ict yearbook 2002 pt 1 - the concrete...
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Yearbook: 2002-2003
CONCRETE TECHNOLOGYINSTITUTE OF
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003
TheINSTITUTE OF CONCRETE TECHNOLOGY
P.O.BOX 7827, Crowthorne, Berks, RG45 6FRTel/Fax: (01344) 752096Email: [email protected]
Website: www.ictech.org
THE ICTThe Institute of Concrete Technologywas formed in 1972 from theAssociation of Concrete Technologists.Full membership is open to all thosewho have obtained the Diploma inAdvanced Concrete Technology. TheInstitute is internationally recognisedand the Diploma has world-wideacceptance as the leading qualificationin concrete technology. The Institutesets high educational standards andrequires its members to abide by a Codeof Professional Conduct, thus enhancingthe profession of concrete technology.The Institute is a Professional Affiliatebody of the UK Engineering Council.
AIMSThe Institute aims to promote concretetechnology as a recognised engineeringdiscipline and to consolidate theprofessional status of practisingconcrete technologists.
PROFESSIONAL ACTIVITIESIt is the Institute's policy to stimulateresearch and encourage the publicationof findings and to promotecommunication between academic andcommercial organisations. The ICTAnnual Convention includes a TechnicalSymposium on a subject of topicalinterest and these symposia are wellattended both by members and non-members. Many other technicalmeetings are held. The Institute isrepresented on a number of committeesformulating National and InternationalStandards and dealing with policymatters at the highest level. TheInstitute is also actively involved in theeducation and training of personnel inthe concrete industry and thoseentering the profession of concretetechnologist.
ICT RELATED INSTITUTIONS & ORGANISATIONS
ASSOCIATION OFCONSULTING ENGINEERSAlliance House12 Caxton StreetLondon SW1H 0QLTel: 020 7222 6557www.acenet.co.uk
ASSOCIATION OF INDUSTRIALFLOORING CONTRACTORS33 Oxford StreetLeamington SpaCV32 4RATel: 01926 833 633www.acifc.org.uk
ASSOCIATION OF LIGHTWEIGHTAGGREGATE MANUFACTURERSc/o: Butterley Aglite LtdWellington StRipleyDerbyshire DE5 3DZ
BRE (BUILDING RESEARCHESTABLISHMENT) LTDBucknalls LaneGarstonWatford WD25 9XXTel: 01923 664000www.bre.co.uk
BRITISH BOARD OF AGRÉMENTP.O.Box 195Bucknalls LaneGarstonWatfordHerts WD25 9BATel: 01923 665300www.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 9000www.bsi.org.uk
BRITPAVEBritish In-Situ ConcretePaving AssociationCentury HouseTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 725731www.britpave.org.uk
CEMENT ADMIXTURES ASSOCIATION38a Tilehouse Green LaneKnowleWest MidlandsB93 9EYTel: 01564 776362
CEMENTITIOUS SLAG MAKERS ASSOCIATIONCroudace HouseGoldstone RoadCaterhamSurrey CR3 6XQTel: 01883 331071www.ukcsma.co.uk
CONCRETE ADVISORY SERVICECentury HouseTelford AvenueCrowthorneBerkshire RG45 6YSTel: 01344 466007www.concrete.org.uk
CONCRETE BRIDGE DEVELOPMENT GROUPCentury HouseTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 762676www.cbdg.org.uk
CONCRETE INFORMATION LTDTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 725700www.concrete-info.com
CONCRETE REPAIR ASSOCIATIONAssociation House99 West StFarnhamSurrey GU9 7ENTel: 01252 739145www.concreterepair.org.uk
THE CONCRETE SOCIETYCentury HouseTelford AvenueCrowthorneBerkshire RG45 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 House99 West StFarnhamSurrey GU9 7ENTel: 01252 739145www.corrosionprevention.org.uk
INSTITUTE OF CORROSIONCorrosion HouseVimy CourtLeighton BuzzardBeds LU7 1FG Tel: 01525 851771www.icorr.org
INSTITUTE OF MATERIALS1 Carlton House TerraceLondon SW1Y 5DBTel: 020 7451 7300www.materials.org.uk
INSTITUTION OF CIVIL ENGINEERSOne Great George StreetLondon SW1P 3AATel: 020 7222 7722www.ice.org.uk
INSTITUTION OF HIGHWAYS& TRANSPORTATION6 Endsleigh StreetLondon WC1H 0DZTel: 020 7387 2525www.iht.org
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 INDUSTRY ASSOCIATION156 Buckingham Palace RoadLondon SW1W 9TRTel: 020 7730 8194www.mortar.org.uk
QSRMCQuality Scheme for ReadyMixed Concrete3 High StreetHamptonMiddlesex TW12 2SQTel: 020 8941 0273www.qsrmc.co.uk
QUARRY PRODUCTS ASSOCIATION156 Buckingham Palace RoadLondon SW1W 9TRTel: 020 7730 8194www.qpa.org
RIBARoyal Institute of British Architects66 Portland PlaceLondon W1B 1ADTel: 020 7580 5533www.architecture.com
SOCIETY OF CHEMICAL INDUSTRY14/15 Belgrave SquareLondon SW1X 8PSTel: 020 7598 1500www.sci.mond.org
UNITED KINGDOM ACCREDITATION SERVICE21-47 High StreetFelthamMiddlesex TW13 4UNTel: 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: 01902 576 586www.ukqaa.org.uk
125
Published by:THE INSTITUTE OF
CONCRETE TECHNOLOGYP.O.Box 7827Crowthorne
Berks RG45 6FRTel/Fax: 01344 752096Email: [email protected]
Website: www.ictech.org
ICT YEARBOOK 2002-2003
EDITORIAL COMMITTEE
Professor Peter C. Hewlett (Chairman)BRITISH BOARD OF AGRÉMENT
& UNIVERSITY OF DUNDEE
Peter C. OldhamCHRISTEYNS UK LIMITED
Dr. Philip J. NixonBUILDING RESEARCH ESTABLISHMENT
Graham TaylorINSTITUTE OF CONCRETE TECHNOLOGY
Laurence E. PerkisINITIAL CONTACTS
Rights reserved. No part of this publication maybe reproduced or transmitted in any formwithout the prior written consent of the
publisher. The comments expressed in thispublication are those of the Author and not
necessarily those of the ICT.
3
Yearbook: 2002-2003
CONCRETE TECHNOLOGYINSTITUTE OF
The
CONTENTS PAGE
FOREWORD 5By Dr Bill Price, President, INSTITUTE OF CONCRETE TECHNOLOGY
THE INSTITUTE 6
COUNCIL, OFFICERS AND COMMITTEES 7
FACE TO FACE 9 - 11A personal interview with Jim Troy
MILESTONES IN THE HISTORY OF CONCRETE TECHNOLOGY. 13 - 21THE ORIGINS OF PORTLAND CEMENT. By Paul Livesey
ANNUAL CONVENTION SYMPOSIUM: 23 - 116PAPERS PRESENTED 2002
ADVANCED CONCRETE TECHNOLOGY DIPLOMA: 117 - 122SUMMARIES OF PROJECT REPORTS 2001
RELATED INSTITUTIONS & ORGANISATIONS 123
4
55
FOREWORD
Welcome to the 2002-2003 ICT
Yearbook which, I am sure you will
agree, continues to meet the high
standard set by previous editions. This year also
marks the thirtieth anniversary of the formation of
the Institute of Concrete Technology and I am
honoured to be only its fifth President. In this year
of change, the Institute also welcomes Rob
Gaimster as the new Vice President and Colin
Nessfield as the new Hon.Secretary. However, I
wish to pay tribute to my predecessor Mike
Connell for all his hard work and sound
leadership during his four-year term as President.
He has successfully guided the Institute through a
turbulent period, in which the concrete industry in
its many forms has seen significant changes in
both structure and personnel. The Institute is
fortunate that he has agreed to remain on
Council to pass on his wealth of experience.
Since its formation in 1972, the ICT has
developed into an organisation with members in
over thirty-five countries around the world. It has
grown in stature and influence over those thirty
years and is still the only organisation specifically
representing professional concrete technologists.
Our annual Technical Symposium is now well
established as a major fixture in the concrete
calendar.
The success of the ICT is testament both to
the original vision of the ‘Founding Fathers’ and
to the continued support and commitment of the
membership. However, compared to other
professional bodies in the construction industry,
we are a relatively small organisation. Increasing
the size of the membership base, whilst
maintaining standards of entry, is vital for
ensuring that the ICT has a strong voice and can
implement measures to improve services to our
members. Only in this way can we improve
industry recognition of the Institute and the value
of the MICT qualification. All members have a rôle
to play in encouraging potential members to join
us.
As many of you are aware, Council is
committed to strengthening our links with the
wider engineering community through the
Engineering Council. ICT is already a Professional
Affiliate of the Engineering Council but our long-
term aim is still to achieve Nominated Body
status, enabling us to nominate our members for
inclusion in the Register of Engineers. It is my
intention as President to continue to pursue this
objective as far as our current resources will
permit.
The yearbook always contains the papers
from the technical symposium and this year is no
exception. This year’s Convention and Technical
Symposium ‘Concrete in the City’, was a
resounding success, with an impressive line-up of
speakers and a welcome increase in the number
of delegates. For the first time, parallel sessions
were introduced into the format of the
symposium, providing both an element of choice
for the delegates and more papers for inclusion in
the yearbook. Once again, the symposium papers
are combined with other interesting material on
the history of materials technology to provide
more varied reading.
I am sure that both ICT members and non-
members alike will find this edition of the
yearbook a worthwhile and enjoyable read.
Let us all look forward to another thirty
successful years for the Institute.
Dr BILL PRICEPRESIDENTINSTITUTE OF CONCRETE TECHNOLOGY
6
INTRODUCTIONThe Institute of Concrete Technology was
formed in 1972. Full membership is open to allthose who have obtained the Diploma inAdvanced Concrete Technology. The Institute isinternationally recognised and the Diploma hasworld-wide acceptance as the leading qualificationin concrete technology. The Institute sets higheducational standards and requires its members toabide by a Code of Professional Conduct, thusenhancing the profession of concrete technology.The Institute is a Professional Affiliate body of theUK Engineering Council.
MEMBERSHIP STRUCTUREA guide on ‘Routes to Membership’ has been
published and contains full details on thequalifications required for entry to each grade ofmembership, which are summarised below:
A FELLOW shall have been a CorporateMember of the Institute for at least 10 years, havea minimum of 15 years appropriate experience,including CPD records from the date ofintroduction, and be at least 40 years old.
A MEMBER (Corporate) shall hold theDiploma in Advanced Concrete Technology andwill have a minimum of 5 years appropriateexperience (including CPD). This will have beendemonstrated in a written ‘Technical andManagerial/Supervisory Experience Report’. Analternative route exists for those not holding theACT Diploma but is deliberately more onerous. A Member shall be at least 25 years old.
AN ASSOCIATE shall hold the City and GuildsCGLI 6290 Certificate in Concrete Technology andConstruction (General Principles and PracticalApplications) and have a minimum of 3 yearsappropriate experience demonstrated in a writtenreport. An appropriate university degree exempts aGraduate member from the requirement to holdCGLI 6290 qualifications. Those who have passedthe written papers of the ACT course but have yetto complete their Diploma may also becomeAssociate members. All candidates for Associatemembership will be invited to nominate acorporate member to act as SuperintendingTechnologist. There is no minimum age limit in thisgrade.
A TECHNICIAN holding the CGLI 5800Certificate in Concrete Practice must also submit awritten report demonstrating 12 monthsexperience in a technician role in the concreteindustry. An alternative route exists for those whocan demonstrate a minimum of 3 yearsappropriate experience in a technician role. Allcandidates for Technician membership will beinvited to nominate a corporate member to act asSuperintending Technologist. There is no minimumage limit in this grade.
A GRADUATE shall hold a relevant universitydegree containing a significant concretetechnology component. All candidates forGraduate membership will be invited to nominatea corporate member to act as SuperintendingTechnologist. There is no minimum age limit in thisgrade.
The STUDENT grade is intended to suit twotypes of applicant.
i) The school leaver working in the concreteindustry working towards the Techniciangrade of membership.
ii) The undergraduate working towards anappropriate university degree containing asignificant concrete technology component.
All candidates for Student membership will beinvited to nominate a corporate member to act asSuperintending Technologist. There is no minimumage limit in this grade. There is a limit of 4 years inthis grade.
Candidates are not obliged to attend anycourse (including the ACT course) prior to sittingan examination at any level.
Academic qualifications and relevant experiencecan be gained in any order for any grade ofmembership.
Corporate members will need to be competentin the science of concrete technology and havesuch commercial, legal and financial awareness asis deemed necessary to discharge their duties inaccordance with the Institute’s Code ofProfessional Conduct.
Continuing Professional Development (CPD) iscommon to most professions to keep theirmembers up to date. All corporate members(fellows and members) are obliged to spend aminimum of 25 hours per annum on CPD;approximately 75% on technical development and25% on personal development. The Institute’sguide on ‘Continuing Professional Development’includes a record sheet for use by members. This isincluded in the Membership Handbook. Annualrandom checks are 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. Detailsare available from the Institute.
THE INSTITUTE
7
EXAMINATIONSCOMMITTEE
COUNCILTECHNICAL AND
EDUCATIONCOMMITTEE
FINANCECOMMITTEE
ADMISSIONS ANDMEMBERSHIPCOMMITTEE
SCOTTISH CLUBCOMMITTEE
EVENTSCOMMITTEE
SOUTHERN AFRICACLUB COMMITTEE
MARKETINGCOMMITTEE
COUNCIL, OFFICERS AND COMMITTEES
Mr. R. RYLEChairman
G. TaylorSecretary
Dr. Ban Seng Choo
Dr. P.L.J. Domone
R. Gaimster
J. Lay
Dr. J.B. Newman
H.T.R. du Preez(corresponding)
R.V. Watson
J.D. Wootten
J.C. GIBBSChairman
C.D. Nessfield
Dr. W.F. Price
W. Wild
K.W. HEADChairman
J.C. GibbsSecretary & Treasurer
L.R. Baker
R.C. Brown
H.T. Cowan
G. Prior
J. Wilson
R.A. Wilson
Dr. W.F. PRICEPresident
R. GaimsterVice President
C.D. NessfieldHon Secretary
J.C. GibbsHon Treasurer
M.D. Connell
I.F. Ferguson
R.E.T. Hall
Dr. B.K. Marsh
P.C. Oldham
B.F. Perry
H.T.R. du Preez(corresponding)
A.R. Price
W. Wild
Dr. B.K. MARSHChairman
J.V. TaylorSecretary
L.K. Abbey
R.A. Binns
M.W. Burton
G.W. David
R. Hutton
J. Lay
C.B. Richards
A.T. Wilson
A.M. HARTLEYChairman
D.G. King(corresponding)
R.J. Majek
P.L. Mallory
C.D. Nessfield
M.S. Norton
G.Taylor
M.D. CONNELLChairman
G. TaylorSecretary
C.D. Nessfield
Dr. W.F. Price
J.D. Wootten
P.M. LATHAMChairman
G. TaylorSecretary
R.G. Boult
I.F. Ferguson
P.L. Mallory
P.C. Oldham
B.C. Patel
G. Prior(corresponding)
H.T.R. DU PREEZChairman
R. Raw
R. Tomes
EXECUTIVE OFFICER
G. TAYLOR
8
9
Q: Jim, could you tell us a little about
your earlier career? How did you get into
concrete?
A: I suppose I drifted into it; it was not a
positive decision. A change in responsibilities
within the company for which I was then
working, a subsidiary of CRH, gave me little
choice; I had been working in lime burning and
quarrying. To gain associate membership of the
Institute of Quarrying I undertook a distance
learning course with Doncaster College, shortly
after graduating in chemistry at the National
University of Ireland in Cork. My first
management role was as Quality and Production
manager for burnt lime, then after a couple of
years I moved to be Quality Control Manager for
all products - I had to undergo a steep learning
curve in both concrete and blacktop! It could be
that a course I attended at C&CA’s Fulmer Grange
Training Centre in 1973 fired me with enthusiasm
for the material. I gradually moved more to the
concrete side, working as a materials engineer in
Kuwait and in ready-mixed concrete in Saudi
Arabia before joining the training staff at Fulmer
Grange.
Q: Tell me about your PhD.
A: It originated from the work environment I
was in at the time; being a chemist at a lime
works. A production problem arose and this lead
to a theoretical analysis followed by an
examination of the factors related to the
interaction of alkaline materials on brick and
concrete refractories and the optimum use of
cooling gases to minimise fusion.
Today, computerisation would have made the
whole thing a lot simpler.
Q: What have been the highlights of your
career so far?
A: There have been several: I enjoyed the
sense of achievement with the development of
the C&CA’s correspondence course on Concrete
Technology and Construction; the introduction of
quality assurance techniques into Tarmac Topmix
(QSRMC had been formed shortly before I joined
Tarmac); becoming Technical Director and
Company Secretary of Topmix and introducing a
technical training system across the company.
More recently, the change of ownership of Tarmac
to being a subsidiary division of Anglo American
has involved a change of responsibilities and some
very challenging new opportunities.
Q: The ready-mixed concrete industry has
seen many changes over the last decade. Do
you have any comments on this and do you
feel that further change is unlikely?
A: I think there are more changes to come;
the industry has become a safer place to work in
but there is still some way to go to reduce
accidents further. Environmental legislation on
pollution (noise and waste) will lead to further
changes. Directives on working hours may well
lead to shift-working at more plants. I think that
the increasing scarcity of raw materials will lead to
the use of more recycled and marginal materials.
In addition, legislation on vehicle movements and
congestion charges will give us some more
challenges.
FACE TO FACEA personal interview with Jim Troy
Dr Jim Troy is a dynamo; constantly on the move andapplying himself to a variety of challenges presentedby the many involvements he has with concrete. He isHead of Concrete and Mortar Technologies with theTarmac Group, which is part of Anglo American plc andsplits his time between their offices in Ettingshall nearWolverhampton and London.
10
The introduction of new European standards
with their concept of conformity is a major
change that we will all have to address.
The consolidation of the ready-mixed concrete
suppliers and their suppliers of raw materials will
lead to changes in the way that concrete
producers view the product. We have recently
seen the growth of other products, concrete’s
rivals, and the industry will have to be much more
pro-active in promoting its services and products
in order to avoid further erosion of its market
share.
Q: You have a very busy work schedule,
with frequent trips away from base. What
drives you and how do you maintain the
impetus?
A: Being busy is what I enjoy. Luckily, I don’t
need a lot of sleep - I normally get up at about 5
a.m. and if I’m going to my own office, I get to
my desk for 6.30. I hate leaving jobs undone
and, on the whole, I enjoy what I do, even all the
travelling I have to do. Gardening is something I
detest, so I get someone else to do that for me. I
have always had the belief that next year will be
quieter and I will have more time. But, as we all
know, next year never comes.
Q: What other interests/positions do you
have in the world of concrete?
A: I am a member of several BSI committees
- cement, admixtures, mortar, screeds and
aggregates and chair the aggregates for mortar
one. Within Europe I sit on the CEN committee
on cement and have been the convenor of the
task group on cementitious screeds. Two QPA
committees take up some of my time, especially
being chairman of the concrete technical
committee. In addition there are the ERMCO and
MIA technical committees and the EMO technical
committee. Then there’s Britpave, where I have
served on council for many years, and as treasurer
for the last four. And finally, nine years on the
QSRMC Regulations review group since 1993.
There’s not a lot of time for anything else. I have
in the past held the post of regional treasurer and
chairman for the Concrete Society in the West
Midlands.
Q: What prevents technologies such as
SCC from advancing and being more widely
used?
A: I think that part of the problem is that
specifiers have too conservative an approach to
innovative products. This has not been helped by
materials suppliers who have not adopted a pro-
active approach to specification selling. As a
result, new technologies are offered as last-
minute substitutes rather than as a core part of a
solution. We must, as an industry, adopt a
unified industry-wide approach to the promotion
of new developments and firmly reject the
parochial attitudes which have sometimes ensured
that new innovations are not taken up; specifiers
and purchasers become confused and mistrustful
of the counter-claims made.
Q: How does the ready-mixed concrete
industry in the UK compare with its
equivalents overseas?
A: In many ways they are very similar. From
discussions within ERMCO, the European trade
association for ready-mixed concrete, it is evident
that we all face the same problems of dwindling
supplies of raw materials, competition from
alternative materials and environmental challenges
due to increased legislation.
Q: A few years ago the Institute
introduced the grade of Technician Member
and, so far, we have only 10 such members.
What is preventing further take-up?
A: I have difficulty in seeing the advantages
to technicians of becoming members; we offer
them very little. Historically, technician
membership of a professional institute was just a
step on the way to associate or corporate
membership but with the changes that have
taken place in higher education, only a small
percentage of individuals see a technician grade
of membership as being a stepping stone to
higher status.
Q: Does the ICT have a future? Do you
envisage any changes that need to occur to
keep it viable?
A: I hope it does! It does, however, need to
change. Initially it was more of a club, started by
those who had been on the first few ACT courses
run within the cloistered walls of Fulmer Grange
and who felt that the camaraderie and bonds of
friendship promoted by this experience should be
carried on. There are now many routes to full
membership, the ACT course is run at three
11
locations and those with ACT diplomas are in the
minority, so the early ethos no longer fully applies.
We are not alone in experiencing declining
membership - some of the largest Institutions are
facing similar problems.
Q: Do you have any interests outside
work or are you strictly a workaholic?
A: I enjoy reading, walking and photography
and, when I have time, I like cooking. As a
family, we have involvement with our local
church. A lot of my spare time is spent studying
on some course or other; I am currently struggling
to get my Latin back to a reasonable standard.
Playing the violin was a passion for many years
but that has gone by the board now, as has horse
riding, on which I was very keen in my younger
days.
Q: Finally, please tell me a little about
your family.
A: We have lived in the same house now for
eighteen years, in Worcestershire, which is a good
location for work and social activities. My wife is
very studious and has collected several degrees
including two from the Open University. As you
can then imagine, our 13-year old daughter is
also quite studious and very sporty. I suppose we
live a fairly average family life, although we don’t
have any pets.
12
13
The imageA Hollywood dramatisation of the birth of
Portland cement would doubtless depict a
contemplative Joseph Aspdin having a sudden
inspiration on the morning of 21 October 1824
before rushing off to the Patent Office to register
his invention. There is no doubt that Joseph
Aspdin did carry forward the concept of Portland
cement, at least establishing the name. Whether
his composition or processing capabilities
achieved the essential requirements for a true, if
early, version of Portland cement is unclear. Also,
it has been verified [4], that his son, William
(Figure: 1), using his father’s patent, did produce a
Portland cement-type material. It is certain that
the evolution of the modern material had its
origins many centuries before, and its refinement
continued for more than a century after, Aspdin.
The materialFor the past century specifications for Portland
cement [1] have been consistent in setting down
three essential requirements: the composition
shall consist of precise amounts of lime, silica,
alumina and iron oxide; the process shall ensure
that these are heated to the point of sintering, or
incipient vitrification, thus forming a clinker and
that the final product shall be a statistically
homogeneous powder. The origins of Portland
cement lie in the gradual understanding of these
principles and the development of processes by
which they could be achieved.
Ancient cementsThe true origin of Portland cement, namely the
development of binders based on calcium
silicates, is lost in early antiquity. Lime, produced
by firing limestone, was used as the basis of a
cement in Minoan and Greek civilisations. It is
more than likely that some of these limestones
had the basic composition to become Portland
cement but there was no understanding of the
basic science to take this forward. Such limes
were deficient in the essential calcium silicates
and aluminates and therefore the practice
developed of using them with active silico-
aluminate materials, the first mixer blends. Most
effective of these were found to be volcanic tuff
such as that on the island of Thera (now
Santorini). Roman engineers refined the art and
discovered similar properties in the volcanic dust
from the area surrounding Mount Vesuvius
naming it Pozzolana after the town of that area,
Pozzuoli. This name has remained and is
THE ORIGINS OF PORTLAND CEMENT. By Paul Livesey
The technology of cement based materials has been developing since the firstconcrete mix was produced. Much of this technology was further improved withtime but much was forgotten (sometimes to be later ‘reinvented’). Somedevelopments have been accidental, such as the discovery of the benefits of airentrainment. Some have been the result of foresight and endeavour, or commercialgain, whilst some have been born of necessity such as those for military andstructural reasons.
This series of articles - ‘Milestones in the history of concrete technology’, willinclude some of the more important steps which the science of materials has taken.Later papers may include the work of pioneers such as Vicat, Hennebique andPowers; the early use of admixtures; the work of the Cement and ConcreteAssociation; no fines concrete and the advent of precast buildings.
This third paper in the series details the origins of Portland cement.
MILESTONES IN THE HISTORY OF CONCRETE TECHNOLOGY
Figure 1: William Aspdin, the firstauthenticated producer of ‘Portlandtype’ cement.
14
nowadays used to embrace all materials
containing silica and alumina capable of being
activated by lime to form calcium silicate
(aluminate) hydrates.
Roman engineeringThe Romans may not have understood the
hydration mechanisms but they had a pragmatic
and efficient approach. Vitruvius [2], a Roman
engineer and architect, provides in his classic
work ‘De Architectura’ much evidence on the
state of the art of using limes and pozzolanas. He
extended the pozzolana sources to the use of
crushed, well-burnt brick or tile stating that if “...
potsherds ground and passed through a sieve, be
added in the proportion of one-third part, the
mortar will be the better for its use”. Nevertheless
he perpetuated the myth proposed 200 years
earlier by Cato [3] that “only the whitest and
hardest stone should be used (to make building
lime)”. There was no conception at this time that
all of the active constituents, lime, silica and
alumina, could be found in one material by the
burning of argillaceous limestone.
The Dark AgesThe state of the art stagnated for many
centuries after the Romans. They had
disseminated their skills to all parts of the Empire
as is evidenced by the many fine examples
remaining. In England there are many examples of
Roman cemented brickwork, mostly incorporating
in the mortar ground tile or brick, but in some
cases pozzolana, probably Dutch Trass, is
reported [4]. With the fall of the Roman Empire the
art was gradually lost from the margins although
some centres of scholarship remained and even
occasionally progressed. Hence Palladio [5] repeats
the version according to Vitruvius that “the
hardest, whitest and heaviest stone produces the
best lime” but goes on to describe what must
have been hydraulic lime produced in the hills of
Padua which “when burnt and mixed as mortar,
hardens immediately and is very suitable for use in
water or for work exposed to the weather”.
John SmeatonThe first significant evolutionary step towards
hydraulic cement was taken by John Smeaton in
1756. An English engineer engaged in the
reconstruction of the fire-ravaged wooden
structure forming the Eddystone Lighthouse, he
sought more durable materials. In order to
cement together his stone construction he
required a mortar setting quickly and hardening
under water. He undertook a series of
experiments which, although unremarkable in
themselves, by deducing the underlying
mechanism achieved the first scientific advance in
the understanding of calcium silicate cements.
Armed with a basic understanding of geology and
acquiring rudimentary chemistry sufficient to
determine acid insoluble fractions (he termed
‘clay’) in limestone he undertook an exhaustive
survey of British limes.
Far from following the traditional adages of
whiteness and hardness for preferred limestone
he deduced that the power of setting under
water relied on the clay content of the original
limestone. He determined that lime produced
from chalk was no different to that from hard
Plymouth marble but that both were inferior to
the Blue Lias lime of Aberthaw. He also
determined that the White Lias lime of Watchet
contained an equal amount of clay and despite its
lighter colour produced an equivalent lime to that
of Aberthaw. His survey confirmed the hydraulic
nature of Dorking and Halling limes, then being
sold in London as ‘Stone limes’ as a means of
overcoming the prejudice against them arising
from their grey colour. The principle was further
confirmed in examination of Sutton, Lancashire,
lime preferred by the Duke of Bridgewater for his
canal works. The colour issue was further
discounted in relation to the ‘Clunch’ lime of
Lewes, favoured for its hydraulicity, demonstrating
that its buff colour and activity related to the clay
content. This latter, occurring in thick beds, also
discounted a further theory that only limestones
with thin bedding were suitable for hydraulic
lime.
Smeaton only published details of his work [6]
some 30 years later but it is apparent from other
workers in the intervening period that his ideas
were widely known. He had overthrown the
perceived knowledge of two millennia. Perhaps
there are limits to the size by which quantum
steps in knowledge can usefully advance but it is
interesting to speculate on what his conclusions
might have been had his understanding of clay
chemistry been greater. His classification of
limestones by clay content, Table 1, provided a
route for further work.
Smeaton’s test method for determination of
hydraulicity is not claimed to be novel but is one
of the first quality control tests to be reported. He
placed the lime on the flat bottom of a pewter
plate, added just enough water to wet it and
worked it into a paste before adding other
15
constituents in stages whilst continuing to work
the mortar. The whole was combined into a ball
of approximately 2 inches diameter, allowed to
stand until sufficiently set to resist finger pressure
before storing under water. The development, or
loss, of strength thus stored was taken as a
measure of hydraulicity. By this means he arrived
at his eventual formulation for the Eddystone
mortar being equal parts of Lias Lime and Italian
Pozzolana.
John ParkerShortly after the publication of Smeaton’s
work, James Parker of Northfleet, Kent, was one
of a number of workers to take out patents for
cement based on the burning of mixtures of
limestone and clay. Although there are no
contemporary details later writers [7] were of the
opinion that Parker’s work displayed a knowledge
of chemistry above that of previous workers. By
experimenting around the formulations reported
by Smeaton he developed a product that was to
dominate construction for the first half of the
nineteenth century. He discovered that certain
rock nodules in the gravels of the Kent coast,
particularly around the Isle of Sheppey, when
burnt in a lime kiln gave a superior hydraulic
cement. These rock deposits consisting of
limestone veins in a clay base, termed septaria,
were to be found in large accumulations wherever
the London clay series and the underlying chalk
formed the shoreline. His analysis of septaria is
given in Table 2.
Initially termed ‘Parker’s’ cement, patent No.
2120 was granted on 27th July 1796 entitled
“Patent for making a certain Cement or Tarras, to
be used in aquatic or other Buildings and for
Stucco Work”. Later Parker described this cement
as ‘Roman’ cement in a pamphlet to promote its
use [8]. The misleading name came from a belief
that the colour approximated to that of remnants
of Roman mortar and intended to imply a
discovery of some ancient Roman art.
Nevertheless it was the most hydraulic material
discovered to that time and in any building or civil
engineering work carried out between 1810 and
1850 whenever the term ‘cement’ was used it
was understood to mean Roman cement.
Although this composition was now close to
that necessary for Portland cement production the
key element of burning temperature was
intentionally kept below sintering point since the
Limestone sourceClay content(% w/w)
Dorking grey, Sussex 6
Buriton, Petersfield, Hampshire 8
Chalk, Guildford, Surrey 10
White Lias, Watchett, Somerset 12
Blue Lias, Aberthaw, Glamorgan 13
Lias limestone, Long Bennington, Lincolnshire 14
Clunch limestone, Lewes, Sussex 19
Sutton limestone, Lancashire 19
Barrow limestone, Leicestershire 21
Table 1: Limestone clay contents determined by Smeaton
ConstituentProportion(% w/w)
Calcium carbonate 66
Magnesium carbonate 1
Iron oxide 6
Manganese oxide 2
Silica 18
Alumina 7
Table 2. Analysis of septaria nodules used for Roman cement
16
perceived wisdom from lime burning was that any
vitrified material was worthless and to be
discarded. However, another development came
with the description of the finishing process
which included grinding, screening and packing
into casks. Hence two of the three essential
criteria for Portland cement had been developed:
composition and homogeneity.
Roman cementsThe significance of Roman cement in the life of
the early nineteenth century can be judged in that
in 1845 Sir Robert Peel announced in Parliament
his intention of taxing cement stone, fearing its
exhaustion and hoping to reserve a supply for
Government work as well as to generate income.
This measure did not progress since, by then,
Portland cement was becoming established and
would shortly supersede Roman cement.
Nevertheless the production of Roman cement
had spread from Sheppey to the Essex coast
around Harwich and to Felixstowe on the other
shore. Over a million tonnes had been removed
from the shoreline and the business turned to
dredging for deposits on the seabed, most
profitably at West Rocks, off Walton-on-the-Naze.
At its peak over 300 smacks were engaged in this
work and cement production was centred at
Harwich, in addition to the original location on
the Kent riverside and even into London. The
Sheppey material was considered to be superior
to that of Harwich and it was customary for
general quality cement to combine one fourth
Sheppey to three fourths Harwich.
Other cements of the ‘Roman’ type began to
be introduced with Atkinson establishing
production using similar nodules found on the
Yorkshire coast near Whitby. Similar deposits were
found throughout Europe such as on the
Boulogne coast of France, at Matala in Sweden,
Argenteuil near Paris and Pouilly in Burgundy. All
of these relied on natural deposits to provide a
suitable chemical composition and all relied on
traditional lime burning temperatures.
Louis Joseph VicatDuring the time Roman cements were
developing in England there was also considerable
interest in France. Louis Joseph Vicat had
established an expertise in road and bridge
construction which led him to investigate the
relative merits of his national limes. In 1818 he
reported [9] the results of his work over the
previous six years. He considered the properties of
the different kinds of lime and limestones, the
calcining process and various methods of slaking.
He was aware of the work of Smeaton but it
should be remembered that this was a time of
considerable political upheaval generating a
degree of competitiveness. He was doubtless
influenced also by French workers [10] such as
Baron Louis Bernard Guyton de Morveau, J B
Vitalis, Collet Descotils and Jean Rondelet who
had established detailed information on the
composition of limestones as well as techniques
of burning and slaking.
Vicat published a second report in 1828 [11]
continuing the work of the previous one so that
the two can be considered as a joint work. He
considered that hydraulic lime was the superior
binder and that Roman cement advocates would
be persuaded if they could have access to quality
hydraulic limes, an unusual lack of objectivity on
his part at this time. He demonstrated that poorer
Table 3. Composition of ‘cement stones’ for the manufacture of Roman cements
Composition Sheppey Sheppey Southend Yorkshire HarwichNo. 1 No.2
Water - 3.0 - - 3.9
Carbonic acid 31.0 29.0 29.8 31.0 22.8
Lime 30.2 35.0 34.1 30.5 29.2
Silica 18.0 17.8 12.0 24.0 9.4
Alumina 3.1 6.7 13.0 6.7 9.5
Magnesia 0.2 0.5 1.5 1.0 -
Oxide of iron 5.3 6.0 8.8 1.3 17.8
Oxide of manganese 6.7 1.0 - - -
Sulphate, soda, etc - - - - 7.5
Loss 5.5 1.0 0.8 5.4 -
17
quality hydraulic limes could be improved by re-
calcining with a suitable quantity of added clay.
This appears to be the first commercial
exploitation of the work of Smeaton.
Vicat’s improved process required the burning
of the lime, slaking it in air, mixing with water
and the requisite amount of clay, forming the mix
into balls which were then dried before re-
calcining. He progressed to a less expensive
process; he mixed soft chalk to a paste, mixed
that with clay before drying and calcining as
previously. This latter route was the basis for the
formation of a major works set up by Messrs.
Bryan and St Leger at Meudon, near Paris. It used
the chalk of that region with the clay of
Vaugirard. The intention of Vicat remained to
produce a superior hydraulic lime rather than an
artificial or Roman cement as was the route
developing in England.
He was the first to apply scientific methods to
test methods and developed an apparatus for
testing the setting time consisting of a needle,
0.12 cm in diameter, filed square at the end and
loaded with a weight of 3 kg. (Figure 2). The lime
was considered to be set when it could bear the
weighted needle without forming a depression.
He devised an impact test to determine mortar
hardness whereby a steel stem, measuring 1.66
mm diameter at the base, loaded with a weight
of 0.9961 kg, was allowed to fall a height of 5
cm onto the surface of the hardened mortar.
The hardness was determined from the depth
of penetration.
Another test involved a mortar prism, held
down within platens supported on a stand, a
stirrup passed over the upper platen to which a
hook was attached and from which was
suspended a box. Sand was run into the box until
the point of failure, when the weight of the
attachment plus sand gave a measure of
compressive strength (Figure 3).
These tests formed the basis for his
classification system for building limes which has
lasted until the present day and served as a base
for many of our modern test methods. His system
for determining the chemistry of limestones and
clays and the ways in which they might be
combined to form a hydraulic binder pre-dated,
and possibly formed the basis for, the final stage
in the origin of Portland cement.
Vicat continued to work on limes, pozzolanas,
natural cements and, eventually, Portland cement.
Once the true composition of hydraulic limes and
cements became known he was commissioned by
the Administration des Ponts et Chaussès to
determine the location and investigate the
chemical composition of limestones throughout
France. His work took from 1824 to 1845 by
which time nearly 10,000 samples from seventy-
nine regions had been classified and catalogued.
Edgar DobbsProgress on cements had continued across the
Channel where Edgar Dobbs had taken out a
patent in 1811 whereby he claimed to produce a
cement by calcining a mixture of chalk and
various clays, loams, slate, road dust, etc. His
Figure 2: Penetrometer to test mortarhardness
Figure 3: Compressive strength test formortar
Mortar sample
Box for accumulated sand
Sand hopper
18
knowledge seems not to have approached that of
Vicat but it was another development of the work
of Smeaton. As with others steeped in the lime
tradition he was careful to avoid temperatures
approaching sintering.
James FrostJames Frost carried out experiments with lime
mixtures and had some success in producing from
chalk and calcined flint a white hydraulic lime he
termed ‘British Marble’. This proved to be too
expensive for its intended market for stucco work.
His second venture was developed after a visit to
Vicat and lead to his patent No. 4679 of 10
August 1822 for a ‘British Cement’. This was
based on the Vicat processing of chalk and clay
mixtures, the cheaper option having been
doubtlessly pursued following the commercial
difficulties with ‘British Marble’. He established a
works at Swanscombe, Kent, in 1825 and traded
there until 1837 when it was taken over by
Messrs. Francis, White & Francis. Still the burning
temperature was controlled below sintering point.
The performance could not match that of Roman
cement although it was improved following
consultation with Charles Pasley when the clay
source was switched to material from dredging at
the mouth of the Medway. In the opinion of
Pasley [7], Frost’s mix lacked the necessary amount
of clay. He had, however, carried forward the
processing technology by introducing a blending
of chalk and clay to give a homogenous mixture
before the calcining process.
Charles PasleyMajor-General Sir Charles William Pasley KCB
FRS, as he was eventually to become, was
appointed director of the Royal Engineers
Establishment at Chatham in 1812 and retained
that position for thirty years. He developed an
interest in limes during service in India and
extended that to the application of the latest
science to the hitherto art of lime, cement,
mortars, concretes and construction. He was
instructed in 1826 by the Duke of Wellington to
set up training in practical architecture for officers
attending the Establishment and published reports
and manuals [7] that were adopted by the British
Army throughout the Empire for much of the
nineteenth century. His small scale experiments
with raw mixtures of chalk with clay, tile dust,
slate and Fuller’s earth led him to the conclusion
that intimate mixtures of finely ground raw
materials were essential to success. Although only
small amounts of material could be burnt in his
experimental kiln at Chatham it was sufficient to
confirm that a cement equal in hydraulicity to the
best Roman cement of the time could be
prepared by mixing separate raw materials. He
also estimated that, if produced on a commercial
scale, they could be 25% cheaper. His opinion
was abundantly verified by subsequent
developments, as was his opinion that the blue
clay of the Medway was the ideal material to be
combined with chalk.
His work included reports of the tests to which
hydraulic cements were subjected at that time.
They were far more engineering based than were
those of Vicat and generally involved the bond
strength of mortar to brickwork. At the start this
consisted of production of a simple brick column
of London Stock bricks jointed with a mortar of
one part hydraulic lime to three parts sharp sand.
The column was laid horizontally, supported in
two places and was loaded in the centre to failure
(Fig. 4). This was further elaborated to the testing
of cantilever beams (Fig. 5) and further refined
(Fig. 6) by the eminent engineer Brunel who built
semi-arches to justify his reinforced masonry arch
designs for the new London Bridge.
Figure 4: Simple masonry beam for load test
Figure 5: Cantilever masonry beam testfor mortar
Mixture C 4 B 5, 31 Bricks.
Length 6’ 111/2“, Weight 186 lbs.
C B, 21 Bricks
C 3 B 4, 28 Bricks.
Length 6’ 5“, Weight 171 lbs.
Length 5’ 101/2“, Weight 160 lbs.
C 2 B 3, 26 Bricks.
Length 4’ 8“, Weight 128 lbs.
19
Joseph AspdinThe development comes full circle to Joseph
Aspdin and his son William. Joseph, a bricklayer
of Leeds, is said to have been experimenting with
the manufacture of a cement as early as 1813. He
obtained the historically significant patent No.
5022 dated 21 October 1824, described as
“An Improvement in the Modes of Producing
an Artificial Stone”
“My method of making a cement or artificial
stone for stuccoing buildings, water works,
cisterns, or any other purpose to which it may be
applicable (and which I call Portland cement) is as
follows: I take a specific quantity of limestone,
such as that generally used for making or
repairing roads, after it is reduced to a puddle or
powder, or the limestone, as the case may be, to
be calcined. I then take a specific quantity of
argillaceous earth or clay, and mix them with
water to a state approaching impalpability, either
by manual labour or machinery. After this
proceeding, I put the above mixture into a slip
pan for evapouration either by the heat of the
sun or by submitting it to the action of fire or
steam conveyed in flues or pipes under or near
the pan, until the water is entirely evaporated.
Then I break the said mixture into suitable lumps
and calcine them in a kiln similar to a lime kiln till
the carbonic acid is entirely expelled. The mixture
so calcined is to be ground, beat, or rolled to a
fine powder, and is then in a fit state for making
cement or artificial stone. This powder is to be
mixed with a sufficient quantity of water to bring
it into the consistency of mortar, and thus applied
to the purpose wanted.”
It is significant that the patent does not
mention the proportions of clay and limestone to
be used. The patent also states that calcination
should be taken until the entire expulsion of
carbonic acid with no suggestion of sintering.
Whether these deficiencies demonstrate that
Joseph Aspdin never produced a Portland type of
cement, as is often stated, or whether he was
eliberately secretive fearing immediate copying,
will never be known. What is clear is that he was
the first to register the name ‘Portland cement’ as
applied to an hydraulic cement and this on the
basis that he considered the colour of his cement
to be similar to that of the stone quarried at
Portland. It is also known that his cement had
superior properties to that of Roman cement. This
is verified since his cement, then produced at
Wakefield, was chosen by Brunel to complete his
Thames Tunnel. It is even claimed [12] that Aspdin’s
cement was the saviour of a beleaguered project
delayed by repeated floodings. On the occasion of
one of these Brunel ‘dumped’ tons of Aspdin’s
cement into the river. This sealed the breach and
allowed the tunnel to be pumped dry. Aspdin’s
cement was used for the re-lining and subsequent
successful completion of the construction.
After the death of Joseph Aspdin in 1855 his
son, James, continued the production at
Wakefield, Yorkshire, on a site close to the
original following a move necessitated by the
construction of the Lancashire and Yorkshire
Railway.
William AspdinThe other son, William (Fig. 1), became
associated with Messrs. Maude, Son & Company
of Rotherhithe, Kent, who in 1843 issued a
circular in which they stated that they had made
arrangements with the son of the patentee for
the manufacture of Portland cement. This was
shortlived as in 1848 William established a
cement works at Northfleet, Kent, trading as
Robins, Aspdin & Co. William also commenced
the building of an extravagant house near
Gravesend. Whether it was the building or
business difficulties is unclear but there was a
disagreement between the partners and he left to
establish a new works in a disused corn mill at
Gateshead on the Tyne.
Further disagreements caused him to leave
England and eventually become associated with
the building of the Luneburg Cement Works in
Germany where he died following a fall in 1866.
Figure 6: Brunel’s trial reinforced masonry semi-arches
20
Confirmation that he did employ a temperature
sufficient to cause sintering is provided by Robert
Blezard [4] . Blezard reported that examination of
the microstructure of ‘preserved’ cement made by
William Aspdin at Northfleet confirmed the
presence of tri-calcium silicate, only to be found
in material heated above sintering temperature.
The cement had a microstructure consistent with
slow cooling as would take place in a batch
production process.
Neither William, nor his father, had any formal
chemistry training yet by ‘rule of thumb’
techniques, and probably accidental incorporation
of fused material hitherto rejected as waste, the
birth of the modern cement was achieved.
Isaac Charles JohnsonIt was left to another to unravel the
fundamentals of the material and the process so
that the manufacture of Portland cement could be
placed on a sound scientific base. Isaac Charles
Johnson took up employment with Messrs. Francis
& White in their Roman cement works at Nine
Elms, London, where his father worked as a
foreman. He gained experience in all departments
of the business after which he served a four year
apprenticeship with a London builder. He worked
for some time with an architect before rejoining
White as manager of a works established by him
at Swanscombe. There they manufactured Roman
cement, plaster of Paris and Frost’s artificial
cement. At this time Aspdin’s cement was
beginning to overtake Roman cement and, as
White failed in an attempt to join with Aspdin,
they determined to develop their own product.
Attempts to gain direct access to Aspdin’s works
or secrets were thwarted by Aspdin’s security
which included a high perimeter wall, non-
disclosure to any workmen and the practice of
personally supervising the charging of the kiln
including carrying in a tray of various substances
“essential to the process” before burning
commenced.
Johnson resorted to obtaining a sample of
Aspdin’s cement and subjecting it to analysis.
Whether the sample was spiked, an incompetent
analyst or the results deliberately changed is
unknown. It is known that the analysis revealed
45 % phosphate of lime and that Johnson wasted
a considerable time in securing supplies of bones
from local butchers and undertaking trial burns
destined to failure. Further samples and more
reliable analyses allowed Johnson to embark on a
more successful series of experiments using local
chalk and the clay then employed in the making
of Frost’s cement. The result was a product which
partially clinkered. Although he had learned from
consultations with Pasley that clinkered material
could not be slaked and should be scrapped he
persisted, ground it and gauged it with water only
to find that it did not seem to harden or give off
heat. He further experimented with mixtures of
the powdered clinker and more lightly burnt
product and found this to set and harden.
However, on examination some days later he
discovered that the mortar made from clinker
alone was much harder than any of the mixtures
and had an attractive dark grey colour.
He developed his formulation and established
its chemistry which concluded with a mix of 5
parts chalk to 2 parts Medway clay. This gave a
result so satisfactory that in the first year
hundreds of tons were made, some of it going to
the French Government works at Cherbourg
Harbour where it was held up as the standard for
quality of subsequent supplies.
The rest, as they say, is history. Johnson
progressed to set up other works, first near
Rochester, then at Cliffe on the Thames. He took
over Aspdin’s abandoned works at Gateshead and
established a large works on the Thames at
Greenhithe, later to become part of the British
Portland Cement Manufacturers. This latter was
not without its problems in getting established
since, although there were no formal planning
regulations at the time, local residents took the
company to law and gained an injunction
stopping production. Remarkable scenes followed
as cement workers for miles around rallied and
held a protest march some 4-5000 strong in
favour of “Success to all Cement Manufacturers”
and “Live and let work”. In the end Johnson hadFigure 7: Isaac Charles Johnson, the firstto understand Portland cement
21
the inspiration to solve it by environmentally
friendly means by patenting and building a
massive 300 feet chimney “to manufacture
without giving cause to anyone in the
neighbourhood”. A fitting tribute to the first man
who personally unravelled the secrets of Portland
cement and carried them through to continuous
production.
References
1. BS EN 197: Part 1: 2000. Composition,specification and conformity of commoncements, British Standards Institution,London.
2. De Architectura, Book II, Vitruvius Pollio, M,circa 10 AD.
3. De De Rustica, Cato Marcus, P, circa 200 BC.
4. Lea’s Chemistry of Cement and Concrete,Hewlett, P C, editor, Chapter 1 History ofcalcareous cements, Blezard, R G, 4th
edition, Arnold. London, 1998.
5. I Quattro libri dell Architectura, Palladio,Andrea, Venice, 1570.
6. A Narrative of the Building and aDescription of the Building of the EddystoneLighthouse with stone. Smeaton, J, Printedby Hughes, Sold by Nicol, London, 1791.
7. Limes, Calcareous cements, mortars, stuccosand concrete, Pasley, C W, John Weale,London, 1838.
8. Parker’s Roman Cement, Thurston, A P,Paper to Inst. of Mech. Eng. London, 1939.
9. Recherches expérimentales sur les chaux deconstruction, les bétons et les mortiersordinaries, Vicat, L J, Annales des Ponts etChausses, Paris, 1818.
10. Some Writers on Lime and Cement fromCato to present time. Spackman, C, Heffer,Cambridge, 1929.
11. Résumé des Connaisances positives actuellessur les qualities, le choix et la convenancéréciproque des materiaux propres à lafabrication des mortiers et ciments calcaires.Vicat, L J, Paris, 1828, translation Smith, J T,Capt., John Weale, London, 1837,reprinted, Donhead, 1997.
12. The History of Blue Circle. Pugh, P,Cambridge Business Publishing, 1988.
22
23
ANNUAL CONVENTION SYMPOSIUM: PAPERS PRESENTED 2002
PAPERS: AUTHORS:
A major part of the ICT Annual Convention is the Technical Symposium, where guestspeakers who are eminent in their field present papers on their specialist subjects. Each yearpapers are linked by a theme. The title of the 2002 Symposium was:
CONCRETE IN THE CITYChairman: Professor Chris Page, Leeds University MA, PhD, MIM, FICE, HonFICT
Edited versions of the papers are given in the following pages. Some papers vary in writtenstyle notwithstanding limited editing.
CANARY WHARF - PROJECTS PAST, Mr. D.M. Wetherill BA, I Eng, AMICE, FIQA, FICTPRESENT AND FUTURE Canary Wharf Contractors Ltd
STRUCTURAL DESIGN OF HIGH-RISE Mr. J. Crack BSc (Hons), MICE, MIStructE, MSM, MBACONCRETE STRUCTURES Canary Wharf Contractors Ltd and
Mrs H. Stanley BSc DIS, CEng, MICEYolles Partnership Ltd
THE PRACTICAL DESIGN AND Mr. J.W. DayPRODUCTION OF HIGH STRENGTH Hanson Premix plcCONCRETE (A COMPARISON OF CASE HISTORIES)
THE ST GEORGE WHARF DEVELOPMENT Dr. R. Moss BSc, PhD, DIC, CEng, MICE, MIStructE- BACKGROUND, RESEARCH Centre for Concrete Construction, BRE Ltd and AND CONSTRUCTION Mr. M. Stephenson
Stephenson Construction Ltd
THE DURABILITY OF CONCRETE Dr. D.W. Hobbs BSc, PhD, CPhys, FInstPConsultant
NEW ADMIXTURE TECHNOLOGIES: Mr. J.C. Payne BSc, CEng, MIM, FICTAN UPDATE Consultant
DECORATIVE CONCRETE Mr. S. Walton FIHT, FICTPieri UK Ltd
SELF-COMPACTING CONCRETE Mr. R. Gaimster BEng, CEng, MICE, MICTRMC Readymix Ltd and Mr. N. DixonRMC Readymix Ltd
SELF-COMPACTING CONCRETE Mr. P. Goring MSc, BSc(Hons), ACGI, CEng, MICE- A CONTRACTOR’S VIEW (ABSTRACT) John Doyle Construction
CONCRETE FINISHES OFF-THE-FORM Mr. G. Talbot Dipl. Arch RIBA I, II & IIIIan Ritchie Architects
STREETSCAPE CONCRETE Mr. D.A. Morrell BSc, MIHTMarshalls Mono Ltd
CONCRETE’S INCREASING Mr. J. McCabeFLEXIBILITY IN THE 21ST CENTURY Lafarge Cement UK
THE SURFACE REGULARITY OF FLOORS Mr. T. Hulett BSc(Hons), MICTAND CONCRETE IMPLICATIONS The Concrete Society
24
25
Mike Wetherill is Senior Quality
Manager for Canary Wharf
Contractors Limited. Because
of his previous experience with
the concrete industry, he has a
particular responsibility for the
technical aspects of the concrete supply to the
Projects.
ABSTRACT Canary Wharf is a major development in East
London which, because of the scale of
development and the relatively short programme,
has presented a variety of logistical and
technical challenges. Canary Wharf Contractors
Limited (CWCL) are the Project Managers
responsible for the management of the design
and construction of the buildings and
infrastructure. As part of the strategy, CWCL have
arranged for a readymix concrete supplier to set
up dedicated concrete plants on site. The benefits
of this have been technical, environmental,
logistical and in terms of quality.
KEYWORDS Canary Wharf, concrete supply, logistics,
pumping, high strength, quality, environment
INTRODUCTIONTo a large extent, this is a descriptive paper
about the work at Canary Wharf. It divides into
three main topics:
Canary Wharf and the Projects
The arrangements for concrete supply
A number of technical issues relating to the
materials and the construction.
CANARY WHARF DEVELOPMENTCanary Wharf is situated on the Isle of Dogs in
East London. It is part of the West India Docks,
which were opened in 1802 and considered to be
the country’s greatest civil engineering structure
of its day. The London docks reached their peak
of activity in 1961, but trade later declined as a
result of containerisation and new technology.
The West India Dock closed in 1980. In 1982 the
Isle of Dogs became an Enterprise Zone and in
1987 a master building agreement was signed
between the developer, Olympia & York, and the
London Docklands Development Corporation.
Canary Wharf Contractors Ltd was set up to
carry out the project management for design and
construction of all the buildings and
infrastructure.
The first phase of the development took place
between 1988 and 1992. Construction during
these four years was intense and included One
Canada Square and the buildings to the West
around Cabot Square and Westferry Circus. On
the transport side, the station for the Docklands
Light Railway (DLR) was completed and opened.
From 1993 to 1996 there was a lull in the
construction programme, but during this time
there was a steady growth in the occupancy of
the completed buildings and in 1997 the next
phase of development began. This includes the
other buildings around Canada Square and the
buildings at Heron Quay. Tenants for these
buildings are signed-up before construction
begins. The majority of the buildings are offices
but to make a mixed and viable development
there are three retail areas (shops and restaurants)
a number of parks and open spaces, estate roads,
car parks and footpaths. Although some water
area has been reduced by the cofferdams, the
waterscapes are still a very important feature. In
1997 the working population of the occupied
buildings (the Phase 1 buildings) was around
21,000. When the Phase 2 buildings are occupied
in 2004 the working population will rise to over
90,000. Meanwhile, transport links were further
improved when London Underground opened the
Jubilee Line Extension from Westminster, via
Canary Wharf, to Stratford.
Future projects are a continuation of existing
work. The buildings at Churchill Place have
started with the new headquarters for Barclays
Bank, now at the stage of piling. At the same
time the basement for another building and retail
area will begin, plus bridges to link to the
remainder of the estate. On the north side of the
estate, design work has started for the buildings
at North Quay (Shed 35) so the concrete plant
will have to move site again. At the west end of
the estate land is available for future
development. As a further improvement to
transport, Canary Wharf Group is heavily involved
CANARY WHARF - PROJECTS PAST, PRESENT AND FUTURE
Mr. D.M. Wetherill. BA, I Eng, AMICE, FIQA, FICT
Canary Wharf Contractors Ltd
26
in the proposed Crossrail link which will provide a
direct rail linkage from Heathrow via the West
End and City to Canary Wharf.
CONCRETE SUPPLYThe development of Canary Wharf has been in
two phases, approximately 1988 to 1992 and
then 1997 to date and ongoing. During both
phases the project was supplied from on-site
dedicated concrete plants. In the first phase the
plants were supplied and operated by RMC Ltd.
In the current phase the plants are supplied and
operated by Hanson Premix Ltd. I will talk mainly
about the current arrangements.
CWCL decided at an early stage that it was
crucial to supply the bulk of the concrete from
dedicated plants on site. This helps to ensure
continuity of supply, which would otherwise be
susceptible to traffic delays during peak rush
hours. The other important consideration is that it
also reduces the impact of the construction work
on the local roads and environment. The majority
of concrete materials (aggregates and most of the
cement) are brought to the plants by barge. Last
year for example approximately 150,000 m3 of
concrete was supplied from the site plants saving
around 27,000 truck movements, and 280,000
tonnes of aggregate was delivered by barge
saving around 15,000 truck movements.
Hanson set up the first plant in July 1999, on
one of the unoccupied building plots, DS3. It is a
Steelfield plant with twin pan mixers and an
Alkon system to give computer control of
production and full print-out of records. The
printouts show the target weights and the actual
weights for every batch of concrete and highlight
any deviations. This is a significant control feature
for Hanson, their customers and CWCL.
In December 2000 the concrete plant had to
vacate DS3 site to make way for a building. As all
land space was now needed for construction,
the plant was relocated onto a pontoon, 80
metres long by 20 metres wide, big enough to
take the plant plus bins, silos, and trucks. By
careful design of the plant, it is possible to have a
“drive-through” system which is essential to
achieve the production rates required. Even so,
more production capacity was needed so a
second plant was set up in mid-2000. By then
another piece of land had been acquired at Shed
35 and Hanson brought in another plant, again
Steelfield with Alkon control system. Backing up
the site plants are Hanson’s permanent plants at
Stratford and Blackwall. Apart from concrete
volumes, the other reason for so many plants is
to cover the range of mixes and materials.
Virtually every day Hanson has to supply concrete
with:
• marine gravel for the “normal” mixes up
to C40
• limestone coarse aggregate for the C50
and C60 mixes
• Lytag for the lightweight concrete floor
slabs.
TECHNICAL ISSUESThe typical structure of a building at Canary
Wharf is:
• A thick basement raft slab on deep bored
piles
• 4 levels of reinforced concrete basement
up to street level
• Reinforced concrete cores to the full
height of the building
• Steel floor beams and perimeter steel
columns with fire protection
• Floor slabs comprising lightweight
concrete on metal deck
• The whole building enclosed with
cladding.
Much of the technology is standard but a few
technical items have needed special
consideration.
Raft slabsThe raft slabs can be 3 metres thick or more,
of C40 concrete, with large pours around 3000
m3 taking approximately 18 hours.
Typical specification requirements initially
included a maximum temperature of 65˚C with a
maximum temperature gradient of 20˚C between
different locations in the pour. The limitation on
peak temperature was to minimise the risk of
delayed ettringite formation (DEF). As some of
the slabs were poured in the summer months this
was quite an onerous requirement, even with a
pfa/PC blend. In discussion with the design
consultants and with advice from BCA and Blue
Circle, some relaxations have been agreed:
• the compliance age for concrete strength
was changed to 56 days, permitting a
lower cement content
• recognising the beneficial effects of the
pfa, and the relatively low C3A and alkali
contents of the cement being used, the
peak temperature limit was raised to 70˚C.
27
The temperature gradient was also redefined
to limit it to 20˚C across the section locally, or
12˚C per metre of separation between points of
measurement. Comprehensive temperature
monitoring takes place and the Contractors are
able to comply with these requirements.
High rise concrete pumpingSome of the concrete mixes have to be
pumped to heights of 200 metres and more.
While by no means a world record, this still
requires careful choice of mix design and
equipment. Having on-site concrete plants is a
great advantage to ensure regular delivery and
avoid workability loss.
For the floor slabs the lightweight concrete
contains Lytag coarse aggregate, imported from
Poland. From previous experience we know there
can be a problem of workability loss caused by
water being forced into the lightweight particles
during pumping to the higher levels. By
arrangement with Hanson, Lytag transport the
material by boat from Poland to Dagenham
where it is transhipped to barges for delivery to
the site plants. On delivery, the material in the
barges is levelled out and ponded with fresh
water for at least three days, to bring the ssd
moisture content to around 22 to 24%.
Jumpform and slipformOther areas of technical interest include the
construction of the cores by either jumpform or
slipform. Both of these construction methods are
standard technology, nevertheless the
management and logistic skills needed to carry
out the scale of work within a limited area and a
tight programme is challenging. From the lessons
we have learnt, we can now specify and achieve
a dimensional tolerance of ± 25 mm over the full
height of the cores, for concrete surfaces and any
openings. The taller buildings have to be
designed to accommodate axial shortening
during construction.
Higher strength concreteThis is covered in detail in a separate paper.
For background, the highest strengths typically
used to date have been C60, in the core walls
and columns. For the future buildings, some
higher strengths may be used so Hanson have
carried out a range of mix designs and trials up to
C100. To ensure we have “realcrete” rather than
“labcrete” the trials have recognised that we will
need high workability, and good workability
retention.
Concrete testingCWCL agreed that Hanson could offer to
Contractors a service whereby Hanson would
arrange for all compliance tests of cube strength.
Hanson technicians take samples of concrete at
the delivery point, witnessed by the Contractor.
The samples are transported the short distance to
the test lab on site, where the cubes are made
and stored awaiting collection. The testing is
carried out by a UKAS-accredited test lab, who
issue test certificates direct to the Contractors,
Consultants, CWCL, Hanson and the Local
Authority. CWCL representatives monitor the
whole arrangement. On other projects if there is
a low strength test, arguments can arise between
the concrete supplier and the testing regime
about the validity of the test. This arrangement
has been very successful in avoiding such disputes
at Canary Wharf.
CONCLUSIONThe construction work at Canary Wharf has
been challenging. Concrete has been used
extensively, and we have benefited from an early
strategic decision to make use of dedicated on-
site concrete plants, installed and operated by a
readymix supplier. We have then further
benefited from a close and co-operative working
relationship with the supplier and Contractors in
order to solve the logistical and technical
challenges that arise.
28
29
John Crack is Senior Design
Manager at Canary Wharf
Contractors Ltd., responsible
for the structural design
aspects of Canary Wharf’s
many current and future
buildings. Mr Crack has worked for leading
structural design consultancies in the UK, Africa
and S.E. Asia. He is a Member of the Institution
of Civil Engineers and the Institution of Structural
Engineers, and has a Master of Science in
Management from Purdue University in the USA.
Heather Stanley is Managing
Director of Yolles Partnership
Ltd., the UK arm of the Yolles
Group, the company
responsible for the design of
One Canada Square, the tallest
building in the UK. Mrs Stanley
is a Chartered Engineer with over 18 years
experience in structural design, working for some
of the foremost consultants in the UK. Current
responsibilities include the design of three of the
high-rise towers currently under construction at
Canary Wharf.
ABSTRACTThis paper outlines the key technical aspects
that influence the structural design of high-rise
structures. The paper gives an overview of the
history of high-rise construction, and identifies
key projects around the world and within the UK.
The paper identifies the determinants of
structural material and structural form and
examines how buildability issues affect the
design. The paper avoids dealing exclusively with
concrete issues and notes the reasons for the
choice of steel in some circumstances.
KEYWORDSHigh-rise, structural design, buildability.
INTRODUCTIONThis paper aims to provide a brief introduction
to the structural design of high-rise structures.
There is an emphasis on building structures,
which partly reflects the authors’ own experience
and partly reflects the vast number of examples.
The paper starts with a brief history of high-
rise structures and identifies significant projects
throughout the last century, and throughout the
world. It then examines the major issues that
affect structural design including the relative
advantages and disadvantages of concrete and
steel.
High-rise structures, especially buildings, are by
their very nature high profile. However, the
events in New York on September 11th have
created an unprecedented level of public interest
in tall buildings. Over the last six months,
structural engineers around the world have
debated the reasons for the collapse of the World
Trade Towers, and whether the design was in
some way deficient. Whilst there is now general
agreement as to the mechanism and cause of the
collapse of each tower, there is far less agreement
on whether the design and construction of high-
rise buildings should be changed in the future
and if so, in what way. The issues are
predominantly technical and cover structural
robustness, fire protection, means of escape and
other issues. Practically all disciplines within the
building process are involved. Construction
professionals, such as architects and engineers,
must inform the debate and assist policy makers,
but it is ultimately for society to decide what if
anything should be done.
This subject is beyond the scope of this paper.
It clearly merits much discussion and many papers
in its own right, and warrants serious research
rather than ill-informed speculation. Research and
debate continue, and the authors follow both
with keen interest.
STRUCTURAL DESIGN OF HIGH-RISE CONCRETE STRUCTURES
Mr. J. Crack BSc (Hons), MICE, MIStructE, MSM, MBA
Canary Wharf Contractors Ltd and
Mrs. H. Stanley BSc DIS, CEng, MICE
Yolles Partnership Ltd
30
THE HISTORY OF HIGH-RISE STRUCTURESTall structures are not a new phenomenon. The
pyramids of Egypt have been around for
thousands of years and medieval churches and
their spires for hundreds. These structures,
constructed from masonry, relied on their sheer
mass to overcome the forces of nature, and had
little usable space inside. It was not until the late
nineteenth century that advances in materials
technology and engineering science combined
with increasing urbanisation to produce the first
true multi-storey buildings. The development of
steel as a structural material and the invention
and development of the electric lift were crucial
factors, along with suitable heating and
ventilation systems.
Some of the first multi-storey buildings were
built in New York City between 1870 and 1875.
Typical of these was the Tribune building which,
at around 10 storeys plus tower, was small by
today’s standards but a landmark in its day.
The economics of high-rise construction were
also a significant factor in the development of
high-rise buildings. As cities grew, land prices in
the business districts soared, so buildings grew
taller to maximise usable space.
However, tall buildings have also been about
status. In 1890 for example, Joseph Pulitzer
commissioned a 94 metre high tower on New
York’s newspaper row to house his newspaper,
the New York World. His building looked down
upon his arch rival William Randolph Hearst’s
New York Journal building, just along the street.
This theme continues today - the tallest buildings
in the world, the Petronas Towers in Kuala
Lumpur, Malaysia, developed by the state oil
company Petronas, are as much about national
pride as the economics of real estate
development.
Notable buildings that have held the tallest
building in the world title through the last
century have included:
• The 187m Singer Building in New York
which was completed in 1908 (and in
1968 became the tallest building ever to
be demolished)
• The 241m Woolworth building (New York
1913), currently 88th in the world
• The Chrysler building (New York 1930,
319m), currently 16th in the world
• The Empire State building (NewYork 1931,
381m), currently 7th in the world. This
building held the world title for over 40
years and is, sadly, once again New York’s
tallest building
• The World Trade Centre Towers (NY 1972-
73, 417m)
• Sears Tower (Chicago 1974, 442m),
currently 3rd in the world
• Petronas Towers (Kuala Lumpur 1998,
452m), the world’s tallest.
The tallest free-standing structure in the world
is the CN Tower in Toronto, a slip-formed
concrete communications tower, which was
completed in 1976 and stands 553m above street
level.
The major structural elements of all of these
buildings except the Petronas Towers and the CN
Tower, were made from steel. There are various
reasons for this. Steel is often the material of
choice in countries that have an indigenous steel
industry, as its attractive qualities (speed of
erection, low weight/high strength, high E-value
etc.) overcome its long lead times and relative
cost. The United States is a good example of such
a country. Other countries, especially those with
little or no indigenous steel industry, and where
labour is cheap, tend to favour concrete for high-
rise construction. When one of the authors was
working in Manila in the mid-1990’s for example,
there were rumoured to be forty buildings of 40-
storeys or more on the drawing board at that
time, none of which were framed in steel. The
reasons: even though steel is cheap (structural
steelwork prices in the UK, for example, are
approximately the same in pound terms today as
they were in the mid-80’s), concrete is cheaper as
it uses local materials, local labour and local
design expertise. Concrete is also a good material
for forming earthquake-resistant ductile sway
frames, a useful characteristic in a heavily seismic
area like the Philippines.
Hong Kong is a mixture: Central Plaza (at
374m, the tallest building in HK) and the
Hopewell Centre (216m) both utilise concrete,
whilst the Bank of China (369m) and the Hong
Kong and Shanghai Bank buildings both use
steel. It is interesting to note that the cost of the
land for the Central Plaza development was three
times the cost of construction.
Europe and the UK have been laggards in the
high-rise buildings world league. This is partly
cultural (Old World v. New World tastes), partly to
do with planning (most cities in Europe have
restrictive planning laws to protect the existing
31
cityscape) and partly technical. It was once said,
for example, that London would never be home
to any high-rise buildings because the bedrock
was too far below the surface. New York, by
contrast, is underlain at modest depth by a strong
layer of schist. Advances in soil mechanics and
foundation design, however, have helped to
overcome the deficiencies of London Clay and the
other deposits beneath London’s streets, allowing
moderate (by world standards) high-rise buildings
to be built.
HIGH RISE AROUND THE WORLDOf the top 100 tallest buildings in the world,
57 are located in the USA and of these 16 are
located in New York and 10 in Chicago. Asia is
home to 29 of the 100. Seventy-seven are used
for office accommodation.
Table 1 provides some interesting statistics on
a selection of buildings around the world,
including the aspect ratio and details of the type
of lateral load resisting system used. The aspect
ratio is defined as the ratio of the height of the
building, H, to the smallest plan dimension of the
building, W. The buildings shown in bold italics
were designed by Yolles.
The choice of lateral system is dependent both
on the overall height of the building, and the
aspect ratio of the smallest plan dimension of the
lateral system to its height. It is these factors
which govern the sway characteristics of the
building. Khan(1) in 1974, attempted to
summarise the choice of lateral systems available
and to indicate the most appropriate for a given
building height.
Khan suggested that the limit for concrete
lateral systems is around 75 storeys but that steel
systems are suitable for buildings of almost twice
that height. The Petronas Towers contradict
Khan’s guidelines, however. Whilst steel beams
are used for the floor spans, the lateral systems
of the Towers are formed entirely in concrete.
Eighteen of the 100 tallest buildings in the world
are concrete, 34 are concrete/steel hybrids and 46
are steel only.
HIGH-RISE BUILDINGS ON CANARY WHARFThe first phase involved the construction of
6 million sq ft of office and retail space. Most of
the buildings are low to medium-rise (10-15
storeys) except for 1 Canada Square which is
some 50 storeys high, and at 237m high,
currently ranks 100th in the world. The architects
for the tower were Cesar Pelli and Adamson
Associates, and Yolles were the structural
designers. The first phase was predominantly
speculative in nature.
Construction of the second phase, in contrast,
has generally started only after a tenant has been
signed to a long-term lease. The key tenants are
generally blue-chip global corporations, notably
financial institutions, who require high-quality,
purpose-built buildings, often of a size suitable to
Title Lateral System Height Width Length H/WH (m) W (m) L (m) Ratio
Petronas Towers Concrete core + 452 48 48 9.4Kuala Lumpur external concrete tube
Sears Tower, Chicago Bundled steel frame 442 69 69 6.4
World Trade Centre, New York External steel tube 417 64 64 6.5
Standard Oil, Chicago External steel tube 346 59 59 5.9
Hancock Centre, Chicago External diagonallybraced steel tube 335 47 81 7.1
First Bank Tower, Toronto External steel tube 285 58 58 4.9
Bay Adelaide Centre, Toronto Internal concrete core 275 51 70 5.4
One Canada Square, Canary Wharf External steel tube 235 57.5 57.5 4.1
Commerce Court, Toronto Internal rigid frame 232 34 68 6.8
25 Canada Square, Canary Wharf Internal concrete core 200 54.5 63 3.7
Table 1
32
act as world or European headquarters. Buildings
range in size from 10 to 42 storeys, from
170,000 square feet to 1.2 million. Currently, 8-
million sq. ft. of buildings are under construction.
The attractions of Canary Wharf to our key
clients are:
• Size of buildings and size of floor plates
• Short construction time
• Quality of design, construction, finishes
and systems
• Rental cost - significantly lower than the
City and the West End.
The choice of structural system and structural
material has a major influence on the last three
items and will be examined in the following
sections.
STABILITY DESIGNIn high-rise buildings, lateral loads become an
increasingly dominant feature of not just the
structural design but of the design of the whole
building. Lateral stability systems can no longer
be fitted within the central core to suit the layout
of the architect and services; instead the
architecture and the services have to be planned
around the structure. This is true not just when
wind loads have to be resisted but also
earthquake loads. However, it is interesting to
note, and perhaps counter-intuitive, that tall
buildings are often safer than shorter buildings in
an earthquake. This is partly because tall
buildings are often better engineered than
shorter buildings, but also, and more importantly,
because tall buildings generally have lower
fundamental frequencies for lateral movement. In
an earthquake, they are therefore subject to
smaller accelerations, and therefore relatively
smaller lateral forces, than a shorter building.
Two principal criteria are used in the
assessment of building stability: drift and
acceleration.
Drift is simply the ratio of the deflection of the
building over its height, and the critical parameter
is usually inter-storey (floor-to-floor) drift rather
than total building drift. A limit of h/500 (where
h is the storey height) have been used in the past
to govern the design, although recent
developments suggest relaxations to h/400 or
even h/300 may be possible. The primary element
affected by relaxation of this criterion would be
cladding, which must be designed to
accommodate the relative movement between
panels.
Building acceleration is a measure of the speed
with which drift occurs and the acceptance
criteria are based on human tolerance of
movement. Tolerance depends on what the
subjects are doing - sensitivity is increased when
lying down rather than sitting or standing. Hence
the acceptance criteria for a residential or hotel
building are tighter than would be required for an
office building.
The following sections examine the three most
popular systems - shear walls, external tubes and
combination or dual systems.
Shear Wall SystemsSome form of shear wall is the usual solution
for low to medium rise buildings. They can be
formed from either solid concrete walls or braced
steel bays and are generally located around key
building features that remain fixed in plan over
many floors, such as stairs, lifts, toilets or plant
rooms. The system relies on linking together
strong elements located at either ends of the wall
Figure 1: An Example of a Internal Core with Concrete Shear Walls.
33
into a dumbbell to create a push-pull to resist the
overturning caused by lateral loads.
Depending on the local economic
circumstances and the aspect ratio of the
building, these systems will often be the most
cost effective for buildings up to 40 or 50 storeys.
External Tube SystemsAs buildings become taller, there comes a
point when the slenderness of a central shear
wall system becomes excessive. However, the
slenderness can be improved if the perimeter of
the building, rather than the central core, is used
for the lateral system. Such systems are known as
external tubes.
External tube systems work by tying the
perimeter columns of the building together to
form a hollow tube. In order to achieve the level
of stiffness required, the perimeter columns must
be closely spaced (typically at 3m centres), and be
rigidly connected together by stiff beams at each
floor level. This system imposes a significant
constraint on the exterior architecture and such a
constraint is not always acceptable.
In theory, tubes can be formed in either
concrete or steel. Steel has better strength and
stiffness characteristics and is often more
architecturally acceptable, though the
connections between columns and beams can
add significant expense.
Combined or Dual Systems Combined, or dual, systems are used where
the slenderness of the building is such that one
system alone cannot provide adequate strength
or stiffness to the building. Such systems are also
used in heavily seismic areas, where a degree of
redundancy is desirable.
In theory, almost any combination of individual
systems is possible, providing the stiffnesses are
reasonably equal. If there are large differences,
the stiffer system may attract a large part of the
load, but may not have the strength to carry it.
Possible combinations might include:
• Internal core with external end bracing.
This is often the choice for long, thin
buildings where the core is unable to cope
on it own
• Internal core with outriggers. The
outriggers are usually stiff steel trusses or
concrete beams, one or two storeys deep,
that mobilise perimeter columns to act
with the core to resist the overturning
moments caused by lateral loads. Because
of their size, the outriggers can normally
only be accommodated within the
building layout at specific points up the
height of the building. These points are
often where the plant rooms are located
• Internal core with perimeter tube. This
method can be used on very tall buildings
where neither the core nor the tube alone
is sufficient to resist all of the lateral
forces. The Petronas Towers are good
examples of this system.
FLOOR SYSTEMSThe number of floor systems suitable for use in
commercial buildings is small. The range of choice
for large span commercial office buildings is even
narrower: steel/concrete composite floors,
prestressed concrete floors and reinforced
concrete floors.
Composite floorsSuch floors were developed in the United
States and were first used in the UK in the early
to mid-80s. Typically a floor will consist of:
• 130mm of lightweight concrete on
profiled metal decking. The decking acts
as formwork during construction and
requires no propping. After the concrete
has gained strength, the decking acts as
the tension reinforcement in a composite
steel/concrete slab
• The slab is generally supported on steel
beams, which act compositely with the
slab via shear studs welded in situ to the
beam.
This is the favoured floor slab for
superstructure floors in all Canary Wharf projects
where clear spans of 13.5m and upwards are
typical. It has also become the industry standard
for commercial office buildings. The method
produces a lightweight floor, which allows large
clear spans and acceptable structural depths. The
floor performs well in service and is tolerant of
post-construction alterations, such as the cutting
of holes for tenant service risers. It is also quick to
construct.
Prestressed concrete floorsPrestressed concrete floor systems are not very
common for commercial buildings in the UK.
However, such systems can have a lot to offer in
selected situations. In some countries, such as
Australia, they are used extensively for the floors
34
of large span high-rise office buildings. The main
forms of construction are:
• Floors containing prestressed concrete
band beams
• Prestressed concrete flat slabs.
Band BeamsA typical band beam floor for a long-span
office might consist of strips of prestressed
concrete slab (band beams), perhaps 1m wide
and at 4.5m centres, with a reinforced concrete
or composite slab between. The band beams
have a dead-end anchorage at one end and a live
anchorage at the other end, where stressing
takes place. This is often at the building
perimeter and the stressing point is usually
accessed from the top of the slab to ease the
stressing operation.
The method produces a floor with clear spans
similar to those produced by the steel composite
option above, but generally with shallower
structural depths. In-service vibration
characteristics should be better due to the greater
concrete mass. The main disadvantages of this
system for high-rise construction are:
• The floors are heavy and this adds to the
cost and size of vertical structure and
foundations
• Flexibility for post-construction alterations,
such as the cutting of holes for tenant
service risers, is limited to areas away from
the band beams.
The main reasons why such a system has not
been used on Canary Wharf, in addition to the
above, are:
• Negative tenant perceptions
• Limited number of specialist
subcontractors
• Risk - Why change from a familiar and
successful system to an unfamiliar one?
Prestressed Concrete Flat slabsPrestressed concrete flat slabs can produce
thin floors with clean, flat soffits. However, they
suffer from the same disadvantages as do band
beam floors, but possess even less flexibility for
post-construction alterations.
PC flat slabs have been used successfully for
multi-storey car park structures in the UK and for
hotel and apartment buildings where some of the
disadvantages noted above are less relevant.
Reinforced Concrete FloorsReinforced concrete floors are not commonly
used for the superstructure floors of high-rise
buildings in the UK. A notable exception is Tower
42 (formerly the NatWest Tower). Concrete’s
weight, the need for large spans and the relative
cheapness of steel mitigates against reinforced
concrete in this role.
RC concrete floors are common in shorter
buildings and in some countries overseas where,
as previously mentioned, other factors apply.
Basement floors, however, are commonly
made from reinforced concrete. In most Canary
Wharf buildings, the basement suspended floors
are reinforced concrete flat slabs. Additional
columns allow for shorter spans and relatively
thin and economic flat slabs can be produced.
Column drops or heads can be incorporated to
thin the slabs down even further.
FOUNDATIONS AND SUBSTRUCTUREThe foundations of most of the Canary Wharf
high-rise buildings consist of a concrete raft on
large diameter bored piles. The piles generally
extend some 20m from raft level into the Thanet
Sands and are base grouted. They support load
by a combination of skin friction and end
bearing, but mostly by end bearing. In some
high-rise buildings, it has not been possible to
provide sufficient piles in the area under the core
to support the load coming down it. A concrete
raft up to 3m thick, has been required to
distribute the loads to piles outside the plan area
of the core.
Sometimes the raft slab has been designed as
a large pile cap, but sometimes it has been
designed to shed some of the load directly into
the soil, known as a piled raft. This has required
careful preparation of the formation.
Construction of a thick raft requires a certain
discipline during construction. The major
concerns on Canary Wharf relate to continuity of
concrete supply and excessive heat of hydration.
A watertight concrete mix has been designed to
minimise thermal and shrinkage cracking using
PFA-replacement and with a 56-day design
strength. Thermocouples within the pour allow
the concrete temperature to be monitored
continuously. Insulating covers are added or taken
off depending on the temperature readings. Both
the maximum temperature and the temperature
gradient within the pour are of concern.
35
CONCRETE CORES
Core Construction and DesignThe efficiency of the cores in any high-rise
building is critical to the overall efficiency of the
building and therefore to the profitability of the
development. Reinforced concrete cores have
several advantages over steel-braced cores in this
respect. However, traditional methods of concrete
construction are too slow for use in high-rise
buildings, leading to the use of jump or slip
formed construction.
When the second phase of Canary Wharf
started, jump forming was the preferred method,
because there were major concerns about
tolerance control with slip forming. However,
CWCL have worked with their trade contractors
to improve tolerance control, and now the choice
between a jump or a slip formed core is based
purely on price and contractor preference.
There is generally little difference in production
rates when the two systems are compared
properly and both are working a normal shift.
However, slip forms have the advantage that they
can be worked 24 hours a day. Jump forms on
the other hand need a period for the concrete to
gain strength before jumping, so the maximum
working day is limited to 12 hours.
There are several major differences however
and these have implications on both the
permanent and temporary design:
• A slip form system will only construct the
walls of the core as it advances, whereas a
jump form system will also allow
simultaneous construction of the floors
within the cores. As a result, the slip form
system often requires temporary bracing
to isolated outstand walls until
construction of the floors takes place
• Construction of the floors at the same
time as the walls using a jump form
system, facilitates early access for
following trades
• There are two main methods for
connecting steel floor beams to the
concrete core walls. The first involves
casting flat plates into the face of the
wall, to which the beam is later
connected. The second involves
constructing a concrete corbel upon which
the beam sits. Depending on the design of
the forming system, a jump form system
can usually accommodate either method,
whereas a slip form system can
accommodate only the flat plate option.
This has implications for the design of the
floor beams especially when complying
with the tying requirements of the current
British Standards. Typical examples of both
systems are illustrated in Figure 2 below.
There are several important considerations that
arise in the design of any high rise slip formed or
jump formed core:
• The loads within the core will reduce with
height up the building. The thickness of
the core walls may therefore be reduced.
This is usually done from the outer face
inwards rather than the inner face
outwards to allow a net increase in lettable
space, but whichever way it is done must
be accommodated by the forming system.
A jump form can make such changes more
quickly than a slip form. Major changes in
the plan shape of a core can also be
accommodated more easily e.g. the
reduction in the plan shape of the core
when the lift banks drop off
• Jump form systems require a relatively high
strength mix (typically C60) in order to
Figure 2: Examples of connections.
Embedded plate Corbel
36
achieve early strengths for jumping. Slip
form systems, on the other hand, can
operate effectively on a C40 mix. The
higher strengths required for a jump form
can be used beneficially in the design to
reduce reinforcement
• Service openings through core walls are
often a major problem. The number and
size of openings can have a major impact
on the structural design of the permanent
works and also on formwork design. It is
therefore important to resolve them at an
early stage
• It is easier to form a better quality concrete
finish with a jump form, especially around
openings
• It is quite common during post-contract
discussions with the formwork contractor,
to change concrete beams within the core
to walls, or vice versa, to facilitate the
forming operations. It is important, then,
for the structural designer to maintain a
degree of flexibility until these discussions
are finalised
• A number of conflicting requirements
often affect the positioning of various
elements within the core. An ideal core
arrangement will facilitate the reduction in
from one end as lift banks stop off at
various heights within the building.
However, regulations governing minimum
distances to escape stairs often prevent
this happening, and isolated sections of
core at either end of the building are often
necessary. The speed and simplicity with
which the form can be adapted at the
change levels can have a major impact on
the overall time to construct the core.
Figure 4 below illustrates an ideal set-back:
Concrete StrengthsIn most concrete works, increasing concrete
strength has limited benefit after a certain point.
With compression members, such as columns and
stability cores, this is not true - the higher the
strength the better.
On Canary Wharf, we commonly use grade 60
concrete in the cores, though higher strengths
are now available. Initial trials have indicated that
buildability issues should not be a concern and
studies have indicated that the higher costs of
higher strength concretes in most cases will be
more than offset by smaller members and
consequent increased lettable space. In some
cases, the core design is not governed by
Figure 3: Change in Shape of Core as Lift Banks Drop Off.
37
strength but by stiffness. In these cases,
increasing the concrete strength may be less
worthwhile.
CONCLUSIONSIn this paper, we have tried to explain in
simple terms the fundamental issues that need to
be addressed when designing high-rise structures.
We have shown that there are often several ways
to design different elements of a building; rarely
is there just one correct way. It is the designer’s
job to establish the best one for a particular
project.
Despite the nature of this symposium, we have
avoided dealing exclusively with concrete issues.
We believe it is important that the reasons steel is
chosen in preference to concrete in some
circumstances should be understood. With
advances in concrete mix design, concrete should
continue to have a major, or possibly an
increasing, role in high-rise construction.
REFERENCES
1. Various papers by Fazlur Rahman Kahn -structural engineer of many great buildingsincluding the John Hancock Tower and theSears Tower in Chicago.
Please note:Any thoughts and opinions expressed in this paperare those of the authors and do not necessarilyrepresent the views of their respective employers.
38
39
John Day is Hanson’s Technical
Manager in Malaysia. He has
spent his working life in a
‘hands on’ capacity developing
and supervising concretes on a
number of projects in Australia,
Malaysia (Petronas Towers) and latterly on
secondment to the UK (Canary Wharf/CTRL).
INTRODUCTIONThis paper, firstly discusses the case history of
the high strength concrete (Grade 80) supplied to
the Petronas Towers in Kuala Lumpur in the mid
1990s with a brief overview of the basic theories
employed in adjusting the mix designs as the
height of the tower increased. Secondly, a
comparison of the mixes employed at the Canary
Wharf project currently against the designs used
at Petronas and of the ongoing (C100) trial
program being undertaken by Hanson at Canary
Wharf for use in future structures at the
development.
PETRONAS TOWERSThe construction of the Petronas Twin towers
posed two very interesting challenges for
Pioneer/Hanson as the sole concrete supplier to
the project. Firstly to design and produce in
excess of 40,000m3 of 80 N/mm2 concrete with
an enforced margin of 15 N/mm2 i.e. Average 56-
day strength of 95 N/mm2 to ensure that the
rolling average of 4 consecutive results did not
fall below 86.15 N/mm2 as specified and secondly
to design and produce grade 40 and 30 concrete
capable of being single staged pumped, vertically
380 metres to level 84 of tower 2. Tower 1 was
pumped; however, concrete was skipped to the
pump approximately 30 floors below the
working deck.
MIX / SELECTIONThe mix design was controlled by the required
maximum water/cement ratio of 0.27. The
second constraint, although not specified, was to
restrict the internal concrete temperature to a
point where the initial temperature rise would
facilitate 12 hour stripping of the 2.5 metre
diameter column forms without producing a
thermal crack due to the differential temperature
shock when the form was removed. Thirdly, to
achieve and maintain sufficient cohesion and
workability to allow full compaction of the
concrete in the very congested corewall
reinforcement and finally to provide early strength
(15 N/mm2 at 12 hours) to allow the contractor
to achieve his very tight construction schedule of
4 days per floor.
MATERIAL SELECTIONBased on the criteria stated above the
materials to be utilized and their proportions
were selected as follows:
CEMENTITIOUS CONTENTThe selection of cementitious content and
their proportions are based as follows:
OPCThe maximum efficient OPC content per cubic
metre is 500 kg. This is based on the prior use of
the manufacturer’s OPC in the general production
of more than 300,000m3 of concrete of different
classes and grades.
The achievable 56-day mean strength expected
from a mix design incorporating 500 kg/m3 at
0.27 water/cement ratio is approximately
85 N/mm2 which, due to the required current
margin of 15 N/mm2, is below the 100 N/mm2
target mean strength required. Therefore it was
necessary to introduce silica fume to the mix to
achieve the target strength.
Silica fumeSilica fume (CSF) was incorporated into the
mix design at 30 kg/m3 based on the CSF being
approximately equivalent to 90 kg/m3 of OPC
which would achieve approximately 18 N/mm2
therefore making the 100 N/mm2 achievable. It
was also noted that the silica fume does not
contribute to the initial temperature rise.
Mascrete‘MASCRETE’ is the trade name for APMC’s
(80% OPC, 20% PFA) blended cement. After the
initial mock up trial of the 2.5 metre diameter
columns using 500 kg/m3 of OPC and 30 kg/m3
THE PRACTICAL DESIGN AND PRODUCTION OF HIGH
STRENGTH CONCRETE (A COMPARISON OF CASE HISTORIES)
Mr. J.W. Day.
Hanson Premix plc
40
CSF the decision to incorporate Mascrete was
made as the mock up columns showed signs of
thermal stress around the steel reinforcement
which was confirmed by the cast-in pressure cell
and strain gauge readings.
It was decided to reduce the total OPC content
by 9% thus the substitution of 225 kg/m3 of
Mascrete was made leaving the final cementitious
blend as follows:
OPC - 280 kg/m3
MASCRETE - 225 kg/m3
SILICA FUME - 30 kg/m3
AdmixturesThe selection of the correct admixture
combination is important as correct selection of
cementitious blend and content as the fresh
properties of the concrete have as much bearing
on the finished quality and constructability of the
structure as the hardened properties. The
admixture combination goals are:
• To attain a slump value of 200mm + 40
mm - 20mm i.e. a range of 180mm - 240
mm. (approximately 550 to 630mm flow)
• To maintain the slump for a period of 45 -
60 minutes
• Give four hours retardation for protection
against cold joints
• Achieve 15 N/mm2 cube strength at 12
hours
• Disperse the CSF evenly through the mix.
The method selected to achieve the above was
to use two admixtures: firstly, a water
reducer/retarder to control the initial set and to
enhance the slump retention capabilities of the
mix; secondly, a non retarding high range water
reducer (superplasticiser) to take the mix from
zero slump to 220mm whilst combining with the
retarder to achieve 45 - 60 minutes slump
retention. These properties are not attainable
with a single dose ‘retarding high range water
reducer’ as the retarding and water reducing
ratios are not commercially available and any
redosing with a retarding plasticiser would affect
initial set and early strength development.
The choice to use (MBT’s) P300N base water
reducer and (MBT’s) R1000 high range water
reducer was based on R1000’s better than
average capability to retain slump and its ability
when combined with P300N to control initial set
and give high early strengths.
After a intensive trial mix programme the dose
rates of P300N and R1000 were determined.
With the exception of the early strength
requirement all of the goals were achieved.
The early strength target of 15 N/mm2 at 12
hours was achievable; however, changes in
ambient conditions, i.e. night castings, made
repeatability difficult.
20mm AggregateThe selected 20mm aggregate is of very good
shape and is a very strong small grained granite
which is ASR free and complies with all the
requirements of BS1881 for 20mm - 5 mm
graded aggregate. The source was chosen based
on QA/QC at quarry, availability of supply and
proximity to the plant.
SandThe selected fine aggregate is natural sand
mined locally. The sand is double washed to
ensure all organic impurities and excessive silt is
extracted. Double washed sand can result in
concrete of inadequate cohesion and pumpability
at normal cement contents but is advantageous
where high cement and silica fume contents are
required.
WaterThe water used for production is mains
supplied and conforms to all aspects of the British
Standards. It is chilled to 3˚C to allow the
concrete to be produced at below 35˚C.
PRODUCTION
PlantThe concrete was produced by two fully
computerised/automated twin shaft wet mix
plants with a theoretical output of 120m3 per
hour per plant. Each had a 3m3 capacity mixer
and incorporated a computer generated batch
quantity reports facility.
The main problem experienced with the
batching system was the age-old problem of
inaccurate sand moisture content adjustment, i.e.
the moisture probes are not accurate enough to
allow the plant to run without manual override of
the moisture probe settings.
The plants are serviced by two 120 HP chiller
units to ensure water temperature would be
maintained at 3˚C thus facilitating the 35˚C
maximum initial concrete temperature even when
experiencing sand moisture contents above 8%.
All other facets of the plant are now standard
items found on all modern batching plants.
41
Weigh sequence1. Fine and coarse aggregate weighed
cumulatively on the same scale and then
conveyed to a waiting hopper directly
above the plant mixer.
2. Admixtures measured by pulse meter en-
route to holding tanks directly above the
plant mixer.
3. Water measured by flow meter en-route
to holding tank above the plant mixer.
4. Cementitious content.
As CSF is the lightest of the three materials
and due the lack of volume per 3m3 batch
(90 kg) it is the most difficult constituent to
weigh. It is also the most critical cementitious
constituent batched as its strength to weight
ratio far exceeds that of OPC.
The plant is fitted with a single 3000 kg
cement bin and, as such, the 3 cementitious
constituents are weighed cumulatively in turn.
This procedure prolongs batch time as each
individual constituent must be allowed to settle in
the weigh bin before the next constituent can be
introduced. In hindsight, the plant should have
been equipped with dual cement scales to allow
CSF to be weighed separately, which would
increase accuracy and speed considerable.
However, the method employed completed the
task successfully even if not efficiently.
Batch sequenceThe sequence or delay of separate constituents
being introduced into the twin shaft mixer are of
the utmost importance in achieving uniformity of
the mixture and to allow the admixtures to have
their most efficient effect whilst not reducing the
plants hourly capacity through unnecessarily
prolonged mixing times.
The sequence employed was as follows :-
1. Batch water + P300N base retarder/water
reducer.
2. Fine and coarse aggregate delivered
together from waiting hopper.
3. Cementitious content introduced prior to
aggregate introduction finishing.
4. Sufficient mixing time allowed for
concrete to become homogenous.
5. Introduction of R1000 (high range water
reducer).
6. Sufficient mixing time given prior to
discharge to truck mixer.
The total mixing times per 3m3 batch and the
various delays for individual constituent
introduction were determined after a prolonged
trial period to reach the most efficient mixing
time to attain the maximum mix uniformity and
full dispersion of the CSF.
Statistical analysisThe concrete cube test results attached in the
appendices represent some 45,000m3 of grade 80
concrete produced for the KLCC Project by
Pioneer Concrete (M) Sdn Bhd. The concrete was
produced over a 12-month period; however, in
the initial 1-month period and the last 3-month
period no substantial amounts of concrete were
produced.
Overall analysis of C80 concrete test results
covers some 603 samples cast between the 18th
March 1994 and 30th March 1995 with no
omissions, even though adjustments were made
to overcome known changes in constituent
materials characteristics. The foremost
consideration was maintaining the 56-day mean
strength, realising that any variation in this would
increase standard deviation and, therefore, reduce
the calculated characteristic strength provided.
These adjustments were made as a result of data
gained from the suppliers and in-house quality
assurance programmes that allow adjustments in
mix design to be made before the material of
changed characteristic is used in the production
of concrete.
The creditable standard deviation of 4.41
N/mm2 and overall mean strength of 101.4
N/mm2 resulted not only from low batch-to-batch
variability but also the ability to make mix
adjustment to combat varying trends in individual
material characteristics over an extend period of
time by using the data gained from the quality
assurance programme.
For the purpose of exhibiting the constant
improvement in overall control the test results
have been divided into 3 periods :
Analysis 122/03/94 - 22/06/94 630 samples
Analysis 2
22/06/94 - 22/09/94 155 samples
Analysis 3
22/09/94 - 02/04/95 241 samples
Analysis 1
Shows a standard deviation of 5.3 N/mm2
which is relatively high. Of 151 results reported
42
some 48 results are concrete produced with a
0.25 water cement ratio which has given a
marginally higher overall mean strength of 103.2
N/mm2 at 56 days. However, when the results
were divided into 2 sub-groups either side of the
noticeable change point on the 24th May 1994
the relatively high standard deviation is explained
as follows :-
Period - 22nd March 1994 - 24th May 1994
96 test results with a mean strength of 105.4
N/mm2 and a standard deviation of 4.4 N/mm2.
Period - 25th May 1994 - 22nd June 1994
56 test results with a mean strength of 99.6
N/mm2 and a standard deviation of 4.6 N/mm2.
Analysis 2
Has a standard deviation of 3.95 N/mm2 which
is a substantial improvement on Analysis 1, this
improvement in standard deviation represents
improved concrete sampling and cube-handling
procedures along with an improving ability to
adjust the mix to combat moving trends in
material characteristics.
Analysis 3
Has a very good standard deviation of 3.04
N/mm2 which is greatly due to APMC’s
improvements in the production of ‘Mascrete’
during this period combined with an ever-
improving understanding of the techniques
required in the production and control of high
strength concrete.
The Petronas towers in Kuala Lumpur, when
completed, were the tallest buildings in the
world; they stand approximately 450 metres high,
the maximum concrete height is 384 metres on
level 84 of the 88 levels accessible to the public,
the last 4 floors are constructed of steel. The
average floor height is 4 metres; however, there
are many hidden floors that do not appear on the
numbering system (approximately 10 floors) as
they are machine floors, etc.
For the purpose of working out pumping
heights one can use 380 metres at level 84 and
then deduct 4 metres/floor. There were only 2
mix designs pumped to this level: the 40SF3 and
30SF. The 40T1 mix design shown on the
placement summary (attached appendix A) as
used from level 80 - level 84 for tower columns
and ring beam was kibbled into place by crane as
the volumes were too small to warrant mobilizing
pumping operations.
In most situations choice of mix design is
based on its ability to meet the quality
requirements of both Pioneer and the client with
cost efficiency being the second but still a major
factor. In this situation compliance to a strength
factor was almost immaterial with the exception
of the grade 80 concrete as previously discussed.
All grades had a specified maximum water/
cement ratio which was lower than required to
achieve the specified compressive strength. This
leaves pumpability, workability and consistency as
the major concerns with cost being a distant 4th.
Mix designs were adjusted progressively as the
structure became taller; the general trend was to
increase cementitious content whilst increasing
sand/aggregate ratio to improve cohesion and
segregation resistance as the pumping pressure
increased.
At approximately level 50 the water contents
were also increased thereby increasing the total
paste content and reducing the chances of inter-
locking aggregate causing line blockage due to
having insufficient paste in the pump-line cross-
section.
At level 62 the mix designs all had silica fume
introduced to them; this was to combat
increasing pumping pressure forcing the water in
the paste to migrate towards the pump-line wall
thereby leaving the central cross-section area
quite dry and therefore increasing the chances of
line blockage due to the aggregate in that section
inter-locking.
Finally Rheobuild 3040 was introduced to the
mix on level 80 to level 84. R3040 is a totally
synthetic superplasticiser that has approximately
25% more solids than R1000 and gives better
cohesion and segregation resistance. Although
the SF40 mix design would have reached the
maximum height, as was later demonstrated with
the SF30 mix design, the decision was taken to
use the 40SF3 design to enhance pumpability and
for further knowledge.
Although mix design is an integral part of a
successful pumping operation it is of no more
importance than the ability to produce consistent
quality concrete both in the correct batch
quantities and with a consistent workability. In
normal situations lack of slump can be overcome
with the simple addition of superplasticiser to
obtain the correct slump; however, when
supplying concrete to high capacity pumps such
as the Schwing 8600s used at KLCC it is
imperative to maintain the correct paste volume
and paste consistency as any deviation in this by
way of lack of water or over addition of water
will lead to severe problems under the 300 bar
pressure that the pump produces.
43
Possibly as critical to a successful pumping
operation is the calibre of the pumping personnel
and the condition of the concrete pump itself.
The pump and pump-line must be maintained in
perfect working order, i.e. all pump-line
connections must be watertight and 100%
aligned as any change in cross-sectional pattern
will disturb the concrete and therefore change its
pumping characteristics. The pump must be
working in a smooth, controlled manner as any
jerking or inconsistent pressure supply will also
lead to the concrete in the line being disturbed;
resulting in changed pumping characteristics and
blockages.
In a perfect world the pumping operation
would be continuous with one truck on the
pump waiting for the previous truck to discharge,
however, this is usually not the case and the
concrete is often stationary in the line. Blockages
occur most frequently when the operator
recommences pumping after a delay because the
concrete settles in the line, which changes the
cross-sectional aggregate pattern. A well-trained
operator would reduce the hydraulic pressure
output initially until the concrete was once again
moving in the line and then gradually increase
output. If the operator commences pumping on
full output the line will block as the disturbed
concrete does not have any chance to get back to
its original cross-sectional pattern.
On the successful completion of the project it
was apparent that we did not get anywhere near
the maximum potential of the 40SF3 mix design
and with the further addition of Meyco 766
pumping aid it is hard to know where the height
limit of concrete produced with locally available
aggregates would have been; however, we
estimate another 40 metres would have been
possible.
CANARY WHARFFor the purpose of this comparison we will
discuss the concrete requirements and the
concrete supplied to DS 5 and HQ 2 on the
Canary Wharf Development.
The high strength concrete requirement for
these towers was C60 concrete for the corewalls
from basement to level 42 at an approximate
maximum height of 220 metres (including pump
tower height). This is in line with the heights the
C60 concrete at Petronas was pumped. The
concrete was placed by pump although the
pumps utilized were Schwing 4000s rather than
the Schwing 8600s used at Petronas. The larger
pump has a higher hydraulic output; however the
main advantage is that the longer piston stroke
reduces impact pressure and therefore can deliver
concrete to the same height at a lower internal
line pressure with reduced potential of
segregation.
As the construction type was identical to that
of the Petronas Towers, i.e. self-climbing jump
form, the requirement of 15 N/mm2 at 12 hours
was the same on both projects to facilitate a four
day cycle.
As with the plants used at Petronas, the
Canary Wharf plants are fully computerized, wet
mix plants; the main difference being the
Petronas plants utilized twin shaft mixers whilst
the Canary Wharf plants have pan mixers. On the
whole there does not appear to be a significant
difference between the 2 types as required mixing
times are almost identical.
The weigh and batch sequences initially
employed at Canary Wharf differed from those at
Petronas with the superplasticiser being added
with the initial water rather than after
homogenous concrete had been produced. This
proved very problematic, with uniform slump
being very difficult to maintain. The decision was
taken to revert to adding the superplasticiser last
and to change the admixture type from Glenium
51 to Glenium 27 which has the same
characteristics at double the dose rate which
allows for far greater consistency in terms of
initial slump and slump retention.
The initial mix designs produced for the G60
were based on the most cost efficient design able
to achieve the strength requirement without
taking into consideration the points previously
discussed; the main factors being pumpability and
slump retention. As such the designs were re-
evaluated on level 7; the revision resulted in mix
designs being produced that closely follow the
designs used at Petronas Towers. (Table 1)
As can be seen in Table 1, mixes C60 AMD
(Petronas Towers) and C60 REV (Canary Wharf)
have very similar batch weights, paste volumes
and sand/aggregate ratios as opposed to the
unsuccessful C60 ORG (CW) that has 5% less
paste and 10% less sand.
The analysis of overall gradings shows that the
C60 AMD design complies very well with the
tried and tested rule for pumpable concrete of
having no less than 2% and no more than 10%
retained on any sieve below 9.5mm. However,
both the C60 ORG and C60 REV display in excess
of 10% retained on the 300 micron sieve and
44
quite sharp falls between other consecutive
particle sizes; this combined with the lack of
paste in the C60 ORG design made it very
difficult to pump. Therefore the revision to C60
REV contains 5% more paste and 10% more
sand which combine to overcome the problems
associated with the overall grading and, very
importantly, adds fluidity to the paste by way of
the 25 kg/m3 increase in water content.
The C60 REV mix design was successfully
pumped to the full height of level 42 with
pumping pressures being approximately 20%
higher than those experienced with the C60
AMD in Kuala Lumpur. This can in part be
assigned to the softer stroke of the pump
employed, but is mainly due to excess material on
the 300 micron sieve and the less continuous
grading.
A major difference in producing concrete of
similar characteristics in London and Malaysia is
the initial concrete temperature, which is directly
affected by ambient conditions. As discussed
earlier, in Malaysia it is necessary to use chilled
water to maintain an initial concrete temperature
of less than 35˚C with the use of PFA replacement
to control temperature rise in thick sections and
substantial dose rates of retarders to maintain
slump life in long pump-lines. In London the
opposite is the case. With initial concrete
temperatures as low as 15˚C it was imperative to
use admixtures with the minimum retarding
affect possible to maintain slump life whilst giving
the best possible early strength gains.
This required the use of the totally synthetic
(Glenium 27) admixture in winter as plasticisers
formulated with organic bases tend to retard set
for long periods in cold conditions at high dose
rates. As ambient temperature rose the addition
of a small dose of glucose based retarder was
incorporated to maintain slump life. It should be
noted that the slump retention capabilities of the
Glenium 27 are some 25-30 minutes greater than
those of the R1000 used at Petronas.
C100 Trial programmeApproximately 7 months ago Hanson Premix
were approached by Canary Wharf Contractors to
initiate a high strength trial program to establish
that concretes with characteristic strengths of
100 N/mm2 were a viable option in London in
particular the Canary Wharf Development.
A mix selection process was carried out in line
with the process discussed earlier for the C80
concrete produced at Petronas with great
emphasis being placed on “Constructability”.
With this in mind the following design criteria
were set.
• Characteristic Strength 100 N/mm2
• Initial flow 650mm with the ability to
maintain a flow of 550mm for 90 minutes
from batching.
• Pumpable to 200 metres
• Early strength of 15 N/mm2 at 12 hours
of age.
As discussed earlier the combination of 20-
5mm limestone aggregate and typical washed
marine sand does not allow for a totally
continuous grading curve, therefore we elected
to trial a mix containing multiple single size
60 AMD 60 REV 60 ORG
OPC 469 370 315
PFA 46 125 105
20 mm 940 942 1035
Sand 820 810 720
Water 160 160 135
P300N 1.42 - -
R1000 4.64 - -
XR 100 - 0.49 -
G 51 - - 2.1
G 27 - 4.90 -
W/C 0.31 0.32 0.32
S/A 0.47 0.46 0.41
PASTE 32.9 % 33 % 28 %
FLOW 550 600 550
Table 1: Mix comparisons.
45
aggregates to allow an acceptable continuous
grading curve to be achieved with the least
possible surface area, which in turn controls
water requirement and ultimately reduces
cementitious content.
Cementitious content (OPC/PFA) is based on
the maximum efficient content as over-addition
increases friction under pressure and increases
water demand without increasing ultimate
strength. The experience gained from producing
large quantities of C60 concrete at the Wharf in
the last 2 years reduced the number of trials
required significantly as some options had already
been fully explored.
The addition of silica fume was required as the
maximum efficient cementitious content could
not achieve the strength requirement when
sufficient total water content was introduced to
attain sufficient paste levels with the required
fluidity to allow the concrete to be pumped to an
estimated 200 metres in the future. Again it
should be noted that silica fume in small
quantities (12 kg/m3) assists in pumping concrete
under high pressure however must be kept at the
bare minimum as over addition will result in
concrete that is very ‘sticky’ causing pump
pressures to rise dramatically. A good rule of
thumb is 5% maximum for strength.
The admixture used in the trials is the latest
generation Polycarboxylate polymer base which
exceeded the characteristics required, achieving
an initial flow of 650mm and maintaining a
580mm flow at the workface after being pumped
to the 30th floor at approximately 240 bar
pressure at a rate of 15m3/hour some 60 minutes
after being batched.
Previous lab and plant trials indicate that
maintaining flow values in excess of 550mm for
periods of more than 90 minutes whilst being
slowly agitated in a truck mixer are readily
achieved.
46
47
Dr Richard Moss is a Senior
Consultant within the Centre for
Concrete Construction at BRE.
His area of expertise is in the
Structural Use of Concrete and
he is a member of the British
Standard Committee dealing with this topic.
Mr. Martin Stephenson is
Managing Director of
Stephenson Construction, a
leading specialist concrete
contractor, and has many years
of practical experience of
concrete frame construction.
ABSTRACTThis paper gives details of a research project
aimed at applying innovations to the construction
of a series of multi-storey in situ concrete frame
structures at the St. George Wharf development
in South London. The innovations to be applied
have largely emanated from the European
Concrete Building Project at Cardington, and
these have been summarised as a series of Best
Practice guides. The aims of the project are to
apply many of these ideas to an actual live
construction project and measure the benefits
that can be achieved under site conditions.
KEYWORDSConcrete, Flat slab, in situ, Innovation, Frame,
Construction
PAPER 1: BACKGROUND ANDRESEARCH - INTRODUCTIONThe European Concrete Building Project at
Cardington[1] has helped advance knowledge in
relation to in situ concrete frame construction and
the logical next step in getting that knowledge
and experience out into practice is to apply many
of the ideas to a live construction project.
The principal objective of this project is
therefore to demonstrate the practical benefits of
adopting many of the innovative features and
techniques used in the design and construction of
the in situ concrete building at Cardington. By
demonstrating these benefits under commercial
conditions the other principal objective is to
further persuade the wider industry of the
quantifiable value to them of taking up these
innovations and approaches, to improve their
efficiency and profitability.
These benefits will be in terms of increased
efficiency and profitability not just on this
particular phased project but also on other
projects in the future. The intended long-term
impact is the more widespread adoption of new
techniques and approaches, which will benefit the
wider industry.
DESCRIPTION OF THE PROJECTThe project involves applying innovations to a
live case study centring on the construction of a
series of flat slab frame structures in a large
residential and mixed use development to
demonstrate continuous improvement, and
establishing this as a demonstration project in its
own right.
The St. George Wharf development in
Vauxhall, South London represents an ideal
opportunity for a number of reasons not least the
nature of the blocks being built in discrete stages
and the opportunities this provides for continuous
improvement. The development is very large
comprising 100,000 sq m of mixed-use
accommodation including 750 homes and is very
high profile occupying as it does 275m of
frontage on the River Thames (Figure 1).
BRE is working directly with St George and
their engineers and contractors to develop and
implement possible solutions and improvements
tailored to the St. George Wharf development.
This approach is being followed so that the
benefits, though specific to a particular project,
are more clearly visible and measurable. The St.
George Wharf development offers the advantage
that it is being taken forward in a series of
THE ST. GEORGE WHARF DEVELOPMENT
- BACKGROUND, RESEARCH AND DEVELOPMENT
Dr. R. MOSS BSc, PhD, DIC, E.Eng, MICE, MIStructE
Centre for Concrete Construction, BRE Ltd and
Mr. M. Stephenson
Stephenson Construction Ltd
48
Figure 1: St. George WharfDevelopment.
repetitive phases enabling benchmarking and
measurement of performance improvements, as a
result of implementing the proposed innovations.
The other principal advantage is that because
of the nature of St George themselves being a
developer/contractor, they effectively have control
over all phases of the project, enabling the
pushing through of new ideas and innovations
which would be more difficult in a more
conventional contractual arrangement.
The intention is that lessons learnt during the
construction of successive blocks will be carried
forward on to the next block so that a process of
continuous improvement can be established. A
team-based approach is being favoured working
closely with the frame contractor so that
maximum benefit can be achieved.
The St. George Wharf development is already
established as a demonstration project with the
Housing Forum. The concrete frame construction
aspects of this project have now been established
as an M4I project in its own right.
A series of case histories will be prepared
summarising the experiences with each of the
innovations adopted during the construction.
These will be promoted to the wider industry
through the Construction Best Practice
Programme (CBPP) and by targeting specific
additional projects to develop and promote
subsequent improvements.
The Trade Associations BCA, RCC and
Construct, who were principal partners for the
original Cardington project, will also play a
leading role in the dissemination process.
PROPOSED INNOVATIONSThe proposed innovations together with the
expected improvements and methods of
measurement are described in the Table below.
Electronic Exchange of rebarinformation
The use of electronic exchange of rebar
information should introduce considerable
efficiencies in the overall rebar supply chain by
the removal of the need to re-key in the
information by different parties. The principal
beneficiary of streamlining this process is
anticipated to be the rebar suppliers themselves.
The benefits for the contractor is early collation
of information relating call-off schedules in terms
of weight and cost which can be used in
valuations to analyse outputs more accurately.
Also the Contractor is able to track the
reinforcement call off through the supply process
and give certainty of delivery on time, which can
assist with logistics on site.
The intention will be to gather information on
the time and cost of preparing schedules and
processing this information by the rebar supplier,
the contractor and St George.
Figure 2 illustrates a blank schedule
downloadable in the form of an Excel
spreadsheet that can be used and is compatible
with the systems of rebar suppliers. The
spreadsheet can be downloaded from
www.structural-engineering.fsnet.co.uk.
Figure 2: Blank electronic schedule.
49
Use of National StructuralConcrete Specification (NSCS)
The intention of the National Structural
Concrete Specification is to have an agreed
common specification for the majority of building
structures. This is seen of particular value to the
contractor in knowing what is required of him at
tender stage. In the context of St. George Wharf
the contractor already has a good understanding
of what is expected of him, so that the benefits
of adopting the NSCS may be limited.
Nevertheless some useful feedback has already
been obtained as a result of applying the
document.
Rationalisation of reinforcementThe basic concept of rationalising the
reinforcement is reducing unnecessary variation in
bar sizes and spacings, making the detailing,
scheduling, supply, call-off and fixing of the
reinforcement more straightforward. Although
material costs can be increased as a result this will
be more than offset by the savings in time and
labour costs. Again logistics/storage on site is
made far more efficient.
In the context of St George the reinforcement
is now highly rationalised. However historical
information is available for a non-rationalised
solution on earlier phases against which
comparisons can be made.
Use of prefabricated punchingshear reinforcement
This is a specific form of reinforcement
rationalisation relating to the provision of
reinforcement to resist punching shear. The same
principles as for reinforcement rationalisation in
general apply, but the benefits can be even more
dramatic because of the huge time savings which
can result compared with fixing many thousands
of individual shear links.
The intention will be to directly compare the
fixing time and costs of a number of proprietary
systems both with each other on a floor to floor
basis, and within a given floor compare different
methods of providing shear links on a column to
column basis. One such proprietary system is
illustrated in Figure 3.
Accurate prediction of deflectionsPrediction of deflections can be a specific
requirement to meet clients’ requirements and
those of follow-on trades such as cladding and
internal finishes. At St. George Wharf a
complicated fixing detail has had to be adopted
to accommodate movements in internal finishes
which it is suspected is unnecessary.
Measurement of the deflections actually
occurring will provide valuable data for calibration
of theoretical models and justification for simpler
and cheaper architectural details on future blocks
along with the opportunity to rationalise the
reinforcement even further.
Early age strength assessmentusing LOK tests
The intention will be to investigate the
practical benefits of using LOK tests for
determining the strength at which the slabs can
be struck. Initially the carrying out of LOK tests
will run in parallel with the making and testing of
cubes, so that confidence can be gained in their
use and comparison made with cube test results.
The relevance of the LOK test is that it gives a
true reading of the concrete strength within each
element.
The costs and convenience of carrying out LOK
tests will be compared with that of making and
testing cubes. Figure 4 illustrates LOK test inserts
fixed to soffit formwork.
Figure 3: Proprietary punching shearreinforcement system.
Figure 4: LOK test inserts.
50
Specification of ‘superstriker’concrete
There may be advantages in specifying a
higher grade of concrete to enable required early
age strengths for striking to be achieved,
especially in cold conditions. The additional cost
associated with this will be weighed up against
the benefits that accrue if this option is pursued.
Revised striking criteriaAs a result from the work at Cardington new
striking criteria have been proposed taking
serviceability criteria as those which are critical.
The opportunity will be taken at St. George
Wharf to assess the practical implications of the
new criteria in terms of promoting early striking,
and the benefits which result from it in terms of
speeding up the floor cycle. In principle every
day saved on the removal of soffit forms on this
type of structure gives the opportunity to reduce
the floor cycle by a day. This is of course limited
to the criteria and logistics of forming vertical
elements, which generally dictates the pace of
the floor cycle.
New criteria for design ofbackpropping
Again as a result from the work at Cardington
improved understanding of the true distribution
of loads through backprops and supporting slabs
has been gained. This potentially will enable the
numbers of levels of backpropping and total
amount of backpropping to be reduced.
Use of CRC JointcastIt is unlikely that CRC Jointcast will be used
extensively during the construction of the two
blocks being investigated in detail. Nevertheless it
is desired to investigate the potential scope the
material would offer for speeding up the
construction of the vertical elements and hence
the overall programme.
Use of self-compacting concreteSelf-compacting concrete offers potential
advantages in terms of reduced noise and
improved health and safety, although its
widespread use is still likely to be ruled out on
cost grounds. Nevertheless the opportunity will
be taken to use it in limited areas to compare
costs and the quality of finish achieved, and the
ease of specifying and obtaining the material.
CONSTRUCTION PROGRAMMEFigure 5 illustrates a sample portion of the
construction programme for the two blocks being
studied in detail.
Site diaries are being kept and this will allow
an as-built programme to be produced alongside
the intended programme above.
Linked to the construction programme is the
determination of pour layouts and the floor cycle.
Optimisation of the floor cycle will depend on
many factors, both technical and logistical. The
project will aim to investigate the constraints
imposed by the method of formation of the
vertical elements and ways in which these could
be overcome if found to be critical.
The optimum floor cycle for this project may
not require very early striking although the
intention is to strike earlier than on previous
phases of the project. Despite this the intention is
Figure 5: Portion of construction programme.
51
to strike some of the slabs earlier than this
optimum time to demonstrate the feasibility and
the lack of serviceability problems as a result.
CONCLUDING REMARKSIn line with Latham and Egan imperatives the
intention of this project is to help establish a
culture of continuous constructing in situ
concrete frame buildings. This will help improve
efficiency and profitability of all those involved in
the supply chains for the construction of such
buildings, and increase the potential market share
for concrete frames within the building frame
market.
This project is intended to contribute to this
overall goal by applying a methodology for
measurement of the practical benefits of
adopting innovations and providing a live case
study to demonstrate the possibilities.
ACKNOWLEDGEMENTSThe authors would like to acknowledge the
funding provided for the project by the DTI under
the Partners in Innovation scheme.
REFERENCES
1. The European Concrete Building Project, TheStructural Engineer, Vol.78, No.2 18 January 2000
PAPER 2: CONSTRUCTION
St. George WharfOur involvement on this St. George Wharf
project goes back to Phase I where we were
invited by St George to tender for the RC frame
for the first floor, which was Phase I, Blocks B & C.
Unfortunately we were not successful on the
first phase, however, we managed to secure
another project for the same developer,
Smugglers Way Wandsworth, at the same time.
Being persistent we lodged our interest in
tendering for future phases of St. George Wharf,
having proved our capabilities on Smugglers Way
Wandsworth we were indeed invited to tender
for Block D and were ultimately successful in
securing Block D. One of the most important
factors in any RC Frame is the opportunity to plan
the whole process in relation to the safe systems
of work, design/detailing, logistics incorporating
access and egress on site.
Cranage is one of the key factors in any RC
Frame. Here we had the opportunity to plan the
crane layout and capacity in line with our own
and St George’s requirements. On the residential
phases the sequence of construction was driven
by St George’s sales and marketing requirements
which were sequenced from river to road. This
meant starting our works on the part of the
building with fewer floors to roof level.
Ultimately the highest part of the structure is on
the road end so we sequenced our works in
parallel to give the earliest completion
programme for the RC Frame as a whole along
with the earliest release date for one Tower crane
to be free to start the external cladding on the
river end of the structure without clashing with
the cranage requirements of the RC Frame.
One of the major benefits of being involved in
this project has been the willingness of the client
to involve Stephensons in the whole process. The
norm in the Industry has been a ‘fait accompli’ -
52
the design is finalised, the logistics are not ideal,
the contract is agreed on the Friday, start
Monday. This gives the Contractor little
opportunity to refine the RC Frame process of the
construction. So as Clients, Contractors or
Developers, please involve the likes of us in the
process earlier.
Our scope of work on this project was to carry
out the temporary sheet piling, cranage, bulk
excavation, drainage, all the RC elements from
top of piles to, and including, the Gull Wing roof.
We appointed White Young Green, Structural
Engineers, to work with us on the development
of the reinforcement and the design detailing of
the structure. The whole concept for St George is
to optimise the speed and efficiency of the RC
frame to accommodate the quick follow-on of
other trades and it is to this end that we are
obviously working to optimising the speed and
efficiency of these structures.
There has already been some advertised
figures on the comparison of man hours on Phase
I, Block B & C and ourselves on Block D & E.
Whilst this tends to show a significant saving
in formwork/concrete operations in terms of man
hours, there are several factors which come into
play when doing a comparison. One is formwork
systems used on the soffit, column and walls. On
Phase II we used our Ischebeck Titan system on
the soffit and our own DOKA framex panels on
walls and columns. From our experience we find
these two systems efficient on this type of
construction. The comparison on the steel
fixing element again shows a slight reduction
which may be due to the way we have detailed
the reinforcement on the Phase II and future
phases. One of the most important factors at the
end of the day is the calibre and motivation of
the operatives on site.
From the structural drawings you will see the
complexity of the sub structures and the relatively
simple floor plates of the super structures,
incorporating the precast balconies which were
stitched in to the floor as work progressed.
Through Construct, of which we are one of the
founding members, they have produced the
National Structural Concrete Specification, which
is being adopted on this project. As a contractor
this gives us an opportunity to work to a known
standard specification throughout each phase of
this project, and to the industry as a whole, with
certainty of expectation.
One of the key elements to allow following
trades to follow us closely was to limit the
overhang of our flying form system. Here we
used our own Ischebeck Titan table system which
allowed us to have fairly large flying form tables
of approximately 80 square metres, weighing
approx 3t, with a nominal overhang with safe
perimeter access. In general this is limited to
approximately 600mm from the edge of the slab.
This was to accommodate marble mosaic, lifting
the external cladding panels close behind us. On
Block E, where each floor was poured on a
53
weekly cycle in one, by concrete pump, the crane
was released to marble mosaic where they fixed
the external cladding panels to the floor below
the flying form table.
On this project all the vertical elements were
formed using the tower cranes on site and the
majority of the horizontal elements, i.e. floor
plates, were poured by concrete pump. With the
use of large soffit forms, which gives you a quick
release of available soffit to fix to reinforcement,
it was vital to detail the reinforcement with speed
and efficiency. Our philosophy on this project
was to detail the reinforcement with as much as
12-metre stock length bar and cut as straight as
possible with the reinforcement detailed to
accommodate the day joint positions. This not
only made it very efficient in labour in terms of
sourcing each bar, it is more economic to buy
stock or straight bar than cut and bent. Following
on from the initial two phases we were now in a
position to use electronic exchange of rebar
information which means our Structural Engineer
could issue the schedules/details electronically, we
could then transmit our requirements to our
supplier, in this case Express Reinforcements. As
indicated, the main benefits to us was that we
were able to track the supply process within
Express Reinforcements production processes and
be certain that deliveries would be met as
required, which limited the amount of double
handling and storage areas required. This also
allowed us, as a company, to correlate the value
of materials earlier and compare relative labour
outputs to tonnage fixed.
Incorporated into the top and bottom mat
reinforcement are some of the key elements of
design, namely punching shear reinforcement.
Over the years we have used various methods
and we have our own internal view on which is
the most cost effective method for each design
requirement. On this project we intend to
demonstrate the comparisons more fully, with the
comparisons on various floors to see what the
effect on man hours and material costs are in
relation to each floor. This will be published to
the industry.
Within our reinforcement detailing and design
we take account of permissible deflections within
floors. The relevance of predicting more accurate
deflections as previously said is to optimise not
only the cladding details but also the floor
finishes. Differing deflections obviously can
impact dramatically on the style and cost of
following flooring systems. As a frame contractor
one of the main problems we have is meeting the
structural tolerances to slabs whether this be
tamp finish, skip float or power float, which can
be achieved when pouring.
One of the most important factors as a
Contractor is to optimise the early strength of the
concrete particularly on slabs, which gives us the
opportunity to strike soffit forms and move on to
the next floor. In simple terms every day gained
on the striking of the soffit forms gives the
opportunity to reduce the floor cycle by a day.
The main restriction on speeding up the floor
cycles is the amount and complexity of the
vertical elements and this at the end of the day
will dictate the pace of most RC frame structures.
So carrying out parallel LOK tests with air cured
cubes and tank cured cubes under the BS
requirements will hopefully produce certainty of
results on the concrete in the slab itself.
As you will see from the programmes the
turnaround on the lower floors is generally two
weeks floor to floor reducing to a week floor
cycle where the floor area reduces on the towers
and infill blocks.
St George being a very demanding client, after
each phase, tend to pick on the fastest floor cycle
achieved and relate that to all the floors no
matter how large and say ‘why can’t you do it
every time’!
Given the nature of the structures of St.
George Wharf, the work we are doing with the
BRE and M4I will give us, as a frame contractor,
the opportunity to formulate our findings in
relation to each element. It will also give us the
potential to reduce our overall construction
programme, clear the floors of back propping at
an earlier stage, give certainty of deflections on
the structure, optimise our reinforcement detailing
even further and move on to the next Phase
producing benefits to ourselves and the client.
54
55
Don Hobbs is a Concrete
Materials Consultant. He
retired from the British Cement
Association in 2001. His main
speciality is the durability of
concrete and mortar. He has
published papers dealing with the strength,
deformation, movement and durability of
concrete.
ABSTRACTConcrete may deteriorate due to inadequate
design and construction practices, lack of
maintenance or because an inadequate concrete
was specified. This paper concentrates on the
material aspects of concrete deterioration. The
most common, and serious, cause of
deterioration in structural concrete members is
due to corrosion of reinforcing steel induced by
chloride ion ingress and oxygen ingress into
concrete. Other less common causes of
deterioration in concrete are freeze-thaw attack,
carbonation-induced corrosion, alkali-silica
reaction and external and internal chemical
attack. In this paper, the causes, diagnosis and
measures to minimize deterioration in new
concrete construction are discussed.
KEYWORDSDeterioration, Diagnosis, Carbonation,
Chlorides, Corrosion, Freeze-thaw attack, Alkali-
silica reaction, Delayed Ettringite formation,
Minimising risk.
INTRODUCTIONWhere concrete and reinforcement cover meet
the prescriptive requirements in standards and
codes, durability problems attributable to
concrete as a material are relatively rare. The
problems, which sometimes arise, are often due
to design and construction faults. For example,
in an analysis, by cost, of building defects in
France [1], it was found that 43% of the building
defects were due to design faults, 43% to
construction faults, 6% to faulty material and 8%
to faulty maintenance. The situation is probably
similar in other countries.
Two construction faults, which have too
commonly lead to deterioration in concrete
members, are inadequate cover to reinforcement
and inadequate compaction of concrete. The
former can lead to premature deterioration due
to chloride - or carbonation - induced corrosion
and the latter to premature deterioration due to
corrosion, freeze-thaw attack, sulfate attack or
acid attack. Two inadequacies in design which
have led to premature deterioration due to
chloride-induced corrosion are the failure of
expansion joints above bridge piers and
abutments, allowing salt-laden water to run onto
and pond on the tops of piers and abutments,
and the presence of cold joints close to ground
level allowing easy access of chloride bearing
water into the concrete [2] (Figure 1).
In the case of chloride-induced corrosion, the
UK Highways Agency in 1995 issued Advice
Notes [3] to improve the durability of highway
structures by drawing to the attention of
designers aspects of design and detailing which
are relevant to the durability of structures but are
not covered adequately in the existing
requirements for the design of these structures.
Thus there is a tacit acceptance that changes in
material specifications, except by using non-
corrodible reinforcement or plain concrete, may
not have major effect on the frequency of
corrosion problems in highway structures.
This paper discusses the causes and diagnosis
of deterioration processes in concrete, how
deterioration can be minimized and where our
understanding of the deterioration processes is
incomplete. This paper is restricted to the
material aspects of deterioration and
concentrates on processes that are considered to
lead to cumulative deterioration. External
chemical attack on concrete is not considered. A
more detailed discussion, including external
chemical attack, is given in reference 4.
CAUSES OF CONCRETE CRACKING AND DETERIORATIONCracking and deterioration of plain concrete
and reinforced concrete can be caused by a
variety of processes:
• structural loading
• plastic shrinkage
THE DURABILITY OF CONCRETE
Dr. D.W. HOBBS BSc, PhD, CPhys, FInstP
Consultant
56
• plastic settlement
• chemical shrinkage or self-desiccation
shrinkage in high strength concrete
• thermal contraction
• drying shrinkage
• movement resulting from the use of a
moisture sensitive aggregate
• chloride-induced corrosion
• carbonation-induced corrosion
• freeze-thaw attack
• external sulfate attack
• external acid attack
• oxidation of iron sulfide minerals in certain
aggregates resulting in internal sulfuric
acid followed by sulfate attack
• alkali-silica reaction (ASR)
• delayed ettringite formation (DEF).
Figure 1: A bridge pier showing, withstraight arrows, possible easy accessroutes for chlorides which can resultfrom inadequacies in both or eitherdesign and construction.
Only cracking due to structural loading is
predictable, for example a partially cracked
concrete beam. The cracking due to the other
processes is caused by external or differential
internal restraint. The causes of cracking shown
in italics in the list above, are the most common
forms of deterioration where remedial actions are
sometimes required. The last five are, in general,
relatively rare causes of deterioration.
DIAGNOSIS OF THE CAUSE OF DETERIORATIONIt is extremely important that the cause or
causes of deterioration in a concrete structure are
correctly diagnosed. Deterioration caused by
reinforcement corrosion, but not pitting
corrosion, is generally easy to recognise as it
results in rust staining, cracking along the lines of
the links or main reinforcement, followed by
spalling of the cover concrete or its removal over
large areas. Deterioration due to other processes
is less easily recognised and the judgement
should be made by a professional who is familiar
with all forms of concrete deterioration and their
recognition. In the author’s experience, all too
often this is not done, frequently resulting in an
incorrect diagnosis leading to inappropriate repair
actions, sometimes unnecessary demolition and
to inappropriate guidance being given on
measures to avoid such damage in future
construction. The age at which cracks first
appear can provide guidance as to the underlying
cause of cracking. Plastic and self-desiccation
cracks take from a few hours to ten hours to
appear, thermal cracks two to ten days, drying
shrinkage cracks less than a year, cracking due to
the use of a moisture sensitive aggregate less
than a year, alkali-silica reaction generally one to
ten years, but longer if the aggregate releases
alkalis, and cracking due to delayed ettringite
formation two to twenty years. The following
points can also assist in establishing the cause or
causes of cracking:
• External restraint of contraction (drying or
thermal) can induce uniformly spaced
unidirectional cracking
• If the outer layers of concrete expand less
or contract more than the heart concrete,
then in lightly loaded and unreinforced
concrete a characteristic visual crack
pattern can be induced which is dissimilar,
but sometimes confused with that induced
by freeze-thaw deterioration of the
cement paste fraction of a concrete
(Figure 2). The visual cracks are
perpendicular to the exposed face
• If the outer layers of concrete expand
more than the heart concrete then cracks
parallel and close to the concrete surface
can be induced (freeze-thaw attack and
external chemical attack are examples).
Such cracking can be inferred by the
hollow sound obtained upon lightly
tapping the concrete with a geologist’s
hammer
57
• Shrinkage can cause joints to open,
displacements and increased deflection of
beams
• Expansion can result in closing up of
joints, displacements and hogging of
beams
• Early age cracks are regular and late age
cracks are often irregular. Spalling is
caused by corrosion or freeze-thaw attack
and is unlikely to be caused by the other
processes. Scaling is caused by freeze-
thaw attack of concrete exposed to de-
icing salts
• Deterioration can be caused by more than
one process, for example, chemical attack
can reduce the freeze-thaw resistance of
the affected concrete and freeze-thaw
scaling can reduce cover to reinforcement
increasing the probability of reinforcement
corrosion.
If it is still unclear as to why deterioration has
occurred, then cores should be taken from cracked
and uncracked sections of the element or structure,
cut along their length, vacuum impregnated with
an ultra-violet (UV) fluorescent dye and the flat
surfaces lightly ground. The sections are then
examined under UV light to establish the pattern of
cracking, as each deterioration process, if acting
alone, can lead to a characteristic internal crack
pattern, the recognition of which can often assist in
diagnosis [4].
Occasionally, it will be necessary to examine
thin sections under the petrographic microscope
to assist in establishing the cause of deterioration.
If the internal cracking is characteristic of that
induced by ASR and evidence of significant ASR is
apparent in thin sections, namely cracked and
reacting aggregate particles and ASR gel in cracks
and pores, then it can be concluded that ASR has
led to expansion and cracking. If peripheral
cracks filled with ettringite, thaumasite or
portlandite are observed around many of the
aggregate particles, then expansion due to
external or internal sulfate attack has probably
occurred If the peripheral coarse aggregate
cracks are greater in width than 15 μm and are
either empty or filled with ettringite and the
concretes have been subject to a severe early
temperature cycle then DEF has led to expansion.
REINFORCEMENT CORROSIONThe steel in a moist concrete is protected
against corrosion by the high alkalinity of the
pore solution in the concrete. At the high pH
levels which exist in concrete, a passive film of
ferric oxide forms on the surface of the steel
protecting it from further corrosion. There are
two ways in which this ferric oxide layer can be
destroyed. One is as a result of the reduced pH
in the cover concrete caused by carbonation and
the other is due to the presence of chloride ions.
Once corrosion has commenced the rate of
corrosion is controlled by the ease at which
oxygen enters the concrete and by the availability
of moisture.
The corrosion product which forms has a
volume two to four times the volume of steel
before it oxidized, consequently internal stresses
can be induced in the concrete which can
eventually lead to cracking along the lines of the
reinforcement, spalling of the concrete, loss of
bond and reductions in member strength.
CRACKING DUE TO CARBONATION-INDUCED CORROSION
When carbon dioxide from the
atmosphere diffuses into concrete, it combines
with pore water, forming
carbonic acid, which then reacts
with alkali hydroxides forming
carbonates. In the presence of
free water, calcium carbonate is
deposited in the pores of the
concrete at the depth at which
carbonation is occurring. As a
consequence of carbonation,
the pH of the pore fluid drops
from a value greater than 12.6
in the uncarbonated region, to
a value of about 8 in the region
of complete carbonation. If this
reduction in alkalinity occurs
Figure 2: a. Visual cracking due to ASR or DEF or theuse of a frost susceptible coarse aggregate.Unreinforced concrete. b). Visual cracking due tofreeze-thaw attack in the absence of external salt.
58
close to the steel, it can cause depassivation. This
depassivation occurs before the carbonation
‘front’, the zone representing complete
carbonation of alkaline species, reaches the steel.
In the presence of moisture and oxygen this can
lead to corrosion followed by corrosion-induced
cracks along the lines of reinforcement, followed
by spalling and loss of concrete section. The
service life of an element under these conditions
is defined in this review as the sum of the
‘initiation period’, which is the period taken for
the carbonation front to reach or approach the
steel, plus the ‘propagation period’ which is the
period between initiation of corrosion and the
visual appearance of cracks.
In practice, carbonation-induced corrosion is
generally regarded as a minor problem compared
with chloride-induced corrosion [5]. However, the
bulk of structural concrete is used in residential,
industrial and office buildings, rather than
engineering structures. Thus the potential service
life of most reinforced concrete is governed by
the rate of carbonation, the cover to
reinforcement and the rate of reinforcement
corrosion. The rate of carbonation depends upon
curing, water/binder ratio, binder type and
aggregate permeability. Most research on
carbonation has been restricted to unreinforced
concrete containing high quality dense
aggregates. Relatively few studies have been
made of carbonation-induced corrosion.
With reducing relative humidity, the
carbonation rate goes up, but after corrosion
commences, the corrosion rate goes down. The
net effect being that the highest risk of
premature deterioration, due to carbonation-
induced corrosion, exists for concrete subject to
an external exposure averaging about 80%RH.
For many concretes subject to sheltered
external exposure in the temperate regions of the
world, the average long-term relative humidity to
which the concretes are exposed is probably
about 80% - 85%. At a relative humidity of
80%, Parrott [6] has deduced that the depth of
carbonation, dc, is related to concrete age, t, by
the expression:
dc α t 0.4 ......................... (1)
Parrott also deduced that when concrete is
subject to long-term exposure at 80% RH,
cracking of the concrete, initiated by carbonation-
induced corrosion, will commence approximately
twenty years after the front of total carbonation
reaches the steel. Data obtained by Brown [7, 8] on
seven UK bridges fifty one to fifty five years of
age broadly supports this deduction. Thus, if the
propagation period to cracking is taken to be
twenty years after the carbonation front reaches
the steel, then for design lives of fifty and one
hundred years, the carbonation depth should not
exceed the cover depth at thirty and eighty years
respectively.
Several investigators at the British Cement
Association (BCA) and the Building Research
Establishment (BRE) in the UK have measured the
depth of carbonation in PC concretes, subject to
sheltered external exposure [7]. The carbonation
depths obtained are shown plotted against free
water-cement ratio in Figure 3. The carbonation
depths plotted in Figure 3 have been normalized
to ages of thirty and eighty years using equation
1. From this figure the minimum water-cement
ratios for fifty and one hundred year service lives
can be deduced for various covers. For a cover of
30mm and for concretes subject to a one-day
cure, maximum free water-cement ratios of 0.65
(C25/30*) and 0.45 to 0.50 (C40/50 or C35/45)
should ensure that the depth of carbonation is
unlikely to exceed the cover until after ages of
thirty and eighty years respectively, giving service
lives of fifty and one hundred years. Data leading
to the same conclusion has been obtained by
non-UK investigators [7].
Figures 4 and 5 show similar plots for
concretes containing 30% to 35% fly ash by
mass of the combination and 50 and 70% slag
by mass of the combination [4]. Note that the
data plotted for slag are limited. To compensate
for slag’s slower strength development, the
formwork for concrete containing more than
35% slag by mass of cement, or combination, is
required to be stripped at a later age than PC
concrete. According to EN 1992-1[9] three days
for a slag concrete is approximately equivalent to
one day for a PC or PC/fly ash concrete.
Examination of Figures 4 and 5 indicates that a
maximum free water-binder ratio of 0.45 for
PC/30% (C28/35) fly ash concretes and PC/70%
slag concretes should result in a fifty year service
life with maximum water-binder ratios of 0.40
(C40/50) and 0.30 respectively being required for
a one hundred year service life. These maximum
water-binder ratios may be taken to be applicable
to concretes made using dense aggregates of low
absorption. Aggregates of higher absorption can
result in greater carbonation depths [4] and hence
for a given cover, shorter design lives.
* Cylinder compressive strength/cube
compressive strength (MPa)
59
In the case of PC/10% silica fume concrete
and PC/15% ground limestone concrete, the
published data is limited. In the case of the
former, similar water-binder ratios to those for PC
concretes should ensure the same service lives [4],
whilst in the case of the latter a reduction in
water-binder ratio of approximately 15% is
required [10].
CHLORIDE-INDUCED CORROSIONChloride ions can be present in concrete as a
result of the application of de-icing salts,
exposure to a marine environment, airborne salt,
or from the concrete constituents, for example,
calcium chloride added as an accelerator to the
concrete. As a consequence of corrosion
problems in field concrete most countries prohibit
the use of calcium chloride in reinforced and
prestressed concrete. In Europe the permissible
maximum total chloride ion levels in fresh
concrete are 0.4% [11, 12] or 0.2% [12] for
reinforced concrete and 0.2% [11] or 0.1% [12] for
prestressed concrete. These limits apply
irrespective of whether or not the concrete is
exposed to external chlorides, the limits being
viewed as conservative. However, recent work [13]
has shown that corrosion can initiate, under wet-
dry cycling, at an added chloride level ‘somewhat
over 0.4%.
For concretes exposed to external chlorides,
the service life is taken to be the sum of the
initiation period, the time taken for the chloride
ion concentration at the steel to reach the
threshold level for corrosion, plus the time taken
for the subsequent corrosion to induce cracking.
The main parameters influencing ingress of
chlorides into concrete are water/binder ratio,
binder type and aggregate permeability [4], the
latter being generally ignored.
In the case of concrete elements exposed to
de-icing salts, chloride ingress into the cover
concrete often occurs by capillary suction; with
subsequent wash-out of some of the chlorides
occurring when the concrete is exposed to rain or
non-salt-laden vehicle spray. Ingress of chloride
ions into the concrete is also complicated by the
process of carbonation which changes the bound
chloride level and the permeability of the affected
concrete. Carbonation can, depending upon the
binder type, reduce or increase the permeability
of the surface layers, the effect being most
marked in concretes containing fly ash and
slag [14, 15]. The influence of carbonation is
greatest in parts of structures protected from
direct rain. For example, in the case of bridge
piers it may be a year or two before they are
subject to their first significant vehicle spray. For
such elements, significant drying and carbonation
of the cover concrete is possible [2].
Figure 3: Dependence of carbonationdepth upon free w/c ratio. PC concretes.Sheltered external exposure. UK data.
Figure 4: Dependence of carbonationdepth upon free w/c ratio; 30-35% fly ash.Sheltered external exposure. UK data.
Figure 5: Dependence of carbonationdepth upon w/c ratio; 50 and 70% slag.Sheltered external exposure. UK data.
60
Measurements of total chloride ingress into
concrete subject to intermittent exposure to salt-
laden water or vehicle spray have been made by
a number of investigators [4]. Some of the results
obtained are plotted in Figures 6 to 8. The data
obtained on concretes containing slag and fly ash
and, particularly, silica fume is limited. On the
basis of Figures 6 to 8 it can be seen that firm
judgements as to whether or not concretes
containing composite cements or combinations
with covers of 30 mm to 40 mm give longer
service lives than PC concretes of the same
water/binder ratio cannot, as yet, be made.
However, at low covers, less than 20 mm,
examination of Figures 6 and 7 indicate that the
use of some composite cements or combinations
may increase the risk of premature deterioration
due to corrosion.
Apart from cover, the magnitude of the
parameters influencing service-life are only
imprecisely known, consequently the view can be
taken that prescriptive
requirements and minimum
cover for concrete for concrete
exposed to de-icing salts should
be based on actual field
performance. Table 1
summarizes observations made
on reinforced and prestressed PC
concrete bridge elements and
precast concrete blocks stored
close to a carriageway beneath
an overbridge [4]. Examination of
Table 1 shows that, with the
exception of concrete exposed to
leakage from a bridge deck, the
quality of concrete as
represented by water-cement
ratio is a major factor influencing service life.
It has been deduced from such performance
data that for in-situ concrete of maximum
water/cement ratio 0.45 a cover of 30 mm to 45
mm is likely to give a fifty year design service life[19]. This deduction is applicable to concretes
containing low levels of inherent chlorides made
using dense aggregates of low absorption (water
absorption <1.0% by mass) subject to a mean
exposure temperature of 10˚C to 15˚C. For the
exposed top face of an in-situ cast element,
Hobbs and Matthews [19] recommend an increase
in cover of 15mm, whilst for factory produced
concrete the UK Highways Agency [3] specifies a
reduction in cover of 10 mm as compared to in-
situ concrete, ie in the above 30 mm to 45 mm
becomes 20 mm to 35 mm.
Figure 6: Chloride concentration (bymass of cement) profiles for bridge piersexposed to de-icing salt. Height 1m.Distance to nearest traffic lane 4.75 to5.0 m. Age 5 years. Vassie [16] .
Figure 7: Chloride concentration (bymass of concrete) profiles for concreteblocks exposed to de-icing salt. Age 9years. Bamforth and Al-Isa [17].
61
Investigator Structures When Concrete ‘Intended’ Water- ConditionBuilt Strength cover cement
(MPa) (mm) ratio
Thomas In-situ 1978 49 - 0.45-0.50+ At depth 35mm,1989 bridge pier low chloride level
at 10 years
Vassie In-situ 1985 C37.5 - 0.45 At depth 25mm1995 bridge piers C30 - 0.47 low chloride levels
at 5 years
Stolzner Bridge piers. 1970 - 30 - 40 0.40 - 0.45 At 21 years1993 Denmark negligible chlorides
below 10mm
Henriksen Columns of 1940-90 - 30 - 40 0.40 ‘Predicts’et al 1993 20 bridges 50 year life
Denmark
Author’s Central About C45? 25 - 28 0.45 At 35 yearsexamination Bridge piers 1960 (2:1:1 mix) condition good1995 M1, UK apart from some
minor spallingwhere cover low(probably <10mm)
Somerville Precast UK From early 60 - 80 >21 - 40 0.35 - 0.42 A history of good1995 pre-tensioned 1940s performance
members
Clark Precast From early - - Probably A history of1992 Post-tensioned 1940s 0.35 - 0.42 good performance
members
Highways Precast - C40 >45 Probably Have generallyAgency UK pre-tensioned C50 >35 0.35 - 0.42 proved to be1995 members durable
Brown Elements of 1961 - 12 - 48 0.32 - 0.57 Spalling where de1987 8 bridges to 1972 -icing salt solution
UK drained from deckacross crossheadsand tops of columns.Otherwise sound.
Anderson Bridge 1956 - 30 - 40 0.40-0.45 Good, Cl- level1997 columns. at 30mm
5 bridges 1956 30 - 40 0.40-0.45 ≤0.02%; ≤0.05%. Denmark 1968 30 - 40 0.40-0.45 ≤0.07%; ≤0.04%
1972 30 - 40 0.40-0.451963 30 - 40 =0.65+ Good, but Cl- up to
0.08% at 30mm
Bamforth Precast 1988 41 10 - 40 0.66 Cl- 0.18% and Al-lsa blocks at 30mm depth1997 48 10 - 40 0.62 Cl- 0.125%
at 30mm depth
Polder Parapet 1965 60 at - 0.45 - 0.55 Cl- <0.1%and Hug wall of 30 years at 30mm depth2000 bridge Cl- <0.05%
at 40mm depth
Table 1: Performance of concrete structures subject to de-icing salt exposure. (+ Estimated).
62
Figure 8: Chloride concentration (bymass of concrete) profiles for bridgepiers exposed to de-icing salt. Age 40years. After Anderson [18].
FREEZE-THAW ATTACKIn the UK freeze-thaw attack is, after
chloride-induced corrosion, the most common
cause of concrete deterioration. Three types of
deterioration are induced by freeze-thaw attack:
• expansion, internal cracking and spalling
• scaling associated with the application of
salt
• pop-outs caused by the use of freeze-
thaw susceptible coarse aggregate
particles.
An example of surface cracking associated
with freeze-thaw expansion is shown in Figure 2.
Within such concretes cracks are present parallel
to the exposed face which decrease in intensity
with depth changing to a random distribution of
cracks often about 100 to 200 microns or more
in width. Under the microscope large crystals of
portlandite can sometimes be seen. The
deterioration associated with expansion can result
in major reductions in compressive and tensile
strength.
Expansion can be caused by ice formation in
the cement paste fraction or within freeze-thaw
susceptible coarse aggregate particles. In order
for internal stresses to be induced by ice
formation, about 90% or more by volume of the
pores need to be filled with water. This is
because the increase in volume of water when it
turns to ice is about 8%. This simple explanation
accords with the experimental observations [20, 21].
However, it is considered that this explanation is
not entirely satisfactory as when ice forms in
capillary pores water tends to move from
unfrozen regions towards these pores [22].
In many countries de-icing salt scaling is
recognised as the most serious freeze-thaw
problem. When de-icing salts are applied to a
thin layer of ice that has formed on a concrete
surface the ice melts, the melting of the ice
requires a large amount of energy and as a
consequence the temperature of the surface
decreases very rapidly and this causes a thermal
shock that can induce cracking and surface
scaling.
A number of field freeze-thaw exposure tests
have been carried out on non-air-entrained PC
concretes, particularly in North America [4, 21]. The
tests show good performance when the
water/cement ratio is below 0.6 and 0.5 for
concretes saturated in the absence of salt and
saturated in the presence of salt respectively.
In the case of concretes containing slag, pfa
and ground limestone there are fewer long-term
field test observations than for PC concretes and
judgements are sometimes based on accelerated
laboratory freeze-thaw tests in which
performance is either based on the magnitude of
the induced expansion or, in the case of concretes
exposed to external salt, to the mass of scaled off
material. These tests have shown that non-air-
entrained concretes containing fly ash, slag or
PLCs, give inferior performance to non-air-
entrained PC concretes of similar water/binder
ratio, perhaps because the entrapped air content
is reduced and similar or inferior performance at
the same grade [4].
It has been known since 1941 that air-
entrainment greatly enhances the freeze-thaw
resistance of concrete both in the absence and
presence of salt. Results obtained by Kleiger [23],
on which American [24] and UK [12] requirements
are probably based, are shown in Figure 8. In
laboratory performance tests, in the absence of
external salt, air-entrained concretes containing
silica fume or fly ash, slag or limestone give
similar performance to PC concretes of the same
grade [21]. In the presence of external salt, air-
entrained concretes containing high quantities of
fly ash [4, 21] (>35%) or slag [4, 21] (>55%) give
inferior performance to PC concretes of the same
grade.
Table 2 gives the minimum qualities of
concretes made using freeze-thaw resistant
coarse aggregates, which based on the literature
should give good freeze-thaw resistance. Due to
lack of published data, guidance is not given for
air-entrained concretes containing more than
65% slag or 20% ground limestone.
63
CRACKING DUE TO ALKALI-SILICA REACTION
The alkali-silica reaction (ASR) is a reaction
between the hydroxyl ions in the pore solution
within a concrete and certain forms of silica
occasionally present in significant quantities in the
aggregates, the most reactive forms of silica
being opaline silica and volcanic glass with
cristobalite and tridymite being of lower reactivity.
It is often stated that crypto and micro-crystalline
quartz and strained quartz are reactive, but this,
in the author’s view, has not been established, ie
by comparing x-ray diffraction patterns of
representative ground samples of an aggregate
before and after dissolution in an alkaline
solution. It is perhaps more correct to state that
reactive silica can be associated with these forms
of silica.
Figure 9: Influence of air content uponexpansion after 300 cycles of freezingand thawing [23].
Exposure Cement or combination Maximum Minimum Entrainedw/c grade (MPa) air-content (%)
Saturated, PC, SRPC 0.55 C32/40 -no external salt
PC/10% sf 0.55 C35/45 -
PC/50% slag 0.50 C35/45 -
PC/30% fly ash 0.40 C35/45 -
All except slag >65%, 0.60 C25/30 3+
ground limestone >20%
Saturated, PC, SRPC 0.45 C40/50 -external salt
PC/10% sf 0.50 C40/50 -
PC, SRPC 0.55 C30/37 3+
fly ash <35%slag <55%silica fume <10%
Table 2: Minimum qualities of concrete for long-term freeze-thaw resistance. (+ Concrete with aggregate of maximum size 20 mm).
The product of the ASR is a gelatinous hydrate
containing silica, sodium, potassium, calcium and
water and its formation and growth can
occasionally induce internal stresses of sufficient
magnitude to induce fine cracking, expansion and
visual macro-cracking in concrete. The reaction
ceases when either of the reactants is depleted or
when the hydroxyl ion concentration is reduced
to a threshold level. Normally for expansion and
cracking to result from ASR an external source of
water is required, expansion only occurring when
the external humidity is in excess of about 90%
to 95% RH [25]. The expansion and severity of
cracking induced by ASR depends upon the form
of reactive silica, the proportion of accessible
reactive silica present in the aggregate, the
porosity of the aggregate and the available alkali
content. Full scale load tests on concrete
members which have expanded due to ASR
indicate that visually severe ASR cracking can be
deceptive and that the expansion and cracking
which ASR induces may not lead to an
unacceptably adverse effect upon the structural
performance of reinforced or prestressed concrete
members. However in parts of structures where
movements are critical, ASR expansion can render
a structure unfit for service until repairs are
carried out, to a lock gate or a turbine housing
for example.
64
The influence of available alkali content of the
concrete upon expansion of concretes containing
chert or flint aggregates and some other
aggregates is shown in Figures 10 and 11. The
alkali levels required to initiate abnormal
expansions vary quite widely, for UK chert-
containing aggregates about 5kg/m3 and for UK
greywackes about 4kg/m3, consequently to
minimize the risk of ASR expansion in exposed
concretes the alkali limit should be related to an
established performance of the aggregate.
The effectiveness of fly ash or slag in reducing
expansion due to ASR, when used as partial
replacement for a high alkali PC (Na2Oe>0.9%), is
dependent upon their total alkali content and the
proportion of PC replaced. At replacement levels
above 20 per cent, expansion is generally
reduced, but at lower replacement levels (≤ 10%)
expansion can be increased indicating an effective
alkali contribution from the fly ash or slag greater
than that from a high alkali PC. Although at
replacement levels above 20 per cent expansion is
reduced, the results obtained by some
investigators on concretes wrapped in wet sleeves
indicate a positive effective alkali contribution
from high alkali fly ash and high alkali slag of up
to 1kg/m3 [4] and that if abnormal expansion
occurs it can take two to six times as long as for
a comparable PC. There is general agreement
that low alkali fly ashes and slag are particularly
effective in reducing expansion due to ASR [29].
CRACKING ATTRIBUTED TO DELAYED ETTRINGITE FORMATIONIn a number of isolated cases, expansion and
cracking has occurred in some precast concrete
elements subject to a severe early heat treatment
followed by wet or moist exposure and in some
in-situ concretes of large section size and high
cement content, again subject to wet or moist
exposure [4]. The cracking in UK elements took
eight to twenty years to manifest itself. In many
instances the cracking was wrongly attributed to
ASR perhaps, in part, because the cracking was
associated with high alkali content concretes.
The affected precast elements are normally of
high quality and made using high alkali RHPC. In
the UK the affected in-situ concretes were placed
in the summer months generally on concrete cast
twenty four hours earlier and their cement
contents and alkali contents were in excess of
450 kg/m3 and 4.0kg Na2Oe/m3 respectively (see
Table 3). Assuming a temperature rise of 12˚C to
14˚C per 100kg/m3 of cement gives a peak early
temperature possibly in excess of 80˚C.
In thin sections taken from parts of the
cracked elements peripheral cracks are observed
around a high proportion of the coarse aggregate
particles (~80-90%) and a proportion of the sand
particles (~50%). These cracks are often filled
with ettringite, but occasionally they are empty.
In cracked concretes, the band widths around the
coarse aggregate particles exceed 15μm, which
for 10mm aggregate particles, implies a concrete
expansion in excess of about 0.3%. In laboratory
concrete specimens (75 x 75 x 250mm in size)
visual cracks appear at an expansive strain of
about 1.0%. In the affected concretes examined
to date in the UK, the degree of ASR reactivity
varies from ‘not detectable’ to ‘moderate’ (gel-
lined cracks) with no evidence that ASR has led to
expansion (see Table 3).
Figure 10: Dependence of expansionupon concrete alkali content. Chert-containing ‘gravels’. 38˚C or 40˚C. PCconcretes [26, 27] .
Figure 11: Dependence of expansionupon concrete alkali content.Greywackes. PC concretes. 38˚C or 40˚C [26, 28].
65
The reasons why the concretes expand is not
clearly understood, but in general the assumption
has been made that the expansion is due to the
formation, at late ages, of excessive quantities of
ettringite. Laboratory tests on concretes and
mortars immersed in water show that expansion
depends upon the peak early temperature and is
unlikely if this temperature does not exceed 70˚C
(Figures 12 and 13). Limited laboratory data on
mortars subject to a peak early temperature of
90˚C indicate that the replacement of a
susceptible cement by at least 20% fly ash or
35% slag is likely to prevent abnormal expansion
from occurring [4].
All of the field cases with which the author is
aware are associated with high alkali cements.
Laboratory test data supports such an observation
(Figure 14) and also shows that a cement’s
susceptibility correlates with its two day strength
class (Figure 15).
From the literature and the discussion above it
follows that cracking due to DEF in concretes
subject to wet or moist exposure can probably be
minimized by complying with the
recommendations in Tables 4 and 5. The
recommendations are applicable to non-air-
entrained concretes. In the case of Table 4, the
recommendations are based in large part on
results obtained on mortars and concretes
immersed in water. These specimens were of
small size, consequently major loss of ions from
the pore solution could have occurred. Until long
Structures Elements Minimum When DEF Cement Cement Intensitysection placed cracking* content alkali of ASRsize (kg/m3) content
(%Na2Oe)
5 bridges, Abutments Large ? Yes ~480 ~0.90 Not Yorkshire & and wing detectableLancashire walls
1 bridge near Wing Large ? Yes High ~0.90 Moderate,Liverpool. but no
internal ASRcracking
Bridge, Beam >1.0m ? Yes ~500 Probably Moderate,Midlands ~0.90 but no
internal ASRcracking
15 bridges, Abutments >600mm Summer Yes ~480 1.05 NotSomerset and wing 1974 to 1.40 detectable
walls. to minor
2 dry docks, Foundations Massive 1973 Yes Very 1.05 -
England and 1974 high to 1.40
Approximately Foundations, 700mm 1969-71 No 420 1.05 High,internal25 structures beams upwards to 550 to 1.40 internal ASRSW England retaining wall cracking
9 storey ~110 1m 1969-71 No+ 460 1.05 Highstructure, foundation upwards to 550 to 1.40SE England pads
Table 3: Delayed ettringite formation in UK in situ concretes.
* In general cracking is observed when the peripheral aggregate bands around more than 70% of
the coarse aggregate particles are greater than 15 μm.
+ A number exhibited internal ASR cracking. No ettringite banding observed in cracked and
uncracked elements.
# Compressive strength of cores taken at twenty years ranged from 40 to 54 MPa with a mean
strength of 48 MPa
66
term expansion results are obtained on wet or
moist specimens from which leaching is
minimized, the recommendation should be
treated with some caution. In the case of Table
5, it has been assumed that the temperature rise
in a mass concrete pour ranges from 14˚C per
100kg/m3 for a 52.5 RHPC to 10˚C per 100kg/m3
for a 32.5 PC.
Figure 12: Relationship betweenultimate expansion and peak earlytemperature. Mortars.
Figure 13: Relationship betweenultimate expansion and peak earlytemperature. Concretes. MountsorrelGranite, UK standard sand.
Figure 14: Relationship betweenexpansion and cement alkali content.(After Kelham [30]).
Figure 15: Relationship betweenexpansion and concrete 2-daycompressive strength of the cement(after Kelham [30]).
Table 4: Limiting concrete temperaturesfor precast concrete : Wet or moistexposure. (+ Low alkali sulfate resistingPortland cement).
Cement Limiting temperature (˚C)
PC 70
LASRPC+ 85
PC/>20% fly ash 85
PC/>35% slag 85
67
CONCLUDING REMARKSThe majority of concrete structures are
performing well. The problems which sometimes
arise are due primarily to design and construction
faults or inadequate maintenance with only a
minority being caused by an inadequate material.
This paper has concentrated on problems
associated with concrete as a material. The main
areas where our understanding is particularly
incomplete and further work is required are:
• The effect of cement type, concrete
quality, cover and environment on
cracking due to chloride-induced corrosion
in concretes subject to wetting and drying
and exposure to de-icing salts, ie: bridges
and multi-storey car parks
• The mechanisms, likelihood of occurrence
and consequences of pitting corrosion of
reinforcing steel
• The effect of cement type and concrete
quality on the freeze-thaw resistance of
non-air-entrained concretes in the absence
of external salt
• The effect of cement type and concrete
quality upon the freeze-thaw scaling
resistance of non-air-entrained and air-
entrained concretes exposed to de-icing
salts
• The effect of aggregate permeability on
concrete durability
• The expansion behaviour of a range of
concretes possibly susceptible to DEF
expansion, maintained in a moist state
rather than immersed in water.
ACKNOWLEDGEMENTSThe author is grateful to the following for
helpful discussions - Mr M G Taylor (BCA), Dr M P
Webster (BOMEL Ltd, previously BCA), Professor
D C Spooner (now retired from BCA), Mr A T
Corish (now retired from Blue Circle Industries),
Dr G K Moir (Blue Circle Industries), Dr S Kelham
(Blue Circle Industries), Dr R Gollop (Blue Circle
Industries) and Mr P Livesey (Castle Cement) and
to Blue Circle Industries for permission to
reproduce Figures 14 and 15.
REFERENCES
1. A C PATERSON. The structural engineer incontext. Structural Engineer, 1984, 62A,335-342.
2. D W HOBBS. Chloride ingress and chloride-induced corrosion in reinforced concretemembers. In ‘Proceedings of a Conferenceon Corrosion of Reinforcement in ConcreteConstruction’ (Editors: C L Page, P BBamforth and J W Figg), The Royal Societyof Chemistry, 1996, 124 - 135.
3. HIGHWAYS AGENCY Design for Durability.BD 57/95. In ‘Design Manual for Roads andBridges’, 1995, 1, Section 3, Part 7.
4. D W HOBBS. Concrete deterioration:causes, diagnosis and minimising risk.International Materials Reviews, 2001, 46, 117-144.
5. L J PARROTT. A review of carbonation inreinforced concrete. BRE/BCA Report C/1,July 1987, 126pp.
Maximum cement content (kg/m3)
Cement or binderAmbient temperature (˚C)
10˚C 20˚C 25˚C 30˚C 40˚C
52.5R+ PC 430 360 320 280 210
52.5+, 42.5R+PC 480 400 360 320 240
42.5+, 32,5R+PC 550 450 400 360 270
32.5+PC 550 500 460 400 300
LASRPC (<0.60% Na2Oe) 550 500 500 450 400
PC/>20% fly ash 550 500 500 450 400
PC/>35% slag 550 500 500 450 400
Table 5: Limiting cement contents for minimising DEF cracking in in situ concrete.Minimum section size 600 mm. Wet or moist exposure. (+ Cement strength class).
Assumption: Temperature rise 14˚C per100 kg/m3 of cement for 52.5 RPC, 12.5˚C for 42.5 RPC,
11˚C for 42.5 PC and 10˚C for 32.5 PC and LASRPC.
68
6. L J PARROTT. Carbonation-inducedcorrosion. In ‘Proceedings of a Seminar onStructures in Distress’, London, January1995. Geotechnical Publishing Ltd, Essex,UK, 1995, pp 97-112.
7. D W HOBBS, B K MARSH, J D MATTHEWSAND S PETIT. Minimum requirements forconcrete to resist carbonation-inducedcorrosion of reinforcement. In ‘MinimumRequirements for Durable Concrete’ (Editor- D W Hobbs), British Cement Association,Crowthorne, 1998, pp 11-39.
8. J H BROWN. The performance of concretein practice. A field study of highwaybridges. TRRL Contractor Report No 43,1987, 61pp, 36 Figs.
9. EUROPEAN COMMITTEE FORSTANDARDIZATION. Eurocode 2: Design ofconcrete structures: Part 1: General rulesand rules for buildings. EN 1992-1, 1999, 225 pp.
10. J D MATTHEWS. Performance of limestonefiller cement concrete. In ‘Euro-Cements.Impact of ENV 197 on ConcreteConstruction.’ (Editors: Ravindra K Dhir andM Roderick Jones), E & F N Spon, 1994, pp 113-148.
11. EUROPEAN COMMITTEE FORSTANDARDIZATION. Concrete - Part 1 :Specification, performance, production andconformity, pr EN 206-1 January 2000,70pp.
12. BRITISH STANDARDS INSTITUTION.Concrete - Part 1. Guide to specifyingconcrete, BS 5328: Part 1, 1997, 24pp.
13. D A WHITING, P C TAYLOR AND M A NAGI.Chloride limits in reinforced concrete.Portland Cement Association, PCA R & DSerial No 2438, 2000.
14. C L PAGE AND V T NGALA. Steady-statediffusion characteristics of cementitiousmaterials. In ‘Proceedings of RILEMInternational Workshop on ChloridePenetration into Concrete’ (Editors: L OMilsson and J P Olliver), St-Remy-les-Chevreuse, France, October 1995, 1995, pp77-84.
15. V N NGALA AND C L PAGE. Effects ofcarbonation on pore structure anddiffusional properties of hydrated cementpastes. Cement and Concrete Research,1997, 27, pp 995-1007.
16. P VASSIE. Transport Research Laboratory,Private communication, 1995.
17. P B BAMFORTH AND M ALISA. Corrosionof reinforcement in concrete caused bywetting and drying cycles in chloridecontaining environments. Unpublishedreport, Taywood Engineering Limited, 1997.
18. A ANDERSON. Investigation of chloridepenetration into bridge columns exposed tode-icing salt. HETEK, The Danish RoadDirectorate, Report No 82, 1997.
19. D W HOBBS AND J D MATTHEWS.Minimum requirements for concrete toresist deterioration due to chloride-inducedcorrosion. In ‘Minimum Requirements forDurable Concrete’, (Editor: D W Hobbs),British Cement Association, Crowthorne,1998, 43-89.
20. A M NEVILLE. Properties of concrete.Fourth and final edition, Longman GroupLimited, 1995, 844pp.
21. D W HOBBS, B K MARSH AND J DMATTHEWS. Minimum requirements forconcrete to resist freeze-thaw attack. In‘Minimum Requirements for DurableConcrete’ (Editor: D W Hobbs), BritishCement Association, Crowthorne, 1998, pp91-129.
22. T C POWERS AND R A HELMUTH. Theoryof volume changes in hardened Portlandcement paste during freezing. Proceedingsof the Highway Research Board, 1953, 32,pp 285-297.
23. P KLIEGER. Further studies on the effect ofentrained air on strength and durability ofconcrete with various sizes of aggregates.Research and Development Laboratories ofthe Portland Cement Association, Bulletin77, 1956.
24. AMERICAN CONCRETE INSTITUTE. Guideto durable concrete. ACI Manual ofConcrete Practice, Part 1: Materials andGeneral Properties of Concrete, ACI201.2R-92, 1992, 41pp.
25. G E BLIGHT. Experiments on the use ofwaterproofing agents to inhibit alkali-aggregate reactions in concrete. ConcreteBeton Third Quarter, 1988, 49, pp 21-26.
26. E SIEBEL AND T RESCHKE. Alkali reactionwith aggregates from the southern regionof the new federal states. BetontechnischeBerichte 1995-1997 (Editor: G Thielen),Vertag Bau & Technik, 1997, pp 117-132.
27. D W HOBBS. Long term movements due toalkali-silica reaction and their production.In ‘Proceedings of the 10th InternationalConference on Alkali-Aggregate Reaction inConcrete’ (Editor: A Shayan), Melbourne,Australia, 1996, pp 316-323.
69
28. B Q BLACKWELL, M D A THOMAS, KPETTIFER AND P J NIXON. An appraisal ofUK greywacke deposits and currentmethods of avoiding AAR. In ‘Proceedingsof the 10th International Conference onAlkali-Aggregate Reaction in Concrete’.(Editor: A Shayan), 1996, pp 492-499.
29. D W HOBBS. Alkali silica reaction inconcrete. In ‘Structure and Performance ofCements’ (Editors: J Bensted and P Barnes),E & F N Spon, 2000, to be published.
30. S KELHAM. Blue Circle Industries, 2000,Private Communication.
31. EUROPEAN COMMITTEE FORSTANDARDISATION. Execution of concretestructures - Part 1: Common. ENV 13670-1; 2000, 60pp.
70
71
John C. Payne is a Consultant,
specializing in concrete
technology and admixtures.
ABSTRACTThis paper reviews the development of new
admixture technologies based on synthetic
polymers designed for use in superplasticisers for
concrete. These are enabling technologies for the
production of high performance concrete (HPC)
and self-compacting concrete (SCC). They offer
problem-solving opportunities to concrete
technologists, and the potential for cost savings
in the construction process. Progress in allied
technologies, for example admixtures that can
improve fresh concrete, reduce drying shrinkage
and improve concrete durability are also
discussed.
KEYWORDSSuperplasticisers, Polycarboxylic ethers,
Shrinkage reducing admixtures, Viscosity
modifying admixtures, Precast concrete
manufacture, Ready-mixed concrete production,
Construction experience, Construction costs.
INTRODUCTIONOver the past six decades there has been a
progressive improvement in admixture
technology. The first admixtures used in concrete
were based on natural materials evaluated by trial
and error. Technology advanced by
improvements in the quality and performance of
raw materials, and by a better understanding of
admixture formulations. Manufactured raw
materials were introduced, and complex
formulations developed to maximize
performance. The latest admixture technologies,
introduced over the last decade, are significantly
different in that their functionality derives from
the molecular architecture of their components.
One measure of the progress of admixture
technology can be illustrated by achievable water
reductions in practical concrete mixes.
Plasticisers, or water reducing admixtures (WRA),
were introduced from the 1940s onward.
Products based on hydroxylated carboxylic acids
give typical water reductions of about 5%;
lignosulphonate based plasticisers can give up to
approximately 12 - 15%. Superplasticisers, or
high range water reducing admixtures (HRWA),
introduced in the early 1970’s, are capable of
water reductions of up to 25 - 30%. The latest
admixture technologies enable water reductions
of 40% to be achieved, whilst at the same time
allowing high workability for ease of compaction.
The superplasticisers normally used today are
based on four groups of chemicals; salts of
sulphonated melamine-formaldehyde
condensates (SMC); salts of sulphonated
naphthalene-formaldehyde condensates (SNC);
derivatives of vinyl copolymers and
aminosulphonic formaldehyde condensates; and
derivatives of polycarboxylate ethers (PCE)[1]. The
latter type has been developed to fulfil the need
for specific improvements in performance in
concrete.
Superplasticisers based on SNC are still the
most widely used. However, in addition to water
reduction, other limitations in their performance
have long been recognized, such as a lack of
extended workability retention, or reduction in
slump loss, which can be a problem in some
circumstances, depending on the requirements
for the fresh concrete with regard to transporting
and placement. Superplasticers based on SMC
loose workability even more quickly, but they are
mainly used in precast concrete manufacture
where slump retention is less critical. Technical
advances in the1980s improved the performance
of superplasticisers in this regard, by using
synergistic blends of raw materials[2].
Superplasticisers have complex influences on the
cement-water system which can vary with the
type of admixture and cement chemistry, but in
simple terms they can be considered to act in two
ways; they affect the forces between cement
particles, and they affect the hydration
mechanisms of the mineral components of
cement[3]. The growth of hydration products can
engulf the adsorbed admixture molecules,
consequently their dispersion effect diminishes.
If SNC based superplasticisers are used at high
dosages, retardation can sometimes be excessive.
Occasionally problems can be experienced with
NEW ADMIXTURES TECHNOLOGIES : AN UPDATE
Mr. J.C. Payne BSc, C.Eng, MIM, FICT
Consultant
72
the quality of concrete surface finishes, and
removal of entrapped air from the mix. Most SNC
based superplasticers contain a sodium salt, and
this will contribute to the total sodium ion
content of the mix, so needs to be taken into
account if alkali-silica reaction (ASR) is a potential
problem. The performance of most conventional
superplasticisers, judged by their affect on
workability, is not linearly proportional to dosage.
For any given cement chemistry and mix design,
an optimum dosage needs to be determined.
NEW ADMIXTURE TECHNOLOGIES
Synthetic polymersNew admixture technologies were developed,
originally in Japan, to overcome the recognized
limitations of superplasticisers based on SMC and
SNC. This involved the development of synthetic
polymers for use in admixtures for concrete,
specifically designed to provide the required
performance characteristics. The first patents for
such polymers were registered in the early 1980s.
These products were made available in both
powder and liquid form.
New chemistries were developed for the
various functional groups, backbone and side
chains which made up the polymer molecules.
Advances in their performance characteristics in
concrete were achieved by designing the
molecular architecture of the polymers to provide
the required functionality[4]. The most widely
used of these synthetic polymers are described
generically as polycarboxylate ethers (PCE). The
influences on the cement-water system of PCE
based superplasticisers are different to those for
conventional SNC and SMC based
superplasticisers. The deflocculation of cement is
increased by additional dispersion mechanisms.
The most significant of these is known as the
steric effect, a powerful dispersive force that acts
by physical interference and repulsion between
the polymer molecules. This mechanism is
additional to the electrostatic dispersion effect
normally understood to occur in cement /
admixture interactions for conventional SNC and
SMC based superplasticisers[5].
PCE are sometimes described generically as
“comb polymers”, because the architecture of
the polymer molecules can be likened to a hair
comb. The shape or morphology of these
synthetic polymers can vary significantly. For
example, the molecular architecture of some
polymers has been designed so that admixtures
formulated with them enhance workability
retention in concrete. This can be achieved in
various ways; one example is the ability of
polymer side chains, the “teeth” of the comb, to
contribute to cement dispersion over longer
periods of time. The side chains are not entirely
engulfed by the growth of gel as hydration
proceeds, consequently dispersion remains active
and workability is retained[6]. Another example is
a polymer with a “ball shaped” molecular
structure with the side chains innermost. This
polymer has a backbone that relaxes and opens
out when exposed to the alkaline environment of
cement paste. Consequently, new dispersive
forces become available and the workability
retention of a concrete mix containing the
polymer is improved[7].
A recent example of such “engineered”
polymers with new morphologies has a
molecular configuration designed to optimise
early cement hydration. Rapid adsorption of the
molecule onto the cement particles, combined
with an efficient dispersion effect, exposes
increased surfaces of the cement grains to
reaction with water. As a result, it is possible to
obtain earlier development of the heat of
hydration, rapid development of the hydration
products and, as a consequence, higher strengths
at an early age. This new chemistry acts on the
hydration kinetics of cement, without affecting
the morphology of the products of cement
hydration. Permeability, creep, cyclic loading,
and bond to steel are equal or better than
concrete containing traditional superplasticisers.
Applications include precast concrete
manufacture, where it is possible to eliminate
steam curing and improve the homogeneity of
mixes[8].
New superplasticisersHigh performance superplasticisers based on
polycarboxylate ethers (PCE) were introduced into
Japan for commercial use in the early 1990s.
They were used initially in high performance
concrete (HPC)[9] and subsequently in the
development of self-compacting concrete (SCC).
These technologies were transferred to other
parts of Asia, the USA and Europe from the mid
1990s onward.
The new generation of superplasticisers
available in the UK is based on improved and
patented synthetic polymers. These products are
sometimes referred to as “hyperplasticisers”.
73
These admixtures can offer exceptional
performance; they can give extremely efficient
plasticising and water reducing effects so that
water reductions of over 40% are achievable;
they can be used to make concrete with true
slump retention with appropriate product
selection and mix design[10]. The relation between
dosage and performance is more directly
proportional. They give minimal retardation, even
at high dosages. Multi-functional
superplasticisers are available, for example
offering high water reduction combined with
good workability retention.
PCE based superplasticisers have some
limitations. They are compatible with most other
admixtures for concrete, but not with SNC based
products. They are somewhat less tolerant of
changes in concrete mix materials. Because they
are powerful dispersants added at low dosage,
excessive variations in batching need to be
controlled.
Shrinkage reducing admixtures(SRA)
The research into new chemistries in Japan in
the early 1980s also led to the development of
shrinkage reducing admixtures (SRA). These
products can reduce the drying shrinkage of
concrete, and have been used for crack control[11].
Patents were issued from 1983 in Japan and
USA[12]. Two types of product were introduced.
The first is an integral concrete admixture, added
to the concrete mix during batching. The second
is post-applied to hardened concrete and
functions by penetration. The beneficial effects of
these admixtures on the long-term characteristics
of hardened concrete have been reported[13].
The theory of how shrinkage reducing
admixtures (SRA) work suggests that the surface
tension within the pore water in concrete
generates forces that contribute to drying
shrinkage. When an SRA is added to the mix
water, it reduces the surface tension within the
pore water, with a corresponding reduction in
these forces[14].
The effect of SRA on drying shrinkage has been
found to vary with materials and mix proportions.
However, reductions in drying shrinkage of up to
50% compared to an equivalent untreated
concrete and improvements in durability have
been reported[15]. The results were for a concrete
mix with a cement content of 300 kg/m3 and a
water/cement ratio (w/c) of 0.53. The SRA was
used at a dosage of 7.5 kg/m3.
SRA technology was transferred to Europe in
the late 1990s, and since then a number of
projects have used these materials. In the UK
interest has been focussed initially on flooring
applications[16]. SRA are appropriate for certain
high performance concrete (HPC) applications
and special problem solving situations where
shrinkage is particularly critical.
APPLICATIONS IN CITY CONSTRUCTION These new admixture technologies have been
used to solve a variety of concrete problems in
many major city construction projects throughout
the world, such as tunnel construction,
infrastructure projects, and high-rise buildings.
Their main applications have been in the
production of high performance concrete (HPC),
high quality precast concrete and self-compacting
concrete (SCC). Significant structural and
engineering benefits have been achieved, and
major cost savings made in the concrete
construction processes.
High performance concreteFor the building owner, architect and
specifying engineer, more durable concrete can
reduce building maintenance costs, reduce the
whole life cost of a structure, and allow planning
for structures with a longer service life. For
example, the improved engineering properties of
HPC concretes can offer cost savings such as
reduced column diameters, increased beam
spans, and increased structural loading capability.
PCE based superplasticisers offer a range of
technical and economical solutions not previously
available for the production of high performance
concretes (HPC). They can give concretes with
very high workability, excellent workability
retention, and little retardation against control,
even at high dosages. If required, all these
advantages can be obtained in the same concrete
by choosing the appropriate admixture and good
mix design. This can be of particular benefit in
the production, transportation and placing of
ready-mixed concrete[17]. Other examples of the
advantages of using such admixtures in HPC
include higher early strength concretes, higher
ultimate strength concretes, and more durable
concretes for extreme environments[18].
74
Precast concrete manufactureDramatic improvements in precast concrete
production efficiency have been reported when
using the most recently developed advanced
superplastisers. Improvements have been made in
precast concrete production in the design of
concrete mixes which eliminate the need for
mechanical vibration, even when filling complex,
heavily reinforced structural elements from a
single filling point. The objectives were to reduce
the threshold value at which concrete would
flow, while at the same time avoiding segregation
and bleed. This has been achieved by
improvements in the formulation of PCE
admixtures, the introduction of suitable viscosity
modifying admixtures (VMA) where appropriate,
and a greater understanding of the relevant mix
design criteria. Water reductions of 40% are
achievable at comparatively low admixture
dosage rates. Such exceptionally high water
reductions can be a significant benefit in precast
concrete production, enabling very high early
strengths, with reduced or eliminated heat curing
costs[19].
In the production of prestressed concrete using
SCC, target stripping strengths of up to 45 MPa
in 12 - 18 hours have been achieved without the
need for auxiliary heating, reducing the energy
requirement for concrete production. Recent
trials have given over 70 MPa at 18 hours with
unheated concrete[20]. The rate of development
of early strength was monitored indirectly from
the temperature rise at the surface of the precast
concrete element, using a simple temperature
data logger linked to a computer.
Other examples of advances in precast
concrete manufacturing include the production of
multiple precast wall panels cast in battery
moulds, with a surface finish specified to be
paintable with no making good[21]. Tunnel
segments for major infrastructure projects have
been manufactured at greatly reduced cost by
using the new admixture technology to
significantly increase production rates. For the
Changi Airport Line, tunnel segments were made
in UK with Grade 60 MPa concrete, maximum
water/cement ratio of 0.45, and a design life
requirement of a hundred years[22].
Self-compacting concrete (SCC)Appropriate mix design for SCC is essential,
and recently issued guidelines recommend the
use of superplasticisers to provide necessary
workability[23]. In practice, in order to obtain
concrete mixes which give true self-compaction,
synthetic polymer based superplasticisers are the
most commonly used. The inclusion of pozzolans
such as slag or PFA in the mix with such
admixtures can be advantageous[24]. If problems
do occur with segregation or bleeding, these can
usually be overcome by including specially
developed viscosity-modifying admixtures (VMA),
for example those based on colloidal silica or
formulated polymers[25].
SCC is widely used in the USA and Europe and
has been successfully used in the UK since
1998[26]. Successful construction projects include
a deep-water marine pier at Immingham, where
SCC was used because of access problems and
congested reinforcement in a 270 m3 continuous
deck pour without any vibration required[27], and
Midsummer Place, Milton Keynes, where Grade
40 SCC was used in heavily reinforced
columns[27]. At Millenium Point, Birmingham,
Grade 60 SCC concrete with slump flow of 600 -
650mm was used in tubular columns 4.5 m high,
450mm diameter to overcome problems of
congested reinforcement. Typical 28 day
compressive strengths of 75 MPa were
achieved[28].
High-rise and infrastructureprojects
The experience of using PCE based
superplasticisers was initially limited to
contractors with knowledge gained within Japan.
Major projects where PCE based superplasticisers
were used included the Akashi Bridge, completed
in 1998, which is the longest suspension bridge
in the world with a central span of 2000 metres.
1.4 million cubic metres of SCC were used for the
foundation work. The Trans Tokyo Bay project,
completed in 1998, is a combination of tunnel
and bridge, linked by a man-made island. 0.25
million cubic metres of SCC was used in its
construction. Other notable contracts using these
new admixtures include the Fukuoka Dome
Stadium Building (0.20 million cubic metres), the
Nanko Tunnel (0.12 million cubic metres) and the
JR Tokai Central Towers (0.22 million cubic
metres).
Dissemination of information outside of Japan
was initially by large contractors working
overseas. During the 1990s local concrete
producers in various parts of Asia gained the
technology. Many major city projects were
successfully completed, including some of the
most prestigious projects in the region. In China
75
the 384 metre high 77 storey Di-Wang Building,
built in Shenzhen in 1996, a polycarboxylate
based superplasticiser was used in 20,000 cubic
metres of high strength concrete. For the World
Plaza Building in Pudong, Shanghai, the main
contractor placed 5000 cubic metres of high
strength concrete using a polycarboxylate based
superplasticiser for pumping where good slump
retention was required. Cement content was
450 kg/m3, at a water/cement ratio of 0.35.
Compressive strength was 70 MPa at 28 days. In
Korea at Incheon a large concrete tank to hold
LNG was completed in 2000. The specification
required a highly workable pumped concrete with
no loss in workability for two hours. The only
solution found was by using a polycarboxylate
based superplasticiser in SCC, with a slump flow
of 680 ± 50mm, pumpability by V-funnel 20±
seconds. 52,000 cubic metres of concrete were
placed. In Hong Kong HPC concrete was placed
into columns on the Kowloon Airport Station
completed in 1998. The requirements were for
Grade 60, with a high workability pump mix, and
with greater than two hours workability
retention. The ready-mixed company reported
excellent slump retention and pumping pressures
at site were about 40% below normal[29].
In Europe the new admixture technologies
started to be used in major projects from the late
1990s. The Viadotto Padulicella, part of the high
speed train line (TAV) from Milan to Naples, used
a PCE based superplasticer in the prestressed box
sections of the viaduct. Each of the 64 box
sections required 430m3 of concrete, which was
poured continuously without vibration. Grade 45
concrete was specified, with a slump of 220mm.
Strengths of over 35 MPa at 24 hours were
achieved, enabling fast cutting of the prestressing
cables thus speeding construction. Other
examples of significant projects include the
Millenium Tower, Vienna where the concrete
decks were supported by composite
steel/concrete columns, with an inner steel tube
of 220mm in diameter and an outer steel tube of
450mm diameter. The annular gap was filled
with SCC, as it was impossible to use
conventional compaction techniques. Concrete
strengths ranged from 40 MPa for the top floors
to 60 Mpa for the ground floors[30].
In the UK these new admixture technologies
have been used successfully on major
infrastructure projects such as the Jubilee Line
and the Channel Tunnel Rail Link, where the
3.2km long tunnel was lined with wet sprayed
concrete which required a slump of 200mm for
pumping and spraying, whilst maintaining a low
water cement ratio of 0.40. An example where
the technology was applied to high-rise structures
is Canary Wharf. The Citygroup Tower, 44 stories
high, was designed with a central concrete core
to resist lateral loading. It was constructed using
a jump form system, which required high early
strength gains to allow fast progress[31]. Grade 40
concrete was required for long-term structural
loading, but 20 MPa was required for form
stripping at 4 days. The concrete mix was
designed with a low water cement ratio to meet
this requirement, resulting in 28 day cube
compressive strengths in excess of 100 MPa[32].
SUMMARYThe driving force behind the rapid adoption of
these new admixture technologies worldwide has
been the considerable savings achievable through
the various construction processes. For example,
contractors found that they could save on
equipment, access, labour and time. A
demonstration of this was in Hong Kong where
within six months of the first approval to use
these materials on a government project, private
contractors were employing PCE based
superplasticisers in the construction of speculative
high-rise flats[29]. In Europe a big market for new
superplasticisers has been in precast concrete
manufacture, where considerable cost savings in
production have been achieved.
Significant cost savings have been achieved in
applications where concrete technology is most
advanced, for example in wet sprayed concrete
for permanent support in tunnel linings[33]. The
total volume of such concrete used in Europe, a
high proportion of which contains advanced
superplasticisers, is now more than 3 million
cubic metres per year[34].
Estimates of admixtures used in concrete in
the UK in 1999 suggest that only 12% are
superplasticisers. This compares with 45% in
Germany, 81% in Belgium, and 85% in Italy[35].
A comparatively small proportion of the
superplasticisers currently used are based on the
new synthetic polymers. In the UK, where the
ability to pump 95 MPa grade SCC concrete to
the top of high-rise city structures is considered
viable[36], there is scope for an increase in the use
of these new technologies. This potential can be
gauged by looking at Japan, where in 1998 it
was estimated that 90% of concrete contained a
superplasticiser, of which 45% were based on the
new synthetic polymers.
76
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14. SATO, T., GOTO, T. and SAKAI, K.Mechanism for Reducing Shrinkage ofHardened Cement by Organic Additives,Cement association of Japan Review 1983,pp. 52-54.
15. TOMITA, R., TAKEDA, K. and KIDOKORO, T.Drying Shrinkage of Concrete UsingCement Shrinkage Reducing Agent.Cement association of Japan (CAJ) Review1983, pp. 52-54.
16. WILLIAMSON, N. Development in admixturetechnology for concrete floors. ConcreteJournal, February 2001.
17. KHURANA R. and SCABINI S. Newgeneration of superplasticisers for longslump retention in ready-mixed concrete,ERMCO 12th European Congress 1998.
18. KHURANA R. and SCABINI S. Admixturesfor ready mixed high strength and durableconcrete, ERMCO 12th European Congress 1998.
19. TORRESAN I. And KHURANA R. New highperformance superplasticiser for eliminationof steam curing in precast concrete, FIP98,Amsterdam 1998.
20. NEW CIVIL ENGINEER. Admixtures - a mixedblessing, November 2001
21. TOOTELL, G. Structural design of precastwall panel systems. Concrete, May 2001.
22. JONES, R. The right recipe, ConcreteEngineering Journal, Sept. 2000.
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28. HENDERSON N. Self-compacting concrete atMillenium Point, Concrete Journal, April2000.
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30. HUBER, G. Structural innovation at theMillenium Tower, Vienna and PICHLER, R.The use of self-compacting concrete in theMillenium Tower. Concrete, June 2001.
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78
79
Steve Walton is the Industry
Sales Manager, Pieri Products,
UK & Ireland, for Grace
Construction Products, the Pieri
Company being acquired by
W R Grace SAS in August
2001. He has spent most of his working life in
the concrete industry working for a major ready
mixed concrete supplier until he joined Pieri UK in
October 2000. He has served on several
committees including BSI, Concrete Society and
the QPA Mortar Industry Association’s Technical
Committee.
ABSTRACTConcrete has been used for thousands of years
and can be considered the backbone of
construction in modern society; however, it is a
much maligned product and open to considerable
criticism about not only its structural properties
but also its appearance.
This paper will look at three common methods
of providing a decorative finish to concrete
which, in the eyes of the majority of the public, is
a product that is all around them and that they
have to put up with. It will show that concrete,
whilst perhaps not being considered a ‘thing of
beauty’ can be considerably enhanced and
improved so that it has even been thought to be
natural stone.
The fourth method of enhancing concrete,
noted in the paper, is a system of photo-
engraving which has generated a considerable
amount of interest in the UK, although to date
very few people have had the courage to
incorporate it in a new construction project.
KEYWORDSConcrete, Exposed aggregate, Acid etched,
Formwork liner, Fhoto-engraved, Architectural,
Retarder.
INTRODUCTIONThe public’s perception of concrete is that it is
grey, boring and fraught with problems. They
recall the concrete tower blocks of the sixties; of
which many have had to be demolished due to
structural problems, bad design, condensation
and in the worst case partial collapse. They do
not like concrete roads/pavements as they are
frequently wide expanses of plain concrete and
when driving are often noisy and they are
constantly reminded of repairs to concrete
bridges on motorways when they are frustrated
by miles of cones.
Indeed, there are some poor examples of the
use of concrete, but in the majority of cases the
problems are not due to the concrete but to a
combination of poor design, specification,
workmanship and materials.
Concrete is all around us in every-day life,
some of it is not seen but visual concrete does
not have to be ‘boring’. In the UK we are
fortunate to possess many types of aggregate
that vary in both colour, texture and shape and
whether used on their own or in conjunction with
pigments there are numerous examples of
‘interesting’ concrete some of which will be
illustrated by this paper.
For over 30 years the Pieri Company has
produced products that will ‘beautify’ concrete,
these include good quality non-staining release
agents, surface retarders, acid gels, pigments,
formwork liners, cleaning and protection
products, admixtures and most recently photo-
engraved concrete. Where practically possible
they have products that are environmentally
friendly in order to ensure the safety of operatives
and to minimise the impact of construction
materials on the environment.
ARCHITECTURAL CONCRETEArchitectural concrete [1] is defined by the
American Concrete Institute as: ‘concrete exposed
either as an interior or exterior surface in the
completed structure, which definitely contributes
to its visual character and is specifically
designated as such in the contract drawings and
specifications’.
The materials, procedures and finishes of
architectural concrete will usually differ from
those for structural concrete and in the UK the
production of architectural concrete is normally
seen as the domain of the precast concrete
industry. Architects believing that concrete units
produced in a factory under controlled
DECORATIVE CONCRETE
Mr. S. Walton FIHT, FICT
Pieri UK Ltd
80
conditions, often having their own concrete
production facilities, using a skilled workforce of
concretors, finishers, carpenters, steelfixers etc.,
would be of far better quality than the same unit
constructed in situ.
Indeed, as you drive around the UK there are
some very poor examples of in situ concrete and
perhaps one could feel that the architect is
correct to think this way. However, advances in
material technology should allow architectural
concretes to be produced both in the precast
factory and in situ on construction sites.
MATERIALSIn the previous section it was stated that the
materials for architectural or ‘decorative concrete’
will usually differ from those of structural
concrete and this is certainly true. In the main,
structural concrete is specified in terms of
compressive strength with limitations placed on
minimum cement content and/or water/cement
ratio. Subject to any restraints placed on the
aggregates, cement type and/or admixtures, the
concrete supplier can normally select the
materials to satisfy the specified requirements,
usually locally available aggregates and Portland
cement with or without ggbs or pfa. Providing
the specification requirements are met, the
contractor can place the concrete and if an
acceptable surface finish is achieved the architect
or engineer is satisfied.
However, with architectural concrete other
factors need to be taken into account depending
on the finish required, and the following must be
considered:
Cement - generally white Portland cement or
rapid hardening Portland cement is used in
precast factories. Both of these give high early
strength which is what the precaster is looking
for in order to demould and lift units.
Architectural concrete is often worked on the day
after casting, either washing if exposed aggregate
or acid etching. In either case the concrete needs
to have sufficient strength to avoid damage when
handled.
Aggregates - where the aggregate is to be
exposed, it needs to be of good quality, free from
impurities, consistent in quality and grading and
pleasing to the eye.
Admixtures - whilst the increase in the use of
admixtures in the UK has been relatively slow
compared to the rest of Europe, they have many
benefits to the concrete producer and the client if
used correctly. Water reducing admixtures enable
the producer to achieve very low water/cement
ratio concrete, whilst still having high workability
and the new range of admixtures for self-
compacting concrete allow the production of very
high quality surface finishes free from blowholes
and blemishes, without the need for vibration.
However, care needs to be exercised in the use of
certain admixtures; for example using an
accelerator with a surface retarder would negate
the effect of the retarder.
In all cases it is prudent to consider the
materials to be used based on the desired result
as combinations of materials may work against
one another.
EXPOSED AGGREGATE CONCRETEThere are several methods of exposing the
aggregate on the surface of concrete, be it a
pavement or façade. Methods include washing
and brushing, sandblasting, bush hammering,
grinding and polishing and fractured rib. All of
these are manual operations and are reliant on a
trained operative having the experience to
achieve the desired finish consistently. Some of
the above methods actually damage or change
the appearance of the aggregate being exposed
and defects below the surface can be
exacerbated by the use of mechanical exposure .
The use of chemical surface retarders has had
limitations in the past due to the nature of the
retarders used. Based on sugar, the retarders did
not always stay in the correct position if used on
a mould. They could move to areas that were not
required to be retarded and leave areas that were
supposed to be retarded with no etch at all. The
depth of etch was inconsistent and the finished
surface would look uneven. In fact a recipe for a
non-proprietary retarder was given in a text
book[2] as : 1 part black molasses, 31/2 parts
water, equal parts of whiting and fine sand
sufficient to give a stiff brushing consistency.
Fortunately, retarders based on resin
technology have changed all that and consistent
exposed aggregate surfaces can be achieved with
the minimum of effort. Combined with the use of
wax release agents, both exposed aggregate and
fair-faced concrete finishes can be produced side
by side, Figure 1.
81
Figure 1: Exposed aggregate and fair-faced concrete panel.
Façades [3]
For a good appearance care must be taken
with the mix design and the following must be
taken into account:
• Depth of exposure required, light etches
require aggregates having a continuous
grading, an angular crushed rock coarse
aggregate provides a better appearance than
a rounded aggregate
• For exposure depths greater than 10mm, a
gap graded mix should be used and either
crushed rock or rounded gravel can be used
to produce satisfactory results
• The correct aggregate size for the required
exposure is important, the aggregate should
be like an iceberg, one third above the
surface, two thirds below. This will ensure
that plucking of the aggregate does not
occur.
It must be remembered that a vertically cast
face will have a different appearance from a
horizontally cast face due to the aggregate
orientation under vibration. The retarder to be
used is also important, it should:
• Not move on the surface of the formwork
during concrete placement
• Allow adequate time to fill the mould and
ensure the concrete is vibrated, before it
starts to react
• Be designed to allow an even and controlled
depth of exposure over a wide temperature
range, 5 - 90˚C, allowing for heat generation
in large mass concrete or when used with
heated precast systems
• Be easy to apply on intricate, vertical or
inclined formwork without specialist
equipment or labour
• Be suitable for use in sensitive environmental
areas and allow for situations where surfaces
are to be subsequently treated
• Allow for delayed stripping times, in terms of
days, without rehydration problems.
Moulds must be non-absorbent, timber should
be treated with a polyurethane sealer prior to use
and plastic or polystyrene should be checked to
ensure that there is no reaction with the retarder.
The mould should be filled in a planned way,
not using vibration to spread the concrete over
the mould, excessive abrasion may remove some
of the retarder. Vibration should be even, regular
and completed in as short a time as possible to
ensure full compaction.
The design must take into account the
additional cover required when placing
reinforcement, as the surface of the concrete is
being removed. Sufficient space must be left
between the reinforcement and the formwork to
allow the coarse aggregate to get close to the
face of the concrete and still allow good
compaction.
Once the concrete has been removed from the
mould, removal of the retarded surface must
proceed immediately as once the retarded
concrete is subject to moisture and air,
rehydration will start to take place.
As with all concrete, exposed aggregate panels
still require curing and protection. Without
correct curing, the work that has gone into the
production of architectural or decorative work
can be wasted.
PavementsLike façades, surface retarders can be used to
provide an attractive, durable and functional
concrete pavement. Concrete can be supplied,
with or without pigment, to complement or
contrast with the surroundings area or buildings.
The requirements are similar to those required
for the production of facades except that instead
of being constructed mainly in a precast factory,
pavements are normally constructed in situ.
82
Figure 2: Exposed aggregate pavementin town centre.
The concrete supplied may need to be redesignedas it will generally require an increased amountof coarse aggregate, approximately 10%, as thisis the feature of the concrete that is to be seen.
Placement of the concrete is important for the
final result, the workability slump should be in
the region of 125mm.
Compaction depends on the type of traffic
expected; normally it is kept to a minimum, but
in every case the workability of the mix must be
appropriate to withstand the applied compactive
effort without causing segregation or excessive
cement-rich laitance. Over-compaction will force
the coarse aggregate downwards which is
contrary to what is wanted.
After compaction, excessive finishing is not
required, closing the surface with a float is all
that is necessary.
The retarder is sprayed onto the finished
surface as soon as possible after finishing. The
retarders are water based and contain an integral
curing membrane which protects the concrete
during the period from placing to wash-off.
Figure 3: Surface retarder being washedoff to expose aggregate.
Under normal circumstances, the retarder is
washed off after 24 hours, but the retarder may
be left on the concrete for up to 3 days before
the surface is washed off, without loss of etch.
However, it is important to test that the concrete
has achieved sufficient strength before wash-off
commences.
Figure 4: Exposed aggregate surface.
Test panels Before any work starts, it is standard practice
to produce a test panel or sample to establish the
depth of etch. For the test it is important to
reproduce as many of the production parameters
as possible. All too often a small sample has been
made only for the actual production piece to look
totally different. The following should be
considered:
• Make the sample in similar conditions to
those expected, especially if the work is to
be carried out on site
• Make trial panels as near to full size as
possible, to ensure that temperature and
strength development within the unit are the
same as will be expected on the production
unit
• If ready-mixed concrete is to be used,
establish the mix design, production
methods and delivery times, and obtain a
guarantee from the supplier
• Use the trial to train operatives and if
necessary, prepare method statements to
take care of problems.
The use of exposed aggregate concrete has
been shown to improve the durability of the
concrete. Research has shown that a rough
surface is preferable to a smooth one in
preventing frost damage, as water is dispersed
more rapidly. Freeze-thaw resistance is also
improved on horizontal surfaces as there is ample
room for water to expand. This is particularly
important in severe weather environments.
Industrial pollutants and acid rain attack the
surface of the alkaline concrete but as this is now
only 10-30% of the exposed area of finish, the
aggregate being unreactive and with the texture
83
acting as a watershed, acid attack is greatly
reduced. Similarly, exposed aggregate finishes
tend to be self-cleaning, the majority of dirt is
absorbed by pores at the surface of the concrete
and as the surface has now been removed, the
non absorbent aggregates do not harbour the
dirt and tend to let it be washed away by rain
water.
Most imperfections are within the top 6mm of
a concrete surface. By removing this to form an
exposed aggregate finish, a good, durable and
long lasting surface should be guaranteed.
ACID ETCHED CONCRETEThe use of acid on the surface of concrete
gives the concrete the texture and appearance of
natural stone and whereas exposed aggregate
finishes can depend on what is ‘in fashion’ acid
etched concrete tends to be always there and its
use is increasing on a yearly basis.
Acid etching is generally confined to precast
plants where safety precautions can be rigidly
enforced. The concrete surface is, after
demoulding, washed with a hydrochloric acid
solution ranging from 5 to 35%; this can be by
spray, brush or even total immersion. This method
is usually limited to siliceous or granite
aggregates which are more resistant to the acid
than limestone-based aggregates which can be
discoloured or damaged.
The use of liquid acid is not recommended on
vertical or inclined in situ walls because of safety
problems and non-uniform etching. When used
on non-horizontal surfaces the acid tends to be
applied at the top and allowed to run down,
leading to a greater depth of etch at the top and
a lighter etch at the bottom.
Acid gels are available that can be used on
vertical, inclined, curved or even inverted
surfaces. These are viscous materials that are
applied by brush but do not run down the
concrete surface, allowing a controlled and
consistent etch on all occasions. This was the case
at the Basilique Notre Dame on the Ivory Coast,
where the cast concrete columns were acid
etched in situ, Figure 5.
The gel also allows for remedial work to be
carried out in localised spots, where the etching
may have been uneven (hard spots), which would
not be possible with the liquid acid [4]. It is
particularly useful for removing cement
contamination on other types of decorative
finishes in selected areas.
Once treated with acid, the concrete should be
washed with copious amounts of clean water to
remove any residue. This ensures that the acid is
neutralised and any acid salts that have been
formed are also removed. These will show up as
white stains, similar to efflorescence on the
surface of the concrete.
For a consistent finish, it is important to design
the concrete mix with a higher proportion of
fines and to use crushed aggregates. Although
the concrete should be well compacted, care
should be taken to avoid physical blemishes such
as blow holes and aggregate arching, as these are
exposed by removing the cement rich surface.
The use of self-compacting concrete with the
correct choice of release agent should prove
beneficial in the production of acid etched units.
Acid washing with a very low concentration of
sulphamic acid is also used to restore colour and
lustre to exposed aggregate surfaces that have
been exposed by other means or coated by
contaminants. This will also remove acid salts and
efflorescence.
Figure 5: Intricate column head at theBasilique Notre Dame, Ivory Coast.
The Scottish Widows Building in Edinburgh
looks as if it is constructed of natural sandstone,
but this effect was achieved by the use of
pigment, carefully selected sand, wax based
release agent and acid gel, which transformed
the 10,000 wet cast concrete panels into the
imitation sandstone building which was
nominated for a Concrete Society award.
As well as imitating natural stone, acid is also
used to provide other effects. The staircases in
the ill fated Millennium Dome had the treads acid
etched to provide a non-slip surface for the
thousands of visitors. It has also been applied to
sawn concrete to roughen up the surface to
provide a key for subsequent epoxied joints.
84
FORMWORK LINERSWhilst perhaps not being architectural
concrete, the use of profiled formwork liners can
add effect to what may be otherwise a plain
concrete wall; they also:
• Extend the life of form faces
• Produce a smoother surface finish
• Provide a profiled, textured or patterned
finish
• Improve surface durability[5].
Patterned finishes on concrete demonstrate
that concrete is a material with both aesthetic
and structural properties.
The qualities of the liner materials and their
characteristics of hardness, permeability and
surface texture all have an impact on the finished
surface of the concrete. In the past difficulties
with fixing methods, mix designs and vibration
techniques lead to the majority of formwork
liners being used by the precast industry.
However, improvements in adhesives, release
agents, admixture technology and the liners
themselves have lead to an enormous increase in
the use of liners on site where concrete is cast in
situ. The development of self-compacting
concrete should make the production of high
quality, blemish free surfaces without the need
for vibration even more commonplace in the
future.
Liner Types1. Plastic moulds/liners are generally used in
the production of flagstones and other
small concrete products, although sheets
are available in sizes up to 0.6 x 7m.
2. Foamed or expanded plastic liners are made
from expanded foam with a density of
40g/litre, these are normally only for a
single use. A limited number of standard
patterns are available and the depth of relief
ranges from 16 to 25mm.
3. Foamed polyurethane liners depend on the
amount of micro cellular expansion and the
use of fillers or reinforcement. There are a
number of grades that can be moulded. The
number of uses varies in the ranges 10-20,
30-40, 60-100 and 100+. The maximum
number of re-uses is subject to careful
handling, depth of pattern, undercuts and
the correct release agent.
4. Polyurethane liners have high tear resistance
and are hard wearing and flexible. Normally
they can be used at least 100 times
producing a quality finish. The flexible liner
is available in widest range of patterns and
is used both in situ and in precast
operations. Most liners are supplied in
standard sizes so that joints can be carefully
constructed to prevent grout loss and
minimise blemishes. Where liners have a
continuous pattern and several pieces have
to be joined together, they are supplied so
that adjoining liners match and the pattern
is continuous throughout the unit being
cast.
Figure 6: Dry stone wall made fromconcrete using a polyurethane liner.
PHOTO-ENGRAVED CONCRETE (SERILITH)The process of transferring images onto
concrete was first developed by Pieri in 1986,
when the library at Lons-le-Saunier was decorated
with drawings by a local artist, Figure 7. Over the
years the system has been enhanced and
developed so that actual photographs, rather
than just drawings, can be reproduced onto a
concrete surface.
Figure 7: Lons-le-Saunier Library -1986.
85
It is generally architects that show an interest
in photo-engraved concrete, but in the UK this
system is relatively new and unfortunately there is
a reluctance to try new ideas. In Europe however,
the system has been utilised on numerous
projects and enquiries have also been received
from Australia, New Zealand and the United
States.
In the UK a project is just being completed at
the side of the River Chelt in Cheltenham. The
Landscape Architects, Partnership Art, found that
the river once contained a lot of fossils and
decided to make the concrete panels at the side
of the river become a feature of the area. Using a
hand drawn image of an ammonite, Figure 8,
thirty two photo-engraved panels were supplied
to a precast concrete manufacturer in Northern
Ireland. The concrete panels not only
incorporated the ammonite, but they were also
pigmented and acid etched, Figure 9.
Interest is also being shown on two other
contracts in the UK, the new Scottish Parliament
Building in Edinburgh and a library at a school in
Bedford, where the architect wants to place the
names of famous authors on the external walls
around the perimeter of the building.
Figure 8: Original drawing of ammonitefor River Chelt.
Figure 9: Panels in position awaitingcleaning.
In Germany, the architects Hertzog & De
Meuron have used both photo-engraved concrete
and glass at the Eberswalde Technical School
Library. The building was only completed in April
1999 and is completely covered in photographic
images, some from the 1936 Olympics.
Figure 10: Eberswalde Library.
Other projects completed on the continent
include the Mair clothing store at Innsbruck, the
Company has a ‘Mother with child’ logo and they
wanted this to be used on the façade of their
building, Figure 11. Each image is 3m x 3.5m and
consists of 12 individual panels and it is repeated
on all six floors of the building, one above the
other.
Figure 11: Mair Store, Innsbruck.
86
Figure 12 - Pfaffenholz Sports Centre.
Photo-engraved concrete has even been used
on the floor, walls and ceiling at the Pfaffenholz
Sports Centre, Figure 12.
MethodThe process starts with the image that is to be
transferred to the concrete, this can be a
negative, photograph or drawing but it needs to
be of good quality, preferably in black and white
and with crisp detail and contrast. The image is
digitally enhanced and the design is then
transferred onto a dense polystyrene sheet using
photo-sensitive chemicals. Surface retarder is then
applied to the plastic sheet using a silk screen
process, but instead of ink being used, a light
etch surface retarder is printed on to the plastic
sheet. Where the photo-sensitive chemicals are
on the sheet, the retarder forms the image
required. The result is that the image is visible on
the plastic sheet, but using retarder rather than
ink.
The plastic sheet is placed face upwards in the
mould, so that the concrete will be in contact
with the retarded surface when the mould is
filled. Concrete, preferably self-compacting to
eliminate vibration and also to ensure speed of
placement, is placed in the mould, which should
be placed where it will be free from vibration.
The retarder starts to react after 30 minutes
therefore speed is essential. The mould needs to
be kept vibration free, so that the retarder does
not move within the mould to areas where it is
not required.
After placing the concrete, it is left in the
mould for approximately 2 days, after which the
concrete is removed and then pressure washed to
expose the image.
The image produced will depend on several
factors, the clarity of the original photograph or
drawing, very detailed photographs/drawings are
difficult to reproduce and some of the detail may
be lost, the aggregates and cement type used,
plain dull aggregates and grey cement do not
stand out well. A dark aggregate using white
cement will give a very good, almost three
dimensional image.
The maximum sheet size is 2.5 x 1.2 metres.
Where an image is larger than this, the image is
transferred on to as many sheets as required and
the sheets are accurately butted together in the
mould to form the complete image.
Until recently, photo-engraved concrete has
only been produced in precast factories where
the plastic sheets could be accurately positioned
in the mould and the concrete could be quickly
placed in the mould, compacted on vibrating
tables and then left without being disturbed until
it was time to demould the concrete.
With the advent of self-compacting concrete,
photo-engraved concrete has been successfully
reproduced in situ as the concrete can be placed
very quickly and the risk of catching the retarded
sheet with a vibrating poker is eliminated, Figures
13 - 16.
Figure 13: Fixing the Serilith sheetsin situ.
Figure 14: Exposing the image.
87
Figure 15: The exposed image (1).
Figure 16: The exposed image (2).
The technique of photo-engraved concrete has
many applications. Enquiries have even been
received for headstones, both for people and
animals, as the system is ideally suited for
transposing images onto headstones or memorial
plaques.
REFERENCES
1. WADDELL J.J., DOBROWOLSKI J.A.,Concrete Construction Handbook, McGraw-Hill, Inc., USA, 3rd Edition 1993.
2. WILSON J.G., Exposed Concrete Finishes, C R Books Ltd, London, 1962, 143 pages.
3. HART I.R., Beautiful and Durable Concrete,Concrete, September/October 1995, Pages30-33.
4. HART I.R., Quality & Special Finishes,Concrete, April 2000, Pages 17-19.
5. HART I.R., Form Liners: Implications forconcrete aesthetics and durability, Concrete,May 2001, Pages 41-43.
88
89
Rob Gaimster is a chartered
civil engineer and is Divisional
Technical Services Manager for
RMC Readymix, the world’s
largest supplier of ready mixed
concrete.
Noel Dixon trained as an
aeronautical engineer but has
since developed his skills in
concrete technology. He is the
Analyst and reports to the
RMC Readymix Divisional
Technical Services Manager. Noel is responsible
for providing analytical services for the Readymix
Divisional Technical Services Team.
ABSTRACTAwareness of self-compacting concrete (SCC)
within the construction industry is growing year
on year since it was developed in Japan in the late
1980’s by Okamura et al [1]. The quest for further
understanding as to its capabilities and limitations
has generated considerable interest in research
world-wide. This paper attempts to summarise key
aspects and to outline the current position.
KEYWORDSCement paste, Formwork, Release agent,
Reinforcement, Segregation, Slumpflow,
Superplasticiser, Viscosity, Yield stress
INTRODUCTIONKhayat et al [2] define SCC as:
“a highly flowable, yet stable concrete that
can spread readily into place and fill the
formwork without any consolidation and without
undergoing any significant separation”.
Feature/benefit analysis would suggest that the
following benefits should result:
• Productivity levels increase leading to
shortened concrete construction time
• Lower concrete construction costs
• Improved working environment
• Improvement in environmental loadings
• Improved in situ concrete quality in difficult
casting conditions
• Improved surface quality.
Non-vibrated concrete is already common
place in the construction industry and is used
with acceptable results, in piling and shotcrete
applications for example. Development of SCC
has mainly focused on congested civil engineering
structures and its acceptance within the market
place has primarily grown in solving technically
difficult casting conditions. It is a niche product, a
problem solver.
Okamura and Ouchi [3] have commented on
the reduction in the number of skilled workers
affecting the quality of construction work in
Japan. With SCC reducing the dependency of
concrete quality on the workforce, further market
penetration can be expected.
MATERIALS AND MIX DESIGNBefore looking at designing a mix for SCC an
understanding is needed of the properties
required for self-compaction and how this can be
optimised utilising materials currently available.
The two main requirements are for a highly fluid
material which has significant resistance to
separation.
To achieve a highly mobile concrete, a low
yield stress is required and for a high resistance to
segregation, a highly viscous material is required.
Water can be added to decrease the yield stress;
unfortunately this addition also lowers the
viscosity. Addition of a superplasticiser will also
lower the yield stress and will only lower the
viscosity slightly. The viscosity of a mix can be
increased by changes in mix constituents or the
addition of a viscosity modifier but this will
increase the yield stress of the paste. Thus, being
able to find a happy medium between the two
parameters is required. Figure 1 shows the
relationship between shear rate and shear stress.
Advances in admixture technology have played
a vital part in the development of SCC. Modern
superplasticisers (based on polycarboxylic ethers)
promote good workability retention and can be
added at any stage of the batching cycle. They
SELF-COMPACTING CONCRETE
Mr. R. Gaimster BEng, CEng, MICE, MICT
RMC Readymix UK Ltd and
Mr. N. Dixon
RMC Readymix UK Ltd
90
achieve this with a mechanism of electrostatic
repulsion in combination with steric hindrance.
Viscosity modifiers can be added to increase
the resistance to segregation, whilst still
maintaining a high fluidity, allowing concrete to
flow through narrow spaces.
Many authors have different mix design
theories but all try to achieve the above. They
mainly look at separating it into a two phase
design, ‘continuous’ which covers the water,
admixture: cement and fillers with a particle size
less than 0.1mm and ‘particle’ which considers
the coarse and fine aggregate. Some of them are
summarised below:
• Ozawa’s [4] ‘General Method’ originating in
the late 1980s from Japan is a very simplified
method looking at basic values such as the
coarse aggregate content being restricted to
50% of the concrete volume. This method is
very conservative giving cement contents in
excess of 600 kg/m3
• Petersson’s [5] ‘CBI Method’ examines the
overall grading of the combined aggregate,
allows for any size of aggregate and
considers actual construction criteria. It
determines aggregate volumes from which a
paste content can be established
• Sedran’s [6] ‘Compressive Packing Model’
considers the material properties such as
bulk density, apparent particle density,
absorption and particle size distribution and
uses this information in software models to
predict the flow behaviour from blocking
and segregation risks. This produces a
theoretical optimum mix from the above and
this mix is trialled and modified through
laboratory tests
• Saak’s [7] ‘Segregation Control Theory’ looks
at how to optimise material additions to
control yield stress, viscosity and the density
of a cement paste matrix. Thus, the rheology
of the matrix can be engineered to produce
SCC.
Fine particles play an integral part in the design
and similar sized particles to cement grains, such
as pulverised fuel ash, ground granulated
blastfurnace slag and silica fume can be added to
the mix to aid the plastic and hardened properties
of the concrete. Limestone filler is used extensively
on the continent.
PLASTIC CONCRETEThere are three main areas to be considered in
the concrete’s plastic state, filling ability,
resistance to segregation and passing ability.
These properties will be looked at in turn along
with methods of assessment [8].
Filling AbilityThis property of the fresh concrete is related
entirely to the mobility of the concrete. The
concrete is required to change shape under its
own weight and mould itself to the restricted
formwork in place.
Figure 1: Rheological properties of concrete.
Addition of stabilisation/finest
Standard concrete (Bingham liquid)T = t0 + h * N
SCC concreteNewtonian liquid
Addition of water
Addition of superplasticiser
Shear Rate N
Shea
r st
ress
t
91
To enable this to occur, the inter-particle
friction of the materials must be reduced. This
can be achieved in two ways:
• Firstly, surface tension can be reduced by the
inclusion of superplasticisers
• Secondly, optimising the packing of fine
particles can be achieved by the introduction
of fillers or segregation-controlling
admixtures.
Measurement of the plastic properties can be
achieved by the following tests:
• The slumpflow utilises a British Standard
slump cone, which is filled in one layer
without compaction. The mean spread value
in millimetres is recorded. Typical values lie
between 650 and 800mm. The test
measures the mobility/deformity under a low
rate of shear (self-weight). Assessment of
segregation can be made subjectively but the
test does not completely measure the filling
capacity of the SCC in question. A further
evaluation can be carried out at the same
time. This is the T50 value, which measures
the time taken to reach a spread of 500mm.
There is some question mark over the value
of slumpflow results when viewed in
isolation
• The BTRHEOM Rheometer. The concrete is
considered as a Bingham fluid and its
behaviour is determined by the shear yield
stress and the plastic viscosity. A low shear
yield stress and a limited plastic viscosity
value are required.
Resistance to SegregationSCC has to be stable under mobile conditions.
Two areas therefore need to be addressed:
• Firstly, the amount of moveable water needs
to be minimised to avoid bleeding. This can
be achieved by the use of superplasticers to
reduce the water demand and separation
through a well-graded cohesive concrete
• Secondly, the liquid phase needs to be
viscous in nature to be able to maintain the
coarse particles in suspension, when mobile.
This can be achieved by a high volume of
fines in the mix and/or the introduction of a
viscosity modifier.
Measurement of the plastic properties can be
achieved by the following:
• The GTM Stability Sieving test, which
measures the degree of separation of the
coarse and mortar fractions. 10 litres of fresh
concrete are placed into a test container.
Over a 15 minute period the coarse
aggregate will settle at the bottom. The
upper part of the concrete in the container is
then wet sieved and the volume of mortar
paste calculated. The higher the value the
more segregation has occurred
• Visual inspection using the slumpflow
method can also be carried out.
Passing AbilityThis is the ability of the concrete to be able to
pass round immovable objects in the formwork,
such as reinforcement. The need for this ability
will depend on reinforcement arrangement for
the individual structures that are cast.
Factors to be considered will be the spaces
between reinforcement, which will influence the
selection of the size and shape of the coarse
aggregate and the volume of the mortar paste.
The more congested the structure, the higher the
volume of paste is required to the amount of
coarse aggregate.
Measurement of the plastic properties can be
achieved by the following tests:
• The L-Box test is useful in assessing different
parameters such as mobility, flow speed,
passing ability and blocking behaviour. The
apparatus consists of a long rectangular
section trough with a vertical column/hopper
at one end. A gate is fitted to the base of
the column allowing discharge of SCC into
the trough. Adjacent to the gate is an
arrangement of bars which permits
assessment of blocking potential to be
made. The flow speed can be measured by
the time taken to pass a distance of 200mm
(T20) and 400mm (T40). Also the heights at
either end of the trough (H1 and H2) can be
measured to determine the levelling ability.
The test appears to be useful although there
is no standardisation on the principal
dimensions of equipment
• A J-Ring can be added to the slumpflow to
also assess the concrete’s passing ability.
These tests for assessing the plastic properties
of fresh SCC are not a definitive list and are at
present not recognised by any standards, but
these are the most common in current use. The
Advanced Concrete and Masonry Centre in
Paisley are, however, coordinating a European
working group investigating test methods for
SCC.
92
HARDENED CONCRETEIn normal concrete, when vibrated, water will
tend to migrate to the surface of the coarser
particles causing porous and weak interfacial
zones to develop.
If SCC has been well designed and produced it
will be homogeneous, mobile, resistant to
segregation and able to be placed into formwork
without the need for compaction. This will
encourage, between the coarse aggregate and
the mortar phase, minimal interfacial zones to
develop. Thus the microstructure of SCC can be
expected to be improved, promoting strength,
permeability, durability and ultimately longer
service life of the concrete. In situ compressive
strengths determined using cores have shown a
closer correlation to standard cube strength than
conventional concrete. Also, work has indicated
that the reduction in compressive strength with
increase in column height is less pronounced,
showing good homogeneity of SCC [9].
Trials were carried out at RMC Readymix
Technical Centre to examine the hardened
properties of SCC, using a total cementitious
content of 480kg/m3 at a slumpflow of 700mm
using a superplasticiser and a viscosity modifier.
The concrete was poured in to a u-shaped mould
as detailed in Figure 2, with obstructions placed
in the unit (shaded).
Ultrasonic pulse velocity tests were performed
over the unit. Cores were taken to determine the
in situ strength and the density within the
structure. The cores were also tested for chloride
and oxygen diffusion.
Satisfactory self-compaction of the fresh
concrete was confirmed by the consistently high
UPV values and density measurements of the core
samples taken throughout the unit. The mean
estimated in situ cube strength was 81% of the
28 day cube strength from concrete sampled
during casting. The chloride and oxygen diffusion
results, significantly less than those required by
many specifications, were 0.304 x 10-12 and
1.44 x 10-8 respectively.
Figure 2: Section of mould used forhardened property tests.
PRODUCTION AND TRANSPORTATIONOwing to the need for the efficient dispersion
of fine particles required to produce a
homogeneous and stable mix, mixing time
compared with normal concrete is increased. In
addition the need for an accurate total moisture
content of the mix requires good knowledge of
the properties of the materials being used.
Consistency from the material supplier of
moisture content and particle size distribution is
critical. Sand grading and moisture content is
particularly important.
SCC has been produced from different types
of batching plants. The only differences between
them being the size of the mixer units and the
efficiency of the mixer which will impact on
different mixing times. Evidence from the UK
suggests that dry batching is perfectly satisfactory
for producing SCC.
SCC is more sensitive compared with normal
concrete and if the concrete has not been
sufficiently mixed before transportation,
slumpflow can be increased due to further
dispersion of the superplasticiser through the
concrete.
These factors need to be considered after
successful trial mixes have been established,
owing to the nature of the controlled
environment in which the laboratory is situated.
PLACEMENTNo special equipment is needed to be able to
place SCC. The same pumps and skips can be
used.
Owing to the nature of SCC being used to
reduce construction time, there will be no real
advantage in skipping the concrete into place as
this time is restricted to the amount of concrete
the skip can hold. Generally, whilst the skip is
returned to be filled up, the compaction of the
concrete is carried out by poker vibrators for
normal concrete.
This leads to SCC being pumped into place as
the main option to save construction time. As
with normal concrete, a well designed SCC can
be pumped considerable distances without any
problems.
Pumping from the base of structures is
feasible.
93
FORMWORKIn order to achieve the benefits of reduction in
construction time, SCC needs to be placed
quicker. With no need for vibration of the
concrete this can be achieved.
This assumes increasing the rate of rise of the
concrete within the structure, which will lead to
an increase in hydrostatic pressure on the
formwork, which could necessitate the need for
formwork re-design to accommodate the
theoretical increase in pressure.
However, one study confirms the properties of
SCC actually give lower form pressures if
compared against normal vibrated concrete at the
same rate of rise. This is because once the kinetic
energy of the fresh concrete has dissipated, the
concrete stiffens in a thixotropic manner, and so
it no longer acts as a liquid [10]. More research is
however required on this subject.
In the meantime, it is sensible to design
formwork assuming full hydrostatic pressure.
SURFACE FINISHIn the UK, surface finish is one of the
perceived key benefits of SCC leading to a whole
myriad of architectural possibilities. There are
several factors however, which interact to give
the final surface finish:
• Mix design
• Workability
• Formwork configuration
• Formwork material
• Mould release agent
• Rate of rise
• Method of placement.
A series of trials were undertaken, at RMC’s
Technical Centre, to examine the effect of
different formwork materials together with
different categories of mould release agent for
the same SCC mix . The mix was designed with a
total cementitious content of 500 kg/m3, a free
water/cement ratio of 0.36 and a polycarboxylate
superplasticiser and VMA, at a slumpflow of
700 mm.
Units were constructed as detailed in Figure 3,
which were able to compare 8 different
combinations of formwork and release agent
(Figure 4). Steel and plywood were used as the
formwork materials in conjunction with several
categories of release agent, shown in Table 1.
The results of the trials are summarised in
Table 1. It gives the ratings (somewhat
subjectively) of the combinations of type of
release agent and formwork material, based on
the general appearance and the number and size
of voids present in an area of 0.06 m2.
As would be expected, plywood provides a
better surface finish than steel. It should also be
noted that the type of mould release agent also
plays an important role in the finished surface.
Surprisingly, the release agents based on
vegetable oil gave the poorest results.
Figure 3: Design of unit.
Figure 4: Surface finish examples; Sameconcrete, same formwork type, differentrelease agent.
1
2 8
7
64
53
94
MIX DESIGN OPTIMISATION-MOVING SCC TO MAINSTREAMCONSTRUCTIONSince the infancy of SCC, a total cementitious
content of approximately 500 - 600 kg/m3 has
been used, typically achieving strengths in excess
of 70 N/mm2. Usually, such high strengths have
not been a structural requirement.
One of the main drawbacks to mix designs in
current use, however, is the increased cost
attributable, in part, to the elevated cement
contents required and state of the art admixture
technology, newer admixtures themselves also
contribute to some degree to concerns in the
specification.
The ability to reduce the total cementitious
contents of mixes and to incorporate additions
would lower the strength, and more importantly
lower the cost, making SCC a more attractive and
competitive proposition for mainstream
construction undertaken by RMC Readymix in
conjunction with BRE [11].
A series of laboratory trial mixes were carried
out over a cement content range of 360 - 500
kg/m3, with blend levels of
30% and 50% of limestone
filler using gravel, initially with
only a superplasticiser. Figure
5 summarises the performance
of the different mixes. It
should be stressed that the
trials were investigating high
performance SCCs, with
realistic slumpflows of
700mm.
RatingCategory of
SurfaceVoids
Release Agent* 10mm 10-5mm 5-2mm <2mm
Excellent A Plywood - - - -
Excellent/Good B Plywood - 3 - -
Excellent/Good C Plywood - 5 - -
Excellent/Good D Plywood - 5 10 -
Good E Plywood - 5 20 -
Good/Fair B Steel - 10 10 3
Good/Fair D Steel 4 10 - -
Fair F Plywood 3 15 >50 -
Fair E Plywood - >50 >50 3
Fair B Steel 2 >50 >50 -
Fair A Steel 2 >50 >50 -
Less than fair G Plywood 20 >50 - -
Less than fair H Plywood 20 >50 - -
Fair/Poor E Steel 2 >50 >50 >50
Fair/Poor F Steel 5 >50 >50 -
Unacceptable H Steel 20 >50 >50 >100
Unacceptable G Steel 20 >50 >50 -
Table 1 Results of trials. (* RMC Categorisation)
Figure 5: 28-day compressive strength results for varyinglevels of limestone filler.
95
The results illustrated that true self-compacting
concrete could not be produced with just the
addition of a superplasticiser below a cement
content of 440 kg/m3. Although the mixes were
highly fluid they segregated. Instability was
created by the excess water needed to achieve
the desired workability in combination with the
insufficient fines needed to maintain the viscosity.
Good strength reductions were achieved, as
expected.
Further trials were then undertaken using a
viscosity modifier at cement contents of 400 and
360kg/m3. The results showed that self-
compacting concrete could be achieved in the
laboratory with a total cementitious content of
around 370kg/m3, using limestone filler. This is
again illustrated in Figure 5.
SCC IN THE CITYWithin structural design, there is a general
move towards slimmer elements [12], particularly in
building structures where the advantages are
chiefly increased useable space and reduced self-
weight, thus also requiring a high strength
concrete.
Slimmer elements can lead to difficulty in
vibration of the concrete because of congested
reinforcement. This gives a great market
opportunity for utilising SCC.
Within a city location, environmental issues are
very important. SCC leads to a reduction in noise
levels for site neighbours due to the elimination of
vibration equipment, thus also reducing the energy
consumption. Material consumption will also be
reduced due to less spillage and due to a reduced
cement consumption, energy consumption and
CO2 emissions will be reduced [13].
Health and safety is an important factor on
any site, but even more so within a city
environment with more congested ground areas
due to buildings being built vertically. Thus
without the need to move pump hoses or
handling vibrator equipment, the working
environment will be significantly improved. Also,
without using handheld pokers which can cause
blood circulation problems, there should be a
reduction in injuries.
Quality of construction work is also vitally
important and with the noticed reduction in the
number of skilled workers, SCC reduces the
dependency of concrete quality on the workforce.
There have been several sites that have already
used SCC in city locations:
Figure 6 shows the congested reinforcement
with the SCC being placed and a core taken from
the structure shows the good distribution of
aggregate.
• John Doyle at HM Treasury, London
• Mann Construction at Moorgate, London
• Guys Hospital, London
• Midsummer Place, Milton Keynes
• Millennium Tower in Vienna
• Ares Tower in Vienna.
Figure 6: Overview of SCC being placedand section of core from structure.
ACKNOWLEDGMENTSThe authors would like to thank all the staff at
RMC Readymix Technical Centre for their
assistance in undertaking all the trial work.
REFERENCES
1. OKAMURA H. Self-compacting highperformance concrete. ConcreteInternational, Vol. 19, No. 7, July 1997, pp 50-54.
2. KHAYAT K. Workability, testing andperformance of self-consolidating concrete.ACI materials journal, Vol.96, No. 3, May-June 1999, pp 346-353.
96
3. OKAMURA H, OUCHI M. Self compactingconcrete - development, present uses andfuture. Proceedings of first RILEMInternational symposium of self compacting concrete, Stockholm, 13-15 September 1999.
4. OZAWA K, MAEKAWA K, OKAMURA H.High performance concrete with high fillingcapacity. Proceedings of RILEM Internationalsymposium on admixture for concrete:Improvement of properties, Barcelona, May 1990.
5. PETERSSON Ö, BILLBERG P VAN BK. A model for self compacting concrete.Proceedings of RILEM Internationalconference on production methods andworkability of fresh concrete, Paisley, June 1996.
6. SEDRAN T, DE LARRARD F. Self compactingconcrete - a rhelogical approach.Proceedings of RILEM Internationalworkshop on self compacting concrete,Japan, August 1998.
7. SAAK A, JENNINGS H, SHAH S. Newmethodology for designing self compactingconcrete. ACI materials journal, Vol. 98, No. 6, November-December 2001.
8. SKARENDAHL A. State-of-the-art of selfcompacting concrete. Proceedings ofseminar of self-compacting concrete,Malmˆ, November 2000, pp 10-14.
9. GIBBS J, ZHU W. Strength of hardened self-compacting concrete. Proceedings of firstRILEM International symposium of selfcompacting concrete, Stockholm, 13-15 September 1999.
10. PETERSSON Ö. Design of self-compactingconcrete, properties of the fresh concrete.Proceedings of seminar of self-compactingconcrete, Malmö, November 2000, pp 16-20.
11. BUILDING RESEARCH ESTABLISHMENT.Practical guide for engineers using SCC.
12. MARSH B, Ove Arup. Personalcommunication, February 2002.
13. GLAVIND M. How does self-compactingconcrete contribute to implementation ofsustainable/clean technologies in theconstruction industry? Proceedings ofseminar of self-compacting concrete,Malmö, November 2000, pp 57-61.
97
Peter Goring is the Technical Director of John
Doyle Construction, the specialist concrete trade
contractor, where he is responsible for all
technical and planning aspects of the entire
construction process. He is a published author
and lecturer and an active member of the
Concrete Society and Construct working parties
and technical research committees, having input
into publications such as those on self-
compacting concrete and the National Concrete
Specification for Building.
ABSTRACTSelf-compacting concrete is seen by the
contractor as a material which permits and
demands different placing and working practices
and as such it has both advantages and
disadvantages. These can be balanced against
each other and the result is that for many forms
of construction self-compacting concrete offers
improvements in ease and speed of placement,
quality of finish and reduced overall cost in
addition to the usual technical benefits of
complete and assured full compaction and
elimination of voids. A number of projects, such
as the Brompton Square and Albion Wharf
developments, have been sucessfully completed
in the heart of London, where self-compacting
concrete has proved to be especially beneficial in
areas that are difficult to vibrate, or where the
noise of vibration could curtail working hours.
The advantages can be summarised below:
• Noise eliminated (safe working
environments)
• Reduced demand for skilled labour
• Faster placing time
• Improved surface finish
• No grout loss
• Reduction in making-good costs
• Can be designed as watertight.
Some approximation of the offset costs can be
calculated. An estimate of these shows the
following:
• Cost of placing concrete £15-20/m3
• Difficult areas £30-40/m3
• Formwork costs £25-35/m3
• Featured formwork £35-60/m3
• Powerfloat surface £3-6/m3
• Watertight concrete £35-60/m3
• Reduced section size.
Limitations can also be measured. These are:
• Acceptance
• Costs of design mixes
• Potentially high alkali content
• Formwork pressures
• Unformed surface areas and finishes
• Forming integral upstands
• Site control.
The design of the concrete mix is rather
different to a normal structure concrete mix and a
typical mix design can be based on the following:
• Coarse aggregate content 50% by volume
• Cement/powder content 420-520 kg/m3
• Water/cement ratio 0.32-0.42
• Superplasticiser 1-1.5%
• Viscosity agent 0-1%
• Slump flow 600-700mm
• Expected strength 60 MPa.
The costs of this typical mix design can be
significantly higher than for conventional
concrete. This cost premium is typically:
• Increased cementitious £6-8/m3
• Superplasticiser £4-7/m3
• Viscosity agent £0-6/m3
SELF-COMPACTING CONCRETE - A CONTRACTOR’S VIEW
Mr. P. Goring MSc, BSc(Hons), ACGI, CEng, MICE
John Doyle Construction
Figure 1: Self-compacting concrete beingpumped into place at Albion Square.
98
Site controls for self-compacting concrete
should be no lower than for conventional
concrete and a single test method should be
adopted to ensure the site control of workability.
Practical issues that also need to be addressed are
the selection of formwork release agent where
finish is important, placing and pumping of the
concrete, any workability loss during delays and
the setting time once placed.
Figure 2: A trial for construction work atthe Treasury was instigated todetermine degree of compaction,reinforcement bar bond and quality offinish.Figure 3: After the formwork wasstripped and the quality of finishagreed, cores were taken to check forvoids and bond. The photo shows thatthe concrete matrix had fully bonded tothe reinforcement and aggregatedistribution shows no sign ofsegregation.
In summary, it is evident that self-compacting
concrete offers to the contractor some significant
advantages over normally placed concrete. Some
of the economic applications where such benefits
may be seen are in precast elements, exposed
walls and columns, watertight basements, secant
wall cladding, dense reinforcement, column
encasement and in top-down construction.
99
Mr. Gordon Talbot is one of
three associates at Ian Ritchie
Architects. The practice has
been responsible for a number
of innovative and award
winning buildings in the UK,
France, Spain and Germany. He is currently
responsible for the realisation of major new
transport infrastructure elements for the White
City development in West London. Between
1990 and 1999 he was responsible for
Bermondsey Station, one of 11 new stations on
the Jubilee Line extension and 6 mid-line vent
and escape shafts.
ABSTRACTThis paper looks at the subject of concrete
finishes off the form from the perspective of a
designer (architect). It forms an overview of the
shifting perceptions of the material, the
dominance of concrete in the visual environment,
the influence of the concrete specialist/
technologist, and the influence of the designer
and some of the possibilities that may exist which
are of particular interest to the author. This
includes a summary of twelve parameters which
the author believes are important in respect of
using concrete. The conclusion draws attention to
the importance of finishes in respect of the future
development of the material.
KEYWORDSConcrete, CPF: Controlled Permeability
Formwork, Designer, Finish, GGBS: Ground
Granulated Blastfurnace Slag, MDOs: Medium
Density Overlays, Surface, Technologist,
Tri-stimulus Y Value
INTRODUCTIONMy immediate and slightly tongue in cheek
response to this title is “The Good, the Bad and
the Ugly”. In the same manner that the film deals
with three personalities, Blondie, Tuco, and Angel
Eyes, appearing in any of the three guises of
good, bad and ugly, concrete also appears in our
cities in any one of these disguises, often in the
same project and certainly in terms of the
perception of the material by other people,
particularly those outside the industry. Concrete is
without doubt a much vilified material. A recent
article in the RIBA Journal underlines the way the
material is perceived. On the one hand it is seen
as unpredictable and unreliable in terms of finish
yet on the other hand it holds an almost alchemic
fascination for architects, a Philosopher’s Stone
somehow always just out of reach. The reasons
why this is the case are not simple. The industry
does not seem to be overly concerned with
aesthetic appearance. Concrete is a long way off
attaining the kind of finish reliability found in the
steel industry. This may be because the concrete
industry is more focused on the mechanical
properties. Is the concrete industry missing out
the potential for a ‘value added’ area of
business?. Surely it must be possible to offer a
reliable standardised set of finishes. There are
sectors of the industry which appear capable of
delivery of finishes and this was brought home to
me during the course of The Jubilee Line
Extension Project, where we were fortunate
enough to be dealing with two entirely separate
and highly competent concrete contractors.
Fundamentally, it appears that the consistent
concrete knowledge and experience lies with the
civil engineering contractors. They have the
continuity of work (within the constraints of the
economic cycle), they appear to be more
accustomed to demanding finishes requirements
which are not born out of the ephemeral notion
of an architect looking for a poetic finish, but the
hard nosed engineer looking for finishes to water
containment chambers or sewage treatment
plants. In these locations exacting finishes are the
result of either avoiding opportunities for bacteria
to accumulate or avoiding the effects of induced
wear due to surface irregularity. Before moving
into the detail concerning finishes off the form, I
would like to outline a context in which concrete
is cited, within the designer’s mind and where it
sits in respect of people outside the industry
(often the end user) and subsequently perhaps a
glance at how designers might see the industry
developing.
CONCRETE FINISHES OFF THE FORM
- THE GOOD, THE BAD AND THE UGLY
Mr. G. Talbot Dipl. Arch RIBA, I, II & III
Registered Architect
100
SHIFTING PERCEPTIONS ABOUT THE MATERIAL
The Motorway IntersectionAt one extreme concrete is synonymous with
the image of the motorway intersection, the no
man’s land below and graffiti covered surfaces.
The term “concrete cancer” has been thrown at
the material and stuck, a reflection of poor
specification and site control. If one adds insult to
injury the scene under the road bridge in Stanley
Kubrick’s film ‘A Clockwork Orange’ located at
Thamesmead stamped a lasting negative identity
on the material in the 1970s, its relationship to
humanity and the social consequences.
The High Rise Sky Line At the opposite extreme concrete is an iconic
and tactile, human skin material which holds a
unique fascination for designers. It has strong
associations with texture, durability and
monumentality and a close association with the
aspiration for taller and more compact cities.
Setting aside the events of September 11th,
which does not appear to bode well for steel and
drylining, concrete has formed an essential part
of the shift of the sky line ever upwards. It has
permitted the plan libre (the free plan) and the
vision of a city of crystal towers and as we look
into the future, concrete has become an essential
part of balancing the thermal environment,
providing soundproofing and shaping the internal
and external environment through the
exploitation of the plastic nature of the material.
MICRO TO MACRO
Concrete As A DesignerPreference
Historically, there are great and inspiring
precedents for the use of concrete. Millart’s
Bridges gracefully span between precipitous cliff
faces in Switzerland. The smooth, pale, shear
surfaces contrast with the angular landscape. The
open form allows light to pass through, they
appear suspended, almost frozen in the space
between. Felix Candela exploited the three-
dimensional form of concrete to produce elegant
spaces for pragmatic functions, bus stations,
market halls, factories, warehouses. Tadao Ando
remains a master of the vertical surface and the
intersection of planes. His recipes for concrete
formwork and finish have attained almost
mythical status amongst designers. It is
interesting that concrete as a purely sculptural
material in the hands of artists is arguably less
successful in attaining the full expression of the
material’s capability and perhaps this is because it
misses the intrinsic structural characteristic which
will always hold a fascination for designers: the
formed material performing as a unified structure
and finish. However, Rachel Whiteread’s short-
lived casting of the interior of a house remains an
outstanding example of the material’s ability to
communicate detail.
The Bar, The Altar, The LivingRoom Artefact
The use of concrete as a material of counter-
point can be pinpointed in buildings such as Truss
House by Ushida Finlay overlapping solid and
space: the poetic geometry of Oscar Nymar
displays the material’s ability to communicate at
vastly different scales with the formed concrete
surfaces. In our work for the Jubilee Line
Extension, we discovered the benefits of
contrasting very rough with very smooth concrete
to the benefit of both materials and contrasting
materials such as coloured glass has similar
benefits for the concrete. During the past ten
years concrete has made inroads into the bar and
leisure environment whereby it is used as a
contrast against other materials and enhanced by
clever and well designed lighting, even Habitat
now sell cast concrete candle holders.
The Most Prevalent ManmadeMaterial
Concrete is generally acknowledged as one of
the most prevalent materials associated with
shaping our environment and it is perhaps its
over-use that has devalued its application within
the construction industry. In conversation with
designers and contractors who were practising
prior to, and during, the Second World War it
appears that concrete was a much more highly
valued material and thereby attracted greater
skill, care and attention in its use. The shift of
design knowledge from the contractors building
ambitious shells and folded plate structures, to
the professional engineer appears to have stunted
the iterative process of designing and building,
and the process of feeding the knowledge gained
from the building process into the design to some
extent has been lost. There is also an element of
stylistic whim and fashion in which certain types
of structure and form are displaced by others. For
example: the almost total elimination of shell and
folded plate structures from our repertoire.
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THE INFLUENCE OF THE SPECIALIST, THE TECHNOLOGISTAs a design practice we recognise the
importance of cross fertilisation between design
and realisation. This occurs in every aspect of our
work. When we became involved in the Jubilee
Line we had very little knowledge about concrete.
To enable us to engage with the civil engineering
pragmatics of the project we required a concise
understanding of the material and its capabilities.
The project performance requirements included
400 year durability below ground, stringent limits
on gas diffusion, alkali silica reaction, chloride
and sulphate attack. At the same time, we set
ourselves targets concerning the visual finishes
forming part of a hierarchy leading from the civil
scale to the human scale. At the outset of the
project we set about learning the detailed
engineering aspects of the material as well as the
best practice that would give us the end results
we were looking for. We used a variety of
organisations to shape our understanding, The
Concrete Society, BCA, The Institution of Civil
Engineers and various research organisations,
both in the UK and Europe, together with some
input from specialist contractors. The output of
this process was an understanding of what we
wanted the material to do and how we would
achieve the desired appearance which would
enable us to convince the project’s civil engineers
and the Jubilee Line Project office that what we
were proposing was feasible, could be achieved
without excessive programme implications (the
project was in a hurry at the outset) and without
incurring excessive costs over and above the
guidelines agreed for the project. Our objectives
were four-fold:
• To expose civil engineering construction
techniques as the final finished material in
public areas
• To employ a concrete that would provide a
warm, pale surface finish without incurring
the costs of using white cement
• To employ a construction sequence that as
far as possible avoided the necessity for
extensive temporary works
• To meet the underlying project performance
criteria for concrete works.
From our research and consultation four pieces
of advice stand out as invaluable. Input from Ove
Arup & Partners influenced the general
arrangement of the structure of the station to
eliminate temporary works by the introduction of
open trusses constructed top down. Input from Dr
Bill Price (then at Taywood Engineering)
introduced us to ground granulated blastfurnace
slag as an alternative to Portland cement as a
means of brightening concrete. Input from Civil
and Marine helped shape the key specification
aspects and avoid the pitfalls associated with the
use of ggbs. They also alerted us to some of the
surprises that can be associated with the use of
ggbs and Bill Monks helped clarify some key
workmanship issues such as panel sizes and pour
rates.
The purpose of highlighting the above process
is the invaluable role that the transfer of
information plays in influencing the final outcome
of a project and providing the necessary practical
backup that enabled us to convince the design
team and client of our proposals. Along the way
we built up a chain of contacts across the
concrete industry which we continued to call
upon. It also gave us an insight into various
aspects of concrete technology at varying stages
of development, which we may use in future
projects.
Critical external input forces the thinking
processes.
THE INFLUENCE OF THE DESIGNERIf we focus the influence of the designer from
the macro level of a total project to the micro
view of a particular material such as concrete, the
role of the designer is that of somebody who can
orchestrate the marshalling of the material
properties, the engineering pragmatics and visual
aspirations into a cohesive vision which is capable
of being realised with the aid of a competent
contractor. I would like to give two examples of
this. Firstly, referring to our work for the Jubilee
Line, this time the Mid Line Vents. We conceived
a family of six vent and escape shafts placed at
approximately 1km intervals along the line. Each
vent comprised a surface structure, subdivided
into plant space, air intake/extract and emergency
access escape stairs. Three of the vents employ an
in situ concrete comprising ggbs at 70% of the
total cementious material and black basalt
aggregate. The surface is ground off
approximately 6mm to reveal a type of in situ
terrazzo but unlike terrazzo the disposition of
aggregate is very irregular and as a result very
interesting to look at, at close range. The use of
ggbs at 70% imposed a number of constraints on
the in situ work, associated with formwork
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pressure, placement rates and prevention of grout
loss and bleeding of the mix. It also required
careful consideration of details to ensure that
aggregate reached the surface of the formwork
in what were heavily reinforced structures.
Secondly, referring to a project which we are
currently working on which includes replacement
of part of an existing viaduct with a new bridge,
we are looking at an engineered structural
composition of steel and concrete elements
comprising a complex bridge slide operation. The
project is highly constrained in terms of
programme and cost. However, we can see
opportunities for harmonising the design of the
new bridge with the existing viaduct born out of
the practicality of how the bridge is installed, and
exploiting aspects of precast work to build in
connections and detailed accuracy, combined
with the virtues of in situ concrete for dealing
with the formation of heavily reinforced
abutments and supports relating to the existing
structure. The aim will be to employ the precision
of precast concrete to deal with certain
engineering aspects and contrast this with in situ
work employing a very different texture and
possibly counter pointing these with
coloured/illuminated translucent glass panels.
EXAMPLES OF POSSIBILITIESThere are four aspects of the use of concrete
that I find fascinating and attractive:
1. Introducing exotic aggregates or materials
such as glass and stainless steel into the
mix and finding ways to ensure they are at
the surface of the finished material -
growing organic material on the surface,
photo-etching.
2. Introducing colour into the material using
synthetic or natural agents. This has been
explored with varying degrees of success.
Obviously, it is more successful with thin
build-up of material where the colouring
agents are disbursed at a reasonable
density to achieve good colour properties.
Up until now it has been less convincing
with thick section in situ or precast
material due to the quantity of colour
agent required. From a designer’s point of
view the integrity, solidity and durability of
the colour is paramount. The question
always posed in respect of coloured
concrete is why not paint it? The simple
answer is that inevitably the paint surface
deteriorates and eventually peels. It also
amplifies any surface defects, in particular
blowholes. It also poses a maintenance
burden and at a more esoteric level it
denies the material integrity. It is
interesting to look at certain concrete
look-alike paints occasionally used by
unscrupulous contractors to rectify
defective surfaces. It is always obvious
when surface treatment has been applied
and the long-term visual durability of the
surface is always prejudiced.
3. Self-compacting concrete: this is an area I
find particularly interesting as it appears to
have the potential to remove one of the
main problems with producing a uniform
concrete finish, that is the variables of the
placement. I don’t have any personal
experience of using this material but
monitoring the discussions taking place in
the UK, Europe, America and Japan it
does appear that with the right
superplasticizing agent it may be possible
to produce a very high quality, dense,
closed surface concrete. I would be
interested to learn how this can work with
ggbs.
4. Controlled permeability formwork: this
appears to offer a number of advantages
in respect of obtainment of a close, dense
surface. The main problem in terms of its
use in respect of architectural finishes
appears to be the ability to fix the material
in such a way that it can be removed and
replaced on a conventional form. My own
personal thoughts about using this would
be to duvet the surface, stretching the CPF
material over mesh panels on a robust
backing frame and exploit the duvet effect
in the appearance of the resulting
concrete.
THE DESIGNERS VIEW OF THE WAY FORWARDReturning briefly to the original subject of
concrete finishes off the form, the basic principles
of achieving good finishes are very succinctly set
out in the BCA publications ‘Appearance Matters’
by Bill Monks and they remain a sound starting
point for designing concrete. ‘Plain Formed
Concrete Finishes’, Concrete Society Technical
Report 52 also provides a good summary of
design issues and specification. However, I would
like to outline some of the parameters which I
think are important.
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1. What is the desired level of finish, is it a
reasonable plain, formed finish, is it a
special finish i.e. including some special
performance such as light reflectants or
grit blasting to expose details of the
matrix or an exotic finish i.e. incorporating
special materials or receiving a specialised
secondary treatment?
2. The form of the structure, element or
component, is it appropriate to precast or
in situ or a hybrid?
3. The method of specification is very
important. The choices that exist are a
purpose-written specification based on no
particular format:
• NBS Specification
• Construct Specification
• The Civils Specification for Highway
Works
• The Civils Specification for the Water
Industry
• BS8110 Based Specification.
I would counsel against using BS8110 as it
appears to create more confusion than clarity in
respect of finishes. The Construct Specification
ties into BS8110 and is backed up by the
reference panels around the country, and it is a
noble effort at sorting out the BS8110 confusion.
However, the panels at Greenwich are not
something I would ever take a prospective client
to see and I believe the ones in Scotland are of a
much higher standard. I would therefore steer
towards the NBS or the Civils Specification
backed up by the appropriate samples and
prototypes.
4. The concrete mix: if lightness is an issue
then the designer should be careful to
select OPCs with a high as possible dry
power brightness value. We have found
best results from using high levels of ggbs
combined with an OPC with a tri-stimulus
Y value of 30 or more. Obviously, the
aggregates are of lesser importance but
using good, white, non sedimentary sand
will help the surface appearance.
5. The formwork material: my preferences at
present lie somewhere between resin
faced plywood and medium density
overlay. The resin faced plywood requires
a pre-treatment with a grout scrub to take
any of the sheen which can result in a
darkening of the surface due to water
being drawn to the surface by vibration
and having nowhere to go. Currently I’m
finding with medium density overlays that
the plywood grain is telegraphing
through. The MDOs can also result in a
slightly dusty surface in their initial casts
and this too may not be desirable.
6. The sealing of the formwork to prevent
grout loss is extremely important and it is
essential that forms built on the ground
are over-designed structurally in order to
prevent opening of the sealed joints
during installation.
7. The formwork details, arrises, openings,
stop ends must all be carefully considered
and the highest quality materials used for
the details. There are some very good
proprietary arris materials available which
are not the conventional PVC materials.
Openings must be carefully considered to
avoid forming voids around the box out
during the placement.
8. A further critical issue in respect of the
formwork is the resistance to the static
head of the concrete and here the
requirement for a placement rate of more
than 2m an hour imposes considerable
stress on the formwork and this is easily
overlooked by designers and engineers. It
is particularly important when using ggbs
at high levels.
9. The layout of the percentage
reinforcement is essential in terms of
ensuring that the concrete matrix can
easily flow to the surface of the form
without creating aggregate dams. A zone
where bars from slabs are lapped into
walls with a consequent doubling or
trebling of the steel work can be
disastrous for a finish.
10. The placement rate for the concrete is an
essential element in terms of colour
continuity. The mysterious figure of a
placement rate greater than 2 vertical
metres per hour seems to be if anything
slightly on the low side, it is certainly
important in terms of sizing the overall
panels and pour and this should be the
defining characteristic for panel sizes.
11. Compaction and room for vibrators is
essential in planning to cover
reinforcement and the gaps between the
reinforcement. There are a number of
104
interesting vibrators from Japan which
appear to have a significant advantage in
terms of mobility and manoverability over
and above traditional vibrators attached to
a static compressor with a heavy hose.
12. The final revibration of the top part of
wall panels is essential to removing those
last blow holes where the concrete
pressure is at its least.
However, there are a number of other, less
obvious issues. The question of precast or in situ is
very clearly a project by project decision but
essentially the highest quality finishes are obtained
by precast work. In situ remains a dominant part
of the construction industry methodology and in
particular civil engineering methodology and
without doubt high quality in situ work can be
achieved by civil engineering contractors.
The method by which the site team engage on
finishing work and is remunerated is an important
issue in terms of the out-turn quality. It is normal
for concreting teams to be paid a bonus
according to placement rates. This may conflict
with the requirements for high quality finishes.
However, it is not beyond the realms of reality to
deal with this problem and I am aware that
certain trade contractors recognise the
importance of this.
CONCLUSIONFrom the designer’s perspective I believe that
the subject of finishes is relegated in terms of its
importance within the concrete industry. I suspect
this is because it is less tangible and analytical
than the mechanical properties. It does appear
that the industry may be missing a trick. The steel
industry is very good at providing designers with
technical backup. It is doing a lot of work on
environmental issues and the role of steel in
terms of thermal environment, a property which
concrete excels at and yet is somewhat taken for
granted. The focus of the Egan Report on Lean
Construction and Industry Efficiency is a subject
that concrete is very well placed to exploit by
virtue of exposed concrete finishes. Yet, exposed
concrete finishes are perceived as risky by clients
and designers. On the other side of the equation
I draw inspiration from the occasions on which I
have discovered impressive finishes which are not
destined to be exposed. Most recently projects on
the South Quay at Canary Wharf exhibit striking,
monolithic, shear walls with beautifully placed
concrete layers which loan a detailed quality of
strata found in stone. Similarly, I have seen
beautiful flat slab constructions ideally suited to a
simple crystal cladding, filled out with suspended
ceilings, brick cladding and miniscule windows.
The industry needs an eye to the future, the
importance of finishes in a range of commercial
infrastructure and domestic environments cannot
be overlooked or if it is overlooked this is at the
industry’s peril.
105
David A Morrell BSc MIHT
graduated in Civil Engineering
and after working for
Nottinghamshire County
Council and West Yorkshire
Metropolitan County Council
joined Marshalls. He is the New Product
Development Manager for the Landscape
Division, is a past Technical Chairman of Interpave
and currently chairs British Standard Committee
for Linear Drainage B505/4/P2.
ABSTRACTA few words that describe concrete are grey,
cheap, depressing and of little added value.
These are perhaps the public’s view of concrete.
What properties can be changed to improve the
perception of concrete, adding colour, changing
surface texture, altering the shape, or improving
the function? This paper considers, with the aid
of three new products, how concrete can become
sustainable, adding value to our environment and
the lives we lead.
KEYWORDSConcrete, Sustainable, Environmental, New
Products, Nitrogen Oxides, Titanium Dioxides.
INTRODUCTIONThe general public perceives concrete as being
a grey material, often depressing, adding little
value to our lives. However, concrete is an
economical construction material that will accept
colouration and can be formed into complex
shapes. With increasing focus on the protection
of our environment it is important that we react
to the changing agendas.
Three recently launched products demonstrate
how concrete can be designed with sustainability
as the major issue, or how by introducing
improved aesthetics concrete can dramatically
improve our streetscapes, or how by changing
the chemistry of the concrete the product can
improve the air we breathe.
New products need to either anticipate or
respond to the evolving customer needs, to fit
the market, the competition and the company.
By understanding these issues AquaPriora, a
permeable concrete block paver; Stein+Design, a
portfolio of striking product designs and Noxer, a
paver that absorbs nitrogen oxide gases from the
atmosphere, have all been developed.
NEW PRODUCT DEVELOPMENTWhy are new products developed? Many
companies strive to be customer focused and
become seen as innovators. The development of
new products helps any business differentiate
itself from the competition.
The reasons for developing new products will
include issues such as anticipating or responding
to the changing needs of the customers ensuring
that customer satisfaction continues to be
delivered. It can also pre-empt or respond to the
competition both from within a market sector
and also from outside. Many ideas should be for
advancement.
To understand new products an organisation
must first define what products it currently has
and what markets it wishes to aim for. There is a
major difference for any organisation between a
line extension, which takes an existing product to
an existing market, and a new idea, that is a new
product to a new market. Also is the product to
become a niche product or accepted by all as a
volume product?
Before products are accepted it is critical that a
screening process is developed to ensure products
being developed are right for the company and
satisfy current or future market demands.
Development of new products is not without
its pitfalls and risk assessments are required to
understand such issues as overstating the likely
speed of adoption of a product, launching a
product that does not live up to expectation,
developing products that merely follows the
competition or allow easy opportunities for others
to copy.
As a major UK supplier of landscape products
it is crucial that we listen to our customers and
develop products that fit the changing demands
of our industry. We need to ensure that we
accept our responsibility for the streetscape in
order to introduce more “concrete in the city”.
STREETSCAPE CONCRETE
Mr. D.A. Morrell BSc, MIHT
Marshalls Mono Ltd
106
AQUAPRIORAThe occurrence of major flooding is becoming
more common and has sent sustainable urban
drainage systems (SuDS) to the top of the agenda
for new developments. AquaPriora is an
innovative block paving system, coupled to a
specific design methodology and sub-base
specification. Together, these contribute to a
SuDS solution, which allows surface water to be
controlled at source, draining directly into the sub-
base. This reduces the requirement for additional
drainage systems whilst at the same time
recharging the natural groundwater, creating a
cost effective and environmentally friendly solution
to the management of surface water run off.
The ProblemTraditionally rainwater has been managed by
the use of surface water sewers, resulting in peak
flows and increased pollution from first flush
occurrences.
The PlanningIncreasingly developers are being required to
consider SuDS solutions in planning applications
as detailed in Planning Policy Guidance Note 25.
The SolutionAquaPriora allows the surface water to drain
naturally at source, eliminating surface ponding
and substantially reducing the risk of pollution
and flooding in the sewer systems. Designers can
also allow for roof water to be discharged directly
into the sub-base via the paving, further reducing
the load on the main sewers.
The StructureAquaPriora blocks are produced in a standard
200 x 100mm module, however, the unique
shape creates voids, which allows the surface
water to pass through the pavement.
Figure 1: Photograph of AquaPriora andbedding material.
The interlocking joint provides stability through
friction to the paved surface without the use of
joint filling sand. The drainage apertures provide
an area in excess of 25,000 mm2/m2 when filled
with 6mm washed aggregate and will allow for
flow rates of 18,750 litres/sec/hectare. Typical
flows for UK rainfall would be 180
litres/sec/hectare.
The Environmental BenefitsThe major environmental benefit of an
AquaPriora permeable pavement is that it
significantly reduces peak flows and total volumes
of water. This avoids any contamination
associated with first flush occurrence. Current
SuDS thinking is that contaminated run off water
is dealt with environmentally, with hydrocarbons
breaking down naturally within the sub-base and
heavy metals remaining trapped at low
concentrations. Similarly, any major spillage
event remains contained within a small area and
does not get channelled in to local river
ecosystems.
NOXERWith more and more cars taking to the road
every year, pollution from exhaust fumes is
becoming a serious problem. In heavily trafficked
areas, Nitrogen Oxides (NOx) will cause poor air
quality leading to respiratory problems, as well as
contributing to acid rain and the greenhouse
effect. Noxer is a unique, environmentally
friendly block paving which effectively neutralises
NOx gasses in polluted air, converting them to
nitric acid, which is harmlessly washed away by
rain. Noxer was developed in Japan by Mitsubishi
Materials Corporation and is now being
introduced into the UK paving market by
Marshalls.
The SolutionNoxer is a concrete block paver, which is
produced using modified concrete containing
titanium dioxide. It is an eco material, as it
derives all the energy it requires from sunlight.
In addition to is remarkable anti-pollution
properties, Noxer meets all the requirements of
standard interlocking concrete block paving and
requires no special skills or equipment to install.
The ReasonNoxer is needed to improve the local air quality
of heavily trafficked routes, along with the
greater environment for us all. Motor vehicle
107
exhaust fumes contain high levels of NOx gasses.
NO, the more abundant, will quickly oxidize to
form NOx, which is the light brown gas
responsible for the familiar urban haze, and
which causes many respiratory problems. Both of
these gasses contribute to acid rain and global
warning.
How it worksWhen the surface of the block is irradiated by
sunlight, active oxygen is created on the surface
of the blocks due to a reaction of ultraviolet rays
in the sunlight and titanium dioxide contained
within the block. Active oxygen has a high
oxidisation efficiency and oxydises NOx in the air
into nitric acid ions.
The resultant nitric acid is then washed away
by rain. Any nitric acid ions remaining on the
surface or permeating the block are neutralized
by the alkaline nature of the concrete.
The PerformanceNoxer removes more than 90% of NOx gasses
under ideal conditions. Even on cloudy days,
removal rates are still around 80%, with high
humidity reducing removal to around 70%.
While removal rates do drop with age, they can
be restored easily by simple surface washing.
Noxer has been successfully compliance tested for
the UK in accordance with BS6717, including
tests for strength, slip/skid, abrasion and
freeze/thaw. It is already used extensively
throughout Japan.
STEIN+DESIGNToday’s streetscapes are as much about
creating exceptional style and quality through
striking design as providing practical solutions to
meet our landscape needs. Stein+design brings
an exciting vision to landscape design that
captures all these elements in a new and
innovative way. This unique collection of paving
products opens up new design opportunities for
both traditional and contemporary schemes alike.
The whole range includes the use of new
manufacturing technology that allows a palette
of colours and textures to be introduced to create
truly distinctive and individual landscape and
streetscape designs. The timeless appeal of
natural tones contrasts with the introduction of
bold new shades. Sophisticated finishes reveal
the high quality aggregates used. These qualities
combined present the specifier with a host of
new design prospects.
CONCLUSIONConcrete is a flexible material and with
innovation in manufacturing techniques or the
use of modified binders and additives concrete
can add value to the life we live. Working
together as an integrated supply chain we can
rise to the challenges and develop new products
that are appropriate for our changing
environment. Concrete need not be grey and
uninteresting; however, with these new product
ideas the public may be mistaken for not
recognising the material as concrete.
Figure 2: Schematic view of how Noxer works.
108
109
John McCabe, National
Specification Manager,
Lafarge Cement UK.
ABSTRACTThe opportunity to use concrete in innovative
building designs has long been underestimated.
This paper discusses how new developments in
concrete are taking it to the cutting edge of
architecture, and why critics of the ‘grey stuff’
should take another look.
INTRODUCTIONConcrete has been the foundation of building
both physically and metaphorically throughout
the past 100 years. Its strength lies in its ability
to be economically moulded into highly-complex
geometry whilst providing tremendous durability
and strength. Name the most famous structures
in the world and almost certainly they will have
been impossible to construct without the use of
concrete. However, despite its on-going high
usage, concrete continues to evoke different
emotions. For instance, ‘concrete jungle’ or
‘concrete facts’ - two opposing views, one
negative and the other positive. Many people,
particularly specifiers, assume that concrete,
because it has such a long history, has little left to
offer in the way of innovation, but times are
changing.
Within the UK, over 200,000 m3 of concrete is
produced for construction per day, making
concrete the most-used construction product on
Earth. Cement and concrete innovation is a key
feature of many countries, with self-compacting
and fibre technologies being actively promoted at
both commercial and government levels in
countries such as Japan, France and the USA.
Within the UK, concrete has lost out to steel in
the past few years. It has not been in vogue,
particularly amongst young architects and
engineers. Recently, the Lafarge Group has
recognised the need to develop products that
provide ‘solutions’ to specifiers. Sir John Egan’s
‘Rethinking Construction’ report further
strengthened the call to identify the needs of the
supply chain members to fully interact and
understand the requirements of all aspects of the
supply chain. While perhaps not necessarily well
promoted, the advantages of concrete are
numerous and include:
• Monolithic, continuous construction
allowing full continuity between columns,
beams and floors
• Very flexible and versatile : can be cast in
any shape / cast in situ or pre cast;
durability and low maintenance contribute
to protect the environment
• Natural fire resistance obviating the need
for additional protection such as
intumescent coatings for steel
• No need to incorporate moving
connections to compensate for frame
flexibility
• In situ concrete is inherently rigid,
meaning that sound vibration is reduced -
an important feature where sensitive
equipment may be required, such as in
hospitals.
Additionally, concrete is a highly resilient,
durable material - it does not rust, decompose or
rot. An illustration of this is the many examples
of early Roman concrete work that still exist
today.
Despite these considerable virtues, concrete
has to continuously evolve if it is to maintain its
reputation as a valuable component in modern
buildings. The tragic consequences of September
11th 2001 have once again re-opened the
discussions on the future of tall buildings and
there is a renewed interest in innovative materials
and construction concepts. However, whilst
concrete is widely recognised for its great ability
to withstand high levels of compressive loading,
its Achilles heel has traditionally been its
weakness when placed under flexural loading.
Ultra-high performance andductile behaviour
In answer to this problem, a recent exciting
innovation has been made in the development of
a new form of ultra-high performance concrete
(UHPC) based upon reactive powder concrete
(RPC) which originally debuted in the mid 1990s.
CONCRETE’S INCREASING FLEXIBILITY IN THE 21st CENTURY
Mr. J. McCabe
Lafarge Cement UK Ltd
110
Demonstrating the potential of UHPC, the
French government is currently sponsoring an
ambitious, unique project as part of the 21st
Century Celebrations. The ‘Footbridge of Peace’
project will see the use of Ductal™ UHPC to
create a 120m footbridge across the Han river in
Seoul, Korea, without any column support or
passive reinforcement (Figure 1).
Figure 1.
The original concept envisaged a traditional
suspension bridge, however the use of Ductal™
UHPC has revolutionised this vision to allow a
beautiful, slender, lightweight design to be
conceived. (Note that in the photograph the arch
is standing by itself across the river: walkways for
its access from the bank are being erected during
the next two months). The arch will consist of six
precast rib elements each 22m by 4.3m with a rib
design. Whilst the ribs are 1.3m in height,
thanks to the unique properties of this material
the footbridge deck will be only 30mm. As the
bridge is erected, the segments are to be
connected by 6 cables strung through the ribs.
Each segment will be prestressed to the
foundation. Significant foundation blocks - one
on each bank of the river - support its total load.
UHPC concretes utilise an advanced concrete
technology to offer a unique combination of
superior ductility, strength and durability whilst
being highly mouldable with a high quality
surface aspect. Using a combination of
traditional concrete technology combined with
modern mineralogical and fibre technologies,
UHPC is able to provide typical compressive
strengths in the range 170 - 240 MPa and, most
significantly, a maximum bending tensile strength
of 50MPa.
Ductal™ provides ultra high strength and
durability with a ductility that has greater capacity
to deform and support flexural and tensile loads,
even after initial cracking. Durability
characteristics are those of an impermeable
material: almost no risk of carbonation or
penetration of chlorides or sulphides, with
significant resistance to acids together with
abrasion performance similar to rock.
Additionally, there is almost no shrinkage or creep
following thermal treatment. Importantly,
another key feature of Ductal™ is its ability to be
easily moulded into intricate shapes, catering for
high-tech and imaginative designs.
Table 1: Some typical values.
The design opportunity for UHPC concrete is
limitless, but typically its uses range from
architectonic claddings to structural elements,
roof covers and footbridges.
Ductal™ UHPC may be used as a fluid or dry
cast under normal curing conditions or
accelerated curing to provide an high early
strength development in excess of 60 MPa in less
than 16 hours. The elimination of passive
reinforcing and reduced cross-sectional area
improves placing conditions, increasing safety and
speed of erection.
Table 2.
Table 3.
The use of innovative structural concretes,
based on highly-advanced reactive powder
111
technology, offers the designer new opportunities
in the creation of designs previously not
considered due to complexity of design or
material concerns. The challenge for both the
manufacturers and designers is to combine their
collective thoughts and needs into identifying the
future potential for these ultra high performance
concretes. A further challenge will be to ensure
the continuing development of codes and
standards to facilitate new innovative design
concepts.
The future of Ultra-high performance materials
based on reactive powder technology remains an
exiting one. Its core advantages are strength,
durability and fluidity, combined with its ‘steel-
like’ strength. Indeed, given its flexibility and
malleable nature, UHPC really may be concrete’s
answer to steel. It seems likely that on-going
investment in UHPC will allow previously
impossible opportunities for the innovative
designer, not only in the established areas of
bridge design but also in building structures. The
imagination, design complexity and desire for
creativity are all elements that will see products
such as UHPC being considered, not on first cost,
but on their ability to provide totally unique,
highly-flexible design solutions to problems and
concepts otherwise thought impossible.
As our buildings are designed and built higher
and higher; as we seek to maximise space, utility
and design with lightweight but highly durable
and strong materials, products such as Ductal™
may offer the innovative designer the opportunity
to create dreams.
112
113
Tony Hulett is a principal
engineer with the Concrete
Society specialising in industrial
floors. He is project manager
and lead author for the third
edition of Technical Report
TR34, Concrete Industrial Ground Floors - A guide
to their Design and Construction
ABSTRACTThis paper discusses the importance of surface
regularity in industrial floors and describes the
methods by which floors are measured and
classified. The importance of the fresh concrete
characteristics are considered as well as the
compatibility of those requirements with the
long-term performance of the concrete floor.
KEYWORDS Regularity, Flatness, Levelness, Dynamic Effects,
Tolerances, Construction Methods, Consistency,
Cohesion, Bleeding, Setting, Shrinkage, Abrasion
Resistance, Abrasion, Strength, Power-trowelling.
INTRODUCTIONIn Autumn 2002, The Concrete Society will
publish the third edition of its Technical Report
TR34, Concrete Industrial Ground Floors - A
Guide to their Design and Construction. The new
edition will provide new advice on the
measurement and classification of floors used in
high bay very narrow aisles.
This paper summarizes some of the key
aspects of floor construction as they impact on
surface regularity. In particular, the role of the
concrete technologist is recognised in the design
of concrete mixes for this particularly demanding
application.
The demands on concrete for floors are
unusual in that it is the only significant
application where the surface regularity is
dependent on the endeavours of the floor laying
operatives instead of the formwork erectors.
THE IMPORTANCE OF SURFACE REGULARITYThe surface profiles of a floor need to be
controlled so that departures in elevation from a
theoretical perfect horizontal plain are limited to
an extent appropriate to the planned use of the
floor. For example, high lift mechanical handling
equipment will require a tighter control on
regularity than will a general low level factory or
warehouse use. An ‘ants’ view of a floor is
illustrated in figure 1 below.
Figure 1: Surface Profiles.
Figure 2: Flatness and levelness.
The elevational differences look dramatic for
the sake of illustration however; they are
measured in the range of 2 to 10 millimetres over
significant areas of floor.
Surface regularity also needs to be limited in
two ways. The floor needs to have an
appropriate degree of flatness to limit, for
example, the bumpiness of the operation of
mechanical handling equipment and an
appropriate degree of levelness to ensure that the
building as a whole with its static and mobile
equipment can function satisfactorily. Figure 2
illustrates the difference between flatness and
levelness.
THE SURFACE REGULARITY OF FLOORS
AND CONCRETE IMPLICATIONS
Mr. T. Hulett. BSc(Hons), MICT
The Concrete Society
114
It can be seen that flatness relates to variations
over short distances whereas levelness relates to
relatively longer distances. These distances are
not easily definable but experience has shown
that it is effective and practical to control flatness
over a distance of 300mm and levelness over a
distance of 3m as well as to a building’s general
datum.
Flatness is a function of both the elevational
difference and the rate at which those elevational
differences change when moving across a floor.
This is illustrated over a short distance in Figure 3.
The difference in elevational differences can
range from 1.5 to 5.0mm.
Figure 3: Change in elevationaldifference over a distance of 600mm.
FLOOR TYPES - FREE AND DEFINED MOVEMENTIn warehouses, trucks are used in broadly two
different areas: areas of free movement traffic
and areas for defined movement traffic. Free
movement will typically be found in factories,
retail outlets, general low level storage and food
distribution. In free movement areas, trucks
travel randomly in any direction. In defined
movement areas, vehicles use fixed paths in very
narrow aisles usually associated with high-level
storage racking. Developments often combine
areas of free movement for low-level activities
alongside areas of defined movement for high-
level storage.
The two floor types require different surface
regularity specifications so that appropriate
performance of the floor can be achieved at an
economic cost. The different specifications are
reflected in the survey techniques used and the
limits on tolerances which are prescribed.
Free movementIn free movement areas it is neither practical
nor necessary to survey all points on the floor. It
is not practical as there are an infinite number of
combinations of points on the floor. It is not
necessary as trucks are operated at a low level
and therefore there is no need to control every
point with precision so as to prevent collision at
high level.
Defined movementIn defined movement areas it is practical to
measure wheel tracks and it is important to limit
all elevational differences and rates of change as
these affect the stability of the trucks and
therefore either the likelihood of collisions with
racking or the need to slow down the operation
of the trucks.
Figure 4 shows how the variation in floor level
across the aisle between the wheel tracks of the
truck is magnified at the top of the mast in direct
proportion to its height. Variations in levels also
induce dynamic movements in the mast which
magnify the static lean by a factor of 3 to 4.
Stresses can be created in the mast and body of
the truck which cause premature failure of welds
and disrupt the performance of electronic
components. Poor flatness characteristics also
create the risk of collision between the truck and
the racking and driver fatigue.
Choosing the SpecificationThere are two points to consider. Firstly, the
higher the standard specified, the greater the
potential cost of the floor. Secondly, higher
flatness tolerances may lead to construction
methods with more formed joints. However,
construction techniques and associated tolerances
are always developing and contractors should be
consulted to find the best combination of
construction technique, particularly the jointing
plan, and surface regularity along with its
associated cost to suit the planned use.
Figure 4: Static Lean.
115
CHANGE OF FLOOR FLATNESS WITH TIMESurface regularity can change over time for
broadly three reasons summarised below.
Floors can be expected to deflect over time
under load. Designers should check that these
anticipated deflections are compatible with the
levelness required.
Unexpected ground settlement or heave could
affect the levelness and to some degree the
flatness of a floor. Such settlement could be the
result of an inadequate soils appraisal or soils
treatment programme.
Levelness and flatness can be changed at the
edges or corners of floor panels as a result of
curling. Curling is caused by the differential
shrinkage of the concrete. The top shrinks more
than the bottom causing the floor to curl
upwards. This effect takes place within about the
first 18 months after construction. Curling
cannot be totally eliminated but it can be reduced
by minimising the shrinkage potential of the
concrete and by reducing bay sizes to minimise
joint openings.
Future Developments in Floor Surveying
The users of warehousing facilities are
becoming increasingly globalised, as are the
suppliers to that industry - the logistics companies
and the suppliers of mobile handling equipment.
In the UK, there are a number of developers who
now operate across Europe and elsewhere. They
are routinely faced with alternative and
sometimes-conflicting specifications from truck
suppliers, an industry which has also become
more globalised with fewer, larger players. In
response to these changes, and as this review for
the next edition of TR34 has progressed, the
need for a common CEN standard or ISO has
become apparent.
Recent research suggests that the across axle
tilt, as measured by TR34 Property III, is the most
important factor as it most directly affects the
interaction of the mast with racking. However,
any excess front to rear tilt, which is not presently
measured, will create a nodding effect which will
contribute to the overall dynamic movement of
the masthead and associated driver fatigue. Both
the US and German systems include consideration
of the effect of the rear wheels.
MIX DESIGN FOR PLACING AND FINISHING IN POWER FINISHED FLOORS.Concrete for floors will require sufficient
workability for the method of laying being used.
For manually placed concrete in long strip
construction methods, a minimum slump of
75mm is recommended. For mechanically placed
concrete in larger areas, slumps up to 125mm
and possibly 150mm are used. Slump is measured
in accordance with BS 1881: Part 102.
The most significant aspect in the production
of concrete for flooring is the need for
consistency. The placing and finishing processes
are particularly sensitive to variations in
consistency both within loads and between loads.
Mix design should be such as to create a
homogenous and moderately cohesive concrete
which will not segregate when being compacted
and finished. Excessively cohesive concrete can
be ‘sticky’ and difficult to finish. Excessive
bleeding should be avoided but some limited
bleed water is required to assist with the
formation of a sufficient surface mortar layer
which can be levelled and closed by the power-
finishing process. Where dry shake toppings are
to be used, sufficient water is required at the
surface for hydration of the topping.
Aggregate content should be maximised using
an overall aggregate grading which provides the
best packing and the minimum effective surface
area. In practice, there may be limitations on the
aggregate gradings available, but a high content
of 10mm material should be avoided as this will
in turn require higher fine aggregate content and
consequently higher cement contents. Where dry
shake toppings are to be used, fine aggregate
contents may be reduced marginally as the
topping will provide the closed finish. This will be
beneficial in increasing workability for a given
water content.
High cement contents (above 400 kg/m3) are
likely to be excessively cohesive and may lead to
finishing problems particularly in warm weather.
Allowance should be made for fibres.
Polypropylene fibres will reduce workability by
about 10mm of slump. Steel fibres will have a
greater effect of over 25mm. The specified
workability should take account of this,
particularly where the steel fibres are to be added
at site.
Workability retention must be adequate and
consistent in order to avoid cold joints and to
116
provide for a consistent use of power-finishing
equipment. Adjacent areas of concrete at
differing stages of stiffening and hardening lead
to problems with levels and the smearing of wet
paste over hardened areas.
Admixtures are useful in creating workability
and either reducing or lengthening workability
retention times. They are beneficial in reducing
water contents and therefore cement paste
volumes and associated drying shrinkage.
Workability as measured by the slump test is
very sensitive to small changes in water content.
After batching, the designed available free water
necessary for workablity can reduce as a result of
absorption by the aggregates and by evaporation.
Traffic delays and warm weather will both
increase these effects. A practical way of dealing
with this is for the concrete producer and
contractor to make provision for the workability
to be adjusted under controlled conditions on
site.
Addition of water should be supervised by a
competent technician. Additions should be
limited to that required to increase the
workability to that originally specified. The
procedure should ensure that the maximum
specified water/cement ratio or the water/cement
ratio required for the specified strength,
whichever is the controlling value, is not
exceeded. Where water is added on site, the
concrete should be adequately remixed. Site
records of water additions should be kept.
SUMMARYThe needs of warehousing and distribution
place particular demands on the concrete floors.
The floor is a working platform and must be
constructed to tight surface regularity tolerances.
To enable specialist flooring contractors to deliver
these floors at economic cost, concrete mix
designs, quality control techniques and delivery
arrangements need to be tailored to this specific
end use. Consistent consistency is a major
priority.
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ADVANCED CONCRETE TECHNOLOGY
DIPLOMA COURSESThe ACT Diploma is the
principal entry qualificationfor 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 of Nottingham and Leeds).
Contact: Dr J Newman, Concrete Structures Section, Dept of Civil Engineering, Imperial College, London SE7 2BU
Tel: +44 (0)20 7594 6035E-mail: [email protected]
IRELAND(Dublin)
Organised under the auspices of the Irish Concrete Society.
Temporary contact: ICT Secretariat, P.O. Box 7827,
Crowthorne, Berks. RG45 6FR, UK
Tel: +44(0)1344 752096E-mail [email protected]
SOUTH AFRICA(Gauteng)
Organised by the Cement and Concrete 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:
Ready Mixed ConcreteWhich third party certification
scheme will you choose?One which has the experience considered essential by the
European Standards organisation? *
• QSRMC is the only UK certification body for ready mixed concrete which has a dedicated full time team of field assessors with a combined experience of more than 100 man-years with the scheme.
• The QSRMC Quality and Product Conformity Regulations were written by concrete specifiers, purchasers and producers to bring togetherindustry best practice and customer requirements in a scheme designedto meet the needs of all sectors of the construction industry.
Demonstrate product conformity with the most widely specified and the onlyUK Certification Body dedicated to the supply of ready mixed concrete
To find out more about the benefits of QSRMC certification contact:
The Quality Scheme for Ready Mixed Concrete, 3 High Street, Hampton. TW12 2SQTelephone: 020 8941 0273. Facsimile: 020 8979 4558. E-mail: [email protected]
or visit our website: www.qsrmc.co.uk
* “An essential element in maintaining the confidence and credibility of the concrete family systemis that the system, the relationship between members of the family and the functioning of thesystem are approved and regularly audited by a third party certification body that has expertise inconcrete technology and production.” (CEN REPORT CR 13901 - ‘The use of the concept of concretefamilies for the production and conformity control of concrete’)
One designed specifically to meet the requirements of concrete producers, purchasers and specifiers?
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117
ADVANCED CONCRETE TECHNOLOGY DIPLOMA:
SUMMARIES OF PROJECT REPORTS 2001
The project reports are an integral and important part of the ACT Diploma.
The purpose of the projects is to show that the candidates can think about a topic or problem in a
logical and disciplined way. The project normally spans some six months. Significant advances can be
made and several of the projects have evolved into research programmes in their own right.
Summaries of a selection of projects submitted during the 2000 - 2001 course are given in the
following pages.
PROJECT TITLE: AUTHOR:
ABRASION RESISTANCE OF POWER-FINISHED CONCRETE T. HulettINDUSTRIAL FLOORS - A STATE OF THE ART REVIEW
PERFORMANCE OF CONCRETE INCORPORATING SAPONITE T.P. MahloAS PARTIAL REPLACEMENT FOR SAND
AN INVESTIGATION INTO SOME PROPERTIES OF FRESH AND HARDENED J.A.T. SchmidtCONCRETE AND MORTAR CONTAINING A CEM II/B-V 32.5 (PORTLAND FLY ASH CEMENT) AND A CEM II/A-L 32.5 (PORTLAND LIMESTONE CEMENT)
OPTIMUM FINES CONTENT FOR DENSE AND IMPERMEABLE CONCRETE M. Sopeng
HOT-DIP GALVANISED REINFORCEMENT AND ITS ADVANTAGES M. Thakholi
A full list of earlier ACT projects, dating back to 1971 when the individual project was introduced as arequirement for the Advanced Concrete Technology Diploma examination, was published in the 2000 - 2001edition of the ICT yearbook.
Copies of the reports (except those that are confidential) are held in the British Cement Association Library andthese can be made available on loan. Subscribers to the BCA’s information service, Concquest, may obtain copieson loan, free of charge. Requests should be addressed to: The Centre for Concrete Information, British CementAssociation, 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.
118
SUMMARYThis ACT report reviews the factors affecting
abrasion resistance in power-finished concrete
industrial floors. It is also a contribution to the
Concrete Society review of its Technical Report
TR34, Concrete Industrial Ground Floors - A guide
to their Design and Construction.
This report consists of two main sections; a
literature review and a report on the review for
TR34. In the latter, test results and practical work
commissioned for the TR34 review are presented
and discussed. Proposals are made for the
development of testing and classification of floors
and also for further research.
The review finds that most industrial buildings
used for warehousing, distribution and
manufacturing have power-trowelled floors. A
floor can be considered durable if the surface
layer or zone of approximately one to two
millimetres thickness has not been penetrated or
removed during its design lifetime.
The abrasion resistance of the surface zone is
predominately a function of the repeated power-
trowelling process and curing and to a lesser
extent it is a function of the fine aggregate used
in the surface of the concrete. Fine aggregate in
the surface zone is either that present in the bulk
concrete used for the floor or it can be a
constituent of a dry shake topping applied to the
surface.
Aggregates for concrete in normal use are
satisfactory. Fine aggregates should have
continuous gradings and fine aggregates
including soft materials or having high contents
of very fine materials should be avoided. Coarse
aggregates have no direct effect on abrasion
resistance.
Toppings can be beneficial either as a result of
their contribution to lowering the water/cement
ratio in the surface zone and/or because of the
aggregates they contain. Aggregates in toppings
will give better performance than the fine
aggregate in the base concrete if they provide
improvements to particle packing, or because
metallic aggregates are used. The hardness of the
fine aggregate in a topping is not a good
indicator of abrasion resistance.
Increasing cement contents beyond the range
of 335 - 350 kg/m3 does not increase abrasion
resistance. It is important to avoid high
water/cement ratios, although abrasion resistance
is not sensitive to water/cement ratios in the
range 0.45 to 0.50 as excess water in the surface
zone can be removed by the process of repeated
power-trowelling or by the use of a topping.
There is a test method for assessing the
potential abrasion resistance of floors. However,
true assessment is difficult because the commonly
used resin-based curing compounds render the
test method ineffective. The long-term effects of
these compounds are not well established and
therefore tests should be taken on samples or
floor areas that have been cured in or under
polythene instead of a curing compound.
Classification for use is described in a British
Standard. This advice needs to be reviewed to
make the service classes less subjective and to
remove the existing prescriptive elements - the
concrete strength classes and the minimum
cement contents. However, general guidance on
cement contents, water/cement ratios and
aggregate selection will still be needed.
ABRASION RESISTANCE OF POWER FINISHED CONCRETE INDUSTRIAL FLOORSBy: T. Hulett
119
SUMMARYThis report covers an investigation into the use
of sand contaminated with saponite (a member
of the smectite clay group) for use in concrete at
the Mohale Dam in the Lesotho Highlands as part
of the Lesotho Highlands Water Project.
The saponite results from a fault running
through the designated Mohale Tunnel Quarry
from which basalt-based aggregates are
obtained.
The saponite material was used as a partial
replacement of the sand. The aggregate (9.5 -
19mm), fine and coarse sands were derived from
the doleritic basalt.
The concrete had a high w/c ratio of 0.6 to
allow for the water demand of the saponite,
yielding a slump of 150 ± 10 mm.
Saponite replaced the fine sand up to 35%
w/w and compressive strength (SABS 863),
oxygen permeability, tensile strength (ASTM 496),
modulus of elasticity and drying shrinkage (SABS
1085) were all determined.
The objective was to establish an optimum
value for saponite addition.
Notwithstanding saponite belonging to the
smectite clay group its addition had little effect
on compressive strength that reached a maximum
at 20% sand replacement. It is suggested
saponite may have pozzolanic properties. Indeed
all other measured properties showed no
deleterious effects within the replacement range
10 - 20%.
The results contradict the accepted trends of
clay addition to concrete and it is recommended
that a thorough study be performed to establish
the pozzolanic properties of saponite together
with long term durability assessment.
PERFORMANCE OF CONCRETE INCORPORATING SAPONITEAS PARTIAL REPLACEMENT FOR SANDBy: T.P. Mahlo
120
SUMMARYThe EN (European Norm) cement specifications
were introduced into South Africa at the
beginning of 1997, replacing the `outdated’ SABS
(South African Bureau of Standards)
specifications, which were in place for a number
of years. This brought some confusion to local
specifiers and cement users (contractors and
resellers) who were used to a certain performance
criteria and `outdated’ terminology concerning
locally manufactured cements under the SABS
specifications. In particular there was no SABS
cement specification for a limestone interground
cement or a masonry cement. Moreover, the use
of CEM II/B-V 32.5 cement as a masonry cement
would be excluded by a requirement of the
NHBRC (National Home Builders Registration
Council), that at least a CEM II/A cement be used
in mortars.
This project compares some of the fresh and
hardened state properties of concrete and mortar
made with CEM II/B-V 32.5 and CEM II/A-L 32.5
cements. Some short-term durability aspects have
also been evaluated.
The evaluation of their performance in
concrete showed that both cement types could
make good, workable, placeable, compactable
and finishable concrete in both strength classes.
Both cement types can be used to produce
concrete mixes that will give the desired strength
if concrete mix design is done correctly. Some
differences in short term durability properties
between the cements were noted. The CEM II/B-V
32.5 cement concrete had higher resistance to
water penetration, water sorptivity and air
permeability, presumably because of the tighter
pore structure in the fly ash concrete. On the
other hand the CEM II/A-L cement concrete had
the lower chloride diffusivity.
All three tested cement types yielded workable
mortar mixes which could be used for a Class II
mortar as prescribed by SABS 0164. In fact the
mortar strengths obtained would allow the mix
proportion to be ‘diluted’ to yield the required
SABS classification strength. This has two
important advantages:
• Uninformed operators do then risk not
having enough ‘glue’/paste in the mix such
that a sudden drop in compressive strength
can be expected if the mortar mix is ‘diluted’
• The mortar is not so strong that it cannot act
as a `crack-path’ between the brickwork if
foundation movements do occur.
Overall it was concluded that there is not
much to choose between the three cements, and
in the South African economic environment for
the foreseeable future it will still be the most
cost-effective cement that will be used.
AN INVESTIGATION INTO SOME PROPERTIES OF FRESH ANDHARDENED CONCRETE AND MORTAR CONTAINING A CEM II/B-V 32.5 (PORTLAND FLY ASH CEMENT) AND A CEM II/A-L 32.5 (PORTLAND LIMESTONE CEMENT)By: J.A.T. Schmidt
121
SUMMARYThis project relates to the Lesotho Highlands
Water Project and in particular the rockfill dam at
Mohale and concrete based upon crushed coarse
and fine aggregates derived from basalt.
The construction project was in two phases.
Phase 1A completed in 1966 and Phase 1B that is
due for completion in 2002.
The objective was to evolve mix designs
resulting in durable concrete. There was already
evidence to show that basalt aggregates varied
from site to site.
The coarse aggregate had a maximum size of
19 mm and was based on crushed doleritic
basalt. Overall the aggregate covered the size
ranges 10 - 19 mm, 5 - 10 mm, 2 - 5 mm and
0 - 2 mm with ultra-fines (-75 µm) obtained by
sieving the 0 - 2 mm range.
OPC and PFA conform to BS 12 and 3892,
respectively.
Two series of mixes were studied with sand
content varying from 49% - 52% on the one
hand and fixing the sand content at 44% but
progressively replacing the sand with ultra-fines
(-75 µm) over the range 0 - 22%.
Compressive strength, splitting tensile strength
and drying shrinkage were determined. In
addition, oxygen permeability using thick
cylindrical slices was also measured.
Shrinkage was determined in accordance with
SABS 1085 and specified not to exceed 0.09%.
Those mixes containing ultra-fines tended to
have associated shrinkage but replacing sand by
ultra-fines material did not give rise to excessive
shrinkage.
For the sand-varied mixes, as sand content
increased, compressive strength decreased and
progressive replacement of sand by ultra-fines
improved strength up to an optimum
replacement of 17%. However, tensile strength
was maximised at only 8% replacement.
Further work is recommended using water
reducing admixtures so that the w/c ratio can be
kept constant or alternatively the w/c ratio may
be lowered resulting in improved durability.
Air entraining admixtures may also improve
the mixes further.
OPTIMUM FINES CONTENT FOR DENSE AND IMPERMEABLE CONCRETEBy: M. Sopeng
122
SUMMARYThis project report describes a literature
investigation of the causes and prevention of
corrosion of reinforcement steel in concrete. In
particular, it describes in detail a method of
protecting steel by the hot-dip galvanising
process and it compares the resistance to
aggressive environments of galvanised
reinforcement steel and black steel. It shows the
great advantages of galvanised reinforcement,
and cites examples where it has been successfully
used.
An initial evaluation of the options for
protecting steel reinforcement examined the
advantages and drawbacks of the following:
• Cathodic protection
• Epoxy coating
• Gloss painting
• Hot-dip galvanising.
The project report then goes on to examine
effects of galvanising on the use of reinforcing
steel in concrete, including the mechanisms by
which galvanising protects the steel, how it is
applied, the effects of galvanising on the bond of
the steel to concrete, the resistance to chlorides
and carbonation and its use in prestressed
concrete. Some case histories of its use are then
reviewed; in particular its use in Bermuda. Finally
a detailed account is given of its use in the
Lesotho Highlands Water project where the
author was an inspector in the precasting yard.
The report finds that the galvanising process is
relatively easy to carry out and galvanised
reinforcement is as easy to handle and use as
black steel. Any damage is easily repaired by an
application of zinc-rich paint.
The galvanising process does not affect the
properties of the steel in a detrimental way and
in fact in many cases it enhances the properties
of the steel.
There is ample evidence for its effectiveness in
resisting corrosion and even in environments
which are so aggressive that the zinc coatings
would be destroyed, the sacrificial dissolution of
zinc usually gives galvanised steel a longer life
than ungalvanised steel.
The initial cost of galvanised steel is higher
than black steel. However, in aggressive
environments, the extension of the life of a
structure and reduced maintenance counters this
higher initial cost.
There are well-documented case studies,
including the Bermuda Island experience, where
galvanised reinforcement has been used
successfully in very aggressive marine
environments.
Overall it is concluded that galvanised
reinforcement performs far better than black
reinforcement in very aggressive environments.
Therefore, coupled with the use of good concrete
quality, which is always of prime importance in
such situations, it is considered to be a solution
to the problem of possible reinforcement
corrosion in these environments.
HOT-DIP GALVANISED REINFORCEMENT AND ITS ADVANTAGESBy: M. Thakholi
ICT RELATED INSTITUTIONS & ORGANISATIONS
ASSOCIATION OFCONSULTING ENGINEERSAlliance House12 Caxton StreetLondon SW1H 0QLTel: 020 7222 6557www.acenet.co.uk
ASSOCIATION OF INDUSTRIALFLOORING CONTRACTORS33 Oxford StreetLeamington SpaCV32 4RATel: 01926 833 633www.acifc.org.uk
ASSOCIATION OF LIGHTWEIGHTAGGREGATE MANUFACTURERSc/o: Butterley Aglite LtdWellington StRipleyDerbyshire DE5 3DZ
BRE (BUILDING RESEARCHESTABLISHMENT) LTDBucknalls LaneGarstonWatford WD25 9XXTel: 01923 664000www.bre.co.uk
BRITISH BOARD OF AGRÉMENTP.O.Box 195Bucknalls LaneGarstonWatfordHerts WD25 9BATel: 01923 665300www.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 9000www.bsi.org.uk
BRITPAVEBritish In-Situ ConcretePaving AssociationCentury HouseTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 725731www.britpave.org.uk
CEMENT ADMIXTURES ASSOCIATION38a Tilehouse Green LaneKnowleWest MidlandsB93 9EYTel: 01564 776362
CEMENTITIOUS SLAG MAKERS ASSOCIATIONCroudace HouseGoldstone RoadCaterhamSurrey CR3 6XQTel: 01883 331071www.ukcsma.co.uk
CONCRETE ADVISORY SERVICECentury HouseTelford AvenueCrowthorneBerkshire RG45 6YSTel: 01344 466007www.concrete.org.uk
CONCRETE BRIDGE DEVELOPMENT GROUPCentury HouseTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 762676www.cbdg.org.uk
CONCRETE INFORMATION LTDTelford AvenueCrowthorneBerks RG45 6YSTel: 01344 725700www.concrete-info.com
CONCRETE REPAIR ASSOCIATIONAssociation House99 West StFarnhamSurrey GU9 7ENTel: 01252 739145www.concreterepair.org.uk
THE CONCRETE SOCIETYCentury HouseTelford AvenueCrowthorneBerkshire RG45 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 House99 West StFarnhamSurrey GU9 7ENTel: 01252 739145www.corrosionprevention.org.uk
INSTITUTE OF CORROSIONCorrosion HouseVimy CourtLeighton BuzzardBeds LU7 1FG Tel: 01525 851771www.icorr.org
INSTITUTE OF MATERIALS1 Carlton House TerraceLondon SW1Y 5DBTel: 020 7451 7300www.materials.org.uk
INSTITUTION OF CIVIL ENGINEERSOne Great George StreetLondon SW1P 3AATel: 020 7222 7722www.ice.org.uk
INSTITUTION OF HIGHWAYS& TRANSPORTATION6 Endsleigh StreetLondon WC1H 0DZTel: 020 7387 2525www.iht.org
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 INDUSTRY ASSOCIATION156 Buckingham Palace RoadLondon SW1W 9TRTel: 020 7730 8194www.mortar.org.uk
QSRMCQuality Scheme for ReadyMixed Concrete3 High StreetHamptonMiddlesex TW12 2SQTel: 020 8941 0273www.qsrmc.co.uk
QUARRY PRODUCTS ASSOCIATION156 Buckingham Palace RoadLondon SW1W 9TRTel: 020 7730 8194www.qpa.org
RIBARoyal Institute of British Architects66 Portland PlaceLondon W1B 1ADTel: 020 7580 5533www.architecture.com
SOCIETY OF CHEMICAL INDUSTRY14/15 Belgrave SquareLondon SW1X 8PSTel: 020 7598 1500www.sci.mond.org
UNITED KINGDOM ACCREDITATION SERVICE21-47 High StreetFelthamMiddlesex TW13 4UNTel: 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: 01902 576 586www.ukqaa.org.uk
125
Published by:THE INSTITUTE OF
CONCRETE TECHNOLOGYP.O.Box 7827Crowthorne
Berks RG45 6FRTel/Fax: 01344 752096Email: [email protected]
Website: www.ictech.org
ICT YEARBOOK 2002-2003
EDITORIAL COMMITTEE
Professor Peter C. Hewlett (Chairman)BRITISH BOARD OF AGRÉMENT
& UNIVERSITY OF DUNDEE
Peter C. OldhamCHRISTEYNS UK LIMITED
Dr. Philip J. NixonBUILDING RESEARCH ESTABLISHMENT
Graham TaylorINSTITUTE OF CONCRETE TECHNOLOGY
Laurence E. PerkisINITIAL CONTACTS
Rights reserved. No part of this publication maybe reproduced or transmitted in any formwithout the prior written consent of the
publisher. The comments expressed in thispublication are those of the Author and not
necessarily those of the ICT.
Yearbook: 2002-2003
CONCRETE TECHNOLOGYINSTITUTE OF
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TheINSTITUTE OF CONCRETE TECHNOLOGY
P.O.BOX 7827, Crowthorne, Berks, RG45 6FRTel/Fax: (01344) 752096Email: [email protected]
Website: www.ictech.org
THE ICTThe Institute of Concrete Technologywas formed in 1972 from theAssociation of Concrete Technologists.Full membership is open to all thosewho have obtained the Diploma inAdvanced Concrete Technology. TheInstitute is internationally recognisedand the Diploma has world-wideacceptance as the leading qualificationin concrete technology. The Institutesets high educational standards andrequires its members to abide by a Codeof Professional Conduct, thus enhancingthe profession of concrete technology.The Institute is a Professional Affiliatebody of the UK Engineering Council.
AIMSThe Institute aims to promote concretetechnology as a recognised engineeringdiscipline and to consolidate theprofessional status of practisingconcrete technologists.
PROFESSIONAL ACTIVITIESIt is the Institute's policy to stimulateresearch and encourage the publicationof findings and to promotecommunication between academic andcommercial organisations. The ICTAnnual Convention includes a TechnicalSymposium on a subject of topicalinterest and these symposia are wellattended both by members and non-members. Many other technicalmeetings are held. The Institute isrepresented on a number of committeesformulating National and InternationalStandards and dealing with policymatters at the highest level. TheInstitute is also actively involved in theeducation and training of personnel inthe concrete industry and thoseentering the profession of concretetechnologist.