g. maximumw/c ratio, these data should be included usingthe procedure described above.
7. POINT OF SAMPLING ANDSAMPLING RATE
The requirements of BS EN 206-1: 2000 are:
From 8.1 The place of sampling forconformity tests shall be chosen such thatthe relevant concrete properties andconcrete composition do not changesignificantly between the place ofsampling and the place of delivery. In thecase of lightweight concrete producedwith unsaturated aggregates, the samplesshall be taken at the place of delivery.
From 8.2.1.2 The minimum rate ofsampling and testing of concrete shall bein accordance with Table 13 of BS EN 206-1: 2000 a the rate that gives the highestnumber of samples for initial or continuousproduction, as appropriate.
Not withstanding the samplingrequirements in 8.1 of BS EN 206-1: 2000,the samples shall be taken after any wateror admixtures are added to the concreteunder the responsibility of the producer,but sampling before adding plasticiser orsuperplasticiser to adjust the consistence(see 7.5 of BS EN 206-1: 2000) is permittedwhere there is proof by initial testing thatthe plasticiser or superplasticiser in the
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quantity to be used has no negative effecton the strength of the concrete.
If higher sampling rates are requiredby the specifier, this shall be agreed inadvance.
From Table 13 Where the standarddeviation of the last 15 test results exceeds1,37σ, the sampling rate shall be increasedto that required for initial production forthe next 35 test results.
BS EN 206-1: 2000 permits, as analternative to sampling on site, sampling at theplant provided water is not added at site underthe responsibility of the producer. Theexception to this is where lightweight concretewith saturated aggregates is supplied.
The benefits of sampling at the plant are:
• lower costs per test result
• the ability to test at a higher rate
• simpler to test the first load of airentrained concrete each productionday.
However there may be practical problemswith sampling at the plant with someproduction systems, particularly in respect ofsafety and obtaining a representative sample.
Table 13 of BS EN 206-1: 2000 uses theterms “production day” and “production week”
without defining what these terms mean.Consequently, the draft BS 8500-2[5] includesthe following definitions:
production day: Day in which 20m3 ormore of designed concrete has been producedor, on days where less than 20m3 of designedconcrete have been produced, the day onwhich a cumulative 20m3 has been producedshall be regarded as one production day. Thesequence is restarted on a new day for eachoccasion when a production day is counted.
production week: A period of 7consecutive days comprising at least 5production days or alternatively, the periodtaken to complete 5 production days,whichever is the longer period.
The rate of sampling is given in Table 13 ofBS EN 206-1: 2000. The volume rates shouldbe taken as the prime sampling rate and onlywhere this rate does not give sufficient testresults, should the time rate of sampling beapplied. Where this is applied, the volume atthe end of the production week/day (asappropriate) is taken as 0. The volume rates arenot time dependent e.g. where there iscontinuous production of 410m3 of concretefrom a family in 1 production week, theminimum rate of sampling is 1 and the last10m3 of production starts the next 400m3 ofproduction.
Minimum rate of sampling for a concrete family
Production Volume of Carry-over Carry-over Minimum rate Commentsweek production in volume of volume of of sampling
production week production production for thefrom previous plus actual concrete familyproduction volume ofweek production
1 350 0 350 1 1/week
2 370 0 370 1 1/week
3 440 0 440 1 1/400 m3
4 565 40 605 1 1/400 m3
5 630 205 835 2 1/400 m3
6 840 35 875 2 1/400 m3
7 790 75 865 2 1/400 m3
8 375 65 440 1 1/400 m3
Example 1: Example of testing rates with continuous production and productioncontrol certification.The minimum rates of sampling given in Table 13 of BS EN 206-1: 2000 are 1/400 m3
or 1/production week.
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In order to achieve the desired number oftest results in an assessment period, it is betterto extend the time taken than to increase therate of testing as an increased rate of testingmay increase auto-correlation. Avoid very highrates of testing as this is likely to give auto-correlation and increases the risk of non-conformity where “n” is relatively low.
The note in Table 13 of BS EN 206-1: 2000to increase the rate of sampling only applieswhere there is a step change in the standarddeviation greater than 1.37σ. It isrecommended that more sensitive systems areused to detect changes in standard deviationand in practice the standard deviation shouldbe changed prior to a change of 1.37σ. Withsuch changes in the standard deviation, thereis no requirement to increase the rate of testingeven if a series of step changes has exceeded1.37σ.
The specifiers option to increase thesampling rate is not helpful. One assumes thatthis means a higher minimum sampling rateand that it only applies to the concreteproduction going to that specifier. Where theconcrete is produced on site with a dedicatedplant, a change in the minimum sampling ratecan be accommodated. However, where thespecifiers requirements represent a small partof the output from a ready-mixed concreteplant, it is not a very easy requirement to satisfyand it could skew the random testing of theproduction (a requirement of BS EN 206-1:2000). Again there are exceptions to thisgeneral advice. Where high strength concretefor critical elements is produced, the specifiermay require each load to be tested. Theseconcretes cannot form part of a family and thehigher rate of testing may be needed to qualifyfor continuous production.
8. NUMBER OF SPECIMENS PERTEST RESULT
The requirements of BS EN 206-1: 2000 are:
From 8.2.1.2 The test result shall bethat obtained from an individual specimenor the average of the results when two ormore specimens made from one sample aretested at the same age.
Where two or more specimens aremade from one sample and the range ofthe test values is more than 15% of the
mean then the results shall be disregardedunless an investigation reveals anacceptable reason to justify disregardingan individual test value.
The number of specimens to be madefrom one sample is decided by the producer.Where two or more specimens are made, it ispossible to run a check on how well thespecimens were made and tested. Wherethere is a low-test result based on a singlespecimen, it will be more difficult to justify itsexclusion from the conformity control and theloss of that single value may mean that theproducer has no information on that batch ofconcrete. There may, however, be arequirement for greater carrying capacity invans and larger curing tanks where two cubesare taken.
9. ASSESSMENT PERIOD
9.1 Requirements of BS EN 206-1:2000.
The requirements are:
From 8.2.1.3 Conformity assessmentshall be made on test results taken duringan assessment period that shall not exceedthe last twelve months.
In Table 14, the criteria are only givenwhere the number of “n” of test results forcompressive strength in the group is 15.
An assessment period is selected andrecorded for every concrete family and everyindividual concrete not within a family.Conformity has to be established for everyconcrete family and every individual concrete ateach assessment period. Assessment periodsmay be different for each concrete family andindividual concrete. Obviously, if a particularconcrete is not produced during an assessmentperiod, there is no requirement to verifyconformity. Conversely, every concrete familyand every individual concrete not within afamily is required to be sampled and tested forconformity. There is no requirement to testevery member of a concrete family, only fortests to be taken at random from the family.
The number of test results in eachassessment period required by BS EN 206-1:2000 is not defined. During the developmentof BS EN 206-1: 2000, it was understood thatthe continuous criteria would apply to 15 ormore results obtained in an assessment period.
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Early drafts of BS EN 206-1: 2000, including theCEN Enquiry version, contained the words “notless than 15”. However, in the voting version ofBS EN 206-1: 2000, the words “not less than”had been deleted. This creates uncertaintyover the conformity provisions as there is norequirement for “n” to be 15 and no definedrequirements for conformity where “n” is notequal to 15. In the view of the BSI, this changewas an error. Unfortunately, to correct thiserror will require an amendment to BS EN 206-1: 2000 that will take some time to pass itsformalities. In the meantime, nationalprovisions should provide requirements onwhat to do when the number of test resultsdoes not equal 15. For example, BS8500-2[5] (atpresent at the public commenting stage)contains the words:
“The criteria given in tables 14 and 16of BS EN 206-1: 2000 for n=15 apply tohigher values of n”.
This restores clarity to the conformitycriteria when n ≥ 15. See 12 for guidancewhen n < 15 in an assessment period.
There is no requirement for theassessment period to be defined in terms oftime, only that the assessment period shall notexceed 12 months. The assessment periodmay be different for certain concretes orfamilies. Different assessment periods mayapply to different aspects of conformity, e.g.strength and chloride content. Theassessment periods within a company do nothave to be constant; it can vary from plant toplant. This flexibility is essential as theassessment period for, say, a busy urban plantis likely to be different to a rural plant producingmainly prescribed concrete.
Methods of defining the assessmentperiod include:
• defined volume of concrete
• number of test results
• period of uniform conditions ofproduction.
It is recommended that a change ofmean strength should not trigger the end of anassessment period and that only in certainconditions should a change in standarddeviation trigger an immediate end to theassessment period. All the above methodsrequire the proviso that the resulting perioddoes not exceed 12 months. Composites ofthe above are permitted and recommended.
Conformity has to be declared only at theend of each defined assessment period. Priorto this the producer should be keeping a watchon the likelihood of achieving conformity andwhere this is in doubt, taking appropriatecorrective measures.
The producer has no requirement todeclare conformity for the period of supply fora particular contract. As it is the norm thatmany contracts are supplied at any one time,this is not a practical option. It would besatisfactory for the producer to declare anyproven non-conformity within a reasonabletime after the end of each relevant assessmentperiod.
9.2 Number of test results in anassessment period
Figure 1 shows operating characteristicsfor conformity rules in which different numbersof test results are used to calculate the mean,fcm. Note that they intersect at a pointcorresponding to a probability of acceptance of50%.
Figure 1 shows that increasing thenumber of test results used to assessconformity:
• increases the probability of accepting aconforming population for which ø < 5%
• increases the probability of rejecting a non-conforming population for which ø > 10%.
Tables 3 and 4 provide some detailedresults to illustrate the effect of the number oftest results on conformity. Table 3 gives theproducer’s margins required to achieve a 98%probability of acceptance when differingnumbers of test results are used to assessconformity.
Table 4 gives the specifier’s risks whendiffering numbers of test results are used toassess conformity, and in the situation whenconcrete is supplied from a population forwhich ø=10%. Table 4 shows that increasingthe number of test results increases theprotection provided by conformity assessmenteven in this situation when the concrete is onlymarginally non-conforming.
The conformity rule is fcm ≥ fck + 1.48σ.The data are auto-correlated (according toTaerwe’s model with parameters 0.4 and 0.2),the mean is calculated from 6, 15, 35 or 70 testresults, and the standard deviation isestablished beforehand (from 35 test results).
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It is recommended that an assessmentperiod for a concrete family contains at least 35test results.
9.3 Effect of auto-correlation onthe probability of acceptance
“Auto-correlation” means that successiveresults in a series of test results are correlated.For example, in the case of positive auto-correlation, which is the case of interest withconcrete, it means that if one test result ishigher than the average for the series, then thenext test result is more likely to be higher thanthe average than lower than the average.
It is recommended that previousproduction data are checked for auto-correlation prior to establishing design margins.This can be done using software such as Excel.
Taerwe[6] examined five series of concretetest results and concluded that the resultscould be modelled by:
(Xn - µ) = 0.4(Xn-1 - µ) + 0.2(Xn-2 - µ) + εn
Here µ is the long-term average of thetest results
X1 , X2 , X3 , ... , Xn are successive testresults
εn (n = 1, 2, ...) are random deviations(normally distributed with mean zero andconstant variance)
Roberts[7] showed that under typicalBritish conditions, test results are not auto-correlated. However, the analysis of UK dataused in the development of this paper gavesome level of auto-correlation, but less thanthat assumed by Taerwe.
The effect of auto-correlation is illustratedby Figure 2. The two operating characteristicsshown with solid lines are auto-correlatedresults that follow Taerwe’s model (and are thesame as two of the lines shown in Figure 1).The two broken lines apply to the samecircumstances as the first two, but when thetest results are independent, not auto-correlated.
Figure 2 shows that if the test results areindependent, this:
• increases the probability of accepting aconforming population for which ø<5%
• increases the probability of rejecting anon-conforming population for whichø>10%.
Table 5 shows the effect on theproducer’s margin of auto-correlation. It isclearly advantageous for the producer to try toensure that the test results are not auto-correlated, particularly if the number of testresults available to assess conformity is only 15.
Number of test Probability of Percentage below Multiplier usedresults used to acceptance specified characteristic to calculate theassess conformity strength producer’s marginn Pa % ø % k
6 98.0 0.2 2.9
15 98.0 0.5 2.5
35 98.0 1.2 2.2
70 98.0 1.8 2.1
Table 3: The effect of the number of test results used to assess conformity on theproducer’s margin.
Number of test Probability of Percentage below Multiplier usedresults used to acceptance specified characteristic to calculate theassess conformity strength producer’s marginn Pa % ø % k
6 43.1 10.0 1.3
15 41.0 10.0 1.3
35 38.2 10.0 1.3
70 35.9 10.0 1.3
Table 4: The effect of the number of test results used to assess conformity on thespecifier’s risk.
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Figure 1: The effect of increasing “n” on the operating characteristic for the conformityrule used with continuous production in BS EN 206-1: 2000.Notes on Figure 1: The conformity rule is fcm ≥ fck + 1.48σ. The operating characteristicshave been obtained by simulation and apply when the data are auto-correlated(according to Taerwe’s model with parameters 0.4 and 0.2), the mean is calculated from6, 15, 35 or 70 test results, and the standard deviation is established beforehand (from35 test results).
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The conformity rule is fcm ≥ fck + 1.48σ.The data are independent, or auto-correlated(according to Taerwe’s model with parameters0.4 and 0.2), the mean is calculated from 15 or35 test results; and the standard deviation isestablished beforehand (from 35 test results).
10. NON-OVERLAPPING ANDOVERLAPPING RESULTS
The requirements of BS EN 206-1: 2000 are:
From 8.2.1.3 Conformity of concretecompressive strength is assessed on:
- groups of “n” non-overlapping oroverlapping consecutive test resultsfcm (criterion 1);
- each individual test result fci
(criterion 2)
NOTE: The conformity criteria aredeveloped on the basis of non-overlapping test results. Application of thecriteria to overlapping test results increasesthe risk of rejection.
The note warns of the increased risk ofrejection if the overlapping test results areused. The producer, not the specifier, selectswhich method of analysis to apply to the dataand it does not appear very sensible to select amethod of analysis that increases the risk ofrejection. Therefore the selection of the non-overlapping option is strongly recommended.
11. ESTIMATION OF STANDARDDEVIATION
BS EN 206-1: 2000 provides no guidanceon the method for determining the estimate ofthe standard deviation. The traditional way ofcalculation and the method programmed intomost calculators is the square root of the sumof the squared deviations of individual resultsfrom the mean divided by the number of resultsless one (RMS method). However such amethod is not appropriate where the processaverage can change as is the case withconcrete production. In the case of concreteproduction, the estimate of the standarddeviation should be based upon:
Estimated standard deviation = 0.886 xmean range of successive pairs of results.
The derivation of this equation can befound in standard statistical works onproduction control such as Oakland[8]. Theaverage range is widely used to provide themeasure of dispersion used in process controlcharts, such as the Cusum system, and so hasstood the test of widespread practical use.
The standard deviation estimated fromaverage range is to be preferred over theconventional sample standard deviation as amethod of estimating the population standarddeviation where the data can contain outlyingresults. This is because the average range isless affected by such results than the samplestandard deviation. In the calculation of thesample standard deviation, the squares of afew large deviations will outweigh those of theother smaller deviations. The estimation of the
Number of test results Producer’s design Probability ofused to assess conformity margin non-conformityn k %
6 (independent) 2.0 12.5
6 (auto-correlated) 2.0 20.4
15 (independent) 2.0 4.7
15 (auto-correlated) 2.0 14.2
35 (independent) 2.0 1.5
35 (auto-correlated) 2.0 7.4
6 (independent) 2.326 2.9
6 (auto-correlated) 2.326 10.0
15 (independent) 2.326 0.3
15 (auto-correlated) 2.326 4.8
35 (independent) 2.326 0.02
35 (auto-correlated) 2.326 1.2
Table 5: The effect of auto-correlation on the producer’s margin.
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population standard deviation from theaverage range does not involve squaring so theeffect of the outlying results is smaller.
Likewise, the use of the average range isto be preferred over the sample standarddeviation where the data contain changes inthe process mean with time. The samplestandard deviation is calculated using thedeviations of the results from the commonarithmetic mean of all the results. Therefore, ifthe results contain a shift in the process mean
at some point in time, all these deviations willbe inflated and the sample standard deviationwill give an inflated estimate of the dispersionof the data. Where the average range is used,such a shift will affect only the one range, orranges, that spans the shift. Hence thepopulation standard deviation estimated fromthe average range will be less affected by sucha shift in mean strength than the standarddeviation calculated from the sample, seeExample 2.
Figure 2: The effect of test results being either independent or auto-correlated onoperating characteristics.Notes on Figure 2: The conformity rule is fcm ≥ fck + 1.48σ. The operating characteristicshave been obtained by simulation, and apply when the test results are eitherindependent or auto-correlated (according to Taerwe’s model with parameters 0.4 and0.2), the mean is calculated from 15 or 35 results, and the standard deviation isestablished beforehand (from 35 results).
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Figure 3a: 30 random data generated assuming a mean strength of 37.0 N/mm2 and astandard deviation of 3.5 N/mm2 (the first group of 15 results are the same as thesecond group of 15 results).
Figure 3b: The same data as in Figure 3a, but with a reduction in mean strength of 5.0N/mm2 introduced at result 16.
Example 215 random data have been generated
assuming a mean strength of 37.0 N/mm2 anda standard deviation of 3.5 N/mm2. These havebeen repeated to give a total of 30 data, seeFigure 3a. The standard deviation of the 30data given in Figure 3a is:
3.6 N/mm2 when determined by thestandard method
3.7 N/mm2 when determined from 0.886x mean range.
To illustrate the effect of a change inmean strength on the standard deviation, anextreme reduction in mean strength of 5.0N/mm2 is introduced at result 16 i.e. data 16 to30 are all 5.0 N/mm2 less than in Figure 3a. Thedispersion of the data around these meanstrengths is unchanged. The standarddeviation of the 30 data given in Figure 3b is:
4.4 N/mm2 when determined by thestandard method
3.8 N/mm2 when determined from 0.886x mean range.
This shows that the standard deviationcalculated from the mean range has been lessaffected by the change in mean strength.
In the context of conformity assessment,both outlying results and shifts in the processmean during an assessment period, are to beexpected.
The standard deviation to be applied tothe first period of assessment of continuousproduction is estimated from at least 35 resultsfrom the period exceeding 3 months thatimmediately precedes the assessment period.
At least every assessment period, thestandard deviation is checked to confirm that ithas not changed significantly. BS EN 206-1:2000 permits two methods of verifying theestimate.
Method 1 calculates the standarddeviation of the latest 15 results, s15, andcompares this with the current estimate of thestandard deviation, σ. If the standard deviationis not within: 0.63σ ≤ s15 ≤ 1.37σa new estimate of σ is calculated using the
22
2
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latest 35 results. This new value of the standarddeviation is applied to the next assessmentperiod. As shown in Table 6, this method ofdetecting changes in the standard deviation isrelatively crude and insensitive. With thismethod where the standard deviation is high, itis very difficult to trigger a change in thestandard deviation.
With Method 1, particular care is neededwhen the standard deviation is reducing and alower value is adopted immediately forproduction. If the target mean strengths arereduced to reflect the lower margin, there couldbe an increase in risk of non-conformity as theassessment is based on the previous (higher)standard deviation. With low initial standarddeviations, further reductions in the standarddeviation can result in the target mean strengthbeing lower than the conformity limit, i.e.negative values as shown in Table 7. A lowervalue of standard deviation should not beadopted until the assessment period is closed.
Whilst Table 7 shows that it is safe toadopt increases in standard deviationimmediately for production, as adoption of thenew value of standard deviation increases themargin. However, certification bodies are likely
to take the view that if the producer hasevidence that the standard deviation hasincreased, they should immediately adopt thenew value for production.
Users of the Cusum technique wouldprobably regard a 0.50 N/mm2 real change instandard deviation as being significant andconsequently Method 2 was introduced into BSEN 206-1: 2000 allowing the use of continuoussystems, such as Cusum R, for checking theestimate of standard deviation. The sensitivity ofsuch systems has to be at least as good as thatgiven by Method 1. Method 2 is not restrictedto systems such as Cusum.
A further advantage of using Method 2with a sensitivity greater than that of Method 1,is that the requirement to increase the rate oftesting to that used in initial production onlyapplies where the change in standard deviationis > 1.37σ.
Where the Cusum and similar techniquesare used for production control, there may becut-off lower and upper limits on standarddeviation within the production control system.The system should be modified to ensure thatcut-off values are not used for conformityassessment.
Current σ, Lower limit, Upper limit, Range,N/mm2 N/mm2 N/mm2 N/mm2
2 1.27 2.73 ±0.73
3 1.90 4.10 ±1.1
4 2.53 5.47 ±1.47
5 3.16 6.84 ±1.84
6 3.79 8.21 ±2.21
7 4.42 9.58 ±2.58
Table 6: Limits on s15 outside of which a new estimate of the standard deviation is required.
Table 7: Difference between the target mean strength and the conformity limit wherethe standard deviation has changed and this new value adopted for production, butwhere conformity is based on the previous value of the standard deviation.
3 4 5 6
+1.5 2.00σ 4.56 5.08 5.60 6.12
+1.0 2.00σ 3.56 4.08 4.60 5.12
+0.5 2.00σ 2.56 3.08 3.60 4.12
0 2.00σ 1.56 2.08 2.60 3.12
-0.5 2.00σ 0.56 1.08 1.60 2.12
-1.0 2.00σ -0.44 -0.08 0.60 1.12
-1.5 2.00σ -1.44 -0.92 -0.40 1.12
Change in Design Difference, N/mm2
σ, N/mm2 margin, Previous value of σ, N/mm2
N/mm2
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12. LOW-VOLUME PRODUCTIONBS EN 206-1: 2000 is not clear on the
issue of low volume production for specialindividual concretes. Whilst BS EN 206-1: 2000permits the application of the initial productioncriteria to continuous production, it has norequirement to apply these criteria to concretesthat have less than 15 results in an assessmentperiod. Special concretes commonly use atleast some of the constituent materials used inthe concrete families. In these cases, thespecial concrete should be linked to the familyand the confirmation criteria and theassessment of relationships should provideadequate control. Where this is not possiblethey should be treated as individual concretes.
In this case, one option is to apply theinitial production criteria to this concrete, butthis will require high margins and still pose asignificant risk of non-conformity. Thefollowing is a recommended procedure wherethe concrete families within a plant are incontinuous production. It is based on theassumption that the standard deviation ismainly a function of the plant.
1. Apply the initial production criteria tothe first assessment period.
2. For the second and subsequentassessment periods:• where n = 1 or 2, apply the
individual result criterion
• where n is the range 3 to 6, applythe initial production criteria to thefirst three and last three results
• where there are more than 6 testresults, apply the criteria forcontinuous production using themain family standard deviation.
Inspection of Figure 1 shows that wherethere are over 6 test results, the operational-characteristic does not enter the unsafe region.However the risk to producers is increasedwhere there are low numbers of test resultsand it is recommended that the producer applya suitable margin with these concretes toreduce the risk of non-conformity. It can beargued that a high margin is reasonable in
these situations to cope with uncertaintyassociated with a low production rate and thespecial nature of the individual concrete.
Special concretes are often producedintermittently and tested frequently duringthese periods of intermittent production. Thismay give a high level of auto-correlation of thetest results.
13. CONFORMITY FOR PROPERTIES OTHER THAN STRENGTH
The conformity requirements forproperties other than strength are spread invarious clauses in BS EN 206-1: 2000. Classlimits are given in clause 4, tolerances on targetvalues in clause 5 and maximum deviationsfrom these class limits or tolerances given inTable 17 of BS EN 206-1: 2000. Table 13combines these requirements and gives thenumber of results that have to fall within theclass limits or tolerances on target values wherethe assessment period is selected, the lastcolumn of Table 13 is not applicable.
Where limits are not given in Table 17 ofBS EN 206-1: 2000, the specification mayintroduce limits. Only exceptional cases wouldwarrant the introduction of additional limits. Itshould be noted that this permission is tointroduce limits where none are given in Table17 of BS EN 206-1: 2000, not introducedifferent limits to those given.
Conformity for properties other thanstrength is based on the method of attributes.In other words the number of results is outsidethe specified limiting values in an assessmentperiod is compared to a maximum permittednumber given in the standard.
The assessment period shall not begreater than 12 months and the minimumsampling rate is also specified in the standard.
Tables 19a and 19b of BS EN 206-1: 2000give the acceptance levels appropriate to theproperty which is being assessed. Table 19a isbased on an AQL of 4% and 19b on an AQL of15%.
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For some properties the upper and lower acceptance ranges will not be the same since table17 of the standard restricts the maximum allowed deviation at each side of the class range.
13.1 ConsistenceTable 18 of the standard gives conformity requirements for Slump, Vebe, Degree of
Compactibility and Flow. These requirements are summarised in Table 8 below, where the limitsshow maximum allowed deviation of single test results from the limits of the specified class or fromthe tolerances on the target value.
Number of Acceptance Test Results Number
1-2 0
3-4 1
5-7 2
8-12 3
13-19 5
20-31 7
32-49 10
50-79 14
80-100 21
Table 19b of BS EN 206-1:2000: AQL = 15%.
Figure 4: Method Attributes.
AcceptanceRange Class Range
NO RESULTSNO RESULTS
AcceptanceRange
Number of Acceptance Test Results Number
1-12 0
13-19 1
20-31 2
32-39 3
40-49 4
50-64 5
65-79 6
80-94 7
95-100 8Where the number of test results exceeds 100,the appropriate acceptance numbers may betaken from Table 2-A of ISO 2859-1: 1999
Table 19a of BS EN 206-1:2000: AQL = 4%.
This method allows for a certain number of results to be outside of the class range butrestricts the absolute value of the allowable deviation for individual results. Figure 4 indicates howthe method works.
Test Method Minimum number Lower Limit, Upper Limitof samples
Table 8: Note:(1) Applicable when samples are taken from initial discharge.
Slump
Vebe time
Degree of Compatibility
Flow
(i) As forcompressivestrength
(ii) When testing air content
(iii) in case ofdoubtfollowing visualinspection
-10mm +20mm-20mm(1) +30mm(1)
-4 sec +2 sec-6 sec(1) +4 sec-0.05 +0.03-0.07(1) +0.05(1)
-15mm +30mm-25mm(1) +40mm
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This is best explained by way of a simple example using slump class S2:
• the range S2 is 50mm - 90mm
• for 40 samples in the assessment period up to 10 results can be within the range -10mmto +20mm outside of the class limit i.e. 40-110mm
• if results are obtained from spot samples of the initial discharge this allowable range is extended to 30-120mm
• no results are allowed outside of these ranges.
The conformity range for all slump classes is shown in Tables 9 and 10 below:
Class Normal Sample Spot Sample
S1 10 - 40 0 - 50
S2 50 - 90 40 - 100
S3 100 - 150 90 - 160
S4 160 - 210 150 - 220
S5* 220 + 210 +
* Slump measurement not recommended at these consistence levels.
Table 9: Class limit tolerances (mm).
Class Normal Sample Spot Sample
S1 0 - 60 0 -70
S2 40 - 110 30 - 120
S3 90 - 170 80 - 120
S4 150 - 230 140 - 240
S5 210 + 200 +
Table 10: Absolute limits for all results (mm).
Lower Limit Upper Limit
Class Range Specified Value Specified Value +4%
Absolute Limit Specified Value - 0.5% Specified Value +5%
13.2 Air ContentAir content conformity is assessed at 4% AQL (Table 19a) and the test frequency required is
1 sample per production day. Air content is specified by a minimum value rather than a target andthe class requirements and allowed tolerances are shown in Table 11 below.
Table 11: Air Content Conformity Criteria.
In practice the producer will target a mid range value and the upper and lower limit valueswill be similar to existing compliance values in BS5328.
13.3 DensityBS EN 206-1: 2000 requires that heavyweight (>2600kg/m3) and lightweight concrete
(≥ 800kg/m3 ≤ 2000 kg/m3) are assessed for conformity at 4% AQL (Table 19a)
Density is specified as a target value which leads to the following conformity criteria:
Lightweight Concrete Heavyweight Concrete
Class Range ± 100 kg/m3 ± 100 kg/m3
Absolute Limit ± 130 kg/m3 ± 130 kg/m3, no upper limit
Table 12: Density Criteria.
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13.4 Maximum w/c ratio andminimum cement content
Clause 5.4.2 of BS EN 206-1: 2000 givesthe methods of verification of conformity tospecified maximum water/cement ratio andminimum cement content.
The reference method for thedetermination of cement content is byinspection of the autographic records or, wherethere is no autographic recorder, by inspectionof the production records. The single resultcriterion is that the determined cement contentshall not be less than 10 kg/m3 below thespecified minimum cement content. For mostresults, the determined cement content has tobe equal to or higher than the specifiedminimum cement content, see Table 13.
With prescribed concrete, the targetcement content is specified and not theminimum. Clause 8.3 of BS EN 206-1: 2000requires this to be batched within ±3% andTable 17 of BS EN 206-1: 2000 allows a smallpercentage of the results to be within therange (target mean strength -3%) and (targetmean strength -3% -10kg/m3)
The reference method for determinationof water/cement ratio is by calculation usingthe determined cement content and theeffective water content (see 5.4.2 of BS EN206-1: 2000). Conformity is established usingthe method of attributes and the single resultcriterion is that the determined water/cementratio shall not be greater than 0.02 above thespecified maximum value.
The requirements for the w/c ratio ofprescribed concrete are given in 8.3 of BS EN206-1: 2000. The ±0.04 of the specified valueshould be taken as the tolerance on thespecified value to which the maximum alloweddeviation of single test results given in Table 17of BS EN 206-1: 2000 apply.
Clause 8.2.3.2 of BS 8500-2: 2001provides an alternative method fordemonstrating conformity to the specifiedmaximum water/cement ratio and theminimum cement content. In principle, thestrengths associated with the maximumwater/cement ratio and minimum cementcontent become the required characteristicstrengths associated with these criteria. Thehighest characteristic strength from thoseneeded to satisfy the strength class, themaximum water/cement ratio and theminimum cement content becomes the
characteristic strength on which conformity ofthe concrete is based. This alternative methodrequires the target strength to have a margin ofat least 2 standard deviations.
For the following analysis, the followingapproximations are made:
25 kg/m3 change in cement content ≅ 5 N/mm2 change in cube strength.
0.05 change in water/cement ratio≅ 5 N/mm2 change in cube strength.
On the basis of these relationships, thesingle result criteria transpose to:
Maximum w/c ratio + 0.02≅ fck -2
Minimum cement content -10kg/m3≅ fck -2
This is less severe than the (fck-4)permitted for the single result criterion forstrength.
Assuming a standard deviation of 4.0N/mm2, the required margin of 2 standarddeviations gives:
Target strength = fck +8
≅ Maximum water/cement ratio -0.08
≅ Minimum cement content +40 kg/m3.
In conclusion, the alternative method ofdemonstrating conformity to the specifiedmaximum water/cement ratio and theminimum cement content is significantly moreonerous than the reference method. However,where strength is the controlling factor in themix design, this method may have no penaltiesother than the criterion for single results.
13.5 Chloride content of concreteClause 5.2.7 of BS EN 206-1: 2000 gives
the method for calculating the chloride contentof concrete. For each constituent material,either the maximum permitted or declaredchloride ion content is used in the calculationor the chloride ion content is calculated frommonthly measurements plus 1.64 times thestandard deviation of these results. If thecalculated value exceeds the maximum value,the mix proportions are adjusted or materialsfrom alternative sources are used. Due to thebuilt-in margin, the fact that the calculatedvalue exceeds the maximum value does notgive rise to non-conformity. Conformity by themethod of attributes is not applicable with thissystem.
53
CONCLUSIONS1. BS EN 206-1: 2000 and BS 8500
introduce an additional degree of complexityinto conformity evaluation of concrete.
2. Even with a high margin, the initialproduction criteria pose a high risk of non-conformity when the standard deviation is low.
3. A structure containing conformingconcrete with strengths below thecharacteristic and equal to or above (fck - 4) willbe adequately strong.
4. Whilst changes in mean strength orstandard deviation indicate a change in theconditions of production i.e. non-uniformconditions, they should not normally trigger animmediate end to an assessment period, theexception being an increase in standarddeviation with more than 6 test results.
5. The use of non-producer datashould be avoided except where it is needed toensure sufficient test data to qualify forcontinuous production.
6. For conformity control, all statisticaloutliers should be identified and investigated.All valid low statistical outliers should beincluded in the conformity assessment.
7. For concretes within a family thatare controlled by requirements other than thespecified strength, the “equivalent” (higher)strengths should be used in the calculation ofthe mean strength in the criterion fcm ≥ (fck +1.48σ).
8. Assessment periods should containa number of criteria and may vary fromconcrete to concrete, from plant to plant andfor different aspects of conformity.
9. For a given probability ofacceptance, the margin for continuousproduction is a function of the number of testresults and the level of auto-correlation.
10. Whenever possible, individualconcrete should be avoided unless sufficientdata can be generated in the assessmentperiod to ensure continuous production and atleast 15 results.
11. The use of non-overlapping groupsof test results in the conformity assessment isrecommended.
12. The estimate of the populationstandard deviation should be based on themean range of successive pairs.
13. BS EN 206-1: 2000, Method 2should be used to determine significantchanges in the standard deviation.
14. The method of conformity thatminimises the risk of non-conformity with low-volume production depends upon theproduction conditions and the rate of testing.
15. Test regimes should be monitoredto prevent autocorrelation of results.
REFERENCES1. BRITISH STANDARDS INSTITUTION. Concrete -
Part 1: Specification, performance, productionand conformity. BS EN 206-1: 2000, pp70.
2. BROWN, B V & GIBB, I. Appraisal of the EN206 strength conformity proposals for initialand acceptance testing. CEN TC 104/SC1/TG3 paper, 1994, pp2.
3. BARBER, P & SYM, R. An assessment of thevariability in ready mixed concrete in theUnited Kingdom. ERMCO Congress, LondonMay 1983, Session W8B, pp6.
4. BRITISH STANDARDS INSTITUTION. Design ofconcrete structures - Part 1: General rules andrules for buildings. Committee draft of prEN1992-1, December 1999, p85.
5. BRITISH STANDARDS INSTITUTION. Concrete -complementary British Standard to BS EN 206-1: 2000 Part 2. Complementary requirementsfor constituent materials, designed andprescribed concrete, production andconformity. BS 8500-2, draft for publiccomment, March 2001, pp35.
6. TAERWE, L. Influence of autocorrelation onOC-lines of compliance criteria for concretestrength. Materials and Structures, Vol. 20,1987, p418-427.
7. ROBERTS, M. Autocorrelation of concretecube results. C&G Concrete Ltd. TechnicalNote 2, 1988, pp6.
8. OAKLAND, J S Statistical process control,Heinemann, 1986, pp281.
GENERAL REFERENCESEUROPEAN COMMITTEE FORSTANDARIZATION. Product standards andconformity assessment guideline. CENDocument BT N 6287 approved by ResolutionBT 68/2000, 2000, pp14.
TAERWE, L. Aspects of conformity control ofready-mixed concrete. ERMCO Congress2001, Berlin.
54
TAERWE, L. A general basis for the selection ofcompliance criteria, IABSE Proceedings P-102/86, 1986, p113-127.
EUROPEAN COMMITTEE FORSTANDARIZATION. Testing fresh concrete -Part 1: Sampling, EN 12350-1, 2000, pp3.
EUROPEAN COMMITTEE FORSTANDARIZATION, 2000. The use of theconcept of concrete families for theproduction and conformity control ofconcrete. CEN Report 13901, 2000, pp14.
ACKNOWLEDGEMENTSThe contents of this paper are based on the
work of a Quarry Products Association Working Partycomprising the following members:
Prof. Tom Harrison The Quarry Products(Chairman) Association
Steve Crompton RMC Readymix Ltd
Clive Eastwood RMC Readymix Ltd
Geoff Richardson Lafarge Readymix
Roger Sym Signalsfromnoise.com Ltd
Their help in analysing the requirements of BSEN 206-1: 2000 and their input into this paper isacknowledged.
55
ENVIRONMENTAL ISSUES - WATER
Mr. A.J. Dowson BA, MICT
MARSHALLS
Allan Dowson is Head ofTechnical Research, Marshalls,Halifax, UK. He has workedfor Marshalls for 36 years,prior to which he worked forthe British Precast Concrete
Federation for 8 years. Allan Dowson haspresented many papers on precast concreteand serves on numerous British Standards,European and Trade Association Committees.He was chairman of the British PrecastConcrete Federation from 1996 to 1998.
ABSTRACTThis paper highlights the problems of the
environmental issues that will affect the PrecastIndustry in the near future. One issue thatcauses concern is the inconsistency inrequirement as each Environment AgencyDepartment imposes different limits on thewater discharged from site. The problem theIndustry has to face is the water that wecontaminate by the process and the rain waterleaving our sites.
KEYWORDSEnvironment, pH, Chromium, Aluminium,
Iron.
INTRODUCTIONWith the ever-increasing pressure from
the environmentalists to conserve our naturalresources and the Environment Agency tominimise pollution of our water, we are underpressure to “clean up our act”. This paperconsiders the two main issues relating to“Water Quality” that will affect the precastindustry and ultimately the whole of theconcrete industry.
The two areas of water issues are:
• The water run-off discharge from oursites
• The water that is rejected from theprocess, including the wash downwater.
In any precast concrete works we canhave numerous applications where water isused and discharged.
POTENTIAL SOURCES OF WATERPOLLUTION
When we cut or grind the product, largequantities of water will be used as a coolant.When we expose the surface of the concrete,water is the normal option to remove thecement paste. In some factories, acid is usedto etch the surface and this requires water toremove the acid left on the surface as well aswash down the surrounding areas. To maintainthe concrete machinery/equipment, it isnecessary to wash off/swill down at the end ofthe shift - or at the end of a day. In someconcrete processes, water is removed from theconcrete during its manufacture which iseither discharged or collected.
Rainwater falling on to our roofs andhardstanding runs to a discharge point at theedge of our factory boundaries. This water issubjected to Environmental Discharge limits.
DISCHARGE LIMITSWhy should we be concerned about the
water being discarded from our works? Theanswer is that the Environment Agency willimpose limits of different chemicals for the“Water Quality” being discharged from the site.These include a level of pH, chromium,aluminium and iron.
Typical discharge levels are given in Table1, however, there are no national standards forthese limits. For example, in areas where thewater sources are acidic, the Water Authoritieswelcome the discharge of alkali water, as thisreduces their costs with water treatment.
Table 2 illustrates typical results for waterbeing from site.
Property LimitSolids 100ppm
pH 6 to 8
Total Iron 400 µg/l
Total Chromium 100 µg/l
Aluminium 400 µg/l
Table 1: Typical discharge limits.
Principal % of finishedactive compound cement
Tricalcium silicate 50 - 70
Dicalcium silicate 20 - 30
Tricalcium aluminate 5 - 12
Calcium aluminoferrite 5 - 12
56
SOURCE OF WATER CONTAMINATION
Where do these chemicals thatcontaminate water come from? The majorcontributor comes from the cement itself.
A typical raw mix used for themanufacture of portland cement consists ofabout four fifths calcium carbonate: this isdecomposed during production of cementclinker to produce calcium oxide, whichremains in the mix to react with other oxides toproduce the essential hydraulic components ofPortland cement. The other major constituentsare silica, alumina and iron oxide. Typical valuesare given in Table 3 and Table 4.
As cement is a strong alkali when itcontaminates water the pH rises from neutralup to 12.3 or higher.
The chrome contained in cement is atlevels of 5 or more parts per million and themain source of this comes from the linings ofthe drum in the firing process and from thegrinding balls.
Iron is contained in the clay or shale thatis in the raw materials component part of thecement production and the aluminium comesfrom the tricalcium aluminates which isproduced in the manufacture of cement.
When reject fresh and hardened concreteare stored in the open and it becomes wetthrough rainfall, we introduce thecontaminants into the discharge water. Typicalexamples are shown in Figure 1, 2 and 3.
PIC
Figure 1: Example of waste concretestorage area.
Property RangepH 12.3 - 12.9
Total Iron 100 - 3000 µg/l
Total Chromium 90 - 1050 µg/l
Aluminium 100 - 880 µg/l
Solids 100 - 1200 ppm
Table 2: A typical range of values forwater discharge from a concrete works.
Table 3: Major constituents of cement.
Typical analysis Typical of raw material raw mix
Silica 14.5
Alumina 3
Iron oxide 1.3
Calcium oxide 44
Magnesium oxide 0.6
Potassium oxide 0.50
Sodium oxide 0.13
Table 4: Raw material breakdown of cement.
Trace element Average mg/kg of cement
Antimony 9
Barium 250
Chlorine 500
Chrome 80
Manganese 300
Nickel 40
Phosphorus 200
Lead 30
Titanium 1400
Table 5: Trace elements in cement.
57
RECYCLING WATERTo resolve these problems of
contamination of discharge water, we cancollect the water and treat it beforedischarging, or we can recycle the water anduse it in our concrete process.
The potential savings on water usage arehigh, providing when we collect rainwater, itcan be stored. An example of the waterquantity that can be collected on a site of200,000 sq m, with a monthly average rainfall
of 75mm, is 15,000 cu m, at an average cost of80p per cu m. this amounts to £12,000 permonth. Whether all this water can be useddepends on the type of product produced.Table 7 gives typical usage of water in concretemanufacture and does not take into accountany other process which could use water.
In the Fielding Wet Press process we canrecover about 50% of the water used in themix as this is the water that is pressed outduring the pressing process.
Figure 2: Example of waste fresh concretestorage.
Figure 3: Example of waste concretecollection.
Although we have no control of rain falling on our stored concrete products and hardstandings, it is our responsibility to control the water run-off from our sites. First flush water is rainwater which has been polluted with the free surface dust on products and surfaces immediatelywhen the two come into contact with each other. Table 6 gives an example of first flush watercontamination.
Location pH Total Chromium Total iron Aluminium Solids
Yard 8.8 12 µg/l 260 µg/l < 10 µg/l 200 ppm
Table 6: Example of first flush water.
Where water is used for coolants in the sawing and grinding process, the discharge waterfrom the process will contain all these contaminants.
WATER REQUIREMENTAs a guide to the water requirement of precast concrete production, Table 7 gives typical
values of the total water required for any of processes used in precast production. Each factorywill have slightly different levels of water addition to their mixes.
Product Typical water quantitiesper 1 tonne of cement
Concrete Block Paving 400 litresW/C ratio 0.4
Vibrated Concrete 500 litresW/C ratio 0.5
Wet Press 1000 litresW/C ratio 1.0
Table 7: Typical water usage in precast concrete.
Where water has been used as thecoolant, then this waste water can be collectedand recycled after the removal of most of thesuspended solids.
Example of using recycled water in theproduction process
As a company, we have at numerouslocations been using recycled water forconcrete production, supplementing the waterrequirement with town’s water for many years.Whether using all recycled water or a blend ofrecycled and town’s water, the products havecomplied with the requirements of the relevantstandards.
As part of an evaluation into the waterquality in the Fielding Wet Press process, wemeasured the pH, total iron, aluminium andsolids content before mixing and after thepressing (dewatering) processing. Table 8illustrates typical results obtained.
Recycling water treatment systemsWhen treating water for off site discharge
of process water, the main issue is in reducingthe high pH to neutral. This can be achievedseveral ways:
• Using hydrochloric acid - this is notonly costly, but needs to be accuratelydosed and monitored carefully as thewater can change from alkali to acidic
• Passing carbon dioxide through thealkali water to form a chemicalreaction. This requires specialistequipment.
If it is possible to separate the processedwater from the surface run off water then thetreatment of run off water is relatively simple.This can be a large lagoon or storage tank andthe water can overflow to the appropriateoutlet as shown in Figure 4.
Using the lagoon as storage, this watercan be recycled by pumping it back into thewater holding system ready for re-use in theprocess.
Where water is collected from the processand treated for recycling back into the system,the two most appropriate methods are settlingtanks or CO2 treatment.
Settling tanksSettling tank design should have the
largest surface area possible in relationship to itsdepth and does not need to be too deep. Thegreater the surface area the more effective thesystem. In most cases three settling tanks arenecessary, the first tank is for coarse settling,where the larger particles fall out quickly (Figure5). The water can be pumped or allowed tooverflow to the second settling tank (Figure 6)and finally to overflow into the final settlingtank, Figure 7, where the water can then bepumped back into the water system.
58
Works A Works B Works C
Test Before After Before After Before After
pH 8 12.6 12 12.1 12.3 12.7
Iron 2 5 0 <2 0 0
Aluminium <5 20 5 20 5 5
Suspended solids 0 1500 100 3000 100 4000
Table 8: Comparison of recycled water.
Figure 4: Lagoon with outlet for discharge. Figure 5: First settling tank.
59
Treatment plantsWhere the space is limited and the
settling tank principle cannot be employed,then chemical treatment systems can be used.One particular system is a series of differentsize silos, where the water is passed from oneto the other thus reducing the suspendedsolids. This water is then stored in a tankwhere carbon dioxide is bubbled through thusremoving more suspended solids and reducingthe pH. Figure 9 shows a typical installationand Figure 10 shows the carbon dioxidetreatment tank.
To improve the effectiveness of treatmentplant, the introduction of a small settling tankto remove the larger suspended solids beforepumping the water to the treatment plant.
CONCLUSIONSWater treatment is just part of a wider
environmental issue and if managed correctly,not only saves resources but reduces thedamaging chemicals that have an effect on theenvironment and our health.
By careful management of the waterissue, we can make major cost savings fromcharges made for town’s water and fordischarging into sewer systems. The ever-increasing environmental pressures beingimposed on industry to clean up theenvironment require industry to address theissues raised in this paper.
The environmental issues will notdisappear and in a short time will come to thetop of the agenda. The pressure to reducelimits of the chemicals contained in dischargewater will increase and will result, if notcomplied in large fines or even factory closures.
We have an unique opportunity to cleanup the environment and to ensure we preserveour resources and by managing them savemoney.
Figure 6: View of second settling tank. Figure 7: View of the overflow from tank2 into tank 3.
Where the volumes of water for recycling are small, then a simple overflow system can beused as shown in Figure 8.
Figure 8: Inline weir treatment system. Figure 9: General installation view.
Figure 10: CO2 treatment tank.
60
61
John Buekett has been anindependent consultant forthe past 11 years. During thisperiod he was Secretary ofthe Cement AdmixturesAssociation and the
European Federation of Concrete AdmixtureAssociations for seven years. Prior to this hespent over 30 years in the precast concreteindustry in UK and North America. He is amember of several European Standardscommittees including CEN/TC104/SC3Admixtures and many BSI committeesincluding B/517/3 Admixtures.
ABSTRACTAdmixtures for concrete, sprayed
concrete, mortar and grout are covered. Thecurrent state of performance standards andtest methods is described and an indication ofthe contents is given, particularly where theyare different from current UK practice. Anaccount of the amendment and withdrawal ofconflicting British Standards is given. Interactionwith other European Standards which coverthe use of admixtures is explained. Someindication of outstanding work is given andhurdles to some work are explained. Thecompletion of harmonized EuropeanStandards, necessary to support theConstruction Products Directive, is alsodiscussed.
KEYWORDSConcrete, Construction Products
Directive, Grout, Harmonized standards,Mortar, Performance requirements, Sprayedconcrete, Test methods.
INTRODUCTIONWork on preparing European Standards
for admixtures commenced in the mid 1980sand as for many other European Standards thework has taken much longer than anticipated.Part of this delay arose from the need to obtainconsensus between countries whose existingstandards and regulations had significantdifferences but, more frustratingly, there havebeen long delays in the administrative process.
Each conflicting national standard, or partof a standard has to be withdrawn by the dateof withdrawal (dow) which is notified by CENwhen the European Standard is published.
The CEN committee (CEN/TC104/SC3)responsible for admixtures has had to keep aconstant watch on nomenclature becauseusage in other languages has led to confusionbetween admixtures, additions and additives.
The following definitions are given in EN206-1:
• Admixture - material added during themixing process of concrete in smallquantities related to the mass ofcement to modify the properties offresh or hardened concrete
• Addition - finely divided material usedin concrete in order to improve certainproperties or to achieve specialproperties.
There is no definition of additive but thefollowing can be used:
• Additive - material added to cementduring the manufacturing process toimprove the process or properties ofthe cement e.g grinding aids.
The tradition in UK has been that BritishStandards are voluntary and theirimplementation generally depends onspecifiers calling them up. For public worksand work by utilities, whether public orprivately owned, European Standards will bemandatory for the products they cover.
CURRENT POSITION AND MATERIALS COVERED
Work initially concentrated on the testmethods and culminated in the publication ofmost of them in 1997. The first performancestandard, for concrete admixtures, followed in1999 and the current position in April 2001 isshown in tables 1 and 3.
Although the Construction ProductsDirective (CPD) was adopted in 1988 andcame into force in 1991, its implementationrelies upon a special form of EuropeanStandard (EN) known as a harmonized EN(hEN) and there was a long delay before the
NEW EUROPEAN STANDARDS FOR ADMIXTURES
Mr. J. Buekett BSc, C Chem, MRSC, MIQA
CEN Observer for EFCA
62
European Commission issued mandates whichare necessary for the preparation of hENs. Theconsequence is that some of the ENs foradmixtures will be replaced with hENs within ashort period of publication as shown in table 1.In the case of EN 934-2 the hEN will alsoinclude some dual function concreteadmixtures not covered in the first edition. Afull list of the admixtures covered is shown intable 2 together with the BS names for thosetypes covered by British Standards.
Of the admixtures covered by EN 934-2,water retaining admixtures are intended toreduce bleeding; they are little used andvirtually unknown in UK. Water resistingadmixtures are used in UK and they have beenincorrectly known as ‘waterproofingadmixtures’. A more correct name is integralpermeability reducing admixtures but waterresisting was preferred by the CEN committee.
In the past, in UK, we have not distinguishedbetween set accelerating and hardeningaccelerating where hardening means strengthdevelopment.
EN 934-4 only claims to cover one type ofadmixture but it does, in effect, cover twobecause the requirements for volume changeat 24 h (S) are as follows;
-1% ≤ S ≤ 5% or when testingexpanding grout admixtures 0 ≤ S ≤ 5%.
In the case of EN 934-5 there is still somedoubt whether bond improving admixtures willbe included in the final draft. Set controladmixture is a long term retarder which permitsmixed sprayed concrete to be prepared awayfrom the spraying area and transported to thespray nozzle where set accelerator is added atthe time of spraying.
NUMBER TITLE CURRENT POSITION
EN 934 Series - Admixtures for concrete, mortar and grout
EN 934-1 Definitions Abandoned, definitions are in each of the other parts.
BS EN 934-2:1999 Admixtures for concrete Published- Definitions and requirements
prEN 934-2:2000 Admixtures for concrete Harmonized version- Definitions, requirements, accepted at formal vote
conformity, marking and labelling 2001.
prEN 934-3:2001 Admixtures for masonry mortar Formal vote- Definitions, requirements, expected shortly.
conformity, marking and labelling
BS EN 934-4:2000 Admixtures for grout for prestressing Publishedtendons - Definitions, requirements and conformity
prEN 934-4:2000 Admixtures for grout for prestressing Harmonized versiontendons - Definitions, requirements, accepted at formalconformity, marking and labelling vote 2001.
prEN 934-5:1998 Admixtures for sprayed concrete Negative vote at- Definitions, specifications and CEN enquiry, revisedconformity criteria draft in preparation.
BS EN 934-6:2000 Sampling, conformity control, Publishedevaluation of conformity, marking and labelling
prEN 934-6:2000 Sampling, conformity control and Revised version to supportevaluation of conformity harmonized standards
accepted at formal vote 2001.
Table 1: Performance standards.
63
PERFORMANCE REQUIREMENTSAND TEST METHODS
Whilst specific constituents such aschloride ion and alkali can be measured byanalysis of admixtures alone, the measurementof effectiveness and some side effects can onlybe done by comparing concrete, mortar orgrout containing admixtures (test mix) withsimilar mixes containing no admixture (controlmix). The test mix and control mix arecollectively known as reference concrete orreference mortar (see EN 480 Parts 1 & 13).
All concrete admixtures are subject to testrequirements for effect on compressivestrength and effect on air content. Otherperformance requirements are specific to thetype of admixture and this is illustrated bytables 4a and 4b where high range waterreducing/superplastizing are subject torequirements in which the test and controlmixes have either equal consistence or equalw/c ratio. It is intended that each admixture ofthis type shall the requirements of both tables.
EUROPEAN STANDARD NAME BRITISH STANDARD NAME
BS EN 934-2:1999 BS 5075
Water reducing/plasticizing Normal water reducing
High range water reducing/superplasticizing Superplasticizing
Water retaining Not covered
Air entraining Air entraining
Set accelerating Accelerating
Hardening accelerating Accelerating
Set retarding Retarding
Water resisting Not covered
prEN 934-2:2000
As listed above plus
Set retarding/water reducing/plasticizing Retarding water reducing
Set retarding/high range water Retarding superplasticizingreducing/superplasticizing
Set accelerating/water reducing/ Accelerating water reducingsuperplasticizing
prEN 934-3:2001 BS 4887
Air entraining/plasticizing mortar admixture Air entraining (plasticizing) admixture for mortar
Long term retarded, ready to usemortar admixture Set retarding admixture for mortar
BS EN 934-4:2000 No equivalent BS
Grout admixture
prEN 934-5:1998 No equivalent BS
Accelerating
Sagging prevention
Set control
Bond improving
Table 2: Admixture types covered by European Standards.
64
NUMBER TITLE CURRENT POSITION
EN 480 Series Admixtures for concrete, mortarand grout - Test methods
BS EN 480-1:1998 Reference concrete and reference Publishedmortar for testing
BS EN 480-2:1997 Determination of setting time Published
BS EN 480-4:1997 Determination of bleeding of concrete Published
BS EN 480-5:1997 Determination of capillary absorption Published
BS EN 480-6:1997 Infrared analysis Published
BS EN 480-8:1997 Determination of the conventional Publisheddry material content
BS EN 480-10:1997 Determination of water soluble Publishedchloride content
BS EN 480-11:1999 Determination of air void characteristics Publishedin hardened concrete
BS EN 480-12:1998 Determination of the alkali content Published of admixtures
prEN 480-13:2001 Reference masonry mortar for testing Formal vote imminentmortar admixtures
Draft EN-480-14 Potentiostatic electrochemical test for In preparationthe measurement of corrosion susceptibility of steel
Parts 3, 7 and 9 were discontinued as it was found that existing ISO test methods could be used.
Table 3: Test method standards.
PROPERTY REFERENCE TEST METHOD REQUIREMENTSCONCRETE
Water reduction EN 480-I Slump EN 12350-2 In test mix ≥ 5 %reference concrete 1 or compared with
Flow EN 12350-5 control mix.
Compressive strength EN 480-I prEN 12390-3:1999 At 7 and 28 days:reference concrete 1 Test mix ≤ 110 %
of control mix.
Air content in EN 480-I EN 12350-7 Test mix ≤ 2 % by fresh concrete reference concrete 1 volume above control
mix unless otherwisestated by themanufacturer.
Table 4a: Specific requirements for high range water reducing/superplasticizingadmixtures (at equal consistence).
65
For these basic properties the testmethods called up by EN 206-1 are used but astable 3 shows some new test methodsstandards have been developed specifically foradmixtures. The EN 480-1 reference mortar fortesting is for the determination of the effect ofadmixtures on setting time by the procedure inEN 480-2. Determination of bleeding ofconcrete (EN480-4) is used for water retainingadmixtures and capillary absorption (EN 480-5)is applied to water resisting admixtures. Infrared analysis (EN 480-6) is used to identify theactive ingredients but is confined to initial typetesting. The conventional dry material content(EN 480-8) is a measure of the non evaporablematerial which is a useful quality control test.In addition to water soluble chloride (EN 480-10), EN 934 calls up ISO 1158 for total chlorinecontent. This is to safeguard against theremote possibility that compounds containingcombined chlorine will break down in contactwith cement and release water solublechloride. Total chlorine only has to bemeasured at initial type testing unless it issignificantly different from water solublechloride when routine testing is required.
EN 480-11 introduces a significantchange from previous UK practice. Theperformance of air entraining admixtures isnow assessed by their effect on air void spacinginstead of the freeze thaw test in BS 5075-2.
EN 480-14 is only at an early draft. It isintended to test the effect of admixtures oncorrosion of reinforcement but indications are
that a test applicable to all admixtures mightnot be achievable.
PRE-EXISTING BRITISH STANDARDSPublication of EN 934-6 completed the
CEN package of EN 934 Parts 2 & 6, and EN480 Parts 1-12. The dow of conflicting nationalstandards was July 2000. In consequence BS5075-2 was withdrawn and BS 5075 Part 1 & 3were amended. When the new edition of EN934-2 is published this will lead to the completewithdrawal of BS 5075 Part 1 & 3. BS 4887 willbe withdrawn consequent on the publicationof EN 934-3 and EN 480-13.
There were no British Standards coveringgrout admixtures and sprayed concreteadmixtures.
EUROPEAN STANDARDS WHICHCALL UP ADMIXTURES
EN 206-1 Concrete - Specification,performance, production andconformance
Clause 5.1.1 includes the following:
Constituent materials shall not containharmful ingredients in such quantities as maybe detrimental to the durability of the concreteor cause corrosion of the reinforcement andshall be suitable for the intended use inconcrete.
Only constituents with establishedsuitability for the specified application shall beused in concrete conforming to EN 206-1.
PROPERTY REFERENCE CONCRETE TEST METHOD REQUIREMENTS
Increase in EN 480-1 Slump EN 12350-2 Increase in slump ≥ 12 %consistence reference concrete IV or from initial (30 ± 10) mm.
Flow EN 12350-5 Increase in flow ≥ 160 mmfrom initial (350 ± 20) mm.
Retention of EN 480-1 Slump EN 12350-2 30 min after the addition theconsistence reference concrete IV or consistence of the test mix
Flow EN 12350-5 shall not fall below the valueof the initial consistenceof the control mix.
Compressive EN 480-1 prEN 12390-3:1999 At 28 days: test mix ≥ 90 %strength reference concrete IV of control mix.
Air content in EN 480-1 EN 12350-7 Test mix ≤ 2 % by volume fresh concrete reference concrete IV above control mix unless
otherwise stated by themanufacturer.
Table 4b: Specific requirements for high range water reducing/superplasticizingadmixtures (at equal w/c ratio).
66
NOTE Where there is no EuropeanStandard for a particular constituent materialwhich refers specifically to the use of thisconstituent material in concrete conforming toEN 206-1, or where there is an existingEuropean Standard which does not cover theparticular product or where the constituentdeviates significantly from the EuropeanStandard, the establishment of suitability mayresult from:
• a European Technical Approval whichrefers specifically to the use of theconstituent material in concreteconforming to EN 206-1
• a relevant national standard orprovisions valid in the place of use ofthe concrete which refers specifically tothe use of the constituent material inconcrete conforming to EN 206-1.
prEN 934-2:2000 restricts potentiallyharmful ingredients as follows:
Water soluble chloride - Either ≤ 0,1 % bymass or not above the manufacturer’s statedvalue. If ≤ 0,1 % the admixture may bedescribed as “chloride free”.
Alkali content (Na2O equivalent) - Notabove manufacturer’s stated value.
Corrosion behaviour - No corrosionpromoting effects on steel embedded inconcrete. (Until there is an accepted EuropeanStandard the national regulations in the placeof use shall apply when required).
The test for corrosion promoting effects isdraft EN 480-14.
Satisfying the requirements for establishedsuitability will require some work by theadmixture manufacturers for those admixturesnot covered by prEN 934-2:2000. This includesadmixtures specifically developed for the precastindustry, established products such as anti-washout admixtures and newer products suchas corrosion inhibitors and shrinkage reducingadmixtures. In the UK the Cement AdmixturesAssociation is proposing a new BS to coverconcrete admixtures not included in EN 934-2:2001 so that they can satisfy the EN 206-1route to acceptance by complying with anational standard valid in the place of use.
BS EN 447:1996 Grout forprestressing tendons - Specifications forcommon grout
This states the following:
Admixtures shall comply with EN 934-4.
It shall be permissible to use admixtures singlyor in combination.
prEN 998-2 Specification for mortarfor masonry - Part 2:Masonry mortar
The harmonized version which will beissued for formal vote shortly is expected torequire the following:
Raw materials shall have characteristicspermitting the finished product to conform withthe requirements of this standard. Themanufacturer shall keep records of howsuitability of materials is established.
An unusual feature of prEN 934-3 is that itstates that admixtures complying with EN 934-2 are deemed to satisfy EN 934-3. Anotheranomaly is that EN 934-3 only coversadmixtures for masonry mortar but theseadmixtures are, in practice, also used forrendering and plastering mortar.
Draft EN AAA-1:2000 Sprayedconcrete - Part 1:Definitions, specificationsand conformity
This has similar requirements to EN 206-1but also requires admixtures to conform to EN934-2 and/or EN 934-5.
prEN 13369:1998 Common rules forprecast concrete products
This has similar requirements to EN 206-1.
IMPACT OF THE CONSTRUCTIONPRODUCTS DIRECTIVE
CE MarkingFollowing publication of the harmonized
versions of EN 934 Parts 2, 3, 4 and 5 there willbe a transition period of 21 months at the endof which the admixtures involved will qualify forCE marking. CE marking will not be obligatoryfor products made and sold in UK but will berequired in most other EU countries. Asadmixtures are widely traded across borders itis likely that they will be CE marked in UK. Alsousers will probably attach some importance toa mark which is supposed to indicate fitness forpurpose.
The label accompanying the CE mark willinclude the type of admixture and a codebased on the table of performancerequirements in the appropriate part of EN 934as follows:
Type of admixture, number of standard,number of table giving requirements (canbe two tables) e.g. High range water
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reducing/superplasticizing admixture forconcrete EN 934-2:T3.1/3.2
It will also include the following:
Maximum chloride content % by mass(i.e. water soluble chloride)
Maximum alkali content % by mass (i.e.Na2O equivalent)
Corrosion behaviour (this requiresreference to any regulations applying inthe place of use. e.g. NEN 3532 appliesin The Netherlands)
Dangerous substances (name) less thanppm (where the admixture incorporatesa dangerous substance listed in the EUweb site Europa)
Attestation of ConformityAdmixtures covered by EN 934 are
subject to system 2+ attestation of conformity.This means that the manufacturer isresponsible for initial type testing and factoryproduction control. A notified body has toaudit and certify the factory productioncontrol.
The tests required for initial type testingand factory production control, together withthe frequency of testing, are listed in EN 934Parts 2-5. Details of the FPC are in EN 934-6which requires an annual inspection by thenotified body. A series of study groups hasbeen set up by the notified bodies to agree aunified procedure for certification under eachharmonized European Standard. So far noconsideration has been given to admixtures.
FUTURE WORKUnder the mandate requirements for anti
washout concrete admixtures will be preparedfor inclusion in EN 934-2. At present it isconsidered that the technology is notsufficiently developed to prepare requirementsfor corrosion inhibiting concrete admixtures.No consideration has been given to other newmaterials such as shrinkage reducing concreteadmixtures.
There was a request from Finland toprepare requirements for anti-freezing concreteadmixtures. Admixtures loosely called “anti-freezing” are generally hardening acceleratingadmixtures but in Finland admixtures whichactually depress the freezing point are used inmixes for jointing precast concrete units andother specialist applications. They contain
active ingredients which are not appropriate(e.g high Na2O equivalent) for use in mass andreinforced concrete. In consequence no workis being done.
BIBM requested the inclusion ofadmixtures for precast concrete.Superplasticizers and other admixtures used instructural concrete are covered by EN 934-2but for other applications, such as paving units,specially formulated admixtures are used.These are currently outside the scope of EN934-2 which covers admixtures for concrete ofnormal consistence. So far no way has beenfound to embrace the diverse admixtureswhich are specially formulated for use in suchunits. One attempt was to apply therequirements for “harmlessness” (i.e. table 1 ofEN 934-2) and require the manufacturer tostate the effect on compressive strength butthis was rejected by CEN/TC104.
In order to facilitate publication of EN 934Parts 2, 3 & 4 as harmonized standards somecompromises have been accepted by CEN andthe European Commission. In particular thereferences to national regulations in the placeof use has been permitted in relation tocorrosion promoting effects and the release ofdangerous substances. This is recognised as apotential technical barrier to trade which isunlikely to be permitted in future editions ofharmonized standards. Dangerous substancesare a problem common to most of the firstgeneration of harmonized standards but theneed to provide MSDS for all products has ledto a much clearer identification of anyingredients which are dangerous and these donot create a significant problem withadmixtures. Corrosion promoting effects is, inthe author’s view, a distraction because themain culprit, calcium chloride, is now strictlycontrolled by the limits on chloride content ofconcrete in EN 206-1.
The impending requirements for materialsin contact with drinking water are likely tonecessitate work on concrete containingadmixtures. In the UK a programme hasalready been undertaken by the Drinking WaterInspectorate.
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CONCLUSIONSPublication of the first generation of
European Standards for admixtures and theirconversion to harmonized standards is almostcomplete. These cover more concreteadmixtures than previous British Standards andinclude grout and sprayed concrete admixturesnot previously subject to standards in UK.
Work continues on some additionaladmixtures and to fully satisfy the ConstructionProducts Directive and may be necessary foradmixtures in concrete in contact with drinkingwater.
The industry will need to adapt to thechange from largely voluntary British Standardsto the mandatory European Standardsparticularly in respect of those admixtures notcurrently covered by the EN 934 series.
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Philip Nixon is TechnicalDirector in the BREConstruction Division. He isresponsible for BRE’s researchinto concrete materials and inparticular, has overseen the
investigation of the Thaumasite form of sulfateattack.
ABSTRACTThe BRE Digest on protection of concrete
in aggressive ground has beencomprehensively revised to reflect and build onthe interim guidance of the Report of theThaumasite Expert Group. Its guidance hasbeen extensively discussed with industry and inparticular, has been discussed at a seminar atBRE in September 2000. It will be issued inconcert with the revision of BS 5328 to giveunified and co-ordinated guidance.
The guidance will be presented in fourparts:
Part 1 - Assessing the AggressiveChemical Environment
Part 2 - Specification of Concrete andAdditional Protective Measures
Part 3 - Design Guides for CommonApplications
Part 4 - Design Guides for Specific PrecastConcrete Products.
New research, which will be coming tofruition over the next few years, will add to theknowledge base on which the digest rests. Ifnecessary, a further revision or amendment willbe undertaken to incorporate these newresults.
KEYWORDSConcrete, Aggregates, Ground,
Guidance, New, BRE.
INTRODUCTIONBRE has evolved its guidance on the
protection of concrete from aggressivechemicals in a series of Digests, the mostrecent of which is Digest 363:1996. However,the recognition of the thaumasite form of
sulfate attack as a separate mechanism,needing its own forms of protection, hasnecessitated comprehensive revision of theguidance and the publication of a new Digestin spring 2001. The new Digest builds on bothDigest 363 and the Report 1 of the ThaumasiteExpert Group (TEG) and additionallyincorporates some other new ideas andprinciples. It is therefore, inevitably, a longerand more complex document. To try to makeits use as straightforward as possible it nowmakes extensive use of Design Guides for themost common concrete components andsituations. These attempt to make as many ofthe decisions for the engineer as possible.Generic rules are, however, still included for theunusual situation or for the engineer whowishes to develop his design from firstprinciples.
EVOLUTION OF GUIDANCE ON THE THAUMASITE FORM OF SULFATE ATTACK
Following the identification ofdeterioration caused by this form of sulfateattack in the M5 bridges in 1998, the Ministerfor Construction set up the TEG under theChairmanship of Les Clark, Professor ofStructural Engineering at BirminghamUniversity. It was asked to report on the natureand threat of this phenomenon and to giveinterim guidance on its avoidance. BREprovided the Secretariat for the Group and BREstaff served as members and supportingtechnical experts. The TEG identified theprimary risk factors necessary for theoccurrence of TSA in buried concrete as:
• Presence of sulfates and/or sulfides inthe ground
• Presence of mobile groundwater
• Presence of carbonate, generally in theaggregate
• Low temperature (generally below 15˚C).
Additionally they identified a number ofsecondary factors which can influence theoccurrence and severity of TSA and its effects:
NEW BRE GUIDANCE ON USE OF CONCRETE
IN AGGRESSIVE GROUND
Dr. P.J. Nixon BSc, DIC, PhD, HonFICT
Centre for Concrete Construction, BRE
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• Type and quantity of cement used inthe concrete
• Quality of the concrete
• Changes to the ground chemistry andwater regime resulting fromconstruction
• Type, depth and geometry of theburied concrete.
In the case of the M5 bridges, a criticalcombination of factors proved to be; the use oflimestone coarse and fine aggregates;groundwater where sulfate concentrationswere unexpectedly high due to the oxidationof pyrite (iron sulfide) in backfill derived fromunweathered Lower Lias Clay, and ponding ofgroundwater within a sump formed by theoriginal construction excavation.
Based on its findings, the TEG developedinterim guidance and recommendations fornew works. Additionally, they recommendedthat the key guidance documents on concretein aggressive ground should be revised to takethis new phenomenon and the work of theTEG into account. Since publication of theReport of the TEG in January 1999, much workhas gone into this. In particular, the BritishStandard for concrete, BS 5328, and the BREDigest have been revised in tandem in whathas been probably the closest ever co-operation between these two bodies.
NEW GUIDANCE IN BS 5328 AND BRE DIGESTS
With the publication of the TEG Report, itwas evident that the existing BRE Digest 363Sulfate and acid resistance of concrete in theground was in need of an update. The timingwas opportune as BRE had in any case beencontemplating a revision of the Digest in orderto clarify the modifications to the initial groundsulfate classification which take account offactors such as acidity, groundwater mobilityand type of construction. So, overall, thereasons for revision were;
• The need to include guidance on thethaumasite form of sulfate attack
• The need to take account of thepotential for enhanced aggressivenessof pyrite-bearing ground
• The need to take better account offactors which can modify the initialground sulfate classification, such asacidity, groundwater mobility and typeof construction
• Compatibility with emerging Europeanstandards.
Similarly, BS 5328 Concrete, which drawsupon the Digest for its recommendations inrelation to exposure of concrete to aggressivechemicals, needed amendment.
To carry out these tasks a Working Party,chaired by Dr Philip Nixon of BRE and includingseveral members of the TEG was established tooversee parallel production of the twodocuments. The Working Party decided at anearly stage that, since the two documentswere highly inter-dependent, they should bereleased simultaneously. Furthermore, it wasdecided that the advice in the BS would berestricted to the requirements for concretequality. All other aspects; ground investigationand classification and any measures additionalto the concrete quality which were necessaryto achieve the structures’ service life, would bereferred to the Digest. Overall, the guidingprinciple in the revision of both the Digest andBS 5328 has been to follow the principles of theTEG Report but to make it as practical anduseable as possible. This has resulted in arevision, which has been more far reaching andhas taken longer than anticipated. However, itis now ready for publication.
The revised Digest, which has yet to beallocated a number, is presented in four Partswith the title Concrete and concrete productsin aggressive ground. The layout and inter-relationships of the Digest are illustrated inFigure 1. Part 1 deals with assessment of thechemical aggressiveness of the ground. Itdefines a new classification, AggressiveChemical Environment for concrete (ACEC) andshows how to derive this throughdetermination of soluble sulfate andmagnesium, potential sulfate (from oxidationof pyrite, when present) and the pH andmobility of groundwater.
Part 2 describes how the ACEC isconsidered together with the proposed use ofthe concrete to arrive at concrete qualitiestermed Design Chemical (DC) classes, bymeans of which the concrete for theconstruction can be specified. Like Table 1 inthe current Digest 363, the revised Digest givesrecommendations for minimum cementcontent and maximum water/cement ratio foreach DC class, of which there are now eightbasic classes as opposed to the current fivebecause acid conditions now have separateclasses. One of the most important
71
recommendations in the TEG Report was forthe classification of aggregates into Ranges A,B and C according to their carbonate contenti.e. their potential for contributing to TSA. Therevised Digest now recommends concretequalities appropriate to the different AggregateCarbonate Ranges.
In addition to the quality of the concrete,previous versions of Digest 363 introduced theneed for additional measures in the form ofsurface protection for the highest sulfate class(Class 5). The revised Digest, building upon theExpert Group report, has extended thisconcept to provide further options foradditional protection. These are known asAdditional Protective Measures (APM) andconsist of the following:
• enhanced concrete quality (i.e. one DCclass higher)
• use of controlled permeability formwork
• provision of surface protection
• inclusion of a sacrificial concrete layer
• addressing site drainage to minimisecontact between groundwater and theconcrete.
The number of APM to be applieddepends in part on the aggressiveness of theground as indicated by the ACEC Class, and inpart on the required purpose and durability ofthe structure as indicated by the designatedStructural Performance Level (SPL).
Parts 3 and 4 of the new Digest are,respectively, Design Guides for specification ofconcrete for common applications and for
some specific precast concrete products. TheseDesign Guides, each for use with a particularconcrete application or product, lead thereader directly from the ACEC to theappropriate DC class and to the recommendednumber of required APM. From this point, therequired concrete quality can be specified andthe specific protective measures selected.
CONCLUSIONThe BRE Digest on protection of concrete
in aggressive ground has been comprehensivelyrevised to reflect and build on the interimguidance of the Report of the ThaumasiteExpert Group. Its guidance has been extensivelydiscussed with industry and in particular, hasbeen presented as a draft for discussion at aSeminar at BRE in November 2000. It will beissued in concert with the revision of BS 5328 togive unified and co-ordinated guidance.
New research, which will be coming tofruition over the next few years, will add to theknowledge base on which the Digest rests. Ifnecessary, a further revision or amendment willbe undertaken to incorporate these newresults.
GENERAL REFERENCE
Thaumasite Expert Group, “The thaumasiteform of sulfate attack: Risks, diagnosis,remedial works and guidance on newconstruction”, Department of theEnvironment, Transport and the Regions,London, 1999.
Figure 1: Layout of new BRE Digest.
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Stuart Bell is an Architect whois Group Technical Director forMarshalls Plc. He specialisesin the development ofmasonry. In particularstructural masonry, for both
building and civil engineering applications. Heserves on many technical committees.
ABSTRACTMasonry has been used for thousands of
years both for building and civil engineeringconstruction. Designers, confident in thehistoric background of masonry construction,consider it to be a relatively straightforwardform of construction. There have however,especially during the last 100 years, been manychanges in the form of masonry constructionused in both building and civil engineeringstructures leading to some confusion, and incases misspecification by designers. Poorconstruction on site by contractors has alsobecome commonplace. This is particularly truein the area of mortars, where the ever-increasing range of mortars available to thespecifier and the introduction of newstandards, and in particular EuropeanStandards and associated test methods, willlead to further concerns for both specifier andcontractor. The paper considers the changesthat have occurred in masonry, and in particularmortars, and the likely areas of concern for thefuture, which unless addressed, will lead to afurther decline in the use of masonry, due to alack of specifier and contractor confidence inthe material, especially in a post-Egan era.
KEYWORDSMortars, European Standardisation, Test
methods, Workmanship, Mortar performancecriteria.
INTRODUCTIONMortar is critical to masonry construction.
Its traditional use provided a relatively weakmaterial which could be used in its wet state tofill the gaps between adjoining masonry unitswhile providing a relatively smooth platform forthe bedding of further units to develop a wall
that was reasonably plumb. After curing, themortar provided some adhesion between theunits, and provided a resistance against thepenetration of weather. In modernconstruction, its performance requirements aremore complex. Not only does it have to providein most cases a bonding element between theunits if the wall is to perform in a satisfactorystructural manner while also developing theaesthetic the designer requires. As walls havebecome progressively thinner, mortar also hasto provide greater weather resistance, especiallyas mortar joints are now thicker due to havingto include other elements within the mortarwhich add to the overall structural stability andenvironmental performance of the masonry,such as wall ties, bed-joint reinforcement anddamp-proof courses. This increase inperformance requirements has shown thevulnerability of mortar to poor specificationand/or workmanship, which in turn hasrequired greater consideration of thecharacteristics of the mortar, and theirstandardisation to enable both specifiers andcontractors to produce satisfactory mortar fortheir purposes. The paper considers thesechanges, and the likely future developmentswith particular reference to European Standardsand their test methods.
HISTORIC CONTEXTSome of the oldest examples of mankind’s
built environment have been constructed inmasonry, and still survive some 5000 years later.Not only have the natural stone masonry unitssurvived, but the mortar between the units inmany cases, still remain durable. In the UnitedKingdom, examples of Roman fortificationssuch as Hadrian’s Wall demonstrate, in arelatively exposed climate, the durability ofmasonry and its associated mortar.
These traditional structures until thebeginning of the 20th century shared manycommon characteristics. The mortar used intheir construction was in the main based onlime. The lime was created by burninglimestone deposits contaminated with clay,which gave a material which had hydraulicproperties when combined with sand inmortars. The hydraulic properties allowed the
A REVIEW OF THE USE AND ABUSE OF MORTAR
Mr. S.E. Bell Dip Arch, RIBA, MIM
Marshalls
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setting and hardening of the mortar at arelatively slow rate, but this was not adisadvantage in thick-skin structures. Themajority of masonry was also constructed as aload-bearing material, with loads from thefloor, roofs and other elements in the structurebearing down on the masonry, which helpedstabilise the masonry. Particularly in structuresbuilt of clay brickwork, the overall thickness ofthe walls allowed the bricklayers to select onlythe best units for the exterior of the walls, withthe less satisfactory units being used asbacking within the thickness of the walls. Bysuch selection, accurately dimensionedbrickwork could be constructed, reducing themortar joints to relatively thin joints, giving anaesthetic very different from modern masonry,whilst providing good weather resistance dueto the thin nature of the joints.
Due to the structural nature of themasonry, and the use of the lime-based mortar,movement joints were not required in themasonry, as the joints provided a degree offlexibility to accommodate cyclic thermalmovement and the irreversible moistureexpansion of the clay units.
Many of these historic buildings are nowtreasured, and in many cases have beenrefurbished for uses very different from theiroriginal purpose. A good example is the use ofthe traditional brick warehouses at the AlbertDock, Liverpool, which have now beenconverted into a thriving centre with domesticaccommodation, museums, art galleries andother commercial uses. Care does howeverhave to be taken when either modifying oraltering such historic structures, as manydesigners and contractors have littleunderstanding of the requirements of suchbuildings, and all too often inappropriatemodern materials such as cement-basedmortars are introduced with unfortunateconsequences. This is also true of civilengineering structures where the flexibility ofthe traditional masonry can be damaged bypatch repairs of modern bricks bedded incement mortars. Valuable guidance in theselection of correct mortars can be obtainedfrom the English Heritage Technical HandbookSeries(1) to ensure sympathetic maintenance.Guidelines to determine the composition of astructure’s existing mortar are also available(2)
with additional research being carried out onthe overall performance characteristics in termsof creep and shrinkage(3). In particular, the
understanding that creep and shrinkage areimportant factors in the mechanism by whichthe traditional masonry wall accommodatemovement without damage emphasise thefact that the masonry wall should be repairedusing the lowest strength and thus highestcreep mortar which will satisfy therequirements of structural loading anddurability. Use of the wrong mortar mix in sucha situation can lead to damage to the adjoiningmasonry units.
RECENT MASONRY CONSTRUCTION
Following the invention of Portlandcement by Aspdin in Leeds, masonry andmortars were relatively slow to take advantageof the new material. Later concerns aboutwater penetration and dampness lead to theintroduction of the “cavity wall concept” formost building construction. This developmentwould not have been possible without theaddition of cement to mortars, as the thinnerwalling required a more rapidly harding form ofmortar which also provided bonding propertiesto not only hold the thinner skin togetherunder higher stresses, but also to resistweather penetration through the relativelythick skin of mortar. The need to tie the twoskins of a cavity wall together lead to anincrease in the size of the mortar joints as therewas need to accommodate wall-ties within themortar joints. While the cement based mortargave greater protection to such ties, there hasstill been extensive problems with thecorroding of mild steel wall ties which has leadto cracking occurring in bed jointscorresponding to the vertical spacing of thewall ties. Detailed guidance on how to replacethe ties within the mortar joints is available(4) (5).Modern ties are either made of various forms ofstainless steel or suitably galvanised carbonsteels to avoid this problem.
As the requirement for improvedinsulation performance from the outer-skingrew, the inner leaf was normally built inlightweight concrete blocks which also carriedthe load from the floors and roof of thestructure. Whilst this resulted in the inner leafbeing compressed, the outer leaf became amere cladding with only it’s self-weight tosupport. In these circumstances, movementbecame more of a problem. The earlier limesand mortars had been able to absorbmovement and repair minor cracking caused by
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movement by autogenous healing. The latercement-based mortars were much stiffer andstronger, and therefore unable to absorb cyclicthermal movement or, depending on thecharacteristics of the masonry material,reversible shrinkage or irreversible moistureexpansion. They also produce reduced abilityto develop autogenous healing. This lead tothe introduction of movement joints in theouter skin of modern masonry where there canbe no denying they often detract from theoverall appearance of the masonry. Theintroduction of damp-proof courses to helpenhance the weather resistance of the outerskin lead to the introduction of thicker joints atthe positions where damp-proof courses wereincorporated due to the need to bed thedamp-proof course on both sides. Failure tocarry out this simple task enhanced themovement characteristics of the masonryabove damp-proof course level due to the lackof bond between the dry masonry unit and thedry DPC layer.
The advent of cavity insulation has had afurther effect upon the performance of themasonry in as much as the outer skin ofmasonry construction is now more isolatedand suffers greater thermal movement. This isparticularly true when full cavity insulation isused on the southern and western faces ofbuildings. The outer skin of masonry alsotends to be slower to dry out, and therebyincreasing the risk of chemical interactionbetween the masonry units, and in particularsulphates from some clay bricks, with themortar. Increased thermal insulation has alsoaffected the mortar on the inner leaf where inorder to provide a uniform thermalperformance, either mortars of a lightweightcomposition or specially formulated to give abed thickness of 1-3mm have been utilised.Lightweight mortars reduce the compressivestrength on average by 63% and the flexuralstrength by on average 49%. Thin-beddedmortars on the other hand increase thecompressive strength by up to 16% andflexural strength by up to 15%.(6)
LATERAL LOADING CAPACITYWhilst the majority of masonry and hence
mortar is used in two storey domesticconstruction in the United Kingdom, andtherefore subject to the structural requirementsof the low-rise building code(7), other masonryapplications are designed to BS5628: Part 1:
1992(8). The design method employed forcompressive strength relates the strength ofthe masonry unit to the mortar designations,the mortar designations being defined in Table1 of the standard. Whilst this design method isrelatively straightforward, greater concern isexpressed with regard to the flexural strengthof the masonry, which for clay bricks is relatedback to the water absorption of the units andrelative mortar designations with blanketfigures for calcium silicate bricks and concretebricks. Concrete blocks characteristic flexuralstrength is developed in relation to theircompressive strength and again the relativemortar designations. The importance of themortar designation and the workmanshiprelated back to the placement of the mortar inachieving flexural strength is highlighted by thelarge amount of research work carried out inthis area. Much of the early work in this areawas produced at the British Ceramic ResearchLtd (now CERAM Building Technology)(9)(10).Edgell published a definitive paper in thejournal of The British Masonry Society in1997(11). One of the conclusions drawn in thepaper was that increasing water retentioneither by the use of lime or air entrainingagents improves the bond between mortarand bricks with a high initial rate of suctionand reduces the bond with bricks having a lowinitial rate of suction. But the paper stillconcluded that the ratio of a characteristicflexural strengths taken from Table 3 of BS5628:Part 1: 1992(8) was not unreasonable, and, ifanything, likely to be conservative. A largeprogramme of work at CERAM BuildingTechnology has continued on both clay brickwork, calcium silicate brickwork and concreteblockwork with a variety of masonryunit/mortar combinations, including mortarswith admixtures. This research has confirmedthat BS5628: Part 1: 1992 still has aconservative approach to design, but it mustbe born in mind this is based upon in the mainlaboratory specimens where high standards ofworkmanship and good curing conditions wereprovided.
Earlier work on concrete block walls byAnderson(12) demonstrated that again concreteblockwork, when built and cured in alaboratory, gave results which supported theTables in the Standard. The concern however isthat work on site does not match thecapacities given within the code.
Since that time, research has been carried
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out to consider how best to test the bond-strength of masonry in actual walls. In April1991 BRE Digest 360(13) gave details of theBRENCH test method for bond strength whichwas a development of a site test used invarious other countries, although principallyAustralia. Slightly earlier BRE had also producedan information paper(14) describingBREMORTEST a rapid method of testing freshmortars for cement content. The bond wrenchmethod of test was considered as a draftEuropean Standard(15) but was not produced asa European Test Method. The reason for theremoval of the test method from European TestMethods was that bond strength ofdesignated masonry mortars is to beaddressed by a proxy test which will be theinitial shear strength test prEN1052-3(16).
The development of masonry hasinvolved greater development in mortars andtheir application rather than the masonry unitwhich in many cases has remained unchangedfor many years, if not in the case of clay bricksand natural stone hundreds of years. Mortar iscritical to the performance of the masonry, butthe author would suggest that for mostspecifiers it is considered of little importanceand is an area of specification which isuniversally weak. As a result, problems withmasonry can often be traced back to aspectsof the mortar specification, “manufacture”, andthe workmanship associated with itsplacement.
SPECIFICATIONFor the average specifier, the amount of
information available on a range of mortarmixes, their admixtures and the resultingcharacteristics is bewildering.
Most specifiers initially turn to BS5628:Part3: 1985(17). This gives general guidanceregarding properties of mortar. It also givesguidance regarding the durability of mortarsrelative to their position in the buildingenvelope although there is often a reluctanceamong both designers and contractors toadjust mortars depending upon the degree ofexposure, firstly for worries about whether thecorrect mortar will be used in the correct area,and secondly, whether or not there will be acolour variation within the mortar caused bythe varying constituent ratio. Valuable advice isalso given in the Standard on the joint profilesavailable for mortar for external walls. TheStandard also allows designers to consider the
aesthetics of their decisions regarding mortaron the overall appearance of the wall, and inparticular, the workmanship required toachieve satisfactory performance from themortar. Further guidance is given in BS4721:1981.(18)
One of the best guides available tospecifiers is “A Basic Guide to BrickworkMortars”(19) which not only identifies thecharacteristics required of the various mortars,but also gives advise on aspects ofworkmanship. Likewise, BRE Digest 362“Building Mortar”(20) overcomes many of thedifficulties of deciding which mortar is best inwhich location. The general-purpose mortar isbased upon designation (iii) mortar as listed inBS5628: part 3: 1985(17), although the caveat ismade that stronger or weaker mixes arepreferable for some uses. Enhanced durabilityis given to the general-purpose mortar over thetraditional designation (iii) mortar by the use ofan air entraining plasticiser which improves thefrost-resistance of both the freshly laid andhardened mortars. It has the other advantageof allowing a reduction in the quantity of waterin the mix, while still maintaining goodworkability. It is still of concern however, thatmany specifiers do not fully appreciate thedifference between the traditional hydrauliclimes used in historic buildings and the non-hydraulic limes now used to aid waterretention and add plasticity to traditionalcement:sand mortars. The author is aware ofat least two cases where ready mixed lime-sand mortar has been used for constructionwithout the addition of cement in the mistakenbelief it will give the same performance as ahydraulic lime:sand mix!
This confusion has been highlighted morerecently by environmental concern suggestingthat hydraulic lime:sand mixes are preferable tothe present day factory mixed cementhydrated lime sand mixes as the latter allowsreclaiming of the masonry units withoutdamage when the buildings serviceable life iscompleted. It is also claimed that the hydrauliclime itself is eco-friendly, and requires lessenergy to manufacture than cement, andreabsorbs over time the carbon dioxideliberated in its manufacture. The newGlyndebourne Opera House is often quoted asan example of the use of lime:sand mortarconstruction, but in fact lime putty was utilisedfor the construction in a 1:2:9 mix.(21) The useof the weak mortar did however allow the
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designers to dispense with some of themovement joints normally associated with abrick building of this size. There are howeverexamples where pure hydraulic lime:sandmixes have been used, both in housing andlarger scale structures . In the former case, itwas calculated that moving from the traditionalcavity wall of the facing brick outer skin, 50mmof insulation and a blockwork inner skin incement:lime:sand mortar as against a solid wallbuilt in hydraulic lime with a dry-lining system,a saving of over £500 was achieved in the costof the walling(22). A larger example of the use ofhydraulic lime mortars is in the new NationalLottery funded World of Glass Museum at StHelens where the traditional glass blowing kilnhas been simulated by a cone-shaped buildingwith its walls being one and a half bricksthick(23). It is however acknowledged that thereis a general lack of experience andunderstanding on the part of both specifiersand site operatives to the special requirementsof lime mortars in respect to specification,storage, protection, laying and curing.Notwithstanding that, environmental pressureswill see in the future, greater use of hydrauliclime:sand mortars in specialist applications. Apaper by Dr Andrew Smith of Hanson Brickprovides an excellent summary of the use oflime mortars(24). While the author is unaware ofany research in the United Kingdom on thefactors influencing architects and contractorsselection of mortar, a paper in the magazine ofMasonry Construction in America(25) suggeststhat architects are more concerned about theproperties related to wall performance, thanproperties related to aesthetics. The greateruse of masonry in the United Kingdom would,as the author suggests, show a differing trendwith appearance and uniformity being ofgreater importance than shown in theAmerican research.
Designers can also enhance theperformance of mortar within the externalskins of masonry by following the guidelines inBS5628: Part 3: 1985(17) to avoid saturation ofthe masonry. Whilst masonry and associatedmortar can be designed to resist destructivemechanisms such as freeze-thaw cycling andsaturation with soluble sulphates, detailingwhich protects the masonry by damp-proofcourse detailing and throated copings and/orsills will produce masonry which has less liabilityto staining. Traditional masonry wallsincorporated drip-courses and other protective
details whereas many masonry buildingsconstructed in the 70’s allowed flush detailingwith consequential staining of the masonry,including additional staining such as free-limefrom the mortar. Flush detailing exposesweaknesses in the construction.
SITE PRACTICEThere have been large advances in the
delivery of mortar to site in the last few years.
Nowadays nearly all major projects utilisemortar which is factory mixed. Mortar can bedelivered ready-mixed dry with cement, limeand sand being stored in silos on the site, andthen mixed with water to form the mortar asrequired. An alternative method is the use ofretarded mortars which are delivered wet witha retarding agent added to allow the mortar tobe workable for up to 36 hours, dependingupon weather conditions and the strength ofthe mortar mix. Higher cement contentmortars tend to have a shorter “shelf-life” thanthe low cement content mortars. Weatherconditions also have an influence on the “set”time.
Both the above methods of mortardelivery ensure high quality product, althoughabuse can still occur by adding too much waterat the point of use, or by leaving the mortar onthe spot-board too long before use. Failure tokeep equipment clean can also lead toproblems.
Mixing of lime:sand mixes with cementon site introduces the problem of variability ofbatching. Many mixes produced on site areweaker than the designer intended. The sandgrading used in the mortar can also have aminor effect upon the performance and theproperties of the masonry, although researchat The Building Research establishment andThe British Ceramic Research Limited at Stoke-on-Trent concluded that the problem was onlylimited to some brick types when laid dry onthe bed of mortar.(26)
The difference in strength between sitemixed mortars and laboratory mixed mortars isrecognised in BS5628: Part 1: 1992(8) where inTable 1 there is up to 30% difference instrength between preliminary laboratory testsand site tests when comparing thecompressive strength of mortar at 28 days.Further research in Germany(27) confirmed thatthe average compressive strength in the jointfor site mix mortars and standard mortars was
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58 ± 18% of the compressive strength oflaboratory prisms. It must however be clearlyunderstood that many factors affect theperformance of mortars in site conditions andit is very difficult to draw clear comparisonsbetween the properties of site-mix mortars andlaboratory-mixed mortars, by just comparingcompressive strength tests.
Several studies have reviewed the effectof workmanship when combining masonryunits with mortar, with particular emphasis onthe dangers of “furrowing” bed joints and“tipping” cross-joints. While the former affectscompressive strength with losses up to 25%,the latter is a major cause of rain penetrationthrough the outer skin of masonryconstruction.
If latent mortar defects are to beprevented, it is important that the mortar hasproperties that allow the bricklayer to workeffectively while avoiding defects. The mortarshould be easily workable with ability to flow asrequired, but also possess sufficient cohesionto stick to the trowel and the masonry unitduring the laying operation. If the mortar is notsuitable for the bricklayer’s requirement, thereis then a real risk that additional ingredients willbe added to the mix to improve the workability,but with consequential loss of performance.Building Research Establishment InformationPaper IP10/90(28) gives good advice on avoidinglatent defects in mortar, with particularemphasis on the workmanship aspects.
Another area that is often ignored is thelaying of mortar during adverse weatherconditions, and in particular, cold weather.Mortar should never be laid on frozen units orindeed used with frozen units. Laying ofmasonry units should also cease when afalling air temperature reaches 3˚C and shouldnot re-commence until it rises to 1˚C and is stillrising. Likewise, in hot weather, highabsorption bricks may require docking toreduce their initial rate of suction, therebyavoiding too much water being drawn fromthe mortar before it is set, thereby reducing itsadhesion, rain-resistance and strength of themasonry. Dense masonry units shouldhowever not be “docked”, otherwise there is arisk that they will “float” on the mortar, andafter a few courses have been built, theconstruction may become unstable as the stillfluid mortar extrudes from the lower courses. Itis also important that both the incomplete walland materials used for the walling are
protected during wet weather, or duringfreezing conditions. The head of the wallshould be covered with polythene sheetinghanging over the newly completed masonry,but still allowing air to circulate between themasonry and the underside of the sheeting. Itis good practice to keep the head of any wallcovered with a waterproof membrane until thefinal capping/coping course or roofconstruction is built over the wall to protect thehead. Several documents are produced ongood site practice, with one of the best beingThe Brick Development Associate BuildingNote Number 1(29).
Changes in mortar mix and/orworkmanship technique can affect the colourof the mortar, which in turn will have a markedaffect upon the overall colour of the masonry.As stated earlier, more and more mortar isbeing produced ready-mixed, thereby lesseningthe risk of variation. There is however still realrisk of colour variation due to a commonpractice of tooling the joint of the face of themasonry when the mortar is at different stagesof curing. If the mortar has started to cure, thejoint will tend to be darker, whereas if themortar is still relatively soft, the joints tend tobe lightened as cement paste is drawn to theface of the joint. Ideally, all the joints should betooled when the mortar has reached the samedegree of stiffness, which is normallydetermined by experience(30).
FAILURES OF MORTARThe majority of mortar produced in the
United Kingdom performs in a satisfactorymanner. However, water penetration is stillone of the major areas of concern, and cannormally be traced back to poor workmanship,be it failure to clean mortar droppings from thecavity and from damp-proof course trays, orpoor fitment of cavity insulation. Unfilled jointswill increase the amount of water entering thecavity, thereby increasing the risk of waterpenetration.
Staining from mortar joints is another areaof concern, which can prove very unsightly.This is normally caused by the masonry beingsaturated during the construction phaseallowing leeching of calcareous solution fromthe material, mainly in the form of dissolvedcalcium hydroxide. When deposited on theexternal surface of the wall, this reacts withatmospheric carbon dioxide to form calciumcarbonate. Acid cleaning can treat such stains,
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but again there are dangers in not wetting themasonry first to ensure the acid is only appliedto the face of the masonry and is not drawninto the body of the unit and the mortar.
The mortar plays a major part in theappearance of masonry and the correct settingout of the brick work to allow the cross jointsto form vertical perpends is one of the majoraesthetic requirements for facing work inmasonry. This is normally achieved by carefulsetting out of the masonry units, allowing eachfourth cross-joint to be 10mm wide and thenthe adjoining three cross-joints adjusted toensure four units and four joints forms acommon module. For the standard 215mmclay brick, this is a 900mm module. Byensuring every fourth cross-joint is a constantthickness, a clearly defined vertical perpendproducing attractive masonry will result.
THE FUTURE FOR MORTARAs already listed, debates about mortar,
its constituents, its use and its performance arewidespread. The amount of research carriedout on mortar, its properties and itsperformance is unfortunately not reflected inthe manner in which it is treated on site.Notwithstanding this abuse, the majority ofmortars perform in a satisfactory manner, as forthe most part they are used on low-risehousing where traditional detailing providesprotection to the majority of the walling.Loading on inner skins is relatively light, andtherefore relatively low stresses are applied tothe mortar. In the United Kingdom,traditionally, there has been little testing ofmortar on site, although test methods arespecified in BS4551: 1980(31).
The introduction of Europeanstandardisation of mortars for masonry is nowproceeding apace with two new standards formasonry mortars EN998-1 Specification forMortar for Masonry-Part 1: Rendering andPlastering mortar with inorganic bindingagents(32) and of more importance to theconstruction of masonry EN998-2 Specificationfor Mortar for Masonry-Part 2: Masonry Mortar(33). Due to the wide range of masonryconstructions covered within the membershipof CEN, the standards have to cover a widerange of masonry units and mortar materials.Particular effort was made in the Standards toavoid the inclusion of prescriptive requirements,but instead, as far as practical, to provideproduct performance requirements as required
by the Construction Products Directive.
Unfortunately the gestation period forthe European Standards has been prolongeddue to the difficulties of agreeing a standardbetween 19 countries with very widely varyingtraditions and methods of constructionfeaturing both mortar for rendering and mortarfor construction. An early review of theStandards was carried out in 1994 byBenningfield(34). Since that time there has beenconsiderable detail development within thestandards and in September 1997, CEN/TC125approved the submission of the ordinaryproduct standards to formal vote with theresult that prEN998-1 failed the formal vote bya narrow margin, whereas prEN998-2 wasapproved in the formal vote as a marketstandard. Since that time, work has progressedin turning the standards into harmonisedversions and the work behind this wasreviewed by Smith(35) in November 2000.
The draft candidate harmonisedstandards incorporating Annex ZA have nowbeen finalised with their supporting testmethods in the EN1015-1 series:
EN1015-1: Methods of test for mortar formasonry - Part 1: Determination of particle sizedistribution (by sieve analysis).
EN1015-2 - Methods of test for mortarfor masonry - Part 2: Bulk sampling of mortarsand preparation of test mortars.
EN1015-6 - Methods of test for mortarsfor masonry - Part 6: Determination of bulkdensity of fresh mortar.
EN1015-7 - Method of test for mortar formasonry - Part 7: Determination of air contentof fresh mortar.
EN1015-9 - Methods of test for mortarfor masonry - Part 9: Determination ofworkable life and correction time of freshmortar.
EN1015-10 - Methods of test for mortarfor masonry - Part 10: Determination of drybulk density of hardened mortar.
EN1015-11 - Methods of test for mortarfor masonry - Part 11: Determination offlexural and compressive strength of hardenedmortar.
EN1015-14 - Method of test for mortar -Part 14: Determination of durability ofhardened masonry mortars (with cementcomprising greater than 50% of the totalbinder mass).
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EN1015-17 - Methods of test for mortar -Part 17: Determination of water-solublechloride content of fresh mortar.
EN1015-18 - Methods of test for mortarfor masonry - Part 18: Determination of waterabsorption coefficient due to capillary action ofhardened rendering mortar.
prEN1015-20 - Methods of test formortar - Part 20: Determination of durability ofhardened masonry mortars (with cementcomprising less than or equal to 50% of thetotal binder mass) (draft in preparation).
EN1052-3 - Methods of test for masonry- Part 3: Determination of initial shearstrength.
EN1745 - Masonry and masonryproducts - Methods for determining designthermal values.
prEN13501-1 - Fire classification ofconstruction products and building elements -Part 1: Classification using test data fromreaction to fire tests.
The range of tests is obviously greaterthan at present in the United Kingdom andwith the Harmonised Standard allowing in theUnited Kingdom, the application of the CEmark if the manufacturer so requires. TableZA:3:1 lists the information to accompany theCE marking. The characteristics, which requireattention, can be summarised as follows:
a) Compressive Strength
The manufacturer will declare this on thebasis of the test method EN1015-11.
b) Proportion of Constituents
The Standard prEN998-2 contains therequirement for the proportion of constituentsof prescribed masonry mortars to be declaredby the manufacturer.
c) Bond Strength
This is defined in end-use conditions andis limited for designed masonry mortarsintended to be used in elements subject tostructural requirements. Initially this was goingto be addressed in prEN1015-3 using thebond-wrench test, but instead will now bedetermined using EN1052-3 - Methods of testfor masonry - Part 3: Determination of initialshear strength.
d) Content of Chlorides
For masonry mortars intended to be usedin reinforced masonry the chloride contentshall be determined by test in accordance with
EN1015-17 or by calculation to show that thelimit will not exceed 0.1%.
e) Reaction to Fire
Whilst mortars containing less than 1% ofhomogeneously distributed organic materialare presumed to be reaction to fire to Class A1without testing, it is likely that no declarationwill be required for products which do not inthemselves form a fire-resisting element but arepart of the construction of a fire-resistingelement.
f) Water Absorption
The declared value of capillary waterabsorption will only be required for masonrymortar for use in external elements. Themanufacturer will declare water absorption onthe basis of the supporting test methodprEN1015-18.
g) Water Vapour Permeability
This again will only apply to externalelements, and cover tabulated values for watervapour diffusion coeffient as given in EN1745Table A12.
h) Thermal Conductivity/Density
This information is required for masonrymortars intended to be used in elementssubject to thermal requirements and will be adeclared value in relation to dry bulk density ofhardened mortar. Again it will be made byreference to EN1745.
i) Emission of Radioactivity
This is an area which is likely to becovered by the “release of dangeroussubstances” regulated on a European orNational level for which a guidance paper hasnow been issued.
j) Durability of PerformanceCharacteristics against Freeze Thaw
Originally, the Draft Test Method to meetthis characteristic was based on the BREMethod of testing mortars for durability, whichincluded tests for chemical attack, andparticular sulphates. However, during the lastyear, industry has decided that the test methodthat can take up to six months to progress wasunacceptable, and therefore it has been agreedthat the temporary solution, member stateswill rely on local experience to determine thedurability of performance characteristics of aparticular mortar against freeze/thaw action.For the future, the characteristics againstfreeze/thaw might be based upon the BritishClay-Brick panel test developed at CERAM
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Building Technology, either using normal sizebricks (215mm x 65mm face) or perhaps asmaller clay unit to increase the number ofmortar joints in the panel. Recently, a “Partnersin Innovation” grant has been given to developthis work which will be carried out jointlybetween CERAM Building Technology and TheMortar Producers Association.
k) Durability PerformanceCharacteristics Against ActiveSoluble Salts
This characteristic is required for mortarsintended to contain embedded metal.
l) Durability of PerformanceCharacteristics Against ActiveSoluble Salts - For Mortars inMasonry Subject to Prolonged WetConditions
This particular test method is requiredfollowing a request from TC125 Masonry Unitswho required a test method to check theaction of the mortar with certain clay units thatcontained soluble salts and in particular solublesulphates at a level that might create problemsif the units were saturated for a period of time.Originally the Mandate from the Commissionwas concerned regarding the protection ofembedded steel within mortar, and this iscovered in the “content of chlorides”characteristic. There was therefore as such noimmediate cause to provide information on thedurability of performance characteristicsagainst active soluble salts, with the result thatthis particular requirement will not now beaddressed within the standard, but rather beaddressed in the national forward to thestandard in countries where it is considered aproblem. The UK will be one such countrywhere obviously there has been some historyof sulphate attack with a small proportion of“N” quality bricks to BS3921: 1985.
CONCLUSIONThe requirements for mortar has changed
dramatically over the years. Not only has therange of products extended dramatically, butthere is now a greater understanding of thecharacteristics of mortars and their likelyreaction with the masonry elements withwhich they interact. If masonry is to survive inthe 21st century, then several aspects of itsconstruction are going to have to be re-thought if it is to remain a mainstream buildingproduct. Critical to the debate will be
workmanship and in particular the training,organisation and motivation of masons.Masonry construction is a craft, but ismainstream construction gearing itself up inthe post-Egan era to craft trades? Factorymanufactured units that can be rapidlyassembled on site regardless of weatherconditions are one of the many aspects ofconstruction being considered in the drive tomake construction more of a manufacturingprocess. The use of small element masonrymaterials with mortar, with the masonryconstructed on site, may well decline from themajor building market, and only be used onrelatively small scale works where the speed ofconstruction, the craft required to produce thatconstruction and the overall scale andappearance of the materials are more in tunewith the aims of the sector.
The requirements of sustainability andrecycling of building materials will have a part toplay in the debate and this will, in the author’sopinion, depend a great deal upon the criteriaset for the lifecycle assessment of materials andconstruction. There can be no denying thatwith the exception of natural stone, masonrymaterials have a high embodied energy at thefactory gate, are heavy to transport and by themethod of laying chosen on site, can lead inthe long term to repetitive strain injuries. Onthe other hand, their long life withoutmaintenance, the human scale they create andthe craft employment they provide are all vitalelements of the sustainability debate. Onepoint is however clear: mortar has for too longbeen treated as an afterthought and has neverbeen given the recognition it deserves as a vitalpart of masonry construction. This problemhas partly been addressed by the larger mortarproducers and RMC in particular produce a first-class continuing professional developmentpackage(36). There is, however, a very largeeducational programme still required ifspecifiers, contractors and indeed masons, areto fully appreciate the implications of theEuropean Standards and their test methods. Itis a task the industry must not shy away from ifit is to maintain its market in the future.Without mortar designed for it’s particularrequirement, correctly specified, properlyproduced and installed with due care andattention, the true potential of masonry will notbe realised.
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ACKNOWLEDGEMENTSThis paper would not have been possible
without considerable assistance from manyfriends and colleagues in the Building Industryand Associated Research Organisations.Particular thanks must be given to NeilBenningfield of RMC Mortar, Professor GeoffEdgell of CERAM Building Technology, BarrieClamp of Ibstock Building Products, andRichard Smith Chief Technical Officer of TheBrick Development Association.
Thanks must also be expressed to mycolleagues at Marshalls who provide a fund ofuseful information on how our masonryproducts in reconstructed stone, clay andnatural stone are combined with mortar toprovide in the main highly successfulstructures, but occasionally with mostinteresting and varied results!
REFERENCES
1 ASHURST, JOHN AND NICOLA, EnglishHertitage Technical Handbook, Volume 3 -Mortars, Plasters and Renders - GowerTechnical Press 1988.
2 SICKELS-TAVERS, LAUREN B, Selecting Mortarfor Historic Preservation Projects, AmericanJournal of Masonry Construction, October1997, Pages 533 - 534, 555 - 557.
3 SICKELS-TAVERS, LAUREN B, Creep, Shrinkageand Mortars in Historic Preservation -American Society for Testing and Materials,Journal of Testing and Evaluation 1995 Pages447 - 452.
4 BUILDING RESEARCH ESTABLISHMENTDIGEST 359 - Repairing Brick and BlockMasonry, March 1991, Building ResearchEstablishment Garston, Watford WD2 7JR.
5 BUILDING RESEARCH ESTABLISHMENTDIGEST 401 - Replacing Wall Ties, January1995, Building Research Establishment,Garston, Watford WD2 7JR.
6 BUILDING RESEARCH ESTABLISHMENTINFORMATION PAPER IP2/98, Mortars forBlockwork: Improving Thermal Performance, A W Stupart and JS, Skandmoorthy,Construction Research Communications Ltd1998.
7 BRITISH STANDARDS INSTITUTION, BS8103:Part 2: 1996, Code of Practice for MasonryWalls for Housing, BSI London 1996.
8 BRITISH STANDARDS INSTITUTION BS5628:PART 1: 1992, Structural Use of UnreinforcedMasonry, BSI London 1992.
9 HASELTINE B.A, West H.W.H. and Tutt J.N,The Resistance of Brickwork to Lateral LoadingPart1: Experimental methods and Results ofTests on Small Specimens and Full Sized Walls.Part 2: Design of Walls to Resist LateralLoading. Technical note 284, The BritishCeramic Research Association, January 1979
10 WEST H.W.H., HODKINSON H.R, GOODWINJ.F. AND HASELTINE B.A., The Resistance toLateral Loads of Walls Built of Calcium SilicateBricks, Technical note 288, The British CeramicResearch Association, July 1979.
11 EDGELL G.J, Factors Affecting the FlexuralStrength of Brick Masonry, MasonryInternational - Journal of the British MasonrySociety Vol. 1 No 1 Pages 18 - 24 1987.
12 ANDERSON C, Lateral Loading Tests onConcrete Block Walls, The Structural Engineer,Volume 54 No 7 July 1976.
13 BUILDING RESEARCH ESTABLISHMENT,Digest 360, Building Research Establishment,Garston, Watford, WD2 7JR 1991.
14 BUILDING RESEARCH ESTABLISHMENT,Information Paper IP8/89 BREMORTEST: ARapid Method of Testing Fresh Mortars forCement Content, Building ResearchEstablishment, Garston, Watford WD2 7JR.
15 EUROPEAN COMMITTEE FORSTANDARDIZATION prEN 1052-5, Methods ofTest for Masonry - Determination of BondStrength by the Bond Wrench Method, July1998.
16 EUROPEAN COMMITTEE FORSTANDARDIZATION prEN 1052-3 - Methodsof Test for Masonry Part 3: Determination ofInitial Shear Strength 1999.
17 BRITISH STANDARDS INSTITUTIONBS5628:PART 3: 1985, British Standard Code ofPractice for Use of Masonry, Part 3, Materialsand Components, Design and Workmanship,BSI London 1985.
18 BRITISH STANDARDS INSTITUTIONBS4721:1981, Ready-Mixed Building Mortars,BSI 1981.
19 HAMMETT M, A Basic Guide to BrickworkMortars, The Brick Development Association,Woodside House, Winkfield, WindsorBerkshire, SL4 2DX 1988.
20 BUILDING RESEARCH ESTABLISHMENT BREDIGEST 362 - Building Mortars, BuildingResearch Establishment, Garston, WatfordWD2 7JR 1991.
21 THORNTON J.A, TURZYNSKI J.G, A NewGlyndebourne Opera House, The StructuralEngineer Volume 75 No 2 1997.
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22 ANON. PROJECT: PROTOTYPE HOUSE,Hydraulic Lime Mortar for the House of theFuture, The Structural Engineer Volume 78 No19 2000.
23 BARNETT MALCOLM, Modern Marriage, TheBrick Bulletin Pages 18 - 19, The BrickDevelopment Association Woodside House,Winkfield, Windsor Berkshire, SL4 2DX, Winter2000.
24 SMITH, DR ANDREW, Lime Mortars: OldTechnology Revisited - draft article circulatedto The Brick Development Association, Bricksand Mortar Standards Working Party 1999.
25 WALLACE, MARK A, How Mortar is Chosen,Masonry Construction, Pages 50 - 54,February 1991.
26 DE VEKEY R.C, EDGELL G.J & DUKES. R, TheEffect of Sand Grading on the Performanceand Properties of Masonry, British MasonrySociety Proceedings No 4, Pages 152 - 1591990.
27 SAHIN Ö, SCHORNING K, KNOFELD ANDMEHLMANN M, Comparison of the Propertiesof Site and Laboratory Mixed Mortars, BulletinMasonry International, Pages 75 - 78 1983.
28 BUILDING RESEARCH ESTABLISHMENT, BREInformation Paper IP10/93 - Avoiding LatentMortar Defects in Masonry, Building ResearchEstablishment, Garston, Watford WD2 7JR1993.
29 KNIGHT T.L, Brickwork - Good Site Practice,Building Note One, The Brick DevelopmentAssociation, Woodside House, Winkfield,Windsor, Berkshire SL4 2DX 1991.
30 SCHIERHORN CAROLYN, Ensuring MortarColour Consistency, Journal of MasonryConstruction, Pages 33 - 35, January 1996.
31 BRITISH STANDARDS INSTITUTE BS4551:1980, Methods of Testing MortarsScreeds and Plasters, BSI London 1980.
32 EUROPEAN COMMITTEE FORSTANDARDIZATION prEN 998, Specificationfor Mortar for Masonry - Part 1: Renderingand Plastering Mortar (draft candidateharmonised standard) April 2000.
33 EUROPEAN COMMITTEE FORSTANDARDIZATION prEN 998-2, Specificationfor Mortar for Masonry - Part 2: MasonryMortar (draft candidate harmonised standard)April 2000.
34 BENINGFIELD N.E, A Review of CEN MortarTests. Masonry International, Pages 5 - 8,Volume 8 No 1 1994.
35 SMITH, R, European Standardization ofMortars for Masonry, paper presentedEMOTECH 2000 Paris, 23/24 November 2000.
36 RMC MORTARS, R.I.B.A CPD ProvidersNetwork, CPD Package Design andTechnology of Masonry Mortars 1999.
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85
THE FUTURE OF RECYCLED AND SECONDARY AGGREGATES
Mr. J. Barritt
Tarmac Recycling Ltd
John Barritt is the ManagingDirector of Tarmac RecyclingLimited, part of the TarmacGroup, and is responsible forestablishing, operating anddeveloping their recycled
aggregate activities in the United Kingdom. Heis also Chairman of the Recycling Committee ofthe Quarry Products Association, the tradeassociation of the aggregate and ready mixedconcrete industries.
ABSTRACTThe paper considers existing patterns of
aggregate supply and the potential for theutilisation of secondary and recycledaggregates in supplying the concreteaggregate market. Consideration is given toGovernment aspirations on the resourcing ofconstruction aggregate demand and thepotential impact on aggregate use. Theaggregate tax and the economics of producingrecycled aggregates are assessed relative totheir influence on supply.
KEYWORDSConcrete aggregates, Recycled and
secondary aggregates, Department ofEnvironment Transport and the Regions(DETR), Sustainable construction, Constructionand demolition waste (C&DW), Marketeconomics.
INTRODUCTIONThe environmental impact of construction
aggregate supply has come under scrutinywithin the broader considerations ofSustainable Construction by the EuropeanCommission and the UK Government. As aconsequence Government policy will
specifically target recycled and secondaryresources as a first choice option forconstruction aggregates in the new MineralsPlanning Guidance document.
The use of recycled aggregates andsecondary aggregates is already wellestablished and these materials hold asignificant market share. The opportunities fortheir increased use is not as great as manywould think because of limited viablesustainable resources, and a realisticassessment of uses that optimise theireconomic potential is required.
The fact that certain materials may betechnically feasible as concrete aggregates isnot the key for their use, as consistency ofsupply and the economics of productiondictate the practical application of resources.
This paper considers the existing marketstructure, the future availability and use ofresources, and speculates on the future make-up of concrete aggregate supply.
1.0. Meeting the demand forconstruction aggregates
The resources used to meet the demandfor construction aggregates have changed overthe last decade:
In 1989 the total market for constructionaggregates (Table 1) was 332 million tonnes ofwhich 90% came from primary resources and10% from recycled and secondary resources.The 1990s saw a significant fall in the totalaggregate demand, initially caused by the fall ineconomic growth and latterly by the change inthe construction market. By 1999 theconstruction aggregate market had fallen to254 million tonnes with primary holding on toa reduced 82% share and recycled/secondarygrowing to 18%.
Tonnes ,000’s 1989 % share 1999 % share % change
Primary 300 90 208 82 -31
Recycled/Secondary c.32 10 c.46 18 +44
TOTAL 332 100 254 100 -23
Table 1: Construction Aggregate Market. (Source: QPA)
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In ten years market demand has dropped23% but primary sales have fallen 31% andsecondary/recycled sales have seen an 44%increase. The trend increased significantly in1997 with the introduction of Landfill Tax, butthe motivation for change is not a lack ofprimary resources but management of cost.
Aggregates are aggregates, regardless ofthe resource from which they are made, and itis their fitness for purpose and price whichdictates their use.
The market for concrete aggregates issubstantial but varies in proportion betweensand and gravel and crushed rock. Thecontribution from recycled and secondarymaterials nationally is not significant althoughthe precast concrete industry uses a proportionof process waste and of course china clay sandis widely used in its local market.
Primary aggregate sales(1) are made upfrom 60% crushed rock and 40% sand andgravel. Concrete aggregates make up 15% ofthe crushed rock market, but a high 70% of thesand and gravel market, giving a combinedtotal of 37% of total primary sales.
To determine future supply ofconstruction aggregates it is logical todetermine the quantity of aggregate demandthat could be sourced in a sustainable wayfrom non-primary resources and then ensurethat sufficient primary materials are available tomeet the balance. The challenge is to projectfuture aggregate demand accurately,something that has never been achievedhistorically, and to quantify the availability ofappropriate sustainable resources.
To put the problem in perspective let usassume Department of Environment Transportand the Regions (DETR) aspire to meet 25% ofaggregate demand from recycled/secondarymaterials in the next five years and that marketdemand remains static. This would result in adecline in primary sales and a growth inavailability of sustainable resources escalatingto an additional 18 m.tonnes a year.
If the concrete aggregate market was topurchase sustainable aggregates proportionateto this change in supply patterns there wouldhave to be resources capable of economicallyproviding up to 5.5 million tonnes ofaggregates a year. However, sustainableconstruction is about using the appropriateresource for the appropriate end use and as themajority of construction aggregate demand is
for non-concrete applications a simple pro rataallocation may not be the best way forward.
2.0. Resource availability ofsustainable aggregates
Materials become resources when theycan be utilised cost effectively. Analysis ofmaterials on or adjacent to a construction sitefor use as, or to replace, aggregates isbecoming common practice, but to meet the25% target better on site waste managementpractices and other resources will be needed.
What realistic targets can be set formaterials meeting the proximity principle suchas Construction and Demolition Waste,highways arisings, Incinerator Bottom Ash,used rail ballast and glass, or those where theenvironmental cost of distribution is lesssustainable like slag, china clay and slate’waste’?
2.1 Construction and DemolitionWaste (C&DW)
The environmental impact of producingand distributing ‘sustainable aggregates’ mustbe less than that of primary resources to meetthe broader objectives of sustainableconstruction. Construction and DemolitionWaste is considered the obvious choice tomatch this criteria, but how much is not being‘beneficially re-used’.
The recent report(2) produced by Symondsfor the Department of Environment Transportand the Regions (DETR) and EnvironmentAgency (EA) on C&DW shows the high level ofrecycling already established in England andWales. The quantity of core Construction andDemolition waste not being ‘beneficially re-used’ is less than 3 million tonnes, and this wasfor 1999. It should be noted that in November1999 Landfill Tax was removed from all inertwastes being used in licensed landfills thatwere quarries undergoing restoration throughlandfill. This was to restore competitive balancewith license exempt, and thereby tax-exemptsites. It could therefore be argued that thesenew tax exempt materials are also beingbeneficially re-used, reducing the availablebalance to an extremely modest figurecompared to the aspired 18 million tonnesneeded.
The flaw in the assessment of C&DWwithin Symond’s report is the principle of‘beneficial re-use’. If the reduction in use ofprimary aggregates is for improved
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environmental management and sustainability,how can DETR and EA justify the disposal ofover 8 million tonnes of core C&DW into overthree thousand unlicensed sites for which theEA have no funding to police, and to which theDETR apply minimal planning control?
There is a further significant volume ofC&DW classified as mixed/contaminatedentering licensed sites, a proportion of thismust be recoverable through better sitesegregation systems.
C&DW remains the source of a possible10 million tonnes but certainly not in the shortterm and not without a major change inexempt site practices and the economics of thelandfill option.
Even so, the concrete and brick fromdemolition waste streams are technically viableas a source for concrete aggregates. BREDigest 433 recommends crushed concrete forconcrete grades up C50, and a 50/50concrete/brick aggregate as 20% blend withprimary aggregates for all applications. Theapproach of the Quality Scheme for ReadyMixed Concrete (QSRMC) is a touch morecautious on the concrete/brick aggregate,preferring a maximum grade of C20.
The technical viability is not the issue forthe recycler, it is profitability and risk. In mostmarkets the cost of producing a 20-5mmconcrete aggregate, to a consistent quality andin consistent quantities, is not covered by thehigher market value. The lower risk, lower costoption is to produce sub-base and fills,materials for which the market demand isgreater than that for concrete aggregates.
2.2 Highways ArisingsRoad maintenance arisings, including
planings, have been recycled as aggregates formany years in areas of high aggregate prices.With the pressure from Local Agenda 21 and abroadening of specifications this resource isalmost fully utilised, and not in lowperformance uses.
Utility companies are re-using theirarisings as sub-bases, pipe bedding and infoamed concrete. Local authorities are usingtheir maintenance arisings in added valueproducts such as cold-lay road base and basecourse, and planings in hot asphalt. TheHighways Agency is developing in situ and exsitu recycling of roads back into roads.
Although materials will be used for higher
performance uses, and foamed concrete withits low strength requirements is a ready market,little of the 18 million tonnes shortfall will beresourced here.
2.3 Used Railtrack BallastTowards the end of 1997 Railtrack
changed their procurement practices for newtrack ballast requiring the provider of the newballast to be responsible for the disposal of oldballast. More importantly they realised that ithad, in most cases, a value, and was not awaste. The providers of new ballast arepredominantly major primary aggregatecompanies and having incurred a cost insecuring the used ballast ensured it wasprocessed and marketed to achieve the bestvalue. This has included use in asphalt andready mixed concrete as well as a high qualitysub-base.
The only additional contribution thisresource will make to recycling will be throughRailtrack’s increased expenditure on trackmaintenance and that will have a relativelysmall impact.
2.4 Incinerator Bottom AshIncinerator bottom ash (IBA) is the main
by-product of the incineration of municipalwaste in Energy from Waste (EfW) plants.Typically 25% of the input to an EfW plantbecomes IBA. The unprocessed IBA containssmall proportions of both ferrous and non-ferrous metals as well as unburnt waste. Inorder to produce a clean and usable aggregateit is necessary to remove these fractions usingmagnetic separation equipment andconventional screening.
IBA can be used in precast blockproduction, hot and cold process asphalt,cement bound macadam and fills.
The UK currently generates 30milliontonnes/year of municipal waste and thisamount is growing at 3% pa. Currently25million tonnes/year are landfilled, but by2020 only 10million tonnes/year will bepermitted by the EU Landfill Directive. If wastegeneration continues at this rate there will be adeficit of around 50million tonnes of waste thatcannot be landfilled by 2020. These materialswill have to be either recycled or incineratedwith energy recovery.
Incineration capacity is realisticallypredicted to grow at around 2milliontonnes/year (between 5 and 7 new plants) and
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there are currently 8 new plants in advancedstages of planning or development. Based onproduction of 25% of input, this alone equatesto 750,000 tonnes/year of IBA production. Ifthe Government’s predictions are right, by2020 there will be 50million tonnes/year ofmunicipal waste either being recycled orincinerated. If we assume conservatively, thatonly 50% is incinerated, then production of IBAwould be 6.25million tonnes/year by 2020.
Taking the next five years initially it ispossible that output of IBA aggregates willincrease by an additional 1 to 2 million tonnesa year. A proportion of this will go intoconcrete, quality and quantity will bereasonably consistent and in the right locationeconomics will work.
2.5 GlassGlass is predominantly silica, if it is
crushed or ground to the grading of a sandthere is no technical problem to incorporating itinto asphalt or blending with other aggregates.RMC have been successful in marketing theirasphalt product Glasphalt, which incorporatesup to 30% glass. Customers are frequentlylocal authorities looking for methods toimprove their recycling performance andreduce the cost of disposal of glass.
Glass should be recycled into glass, it isonly economically viable to use it as anaggregate when its value is very low or nil. Thevalue of recycled glass fluctuates and it cannotbe considered as a consistent source, even if itwere the quantity available is small and ishighly unlikely to reach 700,000 tonnes a year.
Recent experience of using this material inconcrete has resulted in severe problems dueto reaction with the silica, concrete is not thebest market for this material.
2.6 Secondary AggregatesTwenty-four percent of UK industry’s total
energy consumption in 1996 was attributableto the production (12%) and transportation(12%) of construction materials. Sustainabilityshould therefore have an objective of reducingone, and preferably, both of these elements.The proximity principle should indicatematerials of first choice for aggregates andespecially for secondary aggregates. There isnothing to gain in replacing locally producedand distributed, environmentally managedprimary aggregates, with materials incurringsimilar or worse environmental impact in their
production and which require lengthydistribution networks to reach the market.
2.6.1 SlagAll blast furnace slag from the major steel
works in England and Wales is utilised, and theavailability will reduce as output falls and slagproducts are used in higher value processes. Infact the latest announcements by Corus willhave an immediate impact.
Steel slag is almost fully utilised beinglimited only by the economics of distribution,changes in market prices will allow additionalsales from the few operational works remainingbut the combined market impact of blastfurnace and steel slag will now decline.
There will be opportunities for granulatefrom blastfurnace slag as a concrete aggregate,and further use of GGBS with cement, butoverall this is not the resource for growth.
2.6.2 Slate WasteThe locations of slate wastes are in Wales
and the Lake District. The impact of theirextraction, processing and distribution is thesame as primary extraction, their performancewill dictate their end use as predominantly sub-bases and fills necessitating lengthy distributionroutes.
It is estimated that there are 300 to 400million tonnes of slate waste in Wales, with anadditional 3 to 4 million tonnes produced eachyear. Old slate tips are considered by theGwynedd Archaeological Trust to have ‘iconicstatus in the Welsh psyche’ and they willstrongly resist their reworking. New waste fromsites at Blaenau Festininiog will require over£20m of investment in rail infrastructure. Largetonnages from new waste to the north atBethesda will also require substantialinvestment to enable distribution by sea or rail.
Common sense shows that slate waste innot a sensible, let alone sustainable solution,for meeting aggregate demand. As mineralplanning in Wales is now controlled by theWelsh Assembly the DETR cannot assume thatthey will permit the environmental impact ofextraction and traffic in Wales to provide fillmaterials for distant English construction sites,and the potential of this flakey material as aconcrete aggregate must be minimal.
Slate waste will have little impact on the18 million tonnes.
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2.6.3 China Clay WasteThere is around 500 million tonnes of
china clay wastes in Cornwall, and theyproduce a further 25 million tonnes a year. It isonly classified as a waste as there is insufficientdemand within its economic area ofdistribution to match its production. It is reallyan aggregate looking for a market.
Distribution networks and economics arethey key for growth in sales. Large trains are notan option due to weight restrictions on theTamar Bridge and the Devon Bank, so sea is theonly real option. This will require significantinvestment to provide the infrastructure to moveaggregates to the ports and for loading facilities.
Despite the scale of historic stocks and‘waste’ production, the increase in sales ofaggregates from this resource will be slow asthe infrastructure is provided and
competitiveness enables penetration of newmarkets. Imerys, the company controlling mostof this resource, consider that additional saleshave the potential to be 3 million tonnes a yearby 2005, but much of this will be to markets inmain land Europe. Even so there is a possible 2million tonnes towards the 18 million tonnesand concrete must be the end use of choice togive the highest value to the supplier to coverthe costs of distribution. How ‘sustainable’ thisaggregate will be in terms of environmentalimpact compared to locally produced materialis a matter of debate.
3.0. Market EconomicsThe increase in use of sustainable
aggregates depends on availability andeconomics. How does availability compare toDETR’s possible aspirations?
Material Year 2005 NotesMillion Tonnes
Core C&DW 2.0 C&DW Survey: Assuming 75% recovery of C&DWwaste landfilled at licensed sites in 1999 makingallowance for tax changes and contaminants.
Other C&DW 8.0 C&DW Survey: Assuming 75% recovery of C&DWwaste landfilled at exempt sites in 1999, plus 25%recovery of mixed C&DW/soil landfilled at licensedsites, all reductions for contaminants.
Highways Arisings Nil See 2.2 above.
Used Track Ballast Nil See 2.3 above.
Incinerator Bottom Ash 1.5 See 2.4 above.
Glass 0.7 See 2.5 above.
Slag (1.5) See 2.6.1 above.
Slate Waste Nil See 2.6.2 above.
China Clay Waste 2.0 See 2.6.3 above.
Total 12.7
25% target 18.0 See 1.0 above
Variance (5.3)
Table 2: Availability of additional recycled/secondary resources.
Table 2 shows that technically feasiblesustainable resources are, or may be, available,although not to the level some may project.
In the light of this what proportion ofthese additional resources are likely to becomeconcrete aggregates?
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This is not a significant swing in supplypatterns, and should be considered along sidethe possible changes in the existing market.
The present level of recycling ofconstruction and demolition wastes generatesaround 25 million tonnes per year ofaggregates(2). The forthcoming aggregates taxwill not result in these recycled aggregatesbeing marketed at a £1.60 discount to primaryaggregates. There are already more recyclersthan C&DW to meet demand and as aconsequence the value of these resources willrise, with this cost being recovered throughincreased selling prices. The aggregate tax willraise the market price of all aggregates and as aconsequence the increase in use of recycledaggregates in concrete is more likely to bedriven by environmental procurement policiesthan material cost reduction.
Looking again at the total primaryconstruction aggregate market(1), 37% goesinto concrete aggregates, 11% into asphalt,leaving 58% for other markets of which the vastmajority is fill and sub-base. If an objective ofsustainable development is to reduce mineralextraction the logical sector for substitution isthe sector with the highest demand and lowestrisk, i.e. fill and sub-base.
There will be an increase in the use ofprecast and ready mix process waste, with newplant designs incorporating reuse of waste as amatter of course. The utility market will requiremore robust reinstatement materials tominimise their remedial liabilities, generating a
larger market for foamed concrete that utiliseslow grade recycled aggregates generated fromtheir own arisings. In urban areas with highprimary aggregate prices the economics ofproducing a recycled 20-5mm concrete/brickaggregate will be viable but with QSRMCquality criteria this will only go into lowperformance concrete mixes.
Crushed clean concrete undoubtedlymakes a first rate concrete aggregate and onsite-specific demolition and reuse it is a sensibleand economic choice. In an urban recyclingplant the incoming flow of materials is variedand the availability of clean concrete isspasmodic. With limited space the economics ofrecycling require production of a consistentrange of products to provide a reliable service tocustomers and efficient use of space tomaximise throughput. As a consequenceconcrete will be blended with lowerperformance materials to enhance theirperformance and value, it will not go to makeconcrete aggregates.
How does all this impact on the futuresupply of concrete aggregates? If it wereassumed that 10% of recycled aggregatesbeing generated presently from C&DW wereprocessed as concrete aggregates they wouldcontribute 2.5 million tonnes per year. If full useof the growth in resources above were alsoassumed at 3.2 million tonnes by 2005 thenthere would be a total of 5.7 million tonnes ofrecycled/secondary concrete aggregates.
Material Year 2005 Potential AssumptionsMillion concrete Tonnes aggs.
Core C&DW 2.0 0.4 20% recovery of mixed concrete/brick 20-5mmaggregate for r.m.c.
Other C&DW 8.0 0.8 10% recovery of mixed concrete/brick 20-5mmaggregate for r.m.c.
Highways Arisings Nil
Used Track Ballast Nil
Incinerator Bottom Ash 1.5 0.5 33% used in precast concrete products
Glass 0.7 0.0 Too reactive
Slate Waste Nil
China Clay Waste 2.0 1.5 75% used as sand replacement in precast andr.m.c.
Total 14.2 3.2
Table 3: Potential Concrete Aggregates.
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CONCLUSIONAt the moment the demand for primary
concrete aggregates is around 82 milliontonnes per year(1), and despite the falling totaldemand for primary materials, this demand hasshown modest growth over the last few years.Therefore if it were assumed that there was acautious 1% annual growth in this sector ofaggregate demand then the 2005 demandwould be 86 million tonnes.
The above assumptions on recycled andsecondary concrete aggregate meet 5.7 milliontonnes of this 86 million tonnes, pushingprimary supply down to almost 80 milliontonnes, but showing only a proportionalchange in supply distribution to recycledaggregates of just under 7%, leaving over 93%of concrete aggregates being supplied fromprimary resources.
High quality concrete needs high qualityaggregates supplied from consistent sourcesthat are able to guarantee high volumes. Atleast 75% of all construction aggregate
demand will continue to be supplied fromprimary resources, as there are insufficientenvironmentally viable sustainable resources tomeet a larger proportion of the balance.Therefore despite the very worthy technicalresearch into recycled and secondary concreteaggregates the economic and logistical realityis that primary aggregates will continue todominate the concrete aggregate market, asthey should, because this use optimises thepotential of primary resources.
Recycled and secondary aggregates willcontinue to increase their market share in linewith their availability, predominantly replacinglower grade primary materials, but moreimportantly, meeting the changing demands ofcustomers in sustainable construction.
REFERENCES
1. NATIONAL STATISTICS. Business Monitor PA1007, Mineral Extraction in Great Britain 1999.
2. CONSTRUCTION AND DEMOLITION WASTESURVEY, EA Research Project no.P1.366
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Mr. M. PROBSTMartin Probst, Dipl. Engineer (FH), is
proprietor and general manager of ProbstHandling and Laying Systems GmbH insouthern Germany. The company , which wasfounded by his father some 40 years ago,develops, designs and distributes a range ofequipment for the construction industry.
ABSTRACTThe manufacture of quality precast
concrete products requires industrialengineering throughout the entire process,from handling and mixing the raw materialsuntil the finished elements are ready to leavethe factory.
The production process can be improvedby the use of modern, fully automatedequipment. Cost savings are possible by theincrease in efficiency of mechanical handlingequipment: consideration should also be givento health and safety aspects of machinery andlifting devices.
Due to the wide range of shapes andsizes of precast elements to be handled it isquite often difficult to select the most effectiveand efficient option from the range ofequipment available.
This paper, presented to the symposium,gives an illustration of some of the modernequipment that is available to the productionengineer. A selection of the devices is givenbelow.
EXAMPLES OF EFFICIENT MECHANICAL
HANDLING OF PRECAST MATERIALS
Mr. M. Probst Dipl. Engineer (FH)
Probst Handling & Laying Systems GmbH
Figure 1: Clamp for attachment to astandard fork lift truck, for the handlingof vertical steel-strapped cubed packs ofconcrete bricks, masonry blocks, concretepavers, etc. Devices such as this shouldbe fitted with automatic gripper release toensure one-man operation.
Figures 2 and 3: Hydraulic stack rotatingclamps can rotate a stack of products by180 degrees. Used typically for stackingand rotating masonry blocks dry-processed directly on the ground.
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Figures 4 and 5: Examples of mechanicaldevices, which can be fitted to all types oflifting equipment, for lifting and handlingmanhole rings and pipes of up to3,000mm diameter. Automatic releaseallows one-man operation; as no radialpressure is applied it is suitable for lifting‘green’ products, which are subject todamage.
Figure 8: Mechanical grabs which requireonly one operative can be used to lift andmove a wide range of pre-cast elements,such as this hollow-core slab.
Figures 6 and 7: Similar clamps can be used for symmetrical and asymmetrical cones.
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John Newman is Reader inConcrete Structures at theImperial College of Science,Technology and Medicine andhas been concerned for manyyears with various aspects of
research and development, including themanufacture of construction materials fromwastes and the investigation of new structuralconcrete systems. As a director of NustoneLtd, an environmental body providing industrialand environmental consultancy, he specialisesin the conversion of wastes into manufacturedaggregates and other products primarily for theconstruction industry. He also organises theACT course held at Nottingham University.
Philip Owens is Principal ofindustrial and environmentalconsultants Philip L Owens &Partners Ltd., as well asDirector of Nustone Ltd. Heis a Fellow of ICT, a corporate
member of the Institute of WastesManagement and a member of the ConcreteSociety's Materials Group. His BSI committeememberships include aggregates, concrete,highways and characterisation of waste and heis a member of ASTM committees for cementand concrete. His interests include cement,pozzolanas, lightweight aggregates and theutilization of wastes as resources for productsfor use in concrete.
1. INTRODUCTIONThe majority of the 14.5 million
tonnes/annum of waste currently abandonedin London by about 7.25 million people andindustry goes to landfill. However, availableand convenient landfill sites are diminishing ata rate which, it is considered, makes disposalby such means unsustainable. In addition,landfill must be reduced since:
• there is always a risk of polluting theground and groundwater
• it contaminates land and makes itunsuitable for many uses
• landfill gas is dangerous and themethane produced is a greenhousegas
• sites must be engineered forpermanent containment andmaintained accordingly
• there are other significant adverseenvironmental impacts associated withlandfill such as the need to transportlarge volumes of wastes.
Waste should be managed in such a waythat the inherent properties of the materialsforming the wastes are exploited using lowcost options that result in benefits for society.For example, significant opportunities exist toexploit wastes and use them as valuableresources and raw materials in industry. Inparticular, construction needs materials tosatisfy London’s endless demand fordevelopment and expansion. A key objectiveof the scheme presented here is that it useswastes to produce new building materials.These are materials that would otherwise needto be extracted from the environment, at greatcost and potential for environmental damage.The economics of waste disposal andaggregate extraction are changing in ways thatwill allow this to become a reality.
This proposed recycling solution is safeand should be entirely acceptable, as Londonneeds to dispose of wastes, be more self-sufficient in energy and construction productsand reduce the tax burden.
2. BACKGROUND
2.1 Combustible wastesThe London Waste Action Annual Report(1)
made two fundamental points. Firstly, morethan 90% of London’s waste goes to landfillwhich it accepts will continue to play the mainrole in London’s waste management.
RECYCLING LONDON’S WASTE - A BLUEPRINT FOR MANUFACTURING
CONSTRUCTION PRODUCTS
Dr. J.B. Newman, BSc(Eng), ACGI, DIC, PhD, CEng, MIStructE, FICE, MICT
Imperial College
and Mr. P. L. Owens, HNC, MPhil, FICT, MInstWM
Philip L Owens & Partners Ltd
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Secondly, the impact of world economic trendshas caused the prices of collected/reclaimedmaterials to tumble with little likelihood of anincrease in the foreseeable future. The reportrecommends that a breakthrough in increasingthe value of recyclable material is needed inorder to encourage the London Boroughs torecycle. They consider this to be a priority forgovernment policy intervention but it isconsidered that this is best left to London’sgovernment. This proposal develops anintegrated industrial and economic solution tothe waste disposal problem by developing newapplications for waste.
The strategy highlighted in the MELReport ‘Towards a Waste Reduction Plan forLondon(2) is based on an existing sub-division ofthe 33 London Boroughs into 6 geographicalwaste planning areas and 16 ‘waste producingsectors’. Of the 16 waste streams identified byMEL the following waste producing sectorshave been selected as prime candidates forincineration. Fly-tipping would have beenincluded if the relevant data were available. Itis also expected that the amount ofcombustibles will exceed, say, 80% by masswhere front-end sorting is practised.
Hospital wastes have not been included
in the above since it is anticipated that theywould be treated at dedicated facilities.However, if incinerated, the ash produced fromsuch treatment could be used as a resourcematerial for aggregate manufacture.
Table 1 also shows the significance of thevarious waste producing sectors and alsoillustrates the distortion created by focusingmainly on household waste which is onlyapproximately a third of that which can beconsidered suitable for energy reclamation.However, it may be advantageous to organise
aggressive campaigns to reduce householdwaste to draw attention to the wider issuesconcerning other wastes. For example, theLondon Waste Action Annual Report for June1997 to December 1998(1) concentrates onhousehold waste produced by each of 29boroughs. For 1997/98 a mean of 899.3kg (0.9tonnes) of waste was discarded per household.Tower Hamlets produced the lowest amount(0.544 tonnes) with Kensington and Chelsea,Westminster and Lambeth producing slightlymore (about 0.60 tonnes) per household. Atthe other extreme, Hillingdon, Hounslow,Havering and Merton produced more than1.13 tonnes per household.
It is suspected that the more progressiveboroughs have concentrated their efforts onwaste collection methods that encouragesorting and re-cycling such as dual collectionvehicles and ‘bin bags’. Those at the other endof the scale probably make extensive use of‘wheely bins’ which attracts moreincombustible waste since little primary sortingis encouraged. It is thus concluded thatwithdrawal of the ‘wheely bin’ in suchboroughs would assist in the sorting of wastebetween combustible and incombustiblecomponents.
The disposal of old tyres from privatesources, although not included in Table 1, andpublic transport is difficult since they areextremely robust to degradation. It is possibleto reduce old tyres to 50mm chips at the rateof 4 tonnes per hour. No information has beenfound regarding the quantity of old tyres to bedisposed of in London but the rubber particlesform a useful source of energy and could beutilised at one incinerator per planning area.
The other significant point emerging fromthe London Waste Action Report is thatbetween 1996/97 and 1997/98 the increase inhousehold wastes produced was 83,575tonnes while the amount reclaimed was acreditable 43,881 tonnes. It is not clearwhether this latter increase was combustiblewaste.
2.2 Incombustible wastesThere are waste producing sectors that
are not considered suitable for generalincineration due to their special needs (e.g.hospitals as in 2.1) or where their combustiblecontent is less than, say, 20% by mass.
Waste producing sector Tonnes per annumHouseholds 3,300,000Commercial 2,444,600General 1,490,400Banking 873,600Public administration 684,600Hotels 654,800Public transport 418,600Entertainment 202,700TOTAL = 10,069,300
Table 1: Producing sectors for combustiblewastes.
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2.3 Air pollution control (APC)residues
The gaseous emissions from incineratorsand other processes involving combustion arenow governed by regulations such as those inthe Incinerator Directive(3). Although APCresidues have not been included in Table 2 theproposal includes the processing of thosearising from CPH units.
3. THE OPPORTUNITYAbout 7.25 million people are
accommodated within the London Boroughswith an infrastructure supported by extractiveindustries, sited mostly outside the area, for avariety of materials including:
• clay for bricks
• gravels for roads, mortars and concrete
• limestone, chalk and clays for cement
• haematite and limestone for steel andslag
• rocks for traditional masonry
• coal, oil and gas for energy
• limestone for gaseous emissioncontrol.
These have helped make London one ofthe most vibrant capitals of the World and haveprovided the necessary “creation of wealth”which form such an essential part of its ethos.They will remain essential in the developmentprocess which includes renewal andmaintenance of buildings and infrastructure.An example is the redevelopment of theDocklands. However, like many other greatcities/conurbations it could fall victim to its ownsuccess when the wastes that it produces
cannot be accommodated safely andacceptably.
Up to now, most of the sites local toLondon that have been exploited for mineralsby the various extractive industries, especiallyfor use in concrete, have provided cheap landfillsites for wastes. Unfortunately most of thesesites are now full and more remote locationswill have to be found and engineered to makethem suitable as permanent wasterepositories. This will cause a major increase inthe environmental and financial costs of wastedisposal for London.
The continued sustainability of London’sconstruction industry can only be achieved bythe provision of bulk materials, such asaggregates, for use in a whole range ofconstruction products that are now beingimported(4) over distances that were noteconomical 40 years ago by:
• dredged gravels from deposits in theNorth Sea
• crushed limestone brought in by trainfrom the Mendips
• crushed granite brought in by shipfrom the Scottish Isles.
The cost of transportation anddistribution of these imported materials hasnow risen to more that an estimated 80% ofthe cost of extraction and processing, added towhich voids are not being created for animmediate solution to London’s landfillproblem. This highlights the dilemma faced byLondon’s government since, without easyaccess to these excavated sites, there isnowhere to dispose of the wastes produced.
Most Londoners, like the rest of us, havelittle concern about the provision of energy andmaterials or where they come from as long asthey are available. Likewise, they are notconcerned about the disposal of their wastesas long as they are removed from their site andsight. However, London’s Government mustmeet its obligations with regard to theIntegrated Pollution Prevention and Control(IPPC) legislation(5) which is aimed at protectingthe environment by defining how it interfaceswith industry including wastes management.The Landfill Directive(6) and the IncineratorDirective(3) combine to encourage cost-effectivealternatives to monolithic landfilling to preventleachates and toxic gases from degradablematerials entering the ecosystem.
Table 2: Producing sectors forincombustible wastes.
Waste producing sector Tonnes per annum
Component manufacture 1,379,800Construction 1,078,000Assembly and production 625,600of finished goodsHospitals 452,200Municipal non-commercial 350,000Communications 215,600Public utilities 102,800Raw materials extraction 6,400and processingTOTAL = 4,210,400
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In 1996/97 about 14.3 million tonnes perannum of waste were reported as beingavailable for landfill(2). It is considered nighimpossible to dispose of this quantity bysorting and recycling. However, it is worthy tosupport the following objectives, as proposedby Friends of the Earth(7), as a means ofreducing the quantity of wastes deposited inlandfill:
• the expansion of recycling facilitiespreferably by means of comprehensivekerbside collections
• anaerobic digestion and aerobiccomposting
• the provision of public education onminimising waste and re-cycling more
• the minimisation of internal wastesfrom local authorities and specifyingthat materials purchased by theseauthorities should be recycled
• the support of waste exchanges.
Apart from the production of compoststhese proposals are ephemeral in that theyreduce the amount of waste to be disposed ofinto landfill by a delaying process. Althoughthey are vital elements in the wastemanagement process they fail to:
• address the legislation andenvironmental problems associatedwith landfill
• acknowledge that all recycled materialswill eventually re-enter the wastestream
• acknowledge that the use of recycledmaterial is only possible with theincorporation of energy and/or virginmaterial to ensure the requiredperformance
• recognise that other aspects ofrecycling, such as obtaining energyfrom waste, can provide additionalbasic requirements necessary tosustain this proposal such as power,electricity and ash.
There is thus a need for industry to re-usewaste in order to:
• save on the environmental andeconomic costs of raw materials
• educe the amount of waste to landfilland save on the associatedenvironmental and economic costs
• exploit the market opportunities for re-formed products(8).
Recovery of energy from waste shouldnot be considered as a destructive process.Matter cannot be created nor destroyed andthe incineration process converts one form ofmatter (waste) which is inherently a liability intoanother forms of matter (ash and gases) whileextracting useful energy. Thus the followingadditions to the above objectives are proposed:
• the provision of public education onthe benefits of producing energy andproducts from waste
• the acceptance of the expanded roleof incinerators as generators in aforward-looking recycling solution toprovide Londoners with energy andsustainable construction products.
A key advantage of this approach is thatraw materials and products are produced near-market thereby increasing their viability andenvironmental acceptability as:
• energy recovery reduces the volume ofsolid matter to about 90%
• it is a renewable source of energy
• combined heat and power increasesenergy efficiency by about 30%
• it is combined with recovery ofmaterials for recycling and themanufactured products are both cost-effective and desirable.
Furthermore, the aggregates andlightweight masonry produced will be moreefficient in terms of thermal and physicalproperties in that encapsulating air willconserve resources by:
• reducing aggregate density by about50%
• reducing the density of masonry byabout 67%.
Since Roman times, volcanic aggregatessuch as pumice and scoria when used inconstruction have performed the samefunction as dense natural materials and haveprovided durability and greater thermalinsulation(9). Thus lightweight aggregates andmasonry will enhance the EssentialRequirements of the Construction ProductsDirective(10) with the finished product costing nomore than with natural materials, in fact thereare significant savings in construction andheating costs, as hidden but major benefits tothis proposal.
Ten million tonnes of London’s waste isestimated to be combustible and can be used
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for the generation of heat and power. The ashshould be seen not as a waste but as avaluable resource that can be used tomanufacture high quality aggregates for use inconstruction. The manufactured aggregatewould reduce the need to import up to 7million tonnes of natural aggregates fromremote locations and will also help conservelocal mineral resources. To fully exploit theopportunities currently available in London’swaste, the construction of 20 ‘new breed’incinerators are proposed together withintegrated waste processing facilities or‘product generators from waste’ (PGWs). EachPGW would incorporate:
• materials recovery facilities
• heat and power generating plant
• ash-processing facilities to producequality aggregate.
Some PGWs would contain additionalfacilities for:
• recycled aggregates
• masonry production
• aerobic composting.
This proposal capitalises on the energyand metal-free ash derived from wastecombustion so that, apart for the combustiongases, the inorganic non-metallic residues areincorporated efficiently and permanently intohighly desirable engineered constructionproducts.
4. THE NEED TO REORGANISE LONDON’S PLANNING AREAS
In order to reduce some of the disparitiesbetween population and wastes the LondonBoroughs have been re-grouped(including those ‘ungrouped’ in theReport) in an attempt to achieve thefollowing:
• a more even distribution ofboth population and wastes
• the elimination of‘landlocked’ areas
• the provision of optimumaccess to the River Thamesand an ‘external’ boundary
• the encouragement of co-ordination and co-operationbetween boroughs.
These are shown in Figure 1.
5. PRODUCT GENERATORS FROMWASTE (PGWs)
Standardisation of the incinerator,forming part of the PGW, with regard to typeand size is important for optimising theeconomics. A number of factors need to beconsidered when selecting an appropriatecapacity for the PGW.
• Size This must be acceptable to the localcommunity and of such a size toeliminate the need for solid wastetransfer stations.
• AestheticsEach generator would be considerablysmaller than either of the now defunctBattersea or Bankside power stationswith their colossal chimneys. A facilityof the size of SELCHP at Lewisham isappropriate, as it is both effective andrelatively unobtrusive. In addition,much of the hostility to suchstructures can be removed byeliminating the need for unsightly fluestacks. An example of such asignificant advance can be found inMonte Carlo.
• CapacityThe operator needs to processsufficient waste for a commerciallyviable operation. It is expected thatsuch an operation would involve amaterial recycling facility (MRF) in orderto restrict the amount ofincombustible solids entering thegenerator. Experience with theoperation of ready mixed concrete
Figure: 1
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plants shows that carefulconsideration needs to be given to thesiting of the facility relative to thecatchment area to ensure short transittimes for the collection vehicles.Analysis shows that just over 10million tonnes of waste is potentiallyuseable in the whole of London. Eachreorganised planning area will produceabout 1.5 million tonnes of wastewhich is excessive for a single PGW interms of transportation of inputs andoutputs.
In order to solve the problem a ‘standard’CHP unit of about 72 MW absorbing 500,000tonnes per annum of combustible waste isrequired, with each of five planning areashaving three units and Planning Area Easthaving 5 units. To avoid each planning areabearing costly design and build schemes foreach unit, a central Planning and DesignOrganisation (PDO) should be established byLondon’s government. This organisationwould oversee the development andimplementation of the standard unit whichwould incorporate three essential elements:
• an incinerator with MRF at the frontand rear ends, primarily to removemetals and dense non-combustiblemedia
• an integrated lightweight aggregate(LWA) processing plant includingfacilities to grind metal-free IBA and toreceive, dry and process clay
• a single air pollution control (APC) unit forboth incinerator and LWA manufacture.
To put this proposal in perspective, thesize of each of the 20 standard generatingunits distributed across London to process atotal of 10 million tonnes of waste as fuel isinsignificant compared with the enormity oftwo 2000MW coal-fired power stations (e.g.Didcot ‘A’ in Oxfordshire and Kingsnorth inKent) which utilise the same quantity of fuel.Indeed, the compactness and efficiency of astandard generating unit is demonstratedwhen considering the giant cooling systemswhich waste to the environment almost 50%of the energy available from coal. Such coal-fired power stations were designed to operateat 1400˚C for 50% of the time but to burn26,500 tonnes of bituminous or hard coal perday at about 35% efficiency at maximum loadduring the winter. On average, this consumespulverised coal at a rate of about 1,100tonnes per hour to produce 225 tonnes of ashas 45 tonnes of furnace bottom ash (FBA) and180 tonnes of variable quality ‘fly ash’ (PFA).Provision was made for the majority of PFA tobe abandoned in landfill since industries in thepast were not able to absorb such largequantities of variable quality material. It mustbe noted that neither of these power stationshave been retrofitted with flue gasdesulphurisation (FGD) which would haveneeded 700,000 tonnes of limestone toproduce about 1.2 million tonnes per annumof industrial gypsum for which the market haslimited application.
Figure 2: Shows a typical PGW plant for the manufacture of LWA, AAC and compost(peat substitute).
101
Therefore, 20 plants strategically placedaround London to use 10 million tonnes ofcombustible wastes, will reduce the impact ofwaste on each locality and limit transportationdistances both for inputs and outputs of solidsand the distribution of electricity and heatingschemes. This will increase the powergenerating efficiency to more than about 50%.Such units must be designed and operated tocomply fully with the EU Incinerator Directive(3)
for emissions which controls such toxicmaterials as dioxins, furans and heavy metalsexcluding the need to conform to the limits fortotal organic carbon (TOC) remaining in the IBAas any remaining TOC is handled by the LWAproduction.
The following is assumed for each CPHwithin the PGW when operating for 300working days per annum.
The data in Table 2 shows thatconsiderably more incombustible wastes areproduced than those arising from incineratedmaterial. It is estimated that about 2.4 milliontonnes of incinerator bottom ash (IBA) perannum is produced compared with ananticipated 4 million tonnes of incombustiblewastes from other sources. Furthermore,much additional waste arises from primaryconstruction and other activities such as:
• excavation of clay for foundations,basements and tunnels
• road and transport construction
• demolition wastes
• river dredging
• contaminated ground
• wastewater treatment sludge.
There is an urgent need to evaluate thesequantities since they can be used as feedstocks in aggregate manufacture. Forinstance, to absorb 2.4 million tonnes of IBArequires about 1.5 million tonnes of as-dug de-stoned clay as the essential binder and/orexpanding medium in order to produce 3.5million tonnes of manufactured aggregate with
an aggregate particle density of 1300 kg/m3.This is equivalent to 7.0 million tonnes ofnatural aggregate. It is considered that thequantity of clay required would be availablewithin the London area making importationunnecessary but the variability of availablematerial would require commitment toselection and homogenisation.
Other significant resources can bereclaimed from the demolition of redundantbuildings and structures. Bricks with limemortars are mostly reclaimable. However, thetrend since the late 1940s has been to usePortland cement mortars which are strong anddifficult to remove thus increasing the amountof brick rubble. To reclaim more bricks in thefuture it is essential that the London BuildingRegulations be revised to require the use oflime mortar only.
Hardened concrete arising fromdemolition is being partially reclaimed bycrushing and grading for use as aggregateprovided the deleterious materials (particularlythe sulfates) are reduced to specified limits.The amount of fines produced by crushing isabout 50% of the input and these usuallycontain significant but varying amounts ofgypsum (calcium sulfate) from plasters, limefrom mortars and concrete containing silicasands.
The arisings from mortars and concretecan be utilised as resource materials for AAConce they have been ground andhomogenised.
It is concluded from an extensive reviewand examination of lightweight aggregatemanufacture worldwide that the mostessential element for successful aggregateproduction is homogenised feed stock. Waste,by its very nature, is highly heterogeneouswhich presents aggregate manufacturers witha major variability problem. Unlesshomogenous resource materials are used inthe manufacture of lightweight aggregate thevariations in composition will lead to excessive
Item Quantity per hour
Inputs Waste 70 tonnesLime for gas cleaning 0.67 tonnesElectricity generated 36MWSteam generated 36MW equiv.
Outputs IBA 16.6 tonnesRecovered metals 0.8 tonnesAPC residues 2 tonnes
Table 3: Inputs and outputs for a 72MW CHP.
102
variability of the product. Part of the solution isto keep the size of generator withinmanageable proportions and limits as it isestimated that no more than 20 tonnes perhour of ground IBA should be homogenisedthrough a standardised ‘buffer stock silohomogeniser’ of 800 tonne capacity. This isnot a conventional silo, but one which iscontinuously bottom-loaded(11), via densephase conveyors, with the homogenisedproduct being automatically removed from thetop. Similarly, the dried and pulverised claysrequire homogenisation but the requirement isfor not more than 10 tonnes per hour. Thesame size homogeniser can be used to ensurethat both resources are statisticallyhomogenised.
6. MANUFACTURED PRODUCTS FROM THE PGWs AND NON-COMBUSTIBLE WASTES
6.1 GeneralIt is essential for waste recycling that each
PGW be fitted as standard with a LWAmanufacturing plant. It must be accepted thatresources of IBA and available clay at each PGWare unique and vary with time. Suchcharacteristics can be accommodated by theLWA manufacturing process as required by theEU Construction Products Directive(10).Properties of LWA will be specified by theharmonised BS EN 13055-1(12) which allows forthe production of aggregates with particledensities less than 2000kg/m3. Toaccommodate the preferences of users it ispossible to manufacture LWAs of nominalparticle densities 1600, 1300 and 1000 kg/m3
so that their application to concrete is as wideas possible. In order to remove anyunacceptable variations in LWA manufacture apermanent Department within the centralPDO should be established for the overall co-ordination of management decisions relatingto the technical control and policies for all LWAproduced and distributed by PGWs in London.
6.2.1 AggregatesGenerally, the technique used for the
manufacture of a particular lightweightaggregate (LWA) depends on the type ofresource and the physical properties requiredfor appropriate application of the finishedproduct. For IBA, taking due regard toenvironmental protection, it is recommended
that the finished LWA should be used in plainand reinforced concrete as a substitute fornatural coarse aggregate. This concrete can beused in most situations and although it is lessdense (lighter) than conventional concrete itcan be designed to be just as strong anddurable. It has the advantage of being moreductile, fire and frost resistant as well asproviding better thermal insulation. To give theresultant concrete the most advantageousbalance of properties the most appropriateaggregate particle is near-spherical, 16mm indiameter with a rough surface, with a densityof about 1300 kg/m3 and a water absorptionno greater than 5% by mass.
In order to control the size, density andabsorption of the finished LWA particles it isessential that de-stoned clay is a raw materialin the process. When clays become pyroplastic,at about 1150ºC, some are, and others can beinduced to become, ‘bloatable’. In such casesthe ‘bloatability’ of most clays can becontrolled by the inclusion of a compatiblediluent such as ground IBA(13). Bloatingincreases the size of the LWA particles, therebyreducing their density, and provides via aplasma a relatively impermeable vitreouscoating not only to the particles themselvesbut also to the ground IBA. On their own,such source clays when heated to a bloatabletemperature exhibit unstable behaviour similarto “pop corn”. However, with the inclusion ofground IBA the particle density andconfiguration is easier to control(13).
It is proposed to grind the fresh dry IBA toa fine powder as it leaves the incinerator andafter removing any remaining metals. Thefineness of grinding will be dependent on thecomposition of the IBA but, typically, it wouldbe less than 250μm with probably not morethan 10% retained at 150μm. The advantageof this approach is that solids such as glass andceramics will be sufficiently reduced in size tomake homogenisation comparatively easysince grinding will have made the dry/hot IBApowder easier to handle. In addition, anyremaining combustible material in the IBA willbe fine enough to be easily dispersed in thehomogenising process. The ball mill used togrind the IBA should have a rated capacity atleast 20% greater than the average feed rate(about 16 tonnes per hour) of the IBA.
For the bloating process, the amount ofclay required to manufacture the LWA can bebetween 50 and 25% of the total raw feed
103
depending on the bloatability of the clay. Inorder to control bloatability it is recommendedthat, prior to homogenisation, the as-dug claybe de-stoned, dried and pulverised in a ball millto a similar fineness as the IBA. Should the clayresource require encouragement to bloat, smallquantities of organic additions (1 or 2% bymass of clay) can be incorporated. Forexample, finely divided and dried sewagesludge could be included with the ground IBAand dried clay at the mixing stage, togetherwith a small amount of water. For example,this will aid the formation of ‘green’ pellets ofabout 12.75mm diameter capable ofexpansion to about 16mm.
The pellets of the required size and shapeare coated with powdered limestone toimprove the surface zone of the finishedparticles and to ensure separation of theparticles during processing. They are then fedto a 3-stage rotary kiln (pre-heater, kiln andcooler) or similar where they fired attemperatures up to approximately 1200ºC.The density of the pellets is controlled not onlyby the pelletisation process but also by thefiring temperature and rate of throughput.
Where clay bloatability is insufficient, evenwith inducement, another process is availablewhereby the density of the LWA can be pre-determined. This is based on burning out acombustible component at about 600-800∫ Cto leave a voided structure of the required size(e.g. 16mm) before feeding into the kiln. Theprocess generally uses a smaller proportion ofclay (10-25% by mass) and materials with shortfibres capable of being burnt out, obtainedfrom digestion of wastes and dense organicmaterials.
To produce fibrous materials, domesticrefuse can be treated by an autoclaving systemwhich condenses the material to allow moreeffective separation of components. Suchsystems rely on steam for their operation andare claimed to handle up to 100 tonnes ofsuitable waste per 8-hour shift or 300 tonnesper day.
CPH units possess the following principalcomponents of use for aggregatemanufacture:
• dry IBA
• power and heat for drying the clay,grinding both IBA and clay,homogenisation and, where necessary,processing wastes to produce fibrous
materials
• an existing APC system available foruse with the aggregate productionprocess.
6.2.2 MasonryAutoclaved aerated concrete (AAC)
conforming to BS 6037(14) is used for buildingblocks and other units. It is draught-proof,load-bearing and, being low in density,thermally insulating, and yet strong, durableand non-combustible. The method ofmanufacture is to create, by the formation ofgas within the concrete, a micro-cellularstructure. To stabilise the resulting concrete itis autoclaved by steam curing at hightemperature and pressure, so that the finishedAAC can consist of up to 80% voids and 20%mineral matrix.
A prime advantage of AAC is that largerthan normal blocks can be designed to belifted in one hand. Such blocks are easily cut,sawn, chased or worked with ordinary handtools. Accurate cuts ensure less wastage andmaking good. Nevertheless, AAC tends to bemore expensive than masonry made withfurnace bottom ash from coal-fired powerstations and/or lightweight or naturalaggregates. It has thus been less populardespite AAC requiring a significantly lowerlabour content for construction, faster buildingrates and better properties such as thermalinsulation and fire resistance.
The greater price of AAC results mainlyfrom the cost of resources, materialpreparation and the provision of steam forautoclaving. Factories for the manufacture ofAAC are, in fact, similar to bakeries, althoughon a much larger scale. The materials formanufacture usually include Portland cement,anhydrous gypsum, quicklime and a smallamount of aluminium powder as one part bymass and three parts by mass of finely dividedmineral in the form of either silica sand or PFA.These ingredients are mixed with hot waterand the mixture is poured into large moulds of6-8m3 capacity. It is left to rise and stiffen forabout 1.5 hours to reach a “green” strengthsufficient for the concrete to be cut, as a softcake, into required products. These productsattain their final hardness and dimensionalstability through a steam curing process lasting8 to 10 hours in large autoclaves operated atabout 10 atmospheres (1.0 to 1.25MPa) orabove and about 180ºC. Normally, a basic
104
factory unit has five autoclaves, which are largecylindrical tubes that can take up to 90m3 ofAAC which, at completion, is ready for use.However, although AAC does not deterioratewith age, it is usual to supply to site from stockwhich is shrink-wrapped in polythene to keep itdry.
The actual quantities and types ofmaterials used for the manufacture of AACdepend on the density required. This can varyfrom 450 to 850kg/m3 and represents athroughput of materials of about 550 tonnesper day (excluding 35 tonnes per day ofcombined water).
Manufacturers of AAC tend to use 650kg/m3 as a base density resulting in therequirement for the following quantities ofmaterial per annum:
The above quantities can be variedaccording to the required density and othersuitable materials can be used instead of silicasand or PFA. These include ground finesrecovered from reclaimed hardened concrete ormasonry, processed APC residues from whichthe chloride has been removed or ground IBA.
After being partially reclaimed by crushingand grading for use as aggregate, the resultingfines from hardened concrete and bricks arisingfrom demolition form suitable raw materials forAAC. The amount of fines produced bycrushing is about 50% of the input materialand these usually contain significant butvarying amounts of Portland cement, gypsum(calcium sulfate) from plasters, lime frommortars and concrete containing silica sands.
APC residues collected at each PGWamount to about 15,000 tonnes per annum ofwhich approximately 15% is chloride. This APCresidue can be collected on a regular basis fromeach PGW and treated in bulk at two PGWunits to remove the soluble chlorides byevaporation and condensation using available
heat. This will provide about 225,000 tonnes ofmaterial for the manufacture of AAC. Therelatively small amount of chlorides removedwould be processed to produce salt andgypsum.
The availability of power, heat and steamfrom CHP generators, together with theutilisation of some of the solid outputs willmake a significant contribution to theoperating cost of the AAC plant.
6.4 Composting and othermaterials
Large quantities of organic matter areavailable in London and in the past most hasbeen disposed of in landfill. With industrialisedcomposting techniques there is a opportunityto produce high quality peat substitutes.However, it is disappointing that no British orEuropean Standards are available, or inpreparation, for composts which makesproduct definition, control and processingdifficult.
Steam from the CHP unit is a majorsource of energy for industrial application notonly for AAC but to aid composting andthermal separation of fibrous organic material.
Such volumes are best treated by largeaerobic composters which can produce acontrolled peat substitute relatively quickly (in8-14 days) for storage in bales until required.Although only relatively small amounts ofsteam are required to start the compostingprocess at 70-80ºC, installations such as a 20-compartment silo cage continuous flowcomposting system can produce compost fromsludges and organic wastes in about 12 days.Such installations can produce about 12,500tonnes of compost per annum which isequivalent to 25,000m3 at a density of500kg/m3.
7. OVERALL ORGANISATIONAt the planning stage it is envisaged that
London’s government would establish a centralPlanning and Design Organisation (PDO) totake overall control of the scheme. This bodywould co-ordinate the separate elements ofthe wastes and including:
• wastes categorisation andarrangements for collection and/ordelivery from the various wasteproducing sectors to either a specialistMRF or a PGW with its own MRF
Constituent Quantity(tonnes)
Portland cement 27,000
Anhydrous gypsum 1,800
Quicklime 12,000
TOTAL = 40,800
Aluminium Powder 132
Silica sand or PFA 125,000
Table 4: Constituent materials for AAC.
105
• operation of specialist MRFs such asfor the processing of concrete andbricks for aggregate including AAC andcomposting
• operation of the PGWs including MRF,CHP and LWA
• distribution of products to retail outletseither from MRFs (e.g. metals, paper,recycled concrete and brick aggregatesand composts) or heat, power andLWA from PGWs.
8. SEASONAL INFLUENCESThere will be seasonal changes in the
input of wastes and the resulting outputs andthese can be accommodated by buffer stocksof wastes and stockpiling of products. Withthe flexibility to change the density of LWA andAAC there is, in practice, a method foraccommodating some of the variations indemand.
9. EMPLOYMENTEmployment forecasts for the whole
scheme do not extend to the 15,000 jobsanticipated by FoE to be created for a 50%increase in recycling(7). On the basis of normalindustrial practice, it is estimated that thepersonnel required to staff 20 PGWs, 6 AACfactories, specialist MRFs (including recycledaggregates from concrete and bricks) and 2plants for APC residue treatment would be nomore than about 5,000 in total, i.e. 850 perplanning area. Many of the jobs would comefrom those already employed in the wasteindustry.
London taxpayers could, therefore,expect a reduction of taxes due to increasedefficiencies that are obvious or hidden (e.g.lower heating costs and no requirement to payfor the management of future landfill sites asrequired by IPPC and the Landfill Directivewhich becomes enforceable on 16 July 2001).
10. SUMMARY1. There should be a central Planning and
Design Organisation (PDO) for co-ordinating waste management.
2. The PDO should take responsibility forthe design of standard PGW unitsincorporating CHP plant, LWA and AACmanufacture from 500,000 tonnes ofwaste.
3. The PDO should co-ordinate thecategorisation of wastes and theirroute for processing.
4. The PDO should be responsible for theoverall co-ordination of managementdecisions relating to the technicalcontrol and policies for allmanufactured products.
5. London’s government should re-organise the existing 6 planning areason a more equitable basis ofpopulation and waste to retain theintegrity and cohesion of theBoroughs.
6. Siting of generators must be based onthe shortest routes for input wastesand output products.
7. Some PGWs would contain an AACfactory complemented by a recycledaggregate facility for concrete andbricks.
8. Consideration should be given to thewithdrawal of ‘wheely bins’ to providebetter initial sorting of domestic waste.
9. Composting is obviously beneficial andthe establishment of appropriate BritishStandards would increase confidencein the quality of composts.
10. As a device to simplify the recycling ofbricks from construction the LondonBuilding Regulations should requiremortars to be lime-based.
11. Fitting a LWA plant to a CHP plantobviates against TOC in IBA incompliance with the EU IncineratorDirective.
12. The production of LWA conservesnon-renewable mineral resources andreduces environmental impacts.
13. The products manufactured willsatisfy existing demand and maintainprice stability.
14. The amount of clay excavated forfoundation basements and tunnels isunknown. There is an urgent need toevaluate these quantities.
15. London taxpayers will benefit from,and have more control over, themanagement of their waste andrelated expenditure.
106
REFERENCES
1. London Waste Action, Annual Report, June1997-December 1998
2. MEL Research Ltd., Towards a waste reductionplan for London, Report prepared for LondonWaste Action, July 1999
3. European Commission, Proposal for a CouncilDirective on the incineration of waste,Brussels, 7 October 1998 COM (1998) 558
4. Mineral Planning Guidance No. 6, HMSO,London
5. Council Directive 96/61/EC of 24 September1996 covering integrated pollution preventionand control, Official Journal of the EuropeanCommunities L257, Vol. 39, 10 October 1996,pp 26-44 (to become operative 31 October1999)
6. European Commission 1.3.130 Councildirective on the landfill of waste, Commissionproposal OJ. C156 24.5 1997, COM(97), 105;Bull. 3-97 point 1.3.123 (adopted on 26 April1999)
7. Friends of the Earth, Up in Smoke - whyFriends of the Earth opposes incineration, 7December 1999, see Website www.foe.co.uk
8. A way with waste - a draft waste strategy forEngland and Wales, Part 2, Department of theEnvironment, Transport and the Regions, June1999.
9. Owens, PL and Newman, JB, Increasing theenvironmental acceptability of new energyfrom waste plants by integration with costeffective concrete aggregate manufacture,IWM Scientific and Technical review, Nov 1999,pp 21-26.
10. European Commission, Council Directive89/106/EC of 21 December 1988 relating toconstruction products, Official Journal of theEuropean Communities No. L40, Vol. 32, 11February 1989, pp 12-26
11. British Patent Specification No. 22220926,Homogenisation of materials stored in silos,Granted 29 January 1992
12. European Standard BS EN 13055-1:Lightweight aggregates : Part 1:Lightweightaggregates for concrete, mortar and grout
13. British Patent Specification No. 2218412,Lightweight aggregates, Granted 22 April1992
14 BS 6073 -1, Precast concrete masonry units
MAGNETITE CONCRETE
Magnetite is a natural iron oxide, mined in Sweden and having a highnatural density in the range of 4.8 - 5.1 tonnes per m3. When used as a concrete aggregate, densities of up to 4.0 t/m3 can be achieved,some 60% more than traditional concrete.
Traditional concrete has a density of 2.4 t/m3 - a high density concretegives full protection in less space.
With the high cost of floor space this saving becomes very important.
HIGH DENSITY = SAVED SPACE = COST SAVING
Magnetite has a long history of use as a construction material, apartfrom its weight, it has similar characteristics to traditional concrete andcan be placed by skip or pump.
Although the delivered cost of high density concrete is more expensivethan traditional concrete, total construction costs are reduced throughsavings in preparation time, less reinforcing steel, placing costs, planthire and an increase in useable floor space.
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Concrete.Info is a new subscription service fromthe British Cement Association that links youdirectly to its specialist database – one of theworld’s premier sources of information oncement and concrete. All aspects of cement and concrete are coveredincluding raw materials and cementmanufacture, mix design and concreteproduction, architecture and structural design,reinforcement and construction, maintenanceand repair.
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Telford Avenue, CrowthorneBerkshire RG45 6YS, UKIllustrations reproduced by kind permission of Elsevier Science (www.elsevier.com), American
Concrete Institute (www.aci-int.net) and The Bahrain Society of Engineers (www.mohandis.org).
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ADVANCED CONCRETE TECHNOLOGY
DIPLOMA COURSESThe ACT Diploma is the principal entry qualification
for Membership of the Institute.
THE INSTITUTE OF CONCRETE TECHNOLOGY
THE UNITED KINGDOM(Nottingham University)
Organised by COMPACT(A consortium of Imperial College,
London and the Universities ofNottingham and Leeds).
Contact: Dr J Newman, ConcreteStructures Section, Dept of
Civil Engineering, Imperial College,London SE7 2BU
Tel: +44 (0)20 7594 6035E-mail: [email protected]
IRELAND(Dublin)
Organised by the Irish ConcreteSociety in association
with the National University of Ireland, Dublin
Contact: Mr S Mac Craith,Department of Civil Engineering,
NUI Dublin, Earlsfort Terrace, Dublin 2.
Tel: +353 (0)1 706 7472E-mail [email protected]
SOUTH AFRICA(Gauteng)
Organised by the Cement andConcrete Institute,
School of Concrete Technology.
Contact: Mr R du Preez, C&CI, P O Box 168,
Halfway House, 1685
Tel: +27 (0)11 315 0300E-mail: [email protected]
Courses are held in:
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ADVANCED CONCRETE TECHNOLOGY DIPLOMA:SUMMARIES OF PROJECT REPORTS 2000
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 problemin a logical and disciplined way, organise a programme of work and present the same in a wellstructured report. The project normally spans some six months. Significant advances can bemade and several of the projects have evolved into research programmes in their own right.
Summaries of a selection of project reports submitted during the 1999 - 2000 course are givenin the following pages.
A full list of earlier ACT projects, dating back to 1971 when the individual project was introduced as a requirement forthe Advanced Concrete Technology Diploma examination, was published in the 2000 - 2001 edition.
Copies of the reports (except those that are confidential) are held in the British Cement Association Library and thesecan be made available on loan. Subscribers to the BCA's information service, Concquest, may obtain copies on loan,free of charge. Requests should be addressed to: The Centre for Concrete Information, British Cement Association,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 the BCA free of charge.
PROJECT TITLE: AUTHOR:
AN INVESTIGATION INTO THE EFFECTS ON THE MAIN T. BalmerCONCRETE RELATIONSHIPS USING CLASS 42.5N PORTLANDCEMENTS AT VARIOUS COMPLIANCE LEVELS
GUIDELINES FOR DETERMINING THE ACCEPTANCE CRITERIA A. BenitezFOR TESTING OF CONCRETE CONTAINERS USED IN THEDISPOSAL OF MEDIUM AND LOW ACTIVITY RADIOACTIVE WASTE
HIGH PERFORMANCE CONCRETE BRIDGE BEAMS - LATEST DEVELOPMENTS P. Deegan
AN INVESTIGATION INTO THE EFFECTS OF MOISTURE ON R.J. EganTHE CRUSHING STRENGTH OF CONCRETE PIPES
CONCRETE PETROGRAPHY, A POWERFUL TOOL FOR THE L. Fernandez LucoDIAGNOSIS OF CONCRETE DAMAGE
THE FUTURE OF STEEL FIBRES IN INDUSTRIAL FLOORS J. Gauld
SHORT-TERM TESTS FOR LONG-TERM DURABILITY OF CONCRETE T. Hloele
INVESTIGATION INTO THE RELATIONSHIP BETWEEN MIX PROPORTIONS C. LillisAND MATERIAL PERFORMANCE (COMPRESSIVE STRENGTH) FOR DESIGNATION (iii) SAND CEMENT MORTAR TO BS 4721:1981SPECIFICATION FOR READY-MIXED BUILDING MORTARS
HIGH STRENGTH CONCRETE (READYMIX CONCRETE APPLICATION) J. McLoughlin
MECHANICAL PROPERTIES OF MORTAR D. Van Mechelen
SELF COMPACTING CONCRETE AND ITS PRODUCTION P. MulliganFROM IRISH MATERIALS
AN INVESTIGATION INTO THE POSSIBLE USE OF RECYCLED CONCRETE F. O’ByrneDEMOLITION WASTE AS AN AGGREGATE FOR LOW STRENGTH CONCRETE APPLICATION INCLUDING TECHNICAL, REGULATORY, ECONOMIC AND ENVIRONMENTAL CONSIDERATIONS
THE EFFECT OF EARLY AGE CONCRETE TEMPERATURES ON A.J. O’ConnorSTRENGTH-MATURITY RELATIONSHIPS IN IRELAND
AN INITIAL INVESTIGATION OF FERROCEMENT D.W. O’DwyerPERMEABILITY AND SORPTIVITY
THE USE OF LIME AS AN ADMIXTURE TO IMPROVE THE PERFORMANCE R. RankineOF RUBBLE MASONRY CONCRETE MORTARS, WITH PARTICULAR REFERENCE TO BLEEDING
PRODUCING A FINER GROUND GRANULATED SLAG FOR THE R. TomesSOUTH AFRICAN MARKET - DO WE NEED IT?
108
SUMMARYThe objectives of the project were to
examine the effects of using different Portlandcements on the relationship betweencompressive strength and cement content (i.e.the ‘main relationship’).
Whilst all the cements complied with therequirements of BS 12 for Class 42.5N, thefineness and 28 day mortar prism strengthswere different for each cement. Variousmethods of correcting the main relationshipfor changes in cement properties were alsoexamined.
Four Portland cements were examined,three from a single UK clinker but ground todifferent finenesses and a fourth from Greece.Concretes with cement contents ranging from100kg/m3 to 600kg/m3 were investigated. Theconcretes all contained natural gravelaggregates, glacial sand and no admixtures.Concrete mixes were initially generated usingthe Mixsim 98 software.
It was observed that all four cementsgenerated a main relationship curve of thesame general shape (at least in the region upto a strength of 60N/mm2). However, thecement content required to achieve a given 28day compressive strength (say 35N/mm2)varied by up to 35kg/m3 between the fourcements.
It was also noted that whilst the 28 dayprism strengths of the Greek cement and themost finely ground UK cements were identical,the early age strength development wasradically different. This highlighted potentialproblems in predicting 28 day strengths fromearly age data or reliance purely on BS 12, 28day prism tests.
Whilst the report concludes that BS 12cements can be multi-sourced withoutaffecting the main relationship, care must betaken in determining the correlation betweenearly age and 28 day strength for each newcement prior to using it in production.
Cusum systems that incorporatehorizontal or vertical movement of the mainrelationship as a means of correcting forchanges in cement properties are consideredto be less accurate than a system of ‘spinning’the curve around its point of origin.
AN INVESTIGATION INTO THE EFFECTS ON THE MAIN CONCRETERELATIONSHIPS USING CLASS 42.5N PORTLAND CEMENTSAT VARIOUS COMPLIANCE LEVELSBy: T. Balmer
109
GUIDELINES FOR DETERMINING THE ACCEPTANCE CRITERIAFOR TESTING OF CONCRETE CONTAINERS USED IN THE DISPOSALOF MEDIUM AND LOW ACTIVITY RADIOACTIVE WASTEBy: A. Benitez
SUMMARYThis project can be considered as a third
stage in a joint research programme aimed atestablishing the basis for solving the disposalproblem associated with low and intermediateactivity radioactive waste in Argentina.
The programme itself involves theNational Commission of Nuclear Power ofArgentina and the Centre of Development andInvestigation in Construction.
The first stage involved the design ofadequate concrete mixes for the constructionof containers to be used in the storage ofradioactive waste. This step consisted ofthorough characterisation of the concrete tobe used. The second stage consisted of thecasting of prototypes at full scale. In addition itincluded the verification of the main propertiesof the actual containers. It was hoped that thiswould result in recommendations for theimprovement of the design methodology andthe determination of a basic correlationbetween the concrete made in the laboratoryand that actually made under site conditions.
The third stage and the main purpose ofthe project work reported here is aimed atgiving the outline of guidance for determiningacceptance/rejection criteria for the receptionof the finished product during a futureindustrial scale manufacturing programme.
In this regard the main aspect taken intoconsideration was the durability behaviour ofthe concrete containers. In that sense theassessment of the ‘covercrete’ quality andthickness by means of NDT represents the keyaspect to ensure long term service life.
Both ordinary Portland cement, sulphateresisting and ground granulated blastfurnacetype cements were used with potentialcompressive strengths equal to or above 50MPa. The aggregate was crushed granite usedin conjunction with natural sand. In additionhigh range water reducing and air entrainingadmixtures were used.
Characteristics such as penetrability(oxygen permeability, water permeability andcapillary absorption), drying shrinkage,thermal expansion and adiabatic temperaturerise were all evaluated.
It was found that the non-destructivetesting on site had not been exhaustivelydeveloped and definitive answers could not beproposed without further work beingperformed. However, the data collected thusfar introduce a significant advance ascompared to the known recommendationsthat were used as the reference points.Recommendations for future work are given.
110
SUMMARYThis project examines the use of novel
materials for the production of high strengthconcrete (80N/mm2) in Ireland. The studyincluded microsilica, metakaolin and a newlydeveloped superplasticiser with the objectiveof producing a high workability, high strengthconcrete for use in precast/prestressed bridgebeams.
The materials used in the experimentalstudy included both 20mm and 12mmlimestone aggregates, (crushed material andnatural material), 3 types of cement (CEM I42.5R, CEM I 52.5R and low alkali cement)microsilica and metakaolin. A polycarboxylicether based superplasticiser was usedthroughout the project.
Initial mix design was undertaken usingprocedures developed by Nawy.
Trial mixes indicated that 28 daystrengths in excess of 100N/mm2 could beobtained using metakaolin and microsilica.Metakaolin was judged to be more efficientthan microsilica in producing high strengthand also gave better fresh handlingcharacteristics. Of the three cementsexamined, the low alkali 42.5N gave thehighest strength in mixes containingmetakaolin.
Following the initial trials larger batchesof concrete (1m3) were produced from selectedmix designs. These larger batches were usedto provide specimens for the measurement ofmodulus of elasticity and to select mix designsfor the production of full scale precast ‘Y’beams.
The modulus of elasticity (E)measurements (whilst exhibiting a certainamount of scatter), followed a similarrelationship with compressive strength as thatpredicted in BS 8110 but with around a 5%higher value for E.
The high strength concrete mix selectedfor the production of full scale bridge beamscontained 20mm aggregate, a blend of thelow alkali cement and metakaolin andachieved a 28 day strength of around93N/mm2.
A total of 20 full scale beams were castusing this concrete and one 37.35m longbeam was subjected to a flexural load test.The beam was loaded (at third points) to222kN leading to a mid span deflection of95mm (of which 94% was recovered afterunloading).
The conclusions drawn from this projectare that high strength concrete can be madewith materials available in Ireland and usedsuccessfully to produce precast, prestressedconcrete bridge beams.
HIGH PERFORMANCE CONCRETE BRIDGE BEAMSBy: P. Deegan
111
SUMMARYThe project examined the crushing
strength of full size concrete pipes (ranging indiameter from 225 to 525mm). In particular,the research examined the differences inapparent strength between pipes tested in a‘dry’ or ‘wet’ condition.
Pipes were tested using the three-edgebearing method (in accordance with IS.6:1974‘Concrete Sewer Pipes’).
The results of the test programmeindicated that there was a general increase inthe pipe crushing strength if pipes weresoaked in water (typically for 72 hours) beforetesting. The magnitude of the strengthincrease was also greater for the larger pipes.
It was also found that if soaked pipeswere allowed to dry out before testing, thecrushing strength was similar to pipes that hadbeen kept continually dry.
Examination of the pipes after testingrevealed that water penetration in the soakedpipes was only around 12mm from exposedfaces. Even extended soaking for fourteendays failed to increase significantly the degreeof water penetration.
It is postulated that the development of amoisture gradient within the walls of the pipeforms residual compressive stresses in thesoaked region.
As the mode of failure in the three-edgebearing test is essentially in tension, thesecompressive stresses offset the applied tensilestresses under load. Consequently, the pipecan withstand a greater load before failing.
The steeper the moisture gradient, thegreater the initial compressive strength. Thusin the larger pipes the soaked region is smallrelative to the total wall thickness, (i.e. a steepmoisture gradient) and exhibit the greatestincrease in crushing strength when soaked.
The report goes on to conclude that asthe standard permits soaking, satisfactorycrushing strengths could be obtained at lowercement contents by soaking prior to testing.As many pipes are also exposed to externalsources of water during service, this would notlead to any significant reductions in theoperational performance of the pipe.
AN INVESTIGATION INTO THE EFFECTS OF MOISTURE ON THE CRUSHING STRENGTH OF CONCRETE PIPESBy: R.J. Egan
112
SUMMARYThis Report is concerned with the role of
petrography analysis in determining the natureof damage to concrete resulting from a varietyof exposure conditions. The selection ofparticular methods should be related to theproblem being investigated.
Petrographic tests have a place but a gapexists between the petrographer and theengineer and this needs to be addressed inorder for petrography to find an appropriateplace in the list of diagnostic tools.
Petrographic techniques are reviewedthoroughly, including:
• polished sections using stereomicroscopy with reflected light
• thin sections using petrographicmicroscope.
These techniques are used together withdata on the pore structure of the concrete.
Using these methods can identify crystalgrowths such as calcium hydroxide andettringite, fine cracks, the larger capillary voidsand entrained air voids as well as macro voidsand bleeding channels.
Visual evidence of these artifacts ispresented including the effects of carbonationand sulphate attack as well as alkali-silicareactions.
The main causes of damage arereviewed, highlighting that design andconstruction accounts for 88% of concretedefects.
An appreciation of the causes of damageto concrete is essential when correlatingexposure conditions to petrographicobservations.
In this regard sulphate attack, freeze-thaw, acid, alkali aggregate reaction andplastic shrinkage cracking are all considered.
In addition, complementary techniquesare also taken into account, such as gas (air)permeability, carbonation depth, capillaryabsorption, chemical analysis, XRD and SEM.
These options are brought together inthe form of flow charts for diagnosis, linkingthe different techniques to the type ofdeterioration observed.
CONCRETE PETOGRAPHY, A POWERFUL TOOLFOR THE DIAGNOSIS OF CONCRETE DAMAGEBy: L. Fernandez Luco
113
SUMMARYSteel fibres are becoming more popular
and available for inclusion within industrialfloors. This project examines the benefits ofusing steel fibres within industrial floorstogether with the additional flexibility gainedat the design stage.
Certain physical properties of twopopular steel fibres are measured withinconcrete beam samples at different dosagesand cement contents and achieved values arereported upon. Toughness values areexpressed as in Concrete Society TechnicalReport 34, Japanese Standard JSCE - SF4 (i.e.fe3 and Re3 values), American Standard 1018 C-97 (ie. toughness indices) and whereappropriate the application of these valueswithin the design of industrial floors isillustrated. Optimum performance is soughtthrough understanding the mechanismemployed by steel fibres and relating suchperformance to uniformity of fibre spacing anddistribution within the concrete mix designemployed. Effective inclusion of steel fibreswithin the plastic concrete is achieved byincorporating steel fibres at the batching stageas an integral ingredient, with procedures inplace to ensure designed distribution.
The recommendation of this project isthat the ready-mix industry becomes more ofa driving force for change by evaluating how itoperates to accommodate the use of steelfibres as a regular material within a readymixed concrete product.
Within the incoming BS EN 206opportunity arises for the promotion of a“Proprietary Concrete” which is recognised bya title and performance criteria. Proprietaryconcrete can be linked to abrasionclassifications as detailed in BS 8204 andincorporate steel fibres to meet desired Re3
performance values, as detailed in designcriteria of Concrete Society Technical Report34. Combinations of fibre types can beexploited to yield optimum floor toughnessvalues in conjunction with the added benefitsof polypropylene fibres or a reduction in dryingshrinkage though including a polypropyleneglycol ether admixture. Quality Assurance ofpurchased and stocked fibres will have to beevaluated and procedures put in place toensure that subsequent steel fibre reinforcedconcrete will achieve the performance criteriadetailed for a certain proprietary concrete.
It is the belief of the author that greatermechanisation and automation can be gainedthrough using steel fibres leading to greaterefficiency, productivity, profitability andsustainability of industrial floors.
THE FUTURE OF STEEL FIBRES IN INDUSTRIAL FLOORSBy: J. Gauld
114
SUMMARYThe work described in this report relates
to the quality of the concrete tunnel lining onthe Lesotho Highlands Water Project. It isconcerned with assessing the long-termdurability of the concrete using short-termdurability tests.
Tunnel lining durability was the focus ofconcern resulting from contact of the concretewith soft water and its ability to penetrate theconcrete.
The tests chosen were:
• oxygen permeability tests
• Autoclam water permeability test
• water sorptivity test
• Taywood water permeability test.
The report concludes that the studydurability tests are suitable for monitoring thequality of concrete. For instance the oxygenpermeability test is sensitive to variations in themixes and the water sorptivity test to concretequality gradation with depth. The Autoclamperformed in a similar way to the oxygenpermeability test.
The tests provide qualitative indices onwhich concrete can be classified as durable ornon-durable. Further data gathering isrequired to improve the confidence level in theuse of these tests.
The report also contains a detailed reviewof factors affecting durability.
The following recommendations aremade:
• Concrete durability testing should beincorporated into standard code ofpractice for structural concrete
• Further study is required to verify thelevel of aggressiveness of the LesothoHighlands water
• Tests could be used to check theeffectiveness of various types ofprotective coatings that might beapplied to the surface of the tunnellining to reduce its permeability
• Further testing on the correlationaspects of the concrete durability testsis required.
SHORT-TERM TESTING FOR LONG-TERM DURABILITY OF CONCRETEBy: T. Hloele
115
SUMMARYBS 4721 requires mortars to comply both
with limitations on the permissible cementcontent and performance requirements suchas a minimum compressive strength.
Designation (iii) mortar makes up around90% of the Irish market for readymix mortars.The BS 4271 requirements for this type ofmortar can be summarised as:-
• Mass of cement 11.5 wt% to 16.5wt%
• Minimum compressive strength2.5N/mm2.
Changes in the properties of cement overrecent years have resulted in significantincreases in cement strength. The reportexamines a number of combinations ofcement content and air content for therelationship between mix proportions andcompressive strength. The impact of improvedcement performance on the relative strengthof mortars and concrete blocks is alsoexamined. The research concentrated onproducing designation (iii) mortars.
The results indicated that at the highestpermitted level of cement a designation (iii)mortar can have a compressive strength inexcess of 11.5N/mm2. This is considerablygreater than the typical strength of a concreteblock and could lead to problems withblockwork failing before the mortar. Even atcement contents below the minimum fordesignation (iii) mortars, when combined withlow air contents, the minimum strength for adesignation (iii) mortar is exceeded.
The conclusion is reached that BS 4721designation (iii) mortars made with moderncements can satisfy the performance criteriafor the higher strength designation (i) mortar.
The compressive strength criterion fordesignation (iii) mortar can currently beachieved at cement contents well below theupper margin stated in the standard. It issuggested that BS 4721 should be reappraisedin terms of the suitability of the range ofcement contents necessary to achieveminimum strength requirements.
INVESTIGATION INTO THE RELATIONSHIP BETWEEN MIXPROPORTIONS AND MATERIAL PERFORMANCE (COMPRESSIVE STRENGTH) FOR DESIGNATION (iii) SAND CEMENT MORTAR TO BS 4721:1981“SPECIFICATION FOR READY-MIXED BUILDING MORTARS”By: C. Lillis
116
SUMMARYWithin the Irish readymix concrete
industry there has been a steady increase inthe use of higher strength grades of concreteover the last 20 years (greater than 50 MPa).
It is anticipated that higher strengthdemand will increase and the Report wascommissioned in order to determine thefeasibility of supplying higher strengthconcretes using local materials, lower watercontents, high range water reducingadmixtures and pozzolanic additions.
Quality control was considered to be thekey to achieving reliable high strengthconcrete production.
Silica fume was used in a densifiedpowder form together with a high range waterreducing admixture although the selection ofthe admixture was dependent upon thecement type. Three crushed gravels and twotypes of crushed rock were used. Satisfactorymixes were produced with cube strengths of80 MPa at 91 days with good workability andslump retention.
Strength could be increased by 20 MPausing different aggregates.
Whilst the silica fume concrete wassatisfactory, work using high reactivitymetakaolin showed promise for all aggregatetypes although strengths were not as high.
The problem of plastic settlement needssolving before concretes of this type could beused on full-scale applications. However, theprognosis for use of high strength concrete isgood in Ireland and Dublin in particular.
HIGH STRENGTH CONCRETE(READYMIX CONCRETE APPLICATION)By: J. McLoughlin
117
SUMMARYThis project examines the application of
standard soil mechanics techniques forcharacterising the workability of mortars andin particular the influence of aggregate particleshape on flow properties and strengthcharacteristics.
Portland cement was mixed with either afine river sand or a crushed sand atproportions between 4.5:1 and 3:1. Althoughboth the sands used in the experimentalprogramme had a similar grain sizedistribution, they exhibited differences inparticle angularity and texture. Thewater/cement ratio was varied between 0.30and 0.92.
Firstly the dry mortar mix was examinedto determine the cohesion and angle ofshearing resistance, before water was added.The workability was determined using a slumptest (NEN 5956) and a compaction test (NEN-EN 12357) followed by a shear box test toexamine the cohesion and angle of shearingresistance. Samples were also made forcompressive and flexural strength tests.
It was found that the crushed sand hada higher angle of shearing resistance than thenatural river sand and that when the twosands were mixed a maximum angle wasreached at a level of 25% crushed sand.
The angle of shearing increased whencement was added to the river sand butdecreased when cement was added to thecrushed sand.
Adding water to the system changes theabsolute value of the angle of shearingresistance but not the relative variations foundin the study of the dry mixtures.
The angle of shearing resistance wasfound to reach a minimum and cohesionreaches a maximum at around 9% watersaturation (corresponding to 0% empty voids).
When considering hardened mortar, thecompressive strength (both at early age and inthe long term) correlates well with the angle ofshearing of the dry materials, providing thatthe mix proportions (w/c, a/c) remain thesame. No correlation however was found withthe flexural strength.
MECHANICAL PROPERTIES OF MORTARBy: D. Van Mechelen
118
SUMMARYThe aim of this project was to establish if
and how self-compacting concrete could beproduced in the Republic of Ireland usingreadily available materials.
Such feasibility involved investigationswith aggregates, cements and cementcontent, superplasticising and viscositymodifying admixtures as well as fine powderfillers.
The work covered a thorough review ofthe available literature and information andonce the principles underlying the design andproduction of self-compacting concrete theinvestigation was extended to a series oflaboratory trial mixes. Both ordinary Portlandcement complying with IS 1 and BS 12 as wellas PFA modified mixes were considered. Theinvestigation was not extended to the use ofgranulated blastfurnace slag.
The coarse aggregates chosen allconformed to IS 5 and consisted of crushedcarboniferous limestone as well as uncrushedor partially crushed glacial stones and pebbles.
The fine aggregates conformed to IS 5and consisted of siliceous natural sands. Whilstlimestone fillers were considered part of theinitial programme the material was eventuallynot used.
Admixtures consisted of polycarboxylate-based superplasticisers and Whelangum/naphthalene formaldehyde sulphonatemixtures as viscosity enhancing materials.
A total of 11 mix types were used in all.
The study has given rise to Guidelines asto what is required by way of admixture orpowder addition to produce concrete with theflow characteristics relating to self-compactingconcrete with acceptable levels of stabilitywhen working with the particular materialsthat were examined.
The conclusions of the study do not giveanswers to all the questions that are raisedregarding self-compacting concrete. Howeverthe information should prove useful forpotential users of this type of material inIreland and elsewhere.
SELF-COMPACTING CONCRETE AND ITS PRODUCTIONFROM IRISH MATERIALSBy: P. Mulligan
119
SUMMARYThere is little exploitation of recycled
concrete as a concrete aggregate in Ireland.Construction waste is generally used as roughfill material or landfill reclamation covermaterial.
It is estimated that recycled concretecould provide up to 11% of the aggregatedemand in Ireland.
The report discusses government and EUpolicy towards waste recycling including theconsequences of introducing new standardssuch as pr EN 206 and pr EN 12620.
The importance of recycling constructionwaste (including recycled concrete) isrecognised in many official publications.
Barriers to the increased use of recycledconcrete in Ireland include low landfill chargesand abundant natural aggregate resources.Currently the probable cost of recycledaggregate would be around £14/tonnecompared to £9/tonne for primary aggregates.However, possible changes such as increasedlandfill charges or primary aggregate taxeswould tilt the economic balance in favour ofrecycled aggregates.
The report also contains a case study onthe use of recycled concrete aggregate.Demolition waste was obtained from a site inDublin. After crushing and screening, therecycled concrete aggregate was subjected toa series of laboratory tests. In general therecycled material complied with most of therequirements for primary aggregates exceptthat water absorption was higher and the LosAngeles Abrasion value was also increased (i.e.a greater abrasion loss during the test).
Trial mixes were then undertaken usingthe recycled material, in lean mix concrete forroad bases; and a mix for building blocks wereboth examined.
It was concluded that it was technicallyfeasible to use recycled coarse aggregates forlean mix and possibly for building blocks. It isthought that recycled aggregates can play animportant role in serving the needs of roadconstruction in Ireland and thus preservenatural aggregates for other applications. Thedemands placed on natural reserves by theIrish National Plan can be partially reduced bythe substitution of recycled materials fornatural aggregates in some applications.
AN INVESTIGATION INTO THE POSSIBLE USE OF RECYCLEDCONCRETE DEMOLITION WASTE AS AN AGGREGATE FORLOW STRENGTH CONCRETE APPLICATION INCLUDING:TECHNICAL, REGULATORY, ECONOMIC ANDENVIRONMENTAL CONSIDERATIONSBy: F. O’Byrne
120
SUMMARYThe aim of the project was to establish
the effect of elevated concrete temperatures inthe first few hours after mixing on the 7 and28 day strengths of cubes, over a range oftypical ambient temperatures in Ireland (5ºC -30ºC).
Constituent materials were brought tothe required temperature before mixing andthe test cubes were kept at the mixingtemperature for up to six hours, before beingcured under standard conditions until testing.Control cubes cured consistently understandard conditions were also produced. Aspart of the experimental work, a comparisonwas also made between the strength ofconcrete made in steel cube moulds and thatmade in expanded polyurethane moulds. Nosignificant difference was observed.
The experimental results demonstratedthe influence of elevated early agetemperature on the development of 28 daycompressive strength. Reductions in strengthof up to 15% were observed when cubes wereheld at 30ºC for the first six hours. Concretescontaining PFA, however, appear to benefitfrom early age elevated temperature. Thenormal reduction in strength of PFA concretecompared to Portland cement concrete iscounteracted by the accelerated pozzolanicreaction at elevated temperatures.
It was also concluded that strength -maturity relationships of an approximatelyhyperbolic shape (Carino & Lew 1982), doprovide an accurate representation of thestrength gain of concrete for the mixes andconditions considered.
It was also suggested that modelling ofthe relationships between time-temperaturehistory, mix constituents and strength couldusefully be employed by concrete producers tomodify mix designs to compensate for highambient temperatures and the risk of non-compliant cube results.
THE EFFECT OF EARLY AGE CONCRETE TEMPERATURES ONSTRENGTH-MATURITY RELATIONSHIPS IN IRELANDBy: A.J. O’Connor
121
SUMMARYFerrocement has a number of uses but is
widely used in developing countries for lowcost housing. Notwithstanding such use itsdurability is suspect.
A key factor influencing durability is thepermeability of the mortar phase.
This work was aimed at comparingferrocement with traditional reinforcedconcrete to quantify the differences relating tosorption, permeation and ionic diffusion. Thereport is in four parts:
• A Review of ferrocement
• Durability aspects and ingressmechanisms
• Experimental programme
• Examination of results andconclusions.
Aspects of concern are:
• carbonation
• chloride induced corrosion
• galvanic corrosion.
The experimental work was concernedwith four mortar mix types cast as panels. AnAutoclam was used to measure thepermeability (air and water) and sorptivity ofthe panels.
Whilst the depth of cover (1-2 mm) withferrocement makes it vulnerable, thepermeability of the test panels showsferrocement to have the potential of achievingvery low levels of air permeability and sorptivity- comparable to normal concrete treated withSiloxane. As one would expect, poor curing ofthe mortar has a detrimental effect.
The data gathered were not sufficient toestablish if ferrocement could be used safely ina chloride rich environment unless specialprecautions were taken.
AN INITIAL INVESTIGATION OFFERROCEMENT PERMEABILITY AND SORPTIVITYBy: D.W. O’Dwyer
122
SUMMARYRubble Masonry Concrete (RMC) consists
of large irregular boulders placed manually intoa mortar matrix and has recently started to beutilised in South Africa.
It had been noted that failure incompression generally originated at theinterface between the rock boulders and themortar matrix and that furthermore the failuresurfaces are often marked by large voidsresulting from water bleeding from the matrix.
Methods for reduction of bleed (andhence improved strength of the RMC), werereviewed and an experimental programmedesigned to examine the effect of adding limeto the mortar as a means of reducing bleed.Other possible means of bleed reduction, suchas entrained air or the use of silica fume oradmixtures, were discounted for variouspractical reasons.
It was observed that the addition of limeto mortar stiffened the mix (irrespective of thesource of the lime).
The compressive strength of the mortarwas increased by using a 50:50 blend ofPortland cement and Type A2 (hydratedcalcitic) lime.
Load deflection testing showed thatmortar containing lime increased the fracturetoughness. However, the main finding wasthat addition of lime (even at levels as low as1% of the weight of cement) caused areduction in bleed. The exact amount of limerequired to reduce bleeding in RMC to anacceptable amount must be established bytrial and error but a starting point of 5-10%lime addition by weight of cement isrecommended.
Lime addition is considered a practicaland economic method of improving theperformance of Rubble Masonry Concrete(RMC).
THE USE OF LIME AS AN ADMIXTURE TO IMPROVE THEPERFORMANCE OF RUBBLE MASONRY CONCRETE MORTARS:WITH PARTICULAR REFERENCE TO BLEEDINGBy: R. Rankine
123
SUMMARYThe motive for using waste materials
such as slags are:
• environmental
• maximising both the technical andcost benefits.
Slag only became available in substantialquantities in South Africa in the 1940s. Thematerial is usually coarsely ground (3,500cm2/g Blaine). Finer milling is a prospect inorder to improve on early properties, inparticular strength.
In this work comparisons are madebetween 100% ordinary Portland cementconcretes and those made with 50%replacement by the slag as well as 25%replacement with pulverised fuel ash.
Six major cement suppliers were usedand in addition split GGBS sample testing wascarried out using slags of different surfaceareas, 3,500 and 5,000 cm2/g, respectively. Inthese latter tests different cements andadmixtures to the first series were used:
Admixture and steam curing tests werealso performed on the finer slag in order tojudge the feasibility of using 50/50 OPC/GGBSblends in project where only OPC concreteswould normally be used:
Two types of slag are considered, namely,
• blastfurnace slag (GGBS)
• that from the Corex process (GBCS).
Much information is presented in thereport in both tabulated and diagrammaticform. Items considered were:
• the effect of curing temperature andof steam curing.
• the affect of superplasticisingadmixtures
• the cost of grinding the slag to afiner consistency. Milling alone wasnot considered to be the mostappropriate solution.
Other factors have to be considered,including:
• the chemical and physicalproperties of the slag
• the chemical and physicalproperties of the activator ie the cement
• the curing conditions of theconcrete
• the effect of chemical admixtures
• the cost effectiveness of using aslightly more expensive materials,eg. slag 5,000.
Some other considerations noted by theauthor are also worth noting. These were notincluded in this project but may have to beconsidered for future use:
• the effect of finer milled slag on theworkability of the concrete
• the effect of finer milled slag on thedurability of concrete
• the effect of finer milled slag on theheat of hydration
• the effect of finer milled slag on alkalisilica reaction.
Further work could be usefully performedon moist adiabatic curing and deciding uponthe type of mill required for producing cost-effective slag with the desired properties:
Detailed appendices are given coveringthe following aspects:
• chemical properties of cementextenders
• chemical and physical properties ofaggregates
• material prices and calculations ofconcrete mix costs
• particle size analysis of cements andcement extenders
• admixture data sheets.
PRODUCING A FINER GROUND GRANULATED SLAG FOR THE SOUTH AFRICAN MARKET - DO WE NEED IT?By: R. Tomes
124
ICT RELATED INSTITUTIONS & ORGANISATIONS
ASSOCIATION OF INDUSTRIALFLOORING CONTRACTORS33 Oxford StreetLeamington SpaCV32 4RATel: 01926 833 633www.concrete.org.uk/acifc
ASSOCIATION OFCONSULTING ENGINEERSAlliance House12 Caxton StreetLondon SW1H 0QLTel: 020 7222 6557www.acenet.co.uk
ASSOCIATION OF LIGHTWEIGHTAGGREGATE MANUFACTURERSC/O: East Coast Slag Products LtdStantonScunthorpeN.Lincs DN16 1XYTel: 01724 856444
BRE (BUILDING RESEARCHESTABLISHMENT) LTDBucknalls LaneGarstonWatford WD2 7JRTel: 01923 664000www.bre.co.uk
BRITISH BOARD OF AGRÉMENTP.O.Box 195Bucknalls LaneGarstonWatfordHerts WD25 9BATel: 01923 665341www.bbacerts.co.uk
BRITISH CEMENT ASSOCIATIONTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 762676www.bca.org.uk
BRITISH PRECASTCONCRETE FEDERATION60 Charles StreetLeicester LE1 1FBTel: 0116 253 6161www.britishprecast.org.uk
BSI STANDARDSBritish Standards House389 Chiswick High RoadLondon W4 4ALTel: 020 8996 7000www.bsi.org.uk
BRITPAVEBritish In-Situ ConcretePaving AssociationTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 725731www.britpave.org.uk
CEMENT ADMIXTURESASSOCIATION38a Tilehouse Green LaneKnowleWest MidlandsB93 9EYTel: 01564 776362
CONCRETE ADVISORY SERVICE37 Cowbridge RoadPontyclunNr. CardiffWales CF72 9EBTel: 01443 237210www.concrete.org.uk
CONCRETE BRIDGEDEVELOPMENT GROUPTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 762676www.cbdg.org.uk
CONCRETE REPAIR ASSOCIATIONAssociation House235 Ash RoadAldershotHants GU12 4DDTel: 01252 321302www.concreterepair.org.uk
THE CONCRETE SOCIETYTelford AvenueCrowthorneBerkshireRG45 6YSTel: 01344 466007www.concrete.org.uk
CIRIAConstruction Industry Research
& Information Association6 Storey's GateWestminsterLondon SW1P 3AUTel: 020 7222 8891www.ciria.org.uk
CORROSION PREVENTION ASSOCIATIONAssociation House235 Ash RoadAldershotHants GU12 4DDTel: 01252 321302www.corrosionprevention.org.uk
INSTITUTE OF CORROSION4 Leck HouseLake StreetLeighton BuzzardBeds LU7 7TQTel: 01525 851771www.icorr.demon.uk
INSTITUTION OF CIVILENGINEERSGreat George StreetLondon SW1P 3AATel: 020 7222 7722www.ice.org.uk
INSTITUTION OF HIGHWAYS& TRANSPORTATION6 Endsleigh StreetLondon SW1H 0DZTel: 020 7387 2525www.iht.org
INSTITUTE OF MATERIALS1 Carlton House TerraceLondon SW1Y 5DBTel: 020 7839 4071www.materials.org.uk
INSTITUTION OFROYAL ENGINEERSBrompton BarracksChathamKent ME4 4UGTel: 01634 842669
INSTITUTION OFSTRUCTURAL ENGINEERS11 Upper Belgrave StreetLondon SW1X 8BHTel: 020 7235 4535www.istructe.org.uk
INTERPAVEConcrete Block Paving Association60 Charles StreetLeicester LE1 1FBTel: 0116 253 6161www.paving.org.uk
MORTAR INDUSTRYASSOCIATION156 Buckingham Palace RoadLondonSW1W 9TRTel: 020 7730 8194www.mortar.org.uk
QUARRY PRODUCTSASSOCIATION156 Buckingham Palace RoadLondon SW1W 9TRTel: 020 7730 8194www.qpa.org
QSRMCQuality Scheme for ReadyMixed Concrete3 High StreetHamptonMiddlesex TW12 2SQTel: 020 8941 0273
RIBARoyal Institute of British Architects66 Portland PlaceLondon W1N 4ADTel: 020 7580 5533www.architecture.com
CEMENTITIOUS SLAGMANUFACTURERS ASSOCIATIONCroudace HouseGoldstone RoadCaterhamSurrey CR3 6XQTel: 01883 331071www.ukcsma.co.uk
SOCIETY OF CHEMICALINDUSTRY14/15 Belgrave SquareLondon SW1X 8PSTel: 020 7235 3681www.sci.mond.org
UNITED KINGDOMACCREDITATION SERVICE21-47 High StreetFelthamMiddlesexTel: 020 8917 8400www.ukas.org.uk
UNITED KINGDOM CAST STONE ASSOCIATIONCentury HouseTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 762676www.ukcsa.co.uk
UNITED KINGDOM QUALITY ASH ASSOCIATIONRegent HouseBath AvenueWolverhamptonWV1 4EGTel: 0102 576 586www.ukqaa.org.uk
125
ICT YEARBOOK 2001-2002
EDITORIAL COMMITTEE
Professor Peter C. Hewlett (Chairman)BRITISH BOARD OF AGRÉMENT
& UNIVERSITY OF DUNDEE
Peter C. OldhamCHRISTEYNS UK LIMITED
Dr. Bill PriceSANDBERG
Graham TaylorINSTITUTE OF CONCRETE TECHNOLOGY
Laurence E. PerkisINITIAL CONTACTS
Published by:THE INSTITUTE OF
CONCRETE TECHNOLOGYP.O.Box 7827Crowthorne
Berks RG45 6FREmail: [email protected]
Website: www.ictech.org
£50.00
ISSN 1366 - 4824
Yearbook: 2001-2002
CONCRETE TECHNOLOGYINSTITUTE OF
The
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INSTITUTE OF CONCRETE TECHNOLOGYP.O.BOX 7827, Crowthorne, Berks, RG45 6FR
Tel/Fax: (01344) 752096Email: [email protected]
Website: www.ictech.org
THE ICTThe Institute of Concrete Technology was
formed in 1972 from the Association ofConcrete Technologists. Full membership isopen to all those who have obtained theDiploma in Advanced Concrete Technology.The Institute is internationally recognised andthe Diploma has world-wide acceptance asthe leading qualification in concretetechnology. The Institute sets higheducational standards and requires itsmembers to abide by a Code of ProfessionalConduct, thus enhancing the profession ofconcrete technology. The Institute is aProfessional Affiliate body of the UKEngineering Council.
AIMSThe Institute aims to promote concrete
technology as a recognised engineeringdiscipline and to consolidate the professionalstatus of practising concrete technologists.
PROFESSIONAL ACTIVITIESIt is the Institute's policy to stimulate
research and encourage the publication offindings and to promote communicationbetween academic and commercialorganisations. The ICT Annual Conventionincludes a Technical Symposium on a subject oftopical interest and these symposia are wellattended both by members and non-members. Many other technical meetings areheld. The Institute is represented on a numberof committees formulating National andInternational Standards and dealing with policymatters at the highest level. The Institute isalso actively involved in the education andtraining of personnel in the concrete industryand those entering the profession of concretetechnologist.