concrete technology institute of -...
TRANSCRIPT
Yearbook: 2003-2004
CONCRETE TECHNOLOGYINSTITUTE OF
The
The I
NSTI
TUTE
OF
CO
NC
RETE
TEC
HN
OLO
GY
- Y
earb
oo
k:
2003-2
004
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 MANUFACTURERSWellington StRipleyDerbyshire DE5 3DZTel: 01773 746111
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 CENTRECentury HouseTelford AvenueCrowthorneBerkshire RG45 6YSTel: 01344 762676www.concretecentre.com
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 MATERIALSMINERALS & MINING1 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
97
Published by:THE INSTITUTE OF
CONCRETE TECHNOLOGYP.O.Box 7827Crowthorne
Berks RG45 6FRTel/Fax: 01344 752096Email: [email protected]
Website: www.ictech.org
ICT YEARBOOK 2003-2004
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.
Professional Affiliate
3
Yearbook: 2003-2004
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 Philip Owens
MILESTONES IN THE HISTORY OF CONCRETE TECHNOLOGY 13 - 23THE DEVELOPMENT AND USAGE OF HIGH ALUMINA CEMENT:By John Bensted
ANNUAL CONVENTION SYMPOSIUM: 25 - 86PAPERS PRESENTED 2003
ADVANCED CONCRETE TECHNOLOGY DIPLOMA: 87 - 96SUMMARIES OF PROJECT REPORTS 2002 - 2003
RELATED INSTITUTIONS & ORGANISATIONS 97
4
55
FOREWORD
Dr BILL PRICEPRESIDENTINSTITUTE OF CONCRETE TECHNOLOGY
It gives me great pleasure to welcome you tothe 2003-2004 ICT Yearbook, ably andprofessionally produced by the editorial board.
The high standard of the Yearbook continues toreflect creditably on the Institute as a whole.
The past year has been a particularly active onefor the Institute and I have tried to illustrate someof the highlights in this foreword.
The annual Convention and TechnicalSymposium was, yet again, a tremendous success.It was well attended and a number of interestingpapers were presented. There also seemed to meto be a more relaxed atmosphere than usual, withnetworking and the social side of the event playinga major role in the overall success of theConvention.
Despite many production difficulties along theway, the excellent new ICT promotional CD wasalso unveiled at Convention. This is a powerfulmarketing tool for the Institute and any memberwho can make use of it to attract more membersor enhance the awareness of the Institute, isencouraged to obtain a copy from the ExecutiveOfficer. We always need new members!
During the past year the Institute finallysucceeded in establishing a route for our membersto achieve registration with the EngineeringCouncil EC(UK). It had initially been hoped that ICTwould progress towards becoming a LicensedMember (Nominated Body) of EC(UK) andregistering ICT members directly. However, theresources required both to achieve this status andto administer the registration process were toogreat to be sustained by such a small body as theICT. Consequently, whilst ICT remains as aProfessional Affiliate of EC(UK), the Institute hasentered a partnership with the Society ofEnvironmental Engineers, who are a LicensedMember of EC(UK), which enables us to achievethis objective without the same impact on theInstitute’s resources.
Registration as MICT, C.Eng (or as I.Eng orEng.Tech) is now possible via two routes. Firstly, bythe standard route of obtaining the formalqualifications required by EC(UK) combined withsuitable professional experience and secondly, via a‘Mature Candidate’ route. This has been a longstanding aim of the Institute and one whichsurveys of the membership suggested was alsosupported by our members. It is a littledisappointing therefore, that so few ICT membershave taken this opportunity to seek registration.
I would urge all of you to explore the benefits ofbecoming registered with EC(UK) both as a meansof enhancing your individual professional statusand the status of the ICT itself.
2003 also sees the launch of ‘The ConcreteCentre’ the new central market developmentorganisation for the UK concrete industry. The ICTwelcomes the establishment of this neworganisation and will work closely with it,particularly in the fields of education and training.The Institute recognises the need for allorganisations within the concrete industry to formcloser links and alliances in order to strengthen themessage that concrete is the construction materialof choice. The past proliferation of organisationsclaiming to represent the concrete industry has onlysucceeded in diluting this message and a morecoherent approach is greatly to be desired.
I would like to end by thanking all those whohave contributed to the ongoing success of the ICTover the past year, through membership of Councilor other committees or through supporting variousICT events. The Institute relies heavily on thevoluntary efforts of our members to maintain anddevelop our various activities and their efforts aregreatly appreciated.
This is my final year as President of the Instituteof Concrete Technology and I wish to thank themembership for indulging me and trust that RobGaimster will enjoy his term as President as muchas I have.
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 members exceptstudents, are obliged to spend a minimum of 25hours per annum on CPD; approximately 75% ontechnical development and 25% on personaldevelopment. The Institute’s guide on ‘ContinuingProfessional Development’ includes a record sheetfor use by members. This is included in theMembership Handbook. Annual random checksare conducted in addition to inspection at times ofapplication for upgraded membership.
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. A web-based distance learning package is scheduled for2004. Details are 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
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
J. WILSONChairman
J.C. GibbsSecretary & Treasurer
L.R. Baker
R.C. Brown
H.T. Cowan
G. Prior
K.W. Head
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
Dr. W.F. Price
J.D. Wootten
P.M. LATHAMChairman
G. TaylorSecretary
R.G. Boult
I.F. Ferguson
I.E. Forder
P.L. Mallory
P.C. Oldham
B.C. Patel
G. Prior(corresponding)
H.T.R. DU PREEZChairman
R. Page
Y. Staples
R. Tomes
EXECUTIVE OFFICER
G. TAYLOR
8
9
Q: Philip, how did you get into concrete?
A: As a schoolboy I had terrible problems
reading due to dyslexia (which I didn’t realise until
1980) but when, in 1949, I did National Service,
they suggested that I join the Intelligence Corps
because I was good at logics; however, there were
no vacancies so I went into the Military Police.
After National Service I went back to the
Borough Engineer’s office in Colchester for two
years before joining Wimpey’s Central Laboratory
in Southall in 1953. Tony Harman was deputy
head of the concrete section and Len Murdoch
the Laboratory Director; both of them were
passionate about concrete.
Q: How did your early career develop?
A: Dyslexia meant that I couldn’t read and
understand properly but I could get a clue and
had to go away and do it practically. The joy at
discovering something new on the way means
that you have to tell others about it. A classic
was when we made concrete boil at the C&CA’s
Training Centre, where I was on the lecturing staff
for seven years. I was told you couldn’t do that.
It set and we tested it for strength – it was 40
N/mm2 at 21/2 hours. This taught me about the
energy that is locked up in cement and you can
use that if you want to increase production.
I have always been of a questioning nature. If
someone says ‘you can’t do that’ I say ‘why not?’
I always have to have that hands-on experience.
One structure which delights me is the footbridge
in St James’s Park, on which I worked in 1957 –
because it defies all the rules. It’s made with
capstone – a waste material which couldn’t be
used in conventional architectural masonry but is
there in high performance concrete in that bridge.
At the Ministry of Works we did the basement for
the Fleet Telephone Exchange in 1957, with 20%
fly ash and then, 20 years later, the Thames
Barrier which was designed with 20% fly ash but
ended up with 30%.
The moment you question the status quo you
are in for a tough ride. You have to break down
the barrier of the people who have authority. If
the authority doesn’t respect you for what you
are and what you are saying, it is hard to return
that respect.
Q: How has concrete technology
changed?
A: It’s the expression, the word. Look how
simply concrete was described in CP114 and
compare it with EN206. You begin to wonder.
The principles haven’t changed over that time – or
even from when the Coliseum was built in Rome.
The only difference between then and now is that
we can measure what we do to a higher degree
and when you think about it, once you start to
measure things you want higher performance out
of it. Strength is the measurement of something
we don’t really understand because it’s done at a
standard temperature but when you use it in a
structure the temperature, due to the exothermic
reaction, can be considerably greater than 20ºC!
The expression to the technology has changed
because our understanding has changed.
Concrete is mainly sold by strength, which is a
FACE TO FACEA personal interview with Philip Owens
Philip Owens is seen by many as a rebel but his 50-year career in concrete has been guided by questioningauthority and his strong Christian principles. His careerhas been varied but he has always viewed it as a quest.He joined the Institute in 1972 after taking the ACTcourse at Fulmer Grange and became Fellow number 8some 14 years ago.
10
disappointment, and that hasn’t changed in the
last fifty years. If you want performance from in
situ concrete then you have to know how in situ
concrete performs.
If there were more enquiring minds, we might
get over some of the problems. Take ASR, for
example; In 1979 I tried to persuade the UK
industry that putting 25% fly ash into concrete
would solve the problem but the smoke screen
and shenanigans that were raised put a lot of
concrete at risk unnecessarily. I have no problem
with commercial interests but I have no time for
some of the intellectual nonsense that can go
with them.
When I went to Pozzolanic in 1974 it was
viewed as me changing sides but I was mystified. I
was only working in the interests of the
construction industry. At the time, demand for
cement couldn’t be met and I saw the use of all
that surplus ash as being the logical, and
technically beneficial, way out. Taking a radical
route, we got progress. I found myself putting
the extreme view, knowing that there would be a
compromise, and that has been a cross to bear.
Concrete technology does change
fundamentally but it will always change for the
better in practice if the people taking part have a
‘wash and brush up’ now and then and recognise
what it is telling them for the future, because
concrete is always for the future.
Q: Does the industry appreciate concrete
technologists?
A: Yes, I think so, so long as the concrete
technologist has got something to say for himself.
I’m still working because I can give people
confidence to do what I tell them will work.
Personal promotion is by people interacting with
each other and the degree of success that comes
from that interaction. Unfortunately some do not
have the background to understand the
fundamentals.
I’m not sure how the general population react
to us but, recently, whilst delayed at Gatwick
Airport, I met the Master of the Rolls, Lord
Phillips, and his wife by accident; the man who is
number two in law in the country yet, on a social
basis, I could respect him because he gave me
respect. When his wife learned that I was ‘in
concrete’, and when he and others found this
humorous, his wife’s reaction was ‘Oh, a man
with a proper job’. So, there is recognition as
long as we remain challenging.
Q: Do you have any views on the ICT?
A: I wouldn’t be a member if I didn’t respect
it. Whilst I’m working, and I’ve no intention of
retiring, I shall remain a Fellow. There is a value
there whilst ICT has active members. I haven’t
viewed the ICT as a social club but as I passed the
ACT exams I treat the Institute as a worthwhile
technical body. Whether it survives in the long
term depends on members’ interest but I still
believe we need a discipline called Concrete
Technology. Where does our technology go if we
can’t transmit to those who will be taking action
on it? We only dream up the conditions.
Q: Do you have any interest outside
work?
A: Anything goes if I have time to do it. I am
a Christian and that means, when you get to the
point, what other challenges are there? A
Christian has to get on with people, things and
conditions that are. He can’t live a life that
doesn’t rely on other people. Part of the problem
is that I have to respect everybody, and that’s
terribly difficult! I don’t envy anybody but I am
disappointed with other human beings who don’t
appreciate that, for them to live, they have to live
with people like me. And that’s hard. It can be
very lonely.
I plan to do my next sky dive in three years’
time when I’m 75 to raise money for the therapy
centre at Halton for MS, from which my wife has
suffered for the past 37 years. Sky diving is not
really extreme; you’re in the hands of a pilot. I
have also driven a racing car and I climbed up to
see the crater of Mount Vesuvius and spend time,
at least once a year, climbing peaks in the Lake
District.
Q: After fifty years in the industry, what
plans do you have for the future?
A: I don’t intend retiring. Why should I retire?
I see myself as a civil servant – I have a state
retirement pension and I’m paid to do nothing. I
am always challenging things. The latest
challenge is - how do you qualify what is cement?
11
With John Newman we are currently drafting a
paper to be presented next year at CanMet. We
have identified a solution. If you specify a w/c
ratio you have to specify what water and cement
are. We have identified the non-reactive bits in
cement, such as limestone, which is just a diluent,
and this shouldn’t be included in the w/c ratio.
Nustone will be on-going because its potential
has not yet been realised.
This year, I have been co-opted onto the main
BSI Aggregates Committee, B/502. I am there not
representing anyone, and I see this as an
accolade.
Q: Do you have any final comments?
A: Never trust authority; always question it -
without being destructive but to expose any
intellectual inconsistencies. We will only find the
truth if we have the opportunity to do so. The
truth is always there. We’re not allowed to find
anything that hasn’t been invented. I don’t want
anyone to think other than that I’m an ordinary
working class chap who has had to work relatively
hard to get anything - and that is a great
privilege. In addition, I have known some great
people. I also believe in natural justice. For
example, those on community service should
benefit the community, not the community
benefit them. Life is like a piggy bank; one can
never expect to get out more than you put in.
Philip, thank you. I’m sure that, having read
what you have to say here, people will come to
understand you better. We wish you good luck in
your future endeavours and look forward to many
more years of ICT membership.
12
13
IntroductionOriginating from early experiments in the mid-
nineteenth century and commercial production
from 1913, the story of high alumina cement is
remarkably fascinating. The product’s scientific
development and uses tie in strongly with socio-
economic changes almost decade by decade.
From the defences of war to the current fashion
for garden makeovers, high alumina cement
(HAC) plays its part.
High alumina cement has also not been free
from controversy, as the 1970s brought the shock
of building collapses involving the product. With
investigation, these three high profile cases –
widely reported in the press – established site
misuse as the cause. By the 1990s, since no
further building collapses involving HAC had
occurred in the UK, the public and industry
perception started to become more favourable.
The Concrete Society responded by setting up a
working party in 1993 to take a fresh look at high
alumina cement and concrete. Their Report of
1997 was well received and the product saw a
resurgence in use and development. Today, high
alumina cement assumes its rightful place as an
added value quality cement product in the range
of materials available to the concrete industry.
Early historyThe classic 1962 text by Robson[1] charters the
early history of high alumina cement. The origin is
detailed from early experiments in France on
heating mixtures of lime or marble with alumina,
by Ebelman (1848), and Sainte-Claire Deville
(1856). Meanwhile, in Germany Winkler studied
the reactions of calcium aluminates with water,
whilst Michaëlis (1865) and Schott (1906)
confirmed the setting and hardening of the less
basic calcium aluminates. The latter showed that
very high strengths are obtainable.
Serious problems of concrete deterioration in
sulphate-containing soils - particularly on the
capital to coast PLM (Paris, Lyon & Mediterranean)
Railway in the South of France in 1890 and in
some seawater defences - led directly to work by
Bied[2]. This resulted in his patenting in 1908
(France) and 1909 (UK) of the production of high
alumina cement from heating limestone and
bauxite to high temperatures[3].
The 1910s – from peace to warPrimarily because of demand for its resistance
to seawater corrosion as well as general sulphate-
resisting properties, commercial production of
HAC using a hot-blast cupola furnace (an early
type of blastfurnace) began in 1913, at the Le Teil
works in Ardèche (France) of J. and A. Pavin de
Lafarge.
With its relatively long setting times and rapid-
hardening properties at early ages (rather than its
sulphate-resisting properties), HAC came to
prominence with extensive use during World War
I (1914-1918) for the building of gun
emplacements and shelters[1]. More general
marketing of HAC in France by Lafarge, after
extensive trials, began in 1918 under the name
Ciment Fondu.
THE DEVELOPMENT AND USAGE OF HIGH ALUMINA CEMENT. By John Bensted
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.
In this, the fourth ‘Milestone Paper’ – the spotlight falls on the developmentand usage of high alumina cement, with the emphasis on the U.K. scene.
MILESTONES IN THE HISTORY OF CONCRETE TECHNOLOGY
14
The 1920s and beginning of thenext decade – part one of theinterwar years
In 1923 Lafarge financed a company in the UK,
called the Lafarge Aluminous Cement Company,
with a license to sell Ciment Fondu in the UK and,
importantly, the then British Colonies, and also
the later right to manufacture and to the know-
how, if satisfied. The right to manufacture was
exercised soon after, due to the demand for
Fondu concrete for foundations in sulphated
ground and also for use in refractory applications,
which had developed during the 1920s[4].
Consequently, the Lafarge HAC manufacturing
plant opened at West Thurrock, Essex in 1926,
using reverberatory furnaces to produce the
clinker which was ground to the cement. In the
same year, an HAC production plant for Istra
Cement was established at Pula on the Istrian
Peninsula, in what was then Italy. Lafarge were
the licencees of the plant, which had
reverberatory furnaces similar to those at West
Thurrock. HAC produced in this factory was not
marketed in the UK at this time.
In the meantime, competition had developed
in the UK. The Blue Circle Group (trading then as
the British Portland Cement Manufacturers Ltd.
[BPCM]) started producing HAC at their
Magheramorne works in Northern Ireland in 1925
under the name ‘Lightning Brand’ because of its
rapid early hardening.
The overall market for HAC developed further
within the UK during the late 1920s and early
1930s for rapid-hardening and chemical resistance
applications, such as floors, foundations and
pilings, and for refractory usage. A major contract
at the time was for the construction of Pier B at
the Ocean Terminals in Halifax, Nova Scotia,
Canada, during 1929-1931, using Ciment
Fondu[4], which is still in use today (see Figure 1).
During the 1920s HAC manufacture began to
spread to other countries, including the United
States, Spain, Germany, Hungary, Czechoslovakia,
the USSR and Japan. Brazil, China, India, Croatia,
Poland and Romania have also been
manufacturing HAC.
The 1930s – part two of theinterwar years
Since it was not really economically viable to
have two competing production plants for an
individual speciality cement such as HAC within
the then UK market, agreement was reached
between Lafarge and BPCM on resolving this
problem in 1932. All HAC production would be
concentrated at West Thurrock, with BPCM
closing down their HAC manufacturing facility at
Magheramorne. Lafarge agreed to supply BPCM
(the ‘junior’ partner in terms of overall sales at the
time) with as much HAC under the brand name
Lightning as they needed. Lafarge’s direct sales of
the ordinary dark grey/black product would
continue to be marketed as Ciment Fondu[4].
Figure 1: Pier B, Ocean Terminals, Halifax, Nova Scotia, Canada – built of HACexported from West Thurrock.
15
The 1930s were a good period for HAC
employment in construction activity, because of
the development of the motor industry,
particularly in relation to rising refractory use
because of the increased demand for steel. After
World War I, the steel industry had suffered
decline and it was primarily the introduction of
the motor car that led to more steel works – with
larger chimneys – and larger blastfurnaces being
built. The British Standard for HAC (BS 915) was
being developed during this period and was
actually introduced in July 1940.
The 1940s – storms over Europe During World War II HAC production continued
with difficulty, particularly in relation to adequate
bauxite supplies[4]. Emergency measures led to the
use of waste material discarded by aluminium
producers when bauxite became unobtainable for
HAC production. Such material included
aluminium dross and red mud from alumina
production by the Bayer process[6]. However, the
resulting quality of the by-product alumina was
not good.
Due to the low emergency production of HAC,
the material was only allowed to be used where
Portland cement was unsuitable, as in rapid repair
work, so that advantage could be gained from its
ultrarapid-hardening properties at early ages[4].
Consequently, the entire HAC output was used
by the then Ministry of Supply - established by
Prime Minister Winston Churchill - for important
repair jobs. Such work included emergency ship
repairs, where all ships were required to carry a
few bags of HAC for plugging any leaks and
torpedo holes from conflict. Also, bombed
aerodrome runways needed to be repaired with
HAC to render them usable again as soon as
possible.
In maintaining a number of essential industries
during wartime, refractory usage and repairs to
furnaces and chimneys with HAC were very
important.
The 1940s - after World War IIAfter World War II, production and usage of
this speciality cement became consolidated in its
niche market areas where it imparts benefits over
the use of Portland cement. These areas include
chemically aggressive environments, such as pure
waters, seawater, sulphated environments,
chlorides, diluted organic or mineral acids, and
solutions of organic products like beers, wines,
sugars, oils and hydrocarbons with a pH of 4-11.
However, HAC is not resistant to alkalis at high
pH values above 11, so should not be used in
alkaline environments unless they can be fully
neutralised beforehand.
During the late 1940s efforts began in earnest
to broaden the use of high alumina cement by
developing low-iron HAC to extend refractory
applications at higher temperatures than had
been hitherto possible. It was realised that, since
pure CA fused at 1608°C by itself and ordinary
HAC did so at 1100°C or just above, the iron-
containing components needed to be reduced, so
that higher temperature refractories could be
produced.
The 1950s – a time ofreconstruction
Post-war reconstruction established a demand
for higher temperature refractories in
reconstructing the industrial scene including the
steel industry where there was a demand for
better quality products that necessitated higher
production temperatures.
The 1950s, therefore, saw the
commercialisation of white HAC when the first
white HAC (containing ~70% w/w Al2O3 ) was
produced in France. It was named Secar 250
because the first production run took place in
February 1950. It was later in 1957 that
manufacture started at West Thurrock, using
white bauxite and high grade limestone, in a
small gas-fired rotary kiln. Subsequently this
product was renamed Secar 71 because it
contained around 70% w/w Al2O3.
Interestingly, this white HAC is manufactured
to comply with French Standards NF P15-315
(Hydraulic binders - melted aluminous cement)
and NF P15-316 (Hydraulic binders – use of
melted aluminous cement in concrete structures),
because there have been no British Standards nor
any apparent desire to create either British or
European Standards for this type of special
cement.
It is astonishing to note that a pure ‘cement’ of
this type had been produced experimentally as
long ago as 1856 by Sainte-Claire Deville, who
heated together equal parts of powdered alumina
and marble. Combination to calcium aluminate
took place at temperatures far below fusion
point, and that crucibles moulded from this
product and corundum aggregate could
withstand the highest temperatures which he
could apply[1]. It took 94 years – almost a
complete century - from Sainte-Claire Deville’s
initial experiments to commercialisation!
The 1960s – increasing productpopularity
This period in the development of HAC was
marked by considerable interest in its durability, and
in particular with the scientific and engineering
properties associated with hydration and
conversion, together with growing interest in
utilising admixtures (see Table 1). Also, HAC had
become increasingly popular for being a superior
efflorescence inhibitor on exposed surfaces and thus
maintaining a more aesthetically pleasing
appearance[8].
During the 1960s there was a growing interest in
using HAC in many structural applications, including
the production of prestressed concrete at the time[4].
The capacity of HAC for producing high strength
concrete in 24 hours allowed precast concrete
manufacturers to speed up production from their
casting plants[4].
However, Neville had warned in the early 1960s,
that there could be serious long term consequences
for the durability of structures made with HAC if
conversion arose at high water/cement ratios. In the
next decade his words turned out to be prophetic.
MANUFACTUREHAC was and is most commonly manufactured by fusion of a mixture of limestone and bauxite at
1500-1600˚C in reverberatory furnaces. (In some countries sintering in a kiln is employed). The liquidmelt is poured out at the base into pans and solidifies as ingots. This clinker is allowed to cool slowly and is ground to a surface area of around 350 m2/kg (minimum 225 m2/kg), which is the finishedcement. Gypsum addition is not necessary for Calcium Alluminate Cement (CAC) since it does notcontain phases leading to quick setting like C3A in OPC. HAC-gypsum mixes are inclined to set rapidly[5].
Use of admixtures in HAC concrete has paralleled their employment in Portland cement concrete.Some were used pre-1960, but subsequently have been more extensively utlised for improvingconcrete production and quality. Admixtures employed for HAC are set out in this Table.
• Accelerators – include lithium carbonate (Li2CO3), lithium chloride (LiCl), sodium hydroxide(NaOH) and potassium hydroxide (KOH). Lithium salts are very powerful accelerators, especiallythe carbonate. Portland cement, lime and calcium sulphate hemihydrate (CaSO40.5H2O) alsoaccelerate HAC setting.
• Retarders – such as hydroxylic organic compounds that retard OPC setting normally alsoretard HAC setting, e.g. lignosulphonates, sugars, citric acid, gluconic acid and tartaric acid.Many common inorganic salts that generally accelerate OPC setting tend to retard HACsetting, e.g. calcium chloride (CaCl2), sodium chloride (NaCl) and sodium silicate (Na2SiO3).Sugar, sodium borate and glycerine also retard HAC setting.
• Superplasticisers – like the conventional type such as SMFC and SNFC tend to be lesseffective with HAC, for which they generally behave as mere plasticisers, than with OPC.However, with the new generation superplasticisers like the polycarboxylate and polyacrylatetypes, results have so far looked much more promising for HAC in terms of showing actualsuperplasticising behaviour. More work still needs to be done in this area to confirm thegenerality of interesting findings made to-date.
• Waterproofing and hydrophobic additives – do not appear to have been reported for HACfor a long time[5]. Waterproofers have not been recommended for addition to HACs, since theymight seriously affect the strength developed[1]. For hydrophobic agents like lauric, stearic andoleic acids in amounts 0.10-0.25% w/w the water repellant properties rise considerably, butthe setting and compressive strength values up to ca. 7 days are retarded[1,8].
• Anti-settlement agents – like carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC)and carboxymethylhydroxyethylcellulose (CMHEC) also show retardation and viscosification, likePortland cements do in similar circumstances.
• Latexes – such as styrene-butadiene copolymers are utilised to improve bonding to surfaces,as with surface coatings and screeds.
• Air entrainers – like vinsol resins are employed to improve mix plasticity and lower anypropensity to bleed.
• Defoamers – like polypropylene glycols, lower sulphonate oils and lauryl alcohol arecommonly used with organic retarders in small quantities (~0.01%) to avoid foaming withincement slurries that can give rise to bleeding.
Table 1: Admixtures commonly used with HAC
17
HAC HYDRATION AND CONVERSIONThe main phases of ordinary HAC are calcium monoaluminate (CA) (commonly 50-70%) and
calcium aluminoferrite (C4AF) (usually 15-30%). CA hydrates quickly and ferrite at a slower rate.
Minor phases of importance are mayenite (C12A7), which hydrates rapidly, and the silicate phasesmelilite (C2MS2-C2AS solid solution) and larnite (β-C2S), that hydrate slowly and give some neededlater strength. They are each generally present in amounts ca. 2-5%.
White HACs contain CA as the main constituent, with calcium dialuminate (grossite) (CA2) andα-alumina (α-A) usually being significant, and mayenite (C12A7) as a minor constituent, but withnegligible contents of dark phases like ferrite (C4AF), alkalis and sulphates. CA is the main reactantwith CA2 reacting much slower.
HACs generally exhibit set times comparable or slower than ordinary Portland cement, but hardenvery rapidly after setting. As an example, for a concrete with water/cement ratio of 0.40,compressive strength reaches 25 MPa 2-3 hours after setting.
Early strength is given by metastable hexagonal hydrates CAH10 and C2AH8. High transientstrengths of around 70 MPa or more may be obtained with these hydrates. However, this hightransient strength should not be considered for design purposes since it will eventually decrease toreach a lower but stable strength. This strength evolution is due to the conversion phenomenon inwhich metastable hydrates convert to the stable cubic hydrogarnet phase (C3AH6). Conversiondecreases the volume of hydrates and thus raises the porosity and permeability that lowers thestrength.
As the temperature increases, conversion is accelerated. As an example, if temperature ismaintained at 50°C, conversion will occur in 24 hours. For mass concrete, if self-heating is highenough, conversion can occur during hardening and there will be no strength loss later on. Thehydration and conversion process (Figure 2) and the compressive strength development (Figure 3) areillustrated diagrammatically.
Besides CA hydration, some supplementary strength is commonly apparent at greater ages(around 28 days and later) due to formation of strätlingite (C2ASH8) (from melilite) and calciumsilicate hydrate (C-S-H) (from larnite).
Strength after conversion can be easily predicted by laboratory test where conversion isaccelerated by curing concrete under hot water, for example during 5 days at 38°C.
In refractory usage with aggregates like crushed firebrick, the hydrates start to dehydrate as thetemperature rises, and the strength reduces to a minimal value at ca. 900-1100°C. Dehydration hasbeen completed and as the temperature rises further a ceramic bond appears, which increases thestrength once more.
Greater details of the technology of HAC hydration and conversion are given elsewhere[5,7].
Calcium hydroxide is not formed during HAC hydration, which is advantageous in enabling HACto resist formation of unsightly efflorescence in mortar and concrete[8].
Figure 2: Chemical reactions involved in HAC conversion.
18
The 1970s – up to and includingbuilding collapses
In 1972 a revised British Standard with metric
units (BS 915 Part 2) was issued for HAC, to
supercede the 1947 edition. But the 1970s were
to mark the end of an era in which HAC had
increasingly played a more prominent role in new
structural concrete.
Three well publicised collapses of structures
containing HAC concrete has occurred in the UK
in the period 1973-1974[9]. Each one arose in
buildings which used prestressed beams made
from Ciment Fondu. It was widely reported that
workmanship had been inadequate in all three
instances, with design in two of them being
particularly poor. Neville’s 1975 book discussed
the civil and structural engineering aspects of
HAC concrete including the collapses[9]. He
emphasised the dangers of overdosing HAC with
water during construction.
There was naturally considerable concern at
the time and this led to around 50,000 buildings
containing structural HAC concrete being
appraised. Of these buildings, only 38 required
remedial action and only one of these had been
due to the cement. The Department of the
Environment took the step of not recommending
HAC as a construction material (see below). As a
result, the previous large demand for HAC in the
manufacture of precast and prestressed concrete
ceased immediately[4].
These UK collapses led to three noteworthy
official reports10-12] at the time together with a
general rethink in the use of HAC. The main
conclusions were:
• HAC to be used at a water/cement ratio notexceeding 0.4
• A minimum HAC content in the concrete of400 kg/m3 to ensure suitable workability
• To base the compressive strengthrequirements upon the predicted convertedstrengths rather than on the high initialtransient strengths[13]
• Doubt was also expressed about the use ofHAC in prestressed beams[14], which led tothe demise of this use, as alreadymentioned.
The 1970s – post buildingcollapses
As a precautionary measure HAC was banned
from use in structures, because of the inadequacy
of the guidance given in the1972 Code of
Practice (withdrawn 1975) for the manufacture of
durable aluminous cement concrete[13,15]. The
Building Regulations in force at the time and
beyond were modified accordingly.
At the same time extensive work was carried
out on HAC, particularly on the conversion
process[13,17,18] to ascertain where it could be
utilised safely. The rate of conversion was found
to be a more significant factor than the extent of
conversion in contributing to greater strength loss
with consequent increased permeability and
porosity in the hardened cement. Conversion
particularly takes place in warm and damp
environments.
It was felt that where structures are designed
to accommodate strength loss by conversion over
a long time period then HAC concrete could be
used safely.
Figure 3: Strength development of HAC concrete.
19
Following the collapses and loss of the market
for building structures, other opportunities were
sought and opened up. Applications of HAC in
the mining industry took off because rapid setting
and hardening, but not very high strength, are
required. In particular efficient uses came to
include pack-binding to support tunnel roofing
and abrasion resistant flooring.
To satisfy this demand, particularly in the late
1970s, quantities of HAC from Pula started to be
imported by suppliers to the UK mining industry.
HAC production at Pula had previously stopped in
World War II after which most of the Istrian
Peninsula including Pula had been ceded to
Yugoslavia. Production resumed in 1958 following
refurbishment of the state controlled plant.
The 1980s – an added valuespeciality cement
This extensive work on HAC continued well
into the 1980s. Although there had been no
further collapses since the early 1970s, extensive
nervousness remained about possible use of HAC
in structures. For instance, in the 1985 Building
Regulations the following clause was still
included[16]:
High Alumina Cement (HAC):
1.8 HAC or any material which contains this
cement will meet the Requirements of the
Regulations only where it is used as a heat
resisting material. It should not be used in
structural works, including foundations.
More investigations were undertaken to
establish a final converted strength, over a longer
period of time by being able to accommodate
strength loss through conversion.
Converted HAC concrete carried on reducing in
strength even when highly converted and to
attain lower minimum strength than comparable
concrete under dry conditions[19].
It was becoming more commonly realised by
now that HAC was not a competitive product to
Portland cement as such, but an added value
speciality cement that had its own niche
applications (see later).
The Ciment Fondu clinker production plant at
West Thurrock containing the reverbatory
furnaces was closed in June 1985. The Ciment
Fondu clinker has from this time been produced
at the Lafarge plant at Dunkerque in Northern
France and shipped to West Thurrock, for
grinding to give the Ciment Fondu product.
The 1990s – a fresh look at HAC In the 1990s there had been neither further
collapses involving HAC containing structures in
the UK since the 1970s, nor any noteworthy
problems reported for HAC concrete in use[20-23].
Confidence in the use of HAC had been
increasing in consequence. Following renewed
interest, The Concrete Society set up a working
party to take a fresh look at HAC and reassess its
position in construction. Their Technical Report
was published in 1997[24].
The Report did not recommend the use of HAC
in either prestressed concrete (a precautionary
measure, because of the risk, however small, of
overdosing the concrete with water) or in
concrete pipes for the conveyance of drinking
water (where the leach rate of aluminium from
HAC concrete under certain conditions can be
one hundredfold that of ordinary Portland cement
concrete). The main recommendations were:
• Specifiers, users and clients should beencouraged to consider applications whereHACs would have technical and commercialbenefits, either in conventional concreteform or as specialist proprietary products
• A change of emphasis should be consideredfor the Approved Documents to the BuildingRegulations to reflect more fully selection onthe basis of the demonstration of suitabilitycontained in the regulation itself
• To underpin 1 and 2 above, furthercoherent, detailed and independentguidance should be developed as a safebasis for determining in situ strength of HACconcrete for particular structures
• Further to 3, research should be undertakenand guidance developed, which is devotedto understanding more fully the nature andbehaviour of HAC concrete in aggressiveservice conditions. In particular, the role ofthe various cement hydrates andmicrostructure in influencing performanceshould be examined further. The studiesshould include examples of both good andbad performance.
The Concrete Society Report was well received
overall within the construction industry and the
recommendations have been or are being largely
implemented. For example, the Recommendation
2 was enacted in by a Main Change in the 1999
Edition of the Building Regulations[25]:
Materials susceptible to changes in their
properties:
1.7 ………calcium aluminates (HAC)………can
be used in works where these changes do not
20
adversely affect their performance. They will meet
the requirements of the Regulations provided that
their final residual properties, including their
structural properties, can be estimated at the time
of their incorporation in the work. It should also
be shown that these residual properties will be
adequate for the building to perform the function
for which it is intended for the expected life of
the building.
Recommendation 4 is being carried out, viz.
the numerous technical papers in a 2001 HAC
symposium on the cement hydrates and their
microstructure, and good performance as with fire
resistance, fibre reinforcement and applications in
sewers for instance[26]. Also, ‘bad’ performance
has been studied at excessive water/cement ratios
with ingressing sulphates, which demonstrates
that delayed ettringite formation[27] and (at low
temperatures in the presence of carbonate,
silicate and sufficient calcium ions) thaumasite
formation[28] can take place if the conditions of
usage are effectively abused. After all, HAC has
very good sulphate resisting properties when
employed correctly.
In 1991, Castle Cement took over the
importation of HAC from Istra Cement of Pula,
and has marketed it under the brand name Castle
High Alumina Cement. Subsequently, both Castle
Cement and Istra Cement became part of the
Heidelberg Cement Group. In the meantime
Yugoslavia had broken up and Pula was now part
of Croatia. So this one HAC manufacturing facility
located in the same place for well over 70 years
has, in its time, been in three different countries.
Figure 4 illustrates the HAC manufacturing plant
of Heidelberger Aluminates at Pula.
This importation led to competition for markets
with Ciment Fondu and Lightning Brand in the
UK.
In summary, the overall position of HAC for
many applications (see Table 2) grew or remained
strong during the decade. The only notable area
affected by a downswing was the mining industry.
This was a consequence of large scale closures -
in particular coal mines.
The beginning of a new CenturyIn 2001 Blue Circle was taken over by Lafarge.
However, Lightning Brand HAC is still available to
customers from the former Blue Circle
organisation which is now called Lafarge Cement
UK Ciment Fondu (the same product) is of course
available as before from Lafarge Aluminates. The
white HAC Secar 71 continues to be
manufactured by Lafarge Aluminates at West
Thurrock for refractory and other specialist uses.
Castle High Alumina Cement also serves the UK
HAC market as an alternative source to Ciment
Fondu. All these HAC products are manufactured
to current standards and are subjected to rigorous
up-to-date quality assurance and quality control
procedures.
Current applications of HAC are very diverse[5,29]
and are summarised in Table 2 below.
However, it is also important to be aware of
those areas where HAC is not recommended for
use[5]. The primary ones are given in Table 3.
Figure 4: Heidelberger Aluminates HAC factory at Pula, Croatia.
21
• Corrosion Resistance - Reinforcement is protected by alkaline pH (11) of interstitial solution, plusvery low solubility of aluminium hydroxide in pH range 4-11, provided total water/cement ratiodoes not exceed 0.40
• Chemical Resistance - High resistance to chemical attack (including sulphates) largely due to lack ofcalcium hydroxide liberation. Greater resistance than Portland cement concrete against aggressiveagents like pure waters, water- and ground-containing sulphates, seawater, diluted organic ormineral acids, plus solutions of organic products like sugars, oils, beers, wines and hydrocarbons
• Acid Resistance - Better than Portland cements in acidic environments, including sewer pipeswhere bacterial corrosion is present
• Seawater Resistance - Good resistance to seawater is shown
• Chloride Resistance - Often better than that given by Portland cements
• Resistance to Temperature, Thermal Shocks and Abrasion - Good with appropriateaggregates. Better than Portland cements with fluctuating temperatures and fire resistance
• Cold Weather Concreting - Early rapid heat evolution enables concreting to take place attemperatures as low as –10˚C, provided warm water is used for gauging, frozen aggregates are not employed, and the concrete is protected from freezing until it begins to harden and thetemperature starts to rise
• Freeze-Thaw Cycles - Good resistance like Portland cement concretes where porosity is low(below ca.13%)
• Hot Weather Concreting - For success avoid risks by not exposing concrete constituents to thesun, use chilled gauging water, and carefully cure with water as cold as possible during hardening
• Oilwell and Geothermal Well Cementing - Good at low, high and fluctuating temperatureregimes, in deepwater well cementing. and also in special phosphate-containing cements forresisting CO2 corrosion in critical geothermal well applications
• Mining and Tunnelling - For providing support where rapid setting and hardening, but not veryhigh strength, are required
• Rapid Repair Mixes - Usually in proprietorial formulations which may contain a variety ofcomponents, including lime, and/or Portland cement, and/or gypsum and/or various admixtures
• Grouts, Tile Adhesives and Flooring Compounds - As well as ordinary HAC usage, white HACs are increasingly being used here where aesthetic considerations are important
• Refractory Applications - Higher temperatures require white HACs with greater aluminacontents: Their advantages are resistance to temperature fluctuations, as lack of calcium hydroxideis beneficial for overcoming spalling, and good sulphate resistance militates against attack by gases like SO2 produced
• In Garden Furniture - Slow setting and rapid hardening properties are beneficial for quickturnaround of moulds during manufacture
• Efflorescence Inhibition – Very effective on external surfaces of HAC concrete and mortar, dueto absence of residual calcium hydroxide in the hardened cement[8].
• In Prestressed Concrete - A precautionary measure, as overdosing with water can be harmful.
• In Lining Pipes for the Conveyance of Drinking Water - A precautionary measure, since insome situations leaching of aluminium can be one hundredfold that of Portland cements.
• In Alkaline Environments - Due to likelihood of destructive hydrolysis.
• Use with Alkali-Releasable Aggregates - Again, due to likelihood of destructive hydrolysis.
• In Encapsulation of Radioactive Waste - Because of uncertainties about very long term structural integrity where safety is required for hundreds or thousands of years, as a result ofconversion causing increases in porosity and permeability.
• In Encapsulation of Toxic Waste - Insufficient experimental data are as yet available for making clearrecommendations. Various laboratory studies have shown promising results in fixing heavy metals butthe full long term ramifications of the effects of conversion remain to be reliably ascertained.
• At Total Water/Cement Ratios above 0.40 – Another precautionary measure.
Table 3: Where HAC is not recommended for use
Table 2: Applications of HAC
22
Prospects for HAC in the 21st Century
As a result of the greater understanding of the
properties of HAC, resulting from the detailed
investigative work and surveys of recent years, it is
clear that HAC concrete and mortar have a very
useful future ahead during this century:
• It is increasingly becoming realised that HACis not a competitive product to Portlandcement per se, but an added-value specialityproduct that is advantageously employedover Portland cement in a wide range ofniche areas of construction
• HAC is an excellent cement when properlyused, but must not be abused inconstruction
• New generation superplasticisers, like thepolycarboxylate and polyacrylate types, cansubstantially benefit HAC concreting bypermitting better workability of the mixes,where the older superplasticiser types havegenerally tended only to demonstrateplasticising properties with HAC
• HAC is no longer excluded from structuralwork in the Codes of Practice, but care mustbe taken if used in any structuralapplication. If it doubt about any particularaspect of HAC concreting, seek professionaladvice before use
• New HAC standardisation is around. Anupdated version of BS 915 has beenissued[30], which has brought the official testprocedures more into line with those ofPortland and extended cements given inEN197-1:2000. Also, a draft Europeanstandard prEN 14647 under the namecalcium aluminate cement has been issuedfor comment at this stage[31]; the fullstandard, which will replace BS 915, isexpected around 2005
• Encapsulation of Toxic Waste: Numerousexperiments are being carried out to assesswhether HAC can safely fix heavy toxicelements. As yet, it is too early to givedefinitive conclusions in this particular areaof study.
Since high alumina cement first entered the
market place over ninety years ago there have
been decades of ups and downs. Product
development and usage in the UK have
unquestionably shown a fascinating interlink with
the broad sweep of socio-economic and historical
evolution over a lengthy as well as eventful time
period. HAC concrete enters the 21st Century on
an optimistic note, because of this accumulated
knowledge base together with the realism and
quality assurance prevailing today.
AcknowledgementsThe author wishes to thank:
• Lafarge Aluminates for Figures 1,2 and 3,and Tony Newton and Ron Montgomery(Lafarge Aluminates, West Thurrock) forhelpful discussion
• Heidelberger Aluminates for Figure 4, andTom McGhee (Castle Cement, UK) forhelpful discussion.
References
1. T.D. Robson: High Alumina Cement andConcrete. Contractors Record Ltd, London(1962).
2. J. Bensted: Cements: Past Present andFuture. Greenwich University Press, Dartford(1997).
3. J. Bied: British Patent 8193 (1909).
4. L. Grice and M. Grice: Three Score Yearsand Ten. A Personal View of LafargeAluminous Cement Co. Ltd 1923-1993. L. &M. Grice, West Thurrock (1993).
5. J. Bensted: Calcium aluminate cements, inStructure and Performance of Cements, 2ndEdition. (Editors: J. Bensted and P. Barnes),pp.114-139. Spon Press, London (2002).
6. A.V. Hussey: Aluminous cement as a bondfor refractory concrete. Chemistry & Industry(London) No. 3, 53-61 (1937).
7. J. Bensted: High alumina cement – Presentstate of knowledge. Zement-Kalk-Gips 46,No. 9, 560-566 (1993).
8. J. Bensted: The chemistry ofefflorescence./Chemia wykwitów. Cement-Wapno-Beton No. 4, 133-142 (2001).
9. A.M. Neville: High Alumina CementConcrete. The Construction Press, Lancaster(1975).
10. S.C.C. Bate: Report on the failure of roofbeams at Sir John Cass’s Foundation andRed Coat Church of England SecondarySchool, Stepney. BRE Current Paper No. 58.Building Research Establishment, Watford(1974).
11. Building Research Establishment: Highalumina cement concrete in buildings. BRECurrent Paper No. 34 (1975).
12. Building Regulations Advisory Committee:High alumina cement concrete. Report bySub-Committee P40. Structural Engineer 54,No. 9, 352-361 (1975).
23
13. C.M. George: Aluminous cements: A reviewof recent literature (1974-1979). 7thInternational Congress on the Chemistry ofCement, Paris, 1980. Vol. I: PrincipalReports, pp. V-1/1-23. Editions Septima,Paris (1980).
14. C.M. George: The structural use of highalumina cement concrete. Lafarge FonduInternational, Neuilly-sur-Seine (1975).
15. British Standards Institution: The structuraluse of concrete. Code of Practice CP 110.BSI, London (1972).
16. Department of the Environment and theWelsh Office: The Building Regulations1985. Materials and Workmanship.Approved Document to support Resolution7. Her Majesty’s Stationery Office, Norwich(1985).
17. H.G. Midgley and A. Midgley: Theconversion of high alumina cement.Magazine of Concrete Research 27, No. 91,59-77 (1975).
18. J. Bensted: An investigation of theconversion of high alumina cement byinfrared spectroscopy. World Cement 13,117-119 (1982).
19. R.J. Collins and W. Gutt: Research on long-term properties of HAC concrete. Magazineof Concrete Research 40, No. 145, 195-208(1988).
20. R.J. Mangabhai (Ed.): Calcium AluminateCements. Proceedings of the InternationalSymposium held at Queen Mary andWestfield College, University of London, 9-11 July 1990. E. & F.N. Spon, London(1990).
21. J. Bensted: Calcium aluminate cements:Highlights from a recent symposium. WorldCement 21, 452-453 (1990).
22. C.M. George and R.J. Montgomery:Hormigon de cemento aluminoso:durabilidad y conversión. Un nuevo puntode vista sobre un terma antiguo./Calciumaluminate cement concrete: durability andconversion. A fresh look at an old subject.Materiales de Construcción 42, No. 228, 33-50 (1992).
23. Anon.: Neville speaks up for HAC. New CivilEngineer, p. 5, 15 October (1992).
24. R. Cather, J. Bensted, A. Croft, C.M.George, P.C. Hewlett, A.J. Majumdar, P.J.Nixon, G.J. Osborne and M.J. Walker:Concrete Society Technical Report No. 46:Calcium aluminate cements in construction– a re-assessment. The Concrete Society,Slough (1997).
25. Department of Environment, Transport andthe Regions: The Building Regulations 1991,Materials and Workmanship, ApprovedDocument to support Regulation 7, 1999Edition. The Stationery Office, Norwich(1999).
26. R.J. Mangabhai and F.P. Glasser (Eds.):Calcium Aluminate Cements 2001. IOMCommunications Ltd, London (2001).
27. J. Bensted and J. Munn: Formazioneritardata dell’ettringite nell’idratazione delcemento calcio alluminoso./Delayedettringite formation in calcium aluminatecement hydration. L’Industria Italiana delCemento No. 715, 806-812 (1996).
28. J. Bensted and J. Munn (unpublished work).
29. K.L. Scrivener and A. Capmas: Calciumaluminate cements, in ‘Lea’s Chemistry ofCement and Concrete’, 4th Edition, (Ed. P.C.Hewlett), pp. 709-778. Arnold Publishers,London (1988).
30. British Standards Institution: Specificationfor high alumina cement – Part 2: Metricunits, BS 915-2: 1972 (2003 version). BSI,London (2003).
31. Comité Européen de Normalisation: DraftprEN 14647:2003 E, Calcium aluminatecement – Composition, specifications andconformity criteria. CEN, Brussels, March(2003).
24
25
ANNUAL CONVENTION SYMPOSIUM: PAPERS PRESENTED 2003
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 2003 Symposium was:
CONCRETE AND THE INFRASTRUCTURE Chairman: Mr. D. Storrar BSc, CEng, MICE
Edited versions of the papers are given in the following pages. Some papers vary inwritten style notwithstanding limited editing.
KEYNOTE ADDRESS Mr. Paddy TippingMP for Sherwood
CONCRETE FOR PAVEMENTS Mr. Geoffrey GriffithsBSc, MScOve Arup & Partners
OPPORTUNITIES FOR FIBRES Mr. Les HodgkinsonIN CONCRETE Grace Construction Products
THE BRIDGES OF IRELAND - Mr. Nigel O’NeillCURRENT PRACTICE DipEng, BSc(Eng), MSc, CEng, MIEI
Roughan and O’Donovan
CONSTRUCTION OF SUBMARINE Mr. Murray ChapmanSUPPORT FACILITIES – BSc(Hons), FSA, CEng, FICE, MCIWEM, MCIArbDEVONPORT ROYAL DOCKYARD Kellogg, Brown & Root
CONCRETE SUPPLY SOLUTIONS TO Mr. Andrew BourneTHE CHANNEL TUNNEL RAIL LINK BSc(Hons), MSc, AMICT
Brett Concrete Ltd
MODERN SPRAYED CONCRETE Mr. Ross DimmockFOR URBAN TUNNELS BSc(Hons)
Master Builders Technologies
26
27
Ladies and Gentlemen, I’m
sorry to be almost late and to
cause a moment or two of
heartache.
I’m pleased to be here and
guess you are pleased to see
me come in. Let me place the blame elsewhere.
Since the decision to come, the Chancellor
decided to have his budget and, despite the
family friendly hours of the House of Commons, I
was still voting at midnight on the budget and
getting from London to here has not been easy in
that time. The Chancellor calls his budget a
consolidating budget. There’s been a lot of
discussion about what’s in it or, more particularly,
what’s not in it and, when I was talking to
Gordon Brown last week, I was saying that this
notion of a consolidating budget wasn’t very
exciting: you ought to have an image – a fresh
image, a new spin on budget and I suggested to
him that he ought to employ a new spin-doctor
to help him. Mohammed Sahid al Sahaf, Saddam
Hussein’s Minister of Information, has
disappeared at the moment but I firmly expect to
see him, comically, in his green uniform on the
steps of the Treasury. This is my prediction for the
future.
One of the ways that you find out what’s
going on in Westminster (one of the ways that I
used to find out what was going on, when I was
the leader of a very large organisation) was to do
what I call "earwig". As I left the Houses of
Parliament last night, I saw two of the
parliamentary greats there, having an animated
discussion and I thought, "This is my opportunity
to find out what’s going on". And it was Sir
David Steel, the ex-leader of the Liberal Party,
now Lord Steel, talking to my old and good
friend Dennis Skinner, the Beast of Bolsover, in
whose constituency you are today and I have to
say, if you don’t listen to the Chairman and come
back on time after lunch, they’ll set Dennis on
you. He’s more ferocious than armed guards are.
The discussion was going like this. David Steel
said to Dennis "Dennis, we had a by election up
your way last Thursday. A council by election, in
North East Derbyshire, and we the Liberal
Democrats won". Dennis looked him up and
down and said. "That’s very interesting, very
interesting."
"You know, the result was so good" said Sir
David, "When the General Election comes, and I
know it’s a couple of years away now, we’re
going to throw you out of Bolsover Dennis.
You’re gonna lose your seat and we’re gonna
have a Liberal Democrat MP." Dennis looked him
up and down again and said "That’s very
interesting, very interesting."
Sir David was rising to this he said "You know,
the results going to be so good Dennis, that, for
the first time for many, many years, for decades,
we’re not going to have a Labour government,
we’re gonna have a Liberal Democrat
government."
Again, Dennis looked him up and down and
he said " That’s very interesting, very interesting".
David was nonplussed at this and he said
"Dennis, you’re talking like New Labour. You’re
talking like Peter Mandelson."
Dennis said to him "Look, all I know about
New Labour is this, that when Tony Blair won the
second General Election, he called me across to
10 Downing Street and he said "Dennis, after 18
years of the Tories we need not two periods of
the Labour Government, we need three, and you
can help, Dennis".
Dennis said, "How can I help?" And Tony
said" Well I just want you to do one small thing. I
want you to stop talking rubbish". I want you to
stop saying ‘rubbish’ and say ‘very interesting’
instead."
Now, I am confident that at the 31st Annual
Symposium you are going to have some very
interesting discussions, and it’s not just Dennis
who talks in a very interesting way. There are all
kinds of politicians at Westminster who talk in a
very interesting way. My favourite is John
Prescott, the Deputy Prime Minister. Now, I’ve
known John a long time and I have to say, I still
don’t understand what he’s talking about. John’s
problem is this, he once said it to me, he said
"Paddy, I talk so quickly that when I get to the
end of a sentence, I can’t remember how I
started it." And, the other famous example for
John was that when he became in charge of local
government finance. Many of you will know that
this is a very difficult area, it’s a kind of fixed
game sum. If somebody wins, another local
council loses and I kind of gave him a seminar on
KEYNOTE ADDRESS
Paddy Tipping MP
MP for Sherwood
28
this and he seemed to understand and he went
away and came back some weeks later and he
said "Paddy, you’re right, it’s highly competitive,
it’s dog eat dog, or vice versa."
Now, of course John was in charge of
transport policy for four years. I’ll resist the
temptation to say that’s why Labour’s in a mess
on this but, what John would say is that this is a
difficult policy area. First of all, it’s plagued by
decades of under-investment, and, secondly, in
more recent years, under the last Conservative
government (the back end) and during the period
of the Labour government, that under-investment
has been compounded by fairly rapid economic
growth and that puts additional strain on a weak
infrastructure. Thirdly, as John would argue, I
think it’s fairly clear that in the first four years of
the New Labour government, that transport
hadn’t been a very high priority for Labour and
that sufficient investment hadn’t gone into it.
Now, currently, all the political discussion is on
the international agenda on Iraq and Syria and
the Gulf, on the Middle East, on our relationship
with Europe, on our relationship with the United
States. Let me make my second prediction. I think
we will rapidly get back to the domestic agenda
and what runs the domestic agenda is the notion,
as the Prime Minister would put it, of world class,
high quality public services. If you think back to
Labour’s first General Election victory, that’s what
won it for Labour. The campaign about years of
under-investment in public services, particularly in
Education and Health, but also in Transport. In
the last General Election again the argument was
about public services. The phrase then was
"We’re not complacent, this is a work in
progress. We’ve achieved a lot but there’s still a
lot more to do." I think there was some
confidence that the government, after the first
four years, was still moving in the right direction
on public services. I think that when the next
General Election comes, whether it’s in 2 or 3
years time, again the political battleground will
be on public services and there can be no excuse
for a government that then will have been in
power for 8 or 9 years, if it really hasn’t improved
public services. You’ve got to be sure that there
has been real success. Now, what I’m interested
in, and I guess what you’re interested in, is where
transport stands in the hierarchy of public
services. There’s no secret, and perhaps the
reason I’m here is that Labour’s interested in what
the public thinks. The stories you hear about
private polling, about focus groups are right. I
have focus groups for Labour and I’m very keen
to hear what people are saying and thinking
about public services. The truism is that voters
and residents are interested in the bread and
butter services, the NHS and Education. If you
examine, in fact, our recent polling, you’ll see our
second focus from Labour links into crime,
perception of crime, anti-social behaviour,
streetscapes, litter and that whole area of public
concern about anti-social behaviour has come
way up the agenda. You’re interested in where
transport stands and, again, in our own private
polling and our own discussions, in the eyes of
the public, transport lies about 5th, 6th, or 7th,
and I wouldn’t be too alarmed about that
because things can change. The notion of crime
has gone right to the top of the agenda and, at
one point, during the period of the last
government, before the General Election,
transport did come to the top of the agenda. If
you remember the fuel protests during the last
parliament, the only time that Labour was behind
in the polls was during the fuel/transport crisis,
and it was a crisis, and it did have effects. Some
of the effects were reflected in the budget but
going back a bit further to a previous budget, the
notion of the fuel tax escalator was knocked out
because of the protests, so I do think transport is
important in political terms. One of the things
that I think of Gordon Brown is that he’s
interested in investment today for gains in the
future. If you look at the transport sector, you’ll
see that, historically, it’s been under-invested but,
in recent years, investment is beginning to come
in. One of the issues around transport and the
politics of transport is that there’s no quick fix.
Many of you are engineers and will know the
planning cycle from the beginning to the end and
the problem is that politics is a short-term fix. We
do things because events are happening. We’re
already working on plans for the next General
Election. A big capital project can take a decade
from start to finish and this is a hard issue for
politicians to handle: the short-term political cycle
alongside the long-term investment cycle. Extra
money is going in. Let me give you one example:
The ten-year transport plan brings in £180 billion
for the railways. In real terms that’s a 40%
increase. One of the figures that sticks in my
mind, many of you who use the West Coast main
line will know the problems with improvements
but every day and every night £3 million of work
is being done on that main line. I could go
through a whole list of projects where big, long-
term investment is going in; Channel Tunnel Rail
Link, Kings Cross, St Pancras, 72 major road
29
schemes. You will know that investment is taking
place in the transport infrastructure. In
Nottinghamshire, for example, the amount of
money for highway improvements going to the
County Council has gone from £5.3 million in
1996/97 to £16.8 million in the current year and
that’s in real terms.
A lot of the money is capital money and it’s
easier to maintain capital spend than revenue
spend. Again, in the budget this week, the
Chancellor’s had to revise his growth figures, just
over 2% in the current year and an optimistic
3.5% next year. Can he maintain that spending
on creating world class public services? Can he
keep the momentum of public services going? I
actually think he will and that he intends to
because capital investment is easier than day-to-
day revenue investment. Of course, infra-structure
investment alongside pays dividends, it brings
new jobs, but it develops a base now for long
term improvements. So, I expect that the
Chancellor will stick with his current spending
plans. If you want a third prediction, I think that
in the budget next year he will not meet his
growth targets and he will need to borrow even
more. But, having said that, he will still be within
the fiscal rule that he set himself about
borrowing over a long period of time. I’m not
worried about a cut in investment. What worries
me more is about whether this investment can be
achieved. Whether what’s been promised in terms
of transport infrastructure can be delivered. Put
another way: what is promised can be produced.
Can we really build these big road, rail, and
airport projects? I have some doubts. One of the
things that worries me fundamentally is that, if I
look at departmental spending targets on their
capital programme, the slippage is immense. The
money’s in the budget but it’s not being spent. It
seems to be a crazy situation that you have
addressed money to deliver things after a period
of sustained under-investment and you’re not
spending it. A large number of projects, as you
will know, are being committed but not yet
achieved.
That brings me onto a set of issues that I’m
concerned about and the Prime Minister is
fundamentally concerned about which is about
management. In a sense it’s easy to govern, it’s
easy to run the cabinet, it’s easy to get what you
want through the House of Commons, but, in
delivery terms, actually achieving things on the
ground can be very difficult. I think one of the
things that surprised the Labour Government is
how far and how difficult it’s been to create
intent into action on the ground. I work a lot
with Civil Servants and actually help train Civil
Servants. One of the issues that’s around
government is that Senior Civil Servants are good
on policy, they’re good at developing ideas but
they’re not good on implementation. One of the
things that we’re not good at in Government is
revisiting the laws that we pass to see what’s
happened and I think that we’ve got to address
this issue of management within Government
because we’ve got a set of well paid people who,
in project management and delivery terms, just
don’t have the skills. One of the things that this
Prime Minister’s government is particularly
interested in is bringing people from the private
sector in. People who have the notion of how
important it is to have a timetable and to achieve
it, to help us do just that. I think, if you were
looking at changes in the government, you’d see
more focus on that. One of the things that I think
you need to listen to when the Prime Minister or
the Chancellor is talking is the notion of
investment. Both of them talk about investment
and reform on the same side. What they mean
about reform is that we’ve got to look at the way
that we develop policy but, more particularly,
reform the way that we deliver policy. I think
that’s a problem that only 6 years into
government, we’re just beginning to address
properly.
Perhaps I ought to say a word about the
Private Finance Initiative (PFI). PFI is a creation of
John Prescott’s. I’ll always remember the day that
he came in, when we were in opposition, to see
Margaret Beckett who was then the Chief
Secretary. He wanted a load of money to develop
transport policies. In opposition we were very
timid and Margaret told him that it wasn't
possible. John came back and said, "If I can
borrow off the private market to deliver these
things, is that acceptable?" In a sense that’s
where the notion of PFI has come from. PFI has
been fairly controversial within the Labour
Government and remains controversial within the
Government. In a sense it does two things for us.
Firstly it brings in capital which is off balance
sheet and that’s important in the big view of
government financing but, secondly, it transfers
the risk of delivery from the government to the
private sector and that’s why I think we’ll stick
with PFI. I actually think that, in the long term,
PFI will cost the government and the public more
money. I’m very simple: I know that if you buy
things on HP it does, in the long term, cost you
more but in the short term what it delivers is
30
private companies coming in, taking the project
and the risks, then delivering on timetable. That's
why I’m confident that PFI will stay. What I’m not
confident about is around a separate agenda,
which is a skills training agenda. I think the
Institute has been addressing this. We have a
plethora of training schemes. Let me be
confessional for a moment and say I simply don’t
understand our vocational education training
system and I think that there are major gaps and
major skills shortages. I think there is loads of
money going into further education that we’re
not getting the best from. One of the things that
we’ve got to be more sophisticated about is
setting up bridges between the public sector, the
government and the private sector to make sure
that those skill shortages are, first of all,
identified and, secondly, met.
I think that a third constraint on delivery is
around the planning system. Joy of joys, I have
been a member of a group of MPs that has been
considering the planning and compulsory
purchase bill to become law later this year. It
springs from a desire, from the PM, to speed up
the planning system. I think the jury’s out on this.
I’m fairly jaundiced, having dealt with this bill for
some time, that it’s going to make a great deal of
difference. What I am clear about is that people
won’t invest in the long term unless they’re
secure in the knowledge that they’re going to get
planning consent in a relatively fixed timetable.
Extra resources are going in to planning
authorities to try and ensure that we hit planning
timetables. I think there’s a wider issue. I know
planners, I love planners, I moan about planners,
but one things that impresses me about planners
is that they always tell you how difficult things
are, i.e. what the reasons are for refusing things
and I think we just need to change the
perspective and perception in the planning
system from a group of people who tell us how
difficult it is to a group of people who say, "This
investment is important to us. This investment is
going to bring new jobs and new future to this
area. What we’re going to do is determine a way
to make it happen rather than reasons for
making it difficult." I hope that what we’re doing
with planning schools at the moment, will mean
that we can do some work on that.
Finally, one of the constraints on the way
forward is about the environment. I can’t come to
a conference like this without talking about the
environment. The big promises have gone. Do
you remember the Prescott big promise? "I’m
going to reduce the number of people who travel
by car. In real terms I’m going achieve that."
Promises are now far more modest and I think
perhaps are achievable. The promise now is that
we’re going to reduce the increase in car
ownership so car travel will go up but not as
quick as what it might have done. I think we
know from our own experience that that is
achievable. Now, how are we going to do that?
People say to me that the environment isn’t
important to the government. That it’s never
been high on the agenda. That the European
Elections before last when the Green Party and
Environmental Party made a big way forward, has
now ceased. If I were looking in my crystal ball I
think a defining moment for the government and
the environment is the Energy White Paper that
was just published. It had a lot of criticism but
the important thing is what it says and what
people are saying about it. The PM hails it as a
significant milestone and, if it can be achieved,
it’s going to make a significant difference because
what it’s saying is that by 2020, 20% of our fuel
is going to come from renewable sources, that
we’re going to go on and meet the Royal
Commission’s targets but reducing the CO2 by
60% and, fundamentally, we’re going to move to
a low carbon economy. Now transport figures in
the White Paper, in a low-key kind of way. We
have made enormous gains on climate change
but they’ve been easy gains. The gains, really,
have been on the back of closing down the coal
industry and closing down coal generation. If we
want a hard target to try and reduce carbon
emissions, the next frontier must be transport and
I don’t think this is going to be easy. I think there
are some short-term solutions. I think there are
some short-term fixes. I’m running a campaign at
the moment, which we’re beginning to win, and
we’ll win fundamentally in perhaps 18 months
time, to move towards the notion of bio-fuels;
bio-diesel and bio-ethanol. You’ll notice that in
the last two budgets, the rate of duty on bio-
fuels has been reduced by 20p. That won’t make
the industry take off but I think that if we got to
a situation where the rate of duty was 26, 28,
even 30%, then we’d see the bio-fuel industry
take off. The significance of bio-fuels is straight
forward. You can just mix it and put it in your
tanks, so I think that is an early, short-term fix. I
think, more significantly, we need to look at
bigger policy issues and the one that’s on the
table at the moment is congestion charging.
People are anxious about this in London.
Congestion charging, before it was introduced,
31
was all the responsibility of the Mayor, Ken
Livingston. If it messes up, it’s all his fault. Well, it
isn’t messed up and everybody is now trying to
get in on the act. Research is still unclear on this
but congestion charging in London has, basically,
reduced traffic flows by about 30%. That’s a
significant gain. I think we can go on with the
London experiment when we look at the M6 toll
road. That coming on board gives us another
opportunity to play with it and then there are
smaller experiments. Those of you who know
Durham will know that to use the street along to
the cathedral, you’ve got to pay. That’s a clear
environment and streetscape gain. Just down the
road in the Peak District, the National Park is
going, I think, to introduce congestion charging
at weekends. This gives us an area to play with
and I think that congestion charging is back on
the agenda. I think it’s been shown that the
technology can work, I think it’s been shown that
the public can live with it although, maybe, they
don’t like it. Thirdly, I think there’s an issue about
what happens to the revenue from congestion
charging. One of the things that’s not been
readily understood is that Ken Livingston expects
to gain, in rough terms, £120 million of free
money after costs through congestion charging in
Central London. If you look at the long-term
budget for the London authority you will see
that, over the next three years, his grant from
government is going to go down by £150 million
a year so, on the one hand, Transport for London
are, over a period of years, gaining nothing from
congestion charging. That’s a crazy situation. I
think we can sell congestion charging to people if
the charges are held locally and used to develop
new transport initiatives because it’s clear to me
that people will only swap from cars to public
transport if it’s high quality, reliable and decent.
You’ll switch from your cars if it’s good for you in
those terms. I think this issue around the
proceeds from congestion charging remains to be
resolved but the way forward must be to allow it
to remain locally. Edinburgh City council is
looking at congestion charging and they’ve set
up an "arms length" company so that the money
from congestion charging will go, not to the
council, but to the "arms length" company. If the
Scottish Executive are then minded to say "You’re
getting all this money from congestion charging,
we’re going to cut your grant", it will be more
transparent.
I’m conscious that I’m on time and conscious
that I haven’t mentioned the word "concrete" at
all but, what I’ve tried to do is talk about some
wider political issues. Let me put it in a nutshell.
The government is presently reviewing airport
policy. There will be a White Paper at the end of
the year and the notion of environment and
economic growth will run through that White
Paper. Let me give you some examples. There’s
talk of a new airport in the South East. Go to
Ladbrokes and say it won’t be Cliffe in Kent
because of environmental concerns. Secondly, we
need to have a think about aviation fuel. Aviation
fuel isn’t dutiable at the moment but the
significant thing that’s happening at the moment
is that, because of the low budget airlines, 50%
of all people, 50% of all residents travel abroad
by air at least once a year. We have this notion
that airlines pollute the atmosphere, are not good
to live with, are bad for wildlife, but people,
because they are more prosperous and there is
still economic growth in the system, have now
the opportunity to travel abroad each year. That’s
the dilemma: how we can have growth and
prosperity and maintain the environment at the
same time?
When I was a University Lecturer, my students
used to say to me "You never tell us anything". I
used to say, "My job is to ask the questions, not
give the answer." The question for all of us, those
of us in government, those of us who actually
build and develop things, is that question. Can
we have growth, can we have prosperity and can
we protect the environment? I think we can but I
think we’ve got to be clear about how we sell
that idea to the general public. If the private and
public sectors work together, we can ensure that
the demands and the constraints put by
government on the private sector are realistic and
respectable.
Thanks very much.
32
33
Geoffrey Griffiths is an
Associate of Ove Arup &
Partners based in their
Nottingham office. He is a civil
engineer with specialist
knowledge of pavement
engineering and has extensive experience of the
design, construction and specification of
pavements for infrastructure projects. He is
currently the pavement engineer responsible for
the design work associated with M6 Toll on
behalf of CAMBBA’s designer Atkins/Arup.
ABSTRACTThis paper presents a practising engineer’s
views on some standard solutions to concrete
pavements. The paper also examines some of the
problems that are regularly found in undertaking
the design, specification and construction of
cement bound pavement materials. Some
examples of current UK construction methods are
described. The views expressed within the paper
are the views of the author and should not be
considered to be either a Code of Practice or
design advice.
KEYWORDSCBM (cement bound material), CRCP
(continuously reinforced concrete pavement),
pavement quality concrete, specifications and
construction problems
INTRODUCTIONConcrete surface slab systems have many
advantages when compared with bituminous
pavements; a concrete pavement consists of a
system of stiff plates connected together to form
a continuous, hinged slab system.
Cement bound materials are a particularly
useful form of construction, which can be used in
situations where pavements are subjected to
considerable point loads and aggressive
environments. Concrete pavements have a
number of advantages that make them beneficial
when compared with alternative bituminous
designs. Concrete pavements are useful when:
• High point loads are expected
• Diesel spillage or other chemical spills may
attack alternative materials
• Low subgrade strengths are expected
• Heavy axle loads can be anticipated.
The systems are also particularly useful in
providing cost-effective pavement solutions to
projects where large quantities of site-won sands
and gravels can be found.
STANDARD PAVEMENT TYPESExternal trafficked cement bound pavements
fall into three distinct groups:
• High quality surface slab systems; the
conventional 40N, wet laid concretes used
for URC (unreinforced concrete), JRC (jointed
reinforced concrete) and CRCP pavements
• Flexible composite pavements. Pavements
which rely on a combination of the tensile
strength of the CBM and a thin bituminous
surface to carry a significant proportion of
the pavement load. The CBM is a high
quality material produced from good quality
aggregate that is batched and paver laid
• Cement bound sub-base systems. CBM
materials produced from lower quality
aggregates that may be site won and can be
produced by in situ stabilisation techniques.
The CBM is simply used as a construction
platform to support the bituminous
pavement, which carries the majority of the
pavement load.
The boundaries between the three groups of
materials are not precise; each type of
construction is in some way interchangeable.
This paper describes some recent interesting
projects and is intended to share some of the
common engineering problems that can occur in
producing cement bound pavements.
UNREINFORCED CONCRETE (URC)FOR LOW TRAFFICKEDINDUSTRIAL PAVEMENTS
Jointed URC construction has been extensively
used on major highway projects; the system is
currently out of favour in UK highway schemes
but is extensively used on general infrastructure.
The pavement consists of a patchwork of
CONCRETE FOR PAVEMENTS
Mr Geoffrey Griffiths BSc, MSc
Ove Arup & Partners
34
concrete slabs joined together with dowel and tie
bars or crack induced joints. Each slab will consist
of approximately square units. The detailing of
the joint layout is crucial to the successful design,
execution and operation of the pavement.
The system relies on the tensile capacity and
flexural strength of the concrete to resist cracking
and successfully carry a load. When the pavement
is built, the size of the concrete panels is
controlled by the shrinkage strain generated by
the hardening process. As the concrete sets, gains
strength and cools, shrinkage strains generate a
tensile force in the pavement. The size of the
concrete slab controls the magnitude of the
force. If the tensile capacity of concrete is
exceeded, the slab cracks.
A number of rules govern pavement detailing.
The most important feature is to ensure that the
joints are detailed, designed and, most
importantly, spaced correctly. Pavement joints
must be arranged to produce a patchwork of
roughly square panels; the longitudinal joints
running in one direction, with the transverse
joints arranged at 90 degrees. Joint spacing is
controlled by standard practice and is a function
of pavement thickness: thicker pavement slabs
can have greater joint spacing. It is noted that the
recommended maximum ratio of longitudinal to
transverse joint spacing is 1.25. Pavement joints
may be constructed as dowelled or undowelled:
current practice is to construct most pavements
with dowelled tie bars. Removing the steel
dowels reduces the efficiency of the joints and
gives a small increase in pavement thickness.
EXAMPLE OF URC SLABCONSTRUCTION IN ANINDUSTRIAL PROJECT
A simple, cheap but effective form of URC
pavement can be constructed for low trafficked
industrial sites by simply laying a 200mm mass
concrete slab across a crushed rock sub-base. The
mass concrete is then sawn into 4.5m panels that
crack as the concrete shrinks. Figure 2 illustrates
the construction of a slab, Figure 3 shows sawn
joints, Figure 4 shows the action of a crack
inducer and Figure 5 shows the completed loaded
pavement.
The precise specification for the system can be
summarised as:
• 200mm, 40N/mm2, air-entrained concrete,
which can be wet laid in approximately
25m bays
• The joints are sawn in 4.5m bays using crack
inducing techniques
• The slab is constructed over a 250mm thick
crushed rock sub-base system
• No reinforcement, dowels, ties, expansion
joints or debonding plastic membrane
is used.
This system is a simple, effective method of
providing industrial hard standings. The
construction process is simply described as:
• Lay the crushed rock sub-base
• Shutter the intended slab with road forms
and pour the concrete
• 12 hours later cut the pavement joints
• Complete construction by installing a sealant
in the joints.
Figure 1: A typical URC pavement.
35
CONTINUOUSLY REINFORCEDCONCRETE PAVEMENT (CRCP)
A continuously reinforced concrete slab
consists of a regular section of cracked, square
concrete plates connected together by the steel
reinforcement. CRCP pavements are an excellent
form of construction for major highway projects;
the system has been developed from reinforced
concrete pavements. Continuously reinforced
concrete pavements are constructed as long slabs
with longitudinal reinforcement fixed at the
centre depth of the slab. The longitudinal
reinforcement is intended to control shrinkage
cracking. A nominal amount of transverse
reinforcement is also provided to hold the
longitudinal reinforcement in place. The system is
very similar to a mass and reinforced concrete
pavement except that the cracks are formed in a
random fashion and remain unsealed. A second
feature of a continuously reinforced concrete
system is that ground anchors are required at
terminations.
A CRCP slab will move extensively under the
influence of changing environmental
temperatures. The ends of the slab are therefore
anchored to prevent massive movement. Crack
spacing is essential to the efficient operation of
the pavement. Transverse cracks must be spaced
between 1.5 m and 4 m centres; if the cracks are
too closely spaced the blocks of concrete can fail
in shear as punch-outs. Cracks can also be spaced
too greatly; if the cracks are spaced too far apart
aggregate interlock is lost across the joint. Crack
spacing is controlled by the longitudinal
reinforcement content that is currently fixed at
0.6% of the section area using 16mm diameter
high yield bars.
EXAMPLE OF CRCPCONSTRUCTION; M6 TOLL
M6 Toll near Birmingham is the most notable
CRCP pavement that is currently under
construction in the UK. Approximately 50% of
the 3-lane motorway is being constructed as a
CRCP system over a CBM sub-base. All of the
aggregates are site won and processed.
Figure 2: Constructing a URC industrialpavement.
Figure 4: The action of a crack induceron a URC pavement.
Figure 3: Newly sawn crack-inducedjoints.
Figure 5: The completed pavement.
36
The system is summarised as:
• 35mm of 14mm aggregate, open, negative
textures thin wearing course with a 1.5mm
minimum surface texture
• A bituminous emulsion, sprayed bond coat
typically 0.8 litres per m2
• 220mm, CRCP, 40N/mm2 concrete, with
longitudinal reinforcement as 0.6% by
section area using 16 mm diameter Grade
460, deformed bar and nominal secondary
reinforcement of 12 mm bars
• A bituminous sprayed de-bonding
membrane
• 230mm CBM using 10N/mm2 mean 7-day
compressive cube strength concrete with a
smooth, regular even surface
• 3% CBR subgrade
• The pavement ends are anchored into
ground beams with movement joints.
The pavement is constructed progressively
using a number of carefully planned construction
processes which consist of:
• Paver laying sub-base
• Fixing the rebar and crack inducers
• Slipform the pavement slab
• Complete the system with a bituminous
wearing course
These processes are illustrated in Figures
6 to 10.
Figure 6: The completed CBMconstruction platform and thereinforcement laying system.
Figure 7: The completed reinforcementmat
Figure 8: The slipform paver
Figure 9: The completed pavement
Figure 10: The completed, crackedpavement.
37
CBM SUB-BASE SYSTEMS,SUPPORTING A CONVENTIONALBITUMINOUS PAVEMENT
CBM sub-base systems are a very practical
form of construction that is becoming popular
within the UK and Design and Build projects. The
CBM sub-base is formed by adding cement to a
site won granular material. The process can be
either undertaken in situ or batched and then
paver-laid. The UK specifications are described
within the Highways Agency’s Specification (1) as
CBM1, 1A, 2 and 2A. The CBM material has a 7-
day compressive cube strength of between 6 MPa
and 10 MPa and is laid semi-dry.
Cement bound sub-base systems are in many
ways similar to flexible composite pavements; the
essential difference is that the CBM layer acts in a
manner similar to a granular sub-base. The
material can be heavily cracked; the pavement
design will not rely on the tensile capacity of the
cement bound layer.
EXAMPLE OF CBM SUB-BASECONSTRUCTION; M6 TOLL
The recently constructed M6 Toll motorway
has extensive areas of paver-laid CBM material.
Wherever possible the material is used to replace
quarried crushed rock sub-base. M6 Toll uses a
standard CBM1A material that has an average 7-
day compressive cube strength of approximately
13 MPa. The standard pavement construction
consists of:
• 285mm HMB 35pen bituminous material
• 200mm CBM1A, paver laid in one layer
• 250mm conventional capping
• 3% CBR (California Bearing Ratio) at
formation.
The CBM sub-base layer is deliberately
thickened when compared to an alternative
crushed rock system to ensure the sub-base is able
to carry the heavy construction traffic loading.
SURFACE SLAB CONSTRUCTIONPROBLEMS
UK surface slab pavements require a high
strength, 40N/mm2, air-entrained concrete to
successfully operate without premature
deterioration. Many readymix companies are
reluctant to supply 40 N/mm2 air-entrained
concrete and often request a misguided
instruction to change the specification to a lower
strength or an air entrained concrete mix.
LACK OF AIR ENTRAINMENT INCONCRETE
Air entrainment is essential for the durability of
surface slab concretes.
Much debate has occurred around this issue.
Some frost resistant high strength concretes can
be produced, but the technique is not accepted
in the UK. Frost damage is a major problem in
concrete pavements. If the pavement is
constructed in normal un-air-entrained concrete
the surface will be quickly removed by the
weathering action of frost. The concrete must be
air entrained. A number of researchers have
suggested that if concrete achieves 50N/mm2
strength the material will not be susceptible to
frost but UK specifications are unable to define
when a material will be able to work without
adding air.
A typical standard of frost-protected concrete
will be achieved with 5 % ±1.5 % air content.
The air-entraining agent acts as a cracking agent,
reducing the size of any bubbles to a point where
the formation of ice lenses within the pores will
not cause damage to the concrete matrix. In a
conventional concrete, ice lenses are formed in
the voids contained within the structure of the
concrete. The ice is then able to crack the
concrete thus resulting in the formation of
surface scaling.Figure 11: Paver laying CBM sub-base
Figure 12: The CBM sub-base surfacecomplete with the bituminous curingmembrane.
38
Figure 13 illustrates a section of frost-damaged
concrete.
SUB STANDARD LOW STRENGTHCONCRETE
Many materials suppliers are in the misguided
belief that a 35 MPa concrete mix will be of equal
value to the standard 40 MPa mix in producing a
durable pavement design. Regrettably this is not
the case. Reducing the concrete strength will
directly lead to a reduction in the pavement load
carrying capacity. A reduction in the design mix
strength from 40 to 35 MPa will require an
increase in the pavement thickness of 20%.
A reduced concrete strength will also lead to
pavement surface durability problems. A lower
surface strength material will produce a
pavement surface which is susceptible to surface
abrasion. Surface abrasion is an important design
consideration. The surface of a heavily trafficked
pavement will quickly scrub and abrade away
under the action of traffic if the concrete is of an
inadequate strength.
CBM SUB-BASE CONSTRUCTIONPROBLEMS
CBM sub-base systems have a number of
construction problems that are not immediately
obvious when one initially considers using the
materials. The sub-base can offer significant
financial advantages but must be used with care.
The following problems are noted as important
issues that must be considered.
CONSTRUCTION TRAFFICKING THE CBM
CBM is a brittle material that is very
susceptible to construction damage. The material
must not be excessively trafficked. The UK
specifications permit the construction of a
150mm thick low strength slab which, when
construction tolerances are considered, can be
just 100mm thick. If a thin CBM slab is
excessively trafficked the surface can simply fail.
Figure 14 illustrates a failed pavement. A CBM
failed pavement must be reconstructed. The
surface of a CBM sub-base is weak and can be
easily eroded. Figure 15 illustrates a typical
problem. Surface trafficking is not a particularly
serious problem but can require some re-profiling
using a regulating material before the pavement
is completed.
POOR LEVEL CONTROLCBM materials must be laid correctly in one
construction operation. The actions of
compaction and rolling, combined with poor site
level control, can lead to difficult problems.
Figure 16 illustrates a typical problem where the
material has been incorrectly laid too high. The
pavement is being corrected using a motor
grader.
Figure 13: Air entrained concretecompared to non air entrained concrete
Figure 14: A section of failed pavement
Figure 15: Surface scaling resulting fromtraffic abrasion
39
IMPORTANT CBM DESIGNREQUIREMENTS
The author suggests that design engineers
should consider the following issues in producing
a pavement design using cement bound
materials:
• Keep CBM layers thick! Typically 200mm for
CBM and mass concrete
• CRCP pavements are a very successful
alternative to bituminous materials in large
construction projects
• CBM sub-base can be a very successful
alternative to crushed rock systems
• Simple URC slabs may be successfully used in
many industrial applications
• Always use 40N/mm2 air entrained concrete
in surface slab systems.
REFERENCES
1. HIGHWAYS AGENCY, Manual of ContractDocuments for Highway Works, Volume 1,Specification for Highway Works, August2001.
Figure 16: CBM sub-base level controlproblem
4040
4141
Les Hodgkinson is the UK
Technical Services Manager of
Grace Construction Products
Limited. He has spent the last
thirty years in the development
of admixture systems,
admixture standards and the associated concrete
technology involved in the successful transition of
new technology from laboratory to the field.
ABSTRACTFibres are already used in significant quantities
in numerous concretes used in the infrastructure,
but often their prescence goes unnoticed and
unappreciated. For example, internal, industrial
slabs now commonly contain steel fibres. Tunnel
segments may often contain two types of fibre,
both fulfilling differing roles. This paper
summarises the role played by the various types
of fibres in concrete. It describes the types of
fibres avaliable, and compares their properties
and performance. The paper then attempts to
describe, in simple terms, the opportunities
available to the materials technologist, and to the
engineer, by the inclusion of the various types of
fibres in concrete.
KEYWORDSFibres, Alignment, Fibre loading, Fibre length,
Modulus of elasticity, Crack control, Freeze/thaw
protection, Fire protection, Impact resistance,
Toughness, Residual strength factor.
INTRODUCTIONFibres have been included in construction
products since Biblical times, and the first familiar
reference to most of us would be that one in the
Bible where the Israelites were having great
difficulty making bricks without straw.
We have all seen how mud cracks on drying,
and the straw was presumably required to stop
the mud-bricks from cracking when they dried
out. As I was not there at the time, have never
made a mud-brick, and have never met anyone
who has made a mud brick, this is an assumption
based on a reasonable degree of the knowledge
of the materials and a prediction of what is likely
to be happening. On that basis, the aforesaid
analysis could be a load of nonsense and the true
reason for the inclusion of the straw may have
had nothing to do with the control of cracking.
The above practical problem highlights the
difficulty in dealing with composite materials and,
particularly, in understanding what processes are
at play.
Most concrete technologists are very familiar
with the properties of the various Portland
cements, ground granulated blastfurnace slags
and pulverised fuel ashes, and of their mechanical
influence upon concrete. Introduce novel
materials like micro-silica, metakaolin, or poly-
ether based superplasticisers, then there is a
period of uncertainty and learning. But within a
short period, the new materials are incorporated
into the technology because all the new
properties can be quantified in terms that are
familiar and readily understood, such as
compressive strength, permeability or porosity.
But include any reinforcement, in the form of
steel bars or fibres, then the propeties of the
composite become difficult to explain to a
concrete technologist because the terms of
explanation require a knowledge of another
technology; that of mechanical or structural
engineering. On the other hand, the engineers
who do have the engineering skills to calculate
the mechanical and structural requirements of the
end product, often do not understand the basic
properties of the materials. This problem of the
bridging of disciplines is at the root of explaining
why there is so much difficulty in quantifying the
benefits of fibres and why there is so much
misunderstanding about fibres in concrete.
Speaking as a concrete technologist, I am very
much a victim of the problem and have great
difficulty in understanding the mechanical
behaviour of composites other than in the most
basic terms. This paper is an attempt to try and
explain, in simple terms, the fundamental
properties and benefits of the most commonly
encountered fibres and how they affect the
mechanical properties of the composite. In
addition, the paper tries to explain how the
inclusion of fibres could lead to new opportunites
in the use of fibre-concrete composites.
Fibres in ConcreteFibres cannot replace primary, structural steel
OPPORTUNITIES FOR FIBRES IN CONCRETE
Mr. Les Hodgkinson
Grace Construction Products
4242
reinforcement. This steel is designed to transfer
high loads, over significant distances, once the
concrete has cracked. Most technologists, and
even some engineers, do not realise that the
reinforcement does nothing unless the concrete
does crack. Only when the concrete cracks, does
the load transfer onto the bar and the steel then
controls the width of the crack. This means that
every concrete bridge must have thousands of
cracks all over it, but they are so small that you
cannot see them. If this were not so, then the
design engineers would not be spending a small
fortune on all those steel bars to hold it together.
Fibres cannot be used to reinforce in the
conventional sense for other reasons, and their
behaviour is dictated by the following properties.
AlignmentBecause of the random, three-dimensional
orientation of the fibres in concrete, only one-
sixth are effectively aligned in the direction of
stress. This limitation only applies to normally
batched concretes, and this explains why some
glass reinforced concretes are produced in sheets,
with chopped, glass-fibre being sprayed onto
their surface. These fibres are thus aligned in two
dimensions, improving the efficiency of the fibre.
Fibre LoadingFibre loading is also an important
consideration. In normally batched concretes, it is
not practical to incorporate more than
approximately 1% volume of any fibre into
concrete. This limitation may not theoretically
Figure 1: Mechanisms involved in the process of crack propagation
Figure 2: Mechanisms of fibre failure
1) Grain bridging traction
2) Ductile matrix bridging
3) Grain delamination from the matrix
4a) Micro-cracking in the matrix
4b) Intragranular micro-cracking
5) Plastic deformation
1 Damage of the matrix
2 Fibre/matrix debonding
3 Fibre bridging
4 Fibre failure
5 Fibre pull-out
4343
apply to sprayed, chopped glass-fibre but there is
also the consideration of cost. For example, 1%
volume of steel fibre represents a loading of 70kg
per cubic metre, which in most situations would
not be economically viable.
Fibre LengthIn most practical situations, the primary mode
of failure of fibres is pull-out. (see Figure 2). For
this reason, the longer the fibre, then the better
will be its performance in respect of this type of
failure. However, in practice, the ability to achieve
a sufficiently high fibre-loading requires a major
compromise on the length of the fibre because of
the problems of physically incorporating the fibres
into the mix. This compromise on maximum
length is also related to the stiffness of the fibre,
as the incorporation of fibres into plastic concrete
is a very important consideration. Flatter fibres
offer the advantage that they have increased
surface area in contact with the cement matrix.
They also have reduced stiffness, which eases
handling, particularly with respect to the
incorporation of the fibre into the mix.
Modulus of ElasticitySteel has a very high modulus of elasticity and
it is easy to understand why steel fibres perform
well in any performance test involving the pull-
out of fibres. Equally, it is also easy to accept that
polypropylene micro-fibres, with a low modulus
of elasticity, can perform the task of prevention of
plastic cracking, as the loads involved in the
control of plastic shrinkage are very small.
So how do polypropylene macro-fibres control
cracking in the same manner as their steel
counterparts? The answer is that the fibre only
has to have a modulus of eleasticity similar to, or
slightly greater than, the concrete matrix. Steel
has a modular ratio of 15 times that of concrete
and thus its performance is never challenged. The
steel fibre pulls out when the cement matrix fails,
well below that required to induce the steel to
stretch. Polypropylene fibres are now produced
with a modular ratio just in excess of 1. Failure by
pull-out will occur at the same loading, as the
cement matrix still fails at the same loading.
The Role of FibresThis paper is mainly concerned with the three
types of fibre that are normally used in site- and
ready-mixed concretes: steel fibre, polypropylene
micro-fibre, and polypropylene macro-fibre
(synthetic structural fibre). However, given that
the behaviour of any fibre is dictated by the
previously described properties, it should be
possible to predict the behaviour of any natural
or synthetic fibre in concrete.
Polypropylene Micro-fibresThese are typically 6-12mm long, mono-
filament but, at 24 micron in diameter, they are
extremely fine, and very numerous for a given
weight of fibre. ( See Figure 6). They are normally
marketed in 0.5–1.0 kg small bags and, as the
fibre loading is relatively low, this is sufficient to
dose 1m2 of concrete. As pointed out previously,
fibre loading, fibre length and surface area are
important in modifying the failure mode of
hardened concrete. For these reasons,
polypropylene micro-fibres have only a limited
effect on mechanical failure. Their main
application is described below:
CohesionMicro-fibres are helpful in the prevention of
segregation, as they play a role in physically
holding the mix together. They can be used in
any concrete that is prone to bleeding. They can
also be used in self-compacting concrete to assist
in the achievement of high flow without
segregation.
Plastic Shrinkage CrackingWhen concrete udergoes the transition from a
plastic state to a hardened concrete, it is very
vulnerable to the effects of moisture loss, and
exhibits significant shrinkage. (See Fig 3.)
At this transition point, if the plastic shrinkage
exceeds the strain capacity of the concrete, then
a plastic crack will result. (See Figure 4). The
surface tension of the water, effectively tears
open the immature concrete, just like mud
drying. Plastic shrinkage cracks always occur at a
very early age and resemble tears. These features
distinguish plastic shrinkage cracks from drying
shrinkage cracks, which occur much later in the
life of a concrete.
The inclusion of 0.5–1.0 kg per m3 of micro-
fibre has a significant beneficial effect in reducing
the incidence of plastic-shrinkage cracking in
concrete slabs. Small fibres are able to prevent
any plastic cracks propagating, as the loads
involved are very small. This is the most common
application of micro–fibre.
Micro-fibres are particularly useful in external
renders, as renders have a very large surface area
for a given volume of mortar. For this reason,
44
they are prone to plastic-cracking, caused by
moisture loss from evaporation due to exposure
to wind.
Freeze/Thaw ProtectionAs part of a British Board of Agrément (BBA)
test programme designed to ensure that micro-
fibres had no deleterious effects upon the freeze-
thaw resistance of concrete, it was discovered
that micro-fibres did, in fact, have some benefit
in the prevention of freeze-thaw damage.
It is probable that air-entrainment is technically
superior in the prevention of freeze-thaw attack
than the use of micro-fibre, and air entrainment
would probably outperform micro-fibre in most
discerning freeze thaw tests. This has not been
conclusively proved, and such a comparison
would make an excellent ICT project.
44
Figure 3: Early shrinkage of cement and concrete
Figure 4: Early shrinkage strain and cracking
4545
Table 1: Preventive measures to avoid spalling of concrete exposed to fire
Figure 5: Pore pressure profiles in heated concretes
It was initially thought that the fibre coating
was entraining air into the concrete but it would
appear that the micro-fibres do confer protection
in their own right. The mechanism for this is not
clear, but the most logical and simple explanation
would be that the fine-fibres act as crack-
stoppers. That is, any micro-crack stops at the
nearest fibre. There are photo-micrographs that
appear to support this mechanism but the theory
is not really proven.
Fire ProtectionThis is a very important benefit of micro-fibre
and one that illustrates the importance of
technology transfer. Refractory furnace
technologists have been aware of the benefits of
the inclusion of micro-fibres for many years.
When furnaces are being relined, the new liner
has to be cast, cured and control-fired prior to
being put into service. The fibres allow the
moisture, incorporated during casting, to be
driven off, without physically disrupting the
furnace lining.
The inclusion of micro-fibres into
conventional concrete significantly reduces the
effects of fire damage. The same principals seem
to apply as with refractory furnace technology. It
is possible that the voids resulting from the
melting of the polypropylene offer a large
number of voids for the expanding steam to vent
into, reducing the tendency of the concrete to
spall.
Method Effectiveness Comments
Polypropylene fibres Very effective, even in Low-cost solution but may not prevent spallinghigh-strength concrete in expansive ultra-high-strength concrete. Does
not reduce temperatures, only pore pressures
Air-entraining agent Effective, if low moisture content Can reduce strength
Thermal barrier Very effective Reduces concrete temperatures and increasesfire resistance
Moisture content control Reduces vapour pressure Moisture content in tunnels is normally higher thanin buildings and more difficult to control
Compressive stress control Reduces explosive pressure Not economical with larger section sizes
Choice of aggregate Most effective to use low If low-moisture lightweight concrete used, additionalexpansion and small size aggregate fire resistance is possible. In high-moisture conditions,
violent spalling is promoted
Reinforcement Reduces spalling damage Limited spread of spalling in Channel Tunnel fire
Supplementary reinforcement Reduces spalling damage Difficult to use in small, narrow sections
Steel fibres Reduces spalling damage Explosive spalling may be more violent due to extra strain energy stored by steel fibres
Choice of section type Thicker sections reduce spalling damage Important for I-beams and ribbed sections
46
A number of major fires, including one in the
Channel Tunnel, clearly illustrated the vulnerability
of high strength concrete to fire damage.
Exposed to high temperature, the evaporation of
moisture in the concrete causes major spalling of
concrete.
The main factors influencing the degree of
spalling of concrete exposed to fire are heating
rate, permeability of the material, pore saturation
level, presence of reinforcement and level of
external applied load. [1]
High strength, low permeability concretes are
more likely to spall explosively and to experience
multiple spalling than normal concretes. This is
because greater pore pressures build up during
heating, as the moisture is unable to diffuse.
In addition, as illustrated in Figure 5, the peak
pore pressure in high strength concretes occurs
nearer to the surface than it does for normal
concretes.This explains why even thin sections of
high strength concrete can spall in the presence
of fire.
46
Figure 7: Variation of fibre surface area with fibre diameter
Figure 6: Variation of fibre number with fibre diameter
47
Impact ResistanceMicro-fibres are normally dosed at a low fibre
loading of 0.5–1.0 kg/m3 and, for this reason,
have only has a limited benefit on impact
resistance. Not only is the fibre loading small, but
the fibre length is also small. Steel fibres and
polypropylene macro-fibres are much longer, and
dosed at much higher dosages, and for this
reason, are much more effective in this
application.
Steel and Macro-fibres (Structural fibres)
Most macro-fibres or structural fibres used in
site- or ready-mixed concrete are mainly based on
steel or polypropylene. The use of glass-fibre
tends to be restricted to specialist precasters.
Long, glass fibres tend to be handled in a unique
manner, whereby they are handled as a rove;
chopped and co-sprayed with a cementitious
slurry, using a gun, onto a horizontal mould.
There are a number of types of steel fibre,
with a large variety of profiles. Similarly, there are
a mumber of synthetic structural fibres in the
market, again distinguished by their length and
aspect ratio. This paper will not attempt to
differentiate between any of them, but will try
and highlight their general behaviour and
performance.
In general, steel and polypropylene structural
fibres perform a similar role. The weight of steel
fibre used is typically 10–40 kg/m3. Polypropylene,
macro-fibres are dosed at a much lower weight,
typically 2-8kg/m3, but because polypropylene has
a much lower specific gravity, the fibre-loading
expressed in volume terms is similar to that of
steel fibres at 0.2–0.6% volume of concrete.
The number of fibres, for a given weight, is
low compared with micro-fibre. ( See Figure 7).
Because of the coarse nature of both steel fibres
and synthetic macro-fibres, they do not improve
the cohesion of a concrete mix. On the contrary,
they deprive the mix of paste and, for this reason,
the fines content of concretes containing macro-
fibres needs to be increased to preserve cohesion.
Steel fibres and most synthetic structural fibres
confer no benefit in terms of the prevention of
plastic shrinkage cracking. For a given fibre
loading, there are too few fibres available to fulfill
this role.(See Figure 6). The steel fibres are too far
apart to arrest, deflect or modify the behaviour in
any significant way at typical dosage rates. Some
of the flat polypropylene macro-fibres, with a
high aspect ratio, do have some benefit in this
respect, as the number of fibres per unit weight,
is far higher than that for steel.
No macro-fibre shows any benefit with respect
to freeze/thaw protection.
Because of the relatively coarse nature of
macro-fibres, it is unlikely that these will have any
significant benefit in terms of fire-protection. It is
quite normal for concrete to contain both micro
and macro fibre, where the micro-fibre is
incorporated specifically for fire protection and
the macro-fibre for structural purposes.
Toughness (Flexural toughness)Toughness is the key property in understanding
the benefits of the inclusion of macro-fibre in
concrete. Essentially, toughness is the ability of
concrete to retain structural integrity after it has
nominally failed by being exposed to a load
which exceeds its flexural strength.
Plain,unreinforced concrete, when subjected to
a bending load, will withstand that load with very
little movement until the load exceeds its flexural
strength. At this point, the concrete will fail
suddenly and catastrophically and fall to pieces.
This is the classic behaviour of a brittle material
possessing no toughness. That is, it has no
residual mechanical strength after a sudden,
brittle failure.
In most circumstances, the inclusion of fibres
does not improve the flexural strength of
concrete. When subjected to the same load as a
plain concrete, the concrete will fail at the same
loading. This is because the flexural strength is
still a function of the concrete and is also related
to the dimensions of the unit as expressed in the
equation below.
W x LFlexural strength =
Where W is the applied load
L is the length of span
B is the breadth of the specimen
D is the depth of the specimen
But in the prescence of macro-fibre, the
differences become apparent immediately after
failure. (See Figure 9). At failure, the concrete
cracks, but the crack width is initially so small
that it cannot be seen. The load has been
transferred to the fibre. If the concrete unit
continues to be loaded, then the fibres start to
pull out, and the crack starts to widen. At this
stage the unit is broken but is still able to
47
B x D2
48
withstand a large proportion of its maximum
load. This ability to carry load after failure is
called toughness.
In the above test ( See Figure 8), a plain panel
without structural-fibre would have shown no
load bearing capacity after first-crack deflection.
When steel or synthetic fibres are added, the
concrete shows significant flexural toughness.
Toughness IndexToughness indices identify the mode of
material failure. These are determined by dividing
the total area under the load-deflection curve up
to a selected deflection value by the area under
the curve at the deflection at which the first crack
is deemed to have occurred.
48
Figure 8: Load deflection diagram- South African Test Panels
Figure 9: Characteristics of the load deflection curve
4949
In the above diagram, the concrete unit has
failed at point A. Without fibre, it would have
broken into pieces and arrived at point B, having
no ability to retain any load and having exhibited
no flexural toughness.
The same concrete, but containing structural-
fibre, still fails at point A but the fibre now takes
the load, and even though the crack-width
increases to 3 times the original deflection up to
point D, the concrete still shows considerable
residual load bearing capacity at point C.
Values of I5, I10, I20 and I30 respectively, are
defined below. All the concretes show near linear
elastic behaviour up to first-crack, both with and
without fibres. Plain concretes show instant
failure at first-crack with zero residual strength
thereafter.
Definition of Toughness IndicesToughness Index I5 – the number obtained
by dividing the area up to a deflection of 3.0
times the first-crack deflection by the area up to
first crack.
Toughness Index I10 – the number obtained
by dividing the area up to a deflection of 5.5
times the first-crack deflection by the area up to
first crack.
Toughness Index I20 – the number obtained
by dividing the area up to a deflection of 10.5
times the first-crack deflection by the area up to
first crack.
Toughness Index I30 – the number obtained
by dividing the area up to a deflection of 15.5
times the first-crack deflection by the area up to
first crack.
A indices calculated by dividing this area by the area to the first crack OAB
Table 2. Toughness Indices Calculation
Area Index Deflection Plain Elastic-Plastic Observed Range for BasisA Designation Criterion Concrete Material Fibrous Concrete
OACD I5 3δ 1.0 5.0 1 to 6
OAEF I10 5.5δ 1.0 10.5 1 to 12
OAGH I20 10.5δ 1.0 20.0 1 to 25
OAIJ I30 15.5δ 1.0 30.0 -
Values of Toughness Indices
5050
Residual Strength FactorsThe residual strength factors R5,10 and R10,20
represent the average level of strength retained
after first crack as a percentage of the first-crack
strength for the deflection intervals as specified in
ASTM 1018-97.
Opportunites for Fibre ConcreteMany plain concretes used in the infrastructure
are brittle by design but would benefit greatly
from the inclusion of fibres. Having an
understanding of how the behaviour of a brittle
material can be modified by fibres immediately
presents opportunites which can be readily
understood by a concrete technologist.
Any thin or slender unit can be toughened to
dramatically improve its service life.
Concrete roof tiles, promenade tiles and many
unreinforced units can all benefit from the
inclusion of structural fibres. A good example is
paving flags.
Paving flags, designed for pedestrian usage,
regularly fail in service because of overloading
when trafficked by service vehicles. Such failure
has become a major problem in terms of
compensation paid to the general public. In
Leicester, in 2002, the council paid as much in
compensation as it did in actually maintaining
pavements. Toughening of paving flags laid in
public areas represents a significant opportunity
for the use of structural fibres. When overloaded
by service vehicles they still fail, and they still
crack, but because of their flexural toughness
they retain most of their load-bearing capacity.
The general public do not trip on them, and are
blissfully unaware of their initial failure.
Many other simple precast items can benefit
from fibres. Very often it is difficult to place the
steel reinforcement in the right place. Fencing
posts are typical of simple units where
reinforcement is included in a haphazard way. We
have all seen fence posts where the corroded
steel has caused spalling of concrete. With
synthetic fibres this is not a problem. Take out the
badly positioned bars and put in fibres.
Bollards are an example of where toughness
would be an added benefit. A bollard should be
designed to be tough rather than fail
catastrophically. Incorporation of fibres would
enable it to withstand minor collision without any
evidence of failure, but also perform far better in
the event of a major collision.
Concrete barriers should be designed to
deflect, absorb energy and stay in one piece after
a major impact. It would be difficult to think of a
better example of where flexural toughness could
be of value, and of a better application of
structural polypropylene fibres, which would not
cause injury when exposed at the fractured
surface.
Septic tanks, pipes, covers, concrete ducting
and tunnel segments are all examples where
secondary steel can be replaced by structural
fibres. In addition to fulfilling the same function
as mesh, they are also more readily included into
the unit.
Shotcrete is an ideal opportunity for the use of
polypropylene structural fibre to give the required
toughness but without the pumping, spraying
and rebound difficulties, not to mention the
health hazard associated with sprayed steel fibres.
However, the biggest commercial opportunity
for the use of structural fibres in the
infrastructure, lies in their use in concrete flooring
and paving, where their usage can be justified by
the design of thinner and more economic
concrete slabs.
Design Aspects of FibreReinforced Concrete
A discussion of the principles that can lead to
the design of thinner slabs containing structural
fibres is a complicated topic and is worthy of a
paper in its own right.
The arguments need to be presented by an
engineer, as they lead us into that area where
most concrete technologists, including myself,
have great difficulty understanding the principles.
Below is a summary of the basic arguments
justifying the use of thinner slabs when
incorporating structural fibres.
The traditional code-adopted design approach
is based on strength and no post-cracking
behaviour is considered. Recognition of the post-
cracking behaviour at the design level is essential
to transfer the technology of structural fibres to
the industry.
Concrete in the cracked section carries tensile
load in fibre reinforced concrete (FRC), while
concrete after cracking becomes ineffective in
plain concrete (PC), as indicated by a stress-strain
diagram. The bending moment distribution after
cracking is different for FRC. Plain concrete
exhibits a regular hinge, whereas fibre concrete
exhibits a plastic hinge (with yield capacity).
The final design of a plain concrete slab is
5151
governed by slab stiffness and interaction with
the sub-base. The final design of a fibre
reinforced concrete is governed by the interaction
between the positive and negative moment as a
function of slab stiffness and sub-base. The
failure load of a FRC slab is a function of the sum
of the negative and positive moment. The failure
load of a PC is a function of the cracking
moment.
The inclusion of fibres improves flexural
capacity and can significantly modify the design
of structures governed by modulus of rupture.
The concept of equivalent flexural strength is a
measure of performance which takes into
account the toughness obtained from
experiment, by measuring the area under the
load-deflection to a deflection of 3mm (L/150).
This is commonly referred to as the Re,3 value.
The third edition of Concrete Society Technical
Report 34 [2] has recently been published, and the
design approaches in Chapter 15 consider both
the ultimate and serviceability conditions.
Determination of the strength of a concrete slab
based on plastic analysis (as compared to the
traditional elastic analysis), requires that the slab
has adequate ductility. The ductility is now
specified in terms of the Re,3 value. Steel and
synthetic structural fibres may be used, at a
minimum dosage, sufficient to give a value of
Re,3 of at least 0.3; otherwise the concrete shall
be regarded as plain.
In summary, fibres reduce the stresses in the
reinforcing steel at service loads, reduce crack
width, improve ductility and increase confinement
capacity. The reduction of slab thickness, and
elimination of steel mesh, has significant cost
benefits in terms of material cost, material
handling, storage, safety and time.
In terms of the infrastructure, there are a
myriad of applications where fibres are used and
could be used. These include paving slabs,
promenade tiles, posts, panels, bollards, concrete
barriers, concrete roof tiles, concrete paviors,
cover slabs, concrete ducting, septic tanks,
concrete pipes, tunnel segments and internal
flooring.
In the future, the opportunities for the wider
application of fibres in the infrastructure will
undoubtedly spread to the use of structural fibres
in external slabs and paving, and possibly to their
use in thinner concrete pavements for roads and
aircraft pavements and taxiways.
References
1. Passive fire protection in tunnels. G.A.Khoury, Concrete, Feb 2003: Vol 37 No2
2. Concrete Society Technical Report 34 –Concrete Industrial Ground Floors, A guideto their Design and Consruction. ThirdEdition.
5252
53
Nigel O’Neill is an Associate of
Roughan and O’Donovan
Consulting Engineers and is
one of their senior bridge
engineers. He has participated
in many of Roughan and
O’Donovan’s bridge projects.
ABSTRACTThis paper presents some of the design and
technical aspects of current practice in bridge
engineering in Ireland. Bridge engineering in
Ireland is in the middle of an exciting period of
large-scale expansion of the country’s
infrastructure assets. An opportunity to create a
whole new species (the modern bridge) within
the built environment exists and the role of
engineers in accomplishing this is explored. Most
new bridges in Ireland are constructed from
concrete and the materiality of this plastic and
organic medium and its influence on design is
examined. The design of both commonly
occurring and larger bridges is presented with
examples from the work of Roughan and
O’Donovan.
KEYWORDSBridges, Ireland, Design, Aesthetics.
INTRODUCTIONSince the 1980s a large number of new
bridges have been built in Ireland as part of the
construction programme to develop the country’s
transport infrastructure. This process received a
boost with the founding in 1993 of the National
Roads Authority (NRA); the government body
with responsibility for developing and maintaining
the National Primary and National Secondary road
network (5429 km long, roughly evenly divided
between Primary and Secondary). The NRA
provides the centralised planning and funding for
national road schemes and is also the technical
approval authority in matters of national
standards and specifications. It is anticipated that
the founding in 2002 of the Railway Procurement
Agency will provide a similar boost to the railway
network.
In simple terms, Ireland is building her
motorways and main roads about a generation
later than the "advanced" countries of Europe
and North America. However, this has turned into
an unexpected advantage as Irish bridge
engineers have benefited from the experiences
(both successes and mistakes) of others. The
principal lessons that we have learnt from others’
experience is the importance of good design and
of designing for durability. Thankfully, Irish bridge
engineers have not in general inflicted on the
general public a "brutalist" or utilitarian design
philosophy and we are hopeful that our bridge
designs will both last and be a lasting
contribution to the built environment.
In comparison with other countries the scale of
almost all bridges in Ireland would be classified as
"small" to "medium" in scale with the vast
majority falling into the "small" category. Most of
our motorway overbridges and underbridges fall
into this "small" category and occasionally, as in
the case of the cable stayed Boyne Bridge, we
make it into the "medium" category. The
approach in Ireland to the design of "small"
bridges is perhaps something that our fellow
bridge engineers in Europe could benefit from.
DESIGN
AestheticsThe term "aesthetics" has gained some
currency in the language used by bridge
engineers and I think that this is unfortunate
because it tends to convey the impression that
aesthetics is just another criterion along with
durability, function, economy and safety, so that
when money is short, aesthetics is first to get cut
from the list. I prefer to think of "design" as
being more or less equivalent to what people
mean when they say "aesthetics". There is
something forced about isolating those factors in
bridge design as belonging to "aesthetics" when
in fact what makes a bridge a pleasure to
perceive is, in many cases, difficult to express in
words. And after all, we have no problem saying
whether something like a coffee cup is either of
good design or of bad design – let’s use the same
language about bridges. I suppose this slippage in
language has occurred because engineers use the
term "design" when what is really meant is
something like "section design" or "structural
scheme design".
THE BRIDGES OF IRELAND - CURRENT PRACTICE
Mr. Nigel O’Neill Dip Eng, BSc(Eng), MSc, CEng, MIEI
Roughan and O’Donovan
54
MaterialityConcrete dominates the materiality of Irish
bridges. Most modern bridges in Ireland
(approximately 98%) are constructed from
concrete – reinforced concrete, precast pre-
tensioned concrete and post-tensioned concrete
are all commonly used. Steel is an imported
material while cement is natively produced,
thereby making concrete generally more
economical to use. A major fraction of the Irish
landmass sits on top of limestone bedrock
making clinker and aggregates readily available
for cement and concrete production.
Aside from its default material status, bridge
engineers are attracted to concrete because of its
plastic nature. The ability of concrete to take on
virtually any shape, to be in effect moulded,
permits organic and sculptural designs. Piers
provide the most striking examples of freedom
with the materiality of concrete: the variety and
expression to be found on motorway overbridges
clearly exhibit this possibility.
In response to the brutalists who would have
us build dumb, expressionless rectangular walls, it
is worth remembering that piers make up
something like only 7% of the cost of a bridge.
SurfaceComplementary with the bridge engineer’s
freedom with the materiality of concrete is his
freedom to decide on its surface and full use is
made of it to give further expression to the
design – smooth, patterned, coloured coatings,
are all used to effect. Large bland areas of plain
concrete walls, whether on abutments or
retaining walls, are thankfully rare.
Texture can be formed by the use of form
liners (relatively inexpensive two- or three-use
liners are preferred for large pours).
Colour can be chosen by application of a
coating. (Examples: Figures 1 and 2). Concretes in
Ireland with just ordinary Portland cement are
dark grey in colour, which, combined with our
generally overcast grey skies, adds to the overall
depressive effect unless relieved by lightening the
colour. Most bridges in Ireland constructed in the
last fifteen years or so have surface impregnation
of concrete with siloxane and an acrylate-based
coating. In the last few years we have been
experimenting with the use of controlled
permeability formwork and cement replacement
with 50% ground granulated blastfurnace slag
(ggbs) with a view to eliminating the requirement
to surface impregnate and coat the surfaces of
concrete. The lighter colour concrete achieved
when ggbs is used is encouraging, although the
fact that ggbs is an imported material means that
its use is likely to be restricted to specialist
applications such as in bridges and other large
civil engineering structures.
Light and shade are powerful determinants of
the quality of surface. Shadow lines can be made
using chases. (Example: chases in abutments and
deck on Rowan’s Road Bridge –Figure 3: Rowan’s
Road Bridge).
Typology and FormBridge typology provides immediate access,
based on experience, to a wide range of forms
and span arrangements that "work": motorway
overbridges, motorway underbridges, railway and
Figure 1: Killarney Road Bridge Piers
Figure 2: Grange Newbrook Bridge
Figure 3: Rowan’s Road Bridge
55
canal bridges, are types where a form has
converged to an almost standard solution. In the
case of motorway overbridges the two span
arrangement is dominant. (Figure 4: Killarney
Road Bridge.) However, typology can trap the
unwary when atypical site conditions assert
themselves. For example, take a motorway
overbridge where the deck has to have a steep
longitudinal fall because of the road alignment –
a typical two-span arrangement could look
unbalanced and out of proportion because the
abutments might tend to be of different sizes and
the deck could look visually unstable as it slopes
off to one side. Now look at Killarney Road
Bridge: the fascia is curved to express the span
and the abutments have rounded corners and are
inclined so as to balance the visible areas of the
two abutments and to visually anchor the bridge
ends into the sideslopes. The solution is still a
two-span arrangement but careful detailing of
the form integrates it into a difficult geometry. It
is also worth noting that the deck comprises
precast U-beams and the deck erected during
short possessions of the busy N11 National
Primary, which was upgraded to dual
carriageway.
Significant lengths of the National Network
comprise single carriageways and when an
overbridge is required, the type of bridge
emerging almost as a standard is a three span
arrangement.
However, in particular situations with difficult
geometry, such as a steep longitudinal fall in the
deck following the road profile, this type
becomes visually distorted as the lack of
symmetry causes unequal pier heights and
problems with either unbalanced areas of
abutments or unequal end spans – the overall
impression can be one of visual instability. A way
of solving this problem is to break away from the
typology and to design a form that can
harmonise with the constraints: Ballycahill Bridge
on the N7 Nenagh Bypass achieves this ambition
by virtue of an asymmetric form that expresses
the longitudinal fall of the deck instead of
ignoring it. The soffit of the deck was made
horizontal to create a plane of stability for the
observer; the "downside" abutment by its mass
appears to anchor or brace the deck; the short
end-span and inclined pier almost look like the
fingers and thumb of a hand placed against a
surface. An overall impression of balance is
achieved.
The utility of typology breaks down again
when it comes to larger bridges and unusual
situations where the form must evolve from a
more fundamental consideration of the design
constraints. For instance, take the Boyne Bridge
that carries the M1 motorway over the River
Boyne west of Drogheda. This bridge is both a
river bridge and an underbridge; a viaduct could
easily carry out its function. However, the history
and archaeology present on the site of Yellow
Island (directly underneath the bridge), one of the
crossing points of the Battle of the Boyne (a not
insignificant event in Irish history), make it
Figure 4: Killarney Road Bridge
Figure 5: Claremorris Bridge
Figure 6: Ballycahill Road Bridge
Figure 7: Boyne Bridge
56
imperative that the bridge form must span over
this area and not require support off it during
construction. A cable stayed form with a
cantilever form of construction gradually emerged
as the most appropriate solution. In a different,
urban, context Taney Luas Bridge, built to carry
the Luas Light Rail, in the Dublin suburb of
Dundrum demonstrates the similar use of a cable
stayed bridge constructed by the cantilever
method over one of Dublin’s busies traffic
junctions.
Occasionally one gets to use a rare form
because it particularly suits the constraints of a
particular site and the client also wishes to make
a bold statement with a landmark bridge. Such is
the case with Kilmacanogue Footbridge –
Ireland’s only stressed ribbon bridge. Six bearer
tendons are stretched between the abutments
and stressed and these support the precast deck
panels. Four post-tensioning tendons are placed
in the deck and in situ concrete topping added –
the deck is then stressed. The bridge was erected
over the live N11 National Primary – police halted
road traffic for about 15 minutes at a time while
each of the bearer cables was lifted into place.
The deck panels were lifted up at one end and,
using pulleys, were slid into position over the live
road, thereby keeping traffic disruption to a
minimum. The deck is extremely slender: 270mm
thick for a span of 48m.
ENVIRONMENT
HeritageBridge engineering in Ireland is characterised
by a modernist approach to design. However, in
cases where a bridge is required to be inserted
into an existing heritage, such as at canals and
railways, it sometimes becomes necessary to
adopt an almost "arts and crafts" approach to
design if one is to respect the vernacular of the
existing built environment. For example, Moran’s
Bridge in Mullingar, carrying a road over the Royal
Canal, is in fact a reinforced concrete box but it is
clad in stone with the full complement of the
mason’s art expressed: pilasters, quoins, voussoirs
and the like. A similar example is Shaw Bridge,
Kilcock, which combines replacement bridges for
a railway bridge and a canal bridge in quick
succession – the respect for heritage went so far
as to carefully remove a stone plaque from the
parapet wall of the existing canal bridge and re-
set it into the replacement bridge. Honesty is a
key modernist design principal and one can feel
uneasy about hiding concrete instead of
expressing it. However, I feel that when it comes
to replacement bridges, some compromise with
the existing fabric of the area must be made.
LandscapingOne of the pleasures about driving on
motorways in Ireland is enjoyment of the
landscaping: wide grassed central reserves
(sometimes planted with daffodils), sideslopes
planted with low woodland mixed planting and
somewhere along the scheme a commissioned
piece of sculpture (the "one per cent for art"
initiative). Integrating bridges with the
landscaping requires careful design. Regrettably,
some landscape designers take the view that
when it comes to bridges "the taller and thicker
Figure 8: Taney Luas Bridge
Figure 9: Kilmacanogue Footbridge
Figure 10: Moran’s Bridge
57
the planting the better". Tall trees and shrubs
placed adjacent to wingwalls and piers mean that
the abutments and piers are completely
obstructed and all that is visible is a short length
of deck furtively running from one clump of trees
to the next. Such tactics are justified if bridges
are ugly but when it comes to elegant bridges
such camouflage tactics border on vandalism.
Fortunately, communication within design teams
has improved and a truce exists between bridge
engineers and landscape designers so that
planting is now kept low next to bridges and one
can actually see them.
TECHNICAL
NRA Standards and SpecificationsIn 1999 the National Roads Authority formally
adopted the Highways Agency’s Design Manual
for Roads and Bridges (DMRB). Bridge engineers
in Ireland were already familiar with the DMRB
and its formal implementation regularised this
usage. The Roughan and O’Donovan -
FaberMaunsell Alliance was appointed to
implement the DMRB through the use of NRA
Addenda to the standards and, especially in the
area of road and junction design, to prepare new
NRA Standards.
The NRA also maintains a Manual of Contract
Documents, encompassing the Specification for
Road Works, The Method of Measurement for
Road Works and their associated notes for
guidance. As with the DMRB, the Manual of
Contract Documents is similar to the equivalent
Highways Agency documents but with many
variations to suit Irish conditions.
DurabilityBridge engineers are mindful of the
considerable durability problems that have beset
a considerable fraction of the developed world’s
bridge stock. Mistakes made by an earlier
generation of engineers in other countries have
been noted, e.g., inadequate provision of
drainage, overprovision of expansion joints (that
subsequently very often leak), poor weathering
details (lack of drippers and the like), inadequate
deck waterproofing, inadequate site supervision
(e.g., lack of grout in post-tensioning tendon
ducts). Considerable effort is being made to
design for durability and to avoid mistakes even
though there is a considerable rush to create a
sizeable bridge stock in a relatively brief time.
Apart from taking obvious measures such as
making small bridges integral with their
supporting soil, Irish bridge engineers are also
trying out other ideas, such as the use of
controlled permeability formwork (CPF) combined
with ggbs cement replacement (example: Rowan’s
Road Bridge and Airport Bridges – use of CPF).
The use of stainless steel rebar is also becoming
common in selected highly susceptible concrete
elements such as parapet edge beams, piers and
bearing shelves.
ProcurementIn the past, a road would have been designed
directly by the Local Authority and procured in
relatively short lengths (say 10km) and if there
were six bridges on the scheme three separate
consulting engineers would each get two to
design. The merit of this approach was that it
generated great variety in design and when the
designs were good (and thankfully they generally
were) the resulting collection of bridges provided
immediate interest and genuine experience. Now
that vastly greater sums of money are being
invested in infrastructure, the length of schemes
has grown considerably and a single design
organisation (a joint venture of two or more firms
of consulting engineers is common) undertake
the design of both the road and the bridges. No
longer designing a couple of bridges on a
scheme, bridge teams are now designing whole
families of bridges. This might be no bad thing –
too much variety can be discordant – but the
pressure to standardise where the constraints are
not standard has to be resisted. The pace of
development is increasing, putting pressure on
the capacity of bridge design teams: between
1997 and 2002 about 200 bridges were added to
the NRA’s stock; from 2003 to 2010
approximately 500 more bridges on National
Roads will be constructed. Another pressure on
the quality of design is the design and build
(D&B) and public private partnership (PPP)
procurement strategies being adopted. In a
competitive tendering situation the rational
response of bridge engineers is to make their
designs as cheap as possible within the
parameters set by the Employer’s Requirements.
Fortunately the NRA has adopted an approach
whereby the design (i.e., the aesthetic quality) of
bridges is an explicit construction requirement
and must be matched by tenderer’s proposals.
ResearchWith the volume of bridge design going on in
Ireland at the moment its not surprising that
58
there is considerable research interest in the field.
In 1999 the Bridge Engineering Research Group
was founded in University College Dublin and in
2002 plans were set in motion to create an All-
Ireland Bridge Engineering Research Network
involving both academics and practitioners.
CONCLUDING REMARKSFritz Leonhardt sums it up well:
"Bridges have always fascinated people, be it a
primitive bridge over torrent or deep gorge or
one of the magnificent modern bridges whose
immense spans almost defy the imagination. A
variety of qualities are called for to build a
modern bridge; a considerable amount of
knowledge, the courage to take daring decisions
and the ability to lead a large team of fellow
workers to the successful completion of the
project. Bridge building is one of those difficult
constructional endeavours that both attract and
challenge the energetic and self-confident
engineer. The importance of bridge building gives
rise to a correspondingly intense joy and
satisfaction when successfully completed. Bridge
building can grow into a passion that never loses
its freshness and stimulus throughout a man’s
life." [1]
REFERENCES
1. Leonhardt, F. Brücken Bridges, ArchitecturalPress, 1982, pp308.
Figure Credits
1. Killarney Road Bridge Piers, Roughan andO’Donovan with Grafton Architects (N11Bray Bypass, County Wicklow).
2. Grange Newbrook Bridge, Roughan andO’Donovan (Grange to Newbrook LinkRoad, Mullingar, County Westmeath).
3. Rowan’s Road Bridge, Roughan andO’Donovan with Grafton Architects (M1Northern Motorway: Balbriggan Bypass,County Dublin).
4. Killarney Road Bridge, Roughan andO’Donovan with Grafton Architects (N11Bray Bypass, County Wicklow).
5. Claremorris Bridge, Roughan andO’Donovan (Knock Claremorris Bypass,County Mayo).
6. Ballycahill Road Bridge, Roughan andO’Donovan with Grafton Architects (N7Nenagh Bypass, County Tipperary).
7. Boyne Bridge, Roughan and O’Donovanwith Grafton Architects (M1 NorthernMotorway: Drogheda Bypass, CountyLouth).
8. Taney Luas Bridge, Roughan andO’Donovan (Luas Light Rail Transit, SaintStephen’s Green to Sandyford, Dublin).
9. Kilmacanogue Footbridge, Roughan andO’Donovan with Grafton Architects (N11,Kilmacanogue, County Wicklow).
10. Moran’s Bridge, Roughan and O’Donovan(Royal Canal, Mullingar, CountyWestmeath).
5959
Murray Chapman has spent a
large percentage of his
working life with Gibbs, the
Consulting Engineers, working
on docks. He started in 1971
with the design of the
Submarine Refit complex at Devonport and, in
1991, worked on the Trident refit contract for
the same dockyard. After carrying out an
assessment of damaged facilities of the Kuwait
Naval Base following the First Gulf War, he was
seconded to Devonport Management Ltd to
prepare designs and safety cases for the upgrade
of facilities to accommodate the Royal Navy’s
nuclear submarine fleet. He is presently involved
in examining further upgrade works relating to
low-level refuelling of submarines.
ABSTRACTThe paper presents an overview of the design
and construction of the reinforced concrete
ground works that were undertaken during the
period 1997-2002, to provide upgraded facilities
to support the Royal Navy’s nuclear submarine
fleet at Devonport Royal Dockyard. In particular,
to satisfy nuclear regulatory requirements the
structures, amongst other requirements, had to
be designed for extreme loading conditions
during which their behaviour had to be
predictable.
KEYWORDSSafety Case, Nuclear, Dock Structures, Shear
Friction Dowels, Surface Preparation, Caissons,
Ductile Concrete.
INTRODUCTION
The DockyardDevonport Royal Dockyard is situated to the
west of Plymouth on the east bank of the River
Tamar (also known as the Hamoaze at this point).
It covers an area of some 120 hectares with over
5km of deep water berths, 5 fitting out basins
and 14 dry docks.
CONSTRUCTION OF SUBMARINE SUPPORT FACILITIES
- DEVONPORT ROYAL DOCKYARD
Mr. Murray Chapman BSc(Hons), FSA, CEng, FICE, MCIWEM, MCIArb
Kellogg, Brown & Root
Figure 1: View of Dockyard looking south
6060
It is the single largest naval support complex in
Western Europe and offers a wide range of skills
and a level of back-up services which are
fundamental to the continuation of the Royal
Navy as an effective fighting force. Devonport
Royal Dockyard has played a vital role in
supporting the Royal Navy’s nuclear submarine
fleet through repair and refit of the vessels since
the early 1970s following construction of the
Submarine Refit Complex (SRC).
In 1993, the Secretary of State for Defence
announced that Devonport would be the single
UK site that would carry out future maintenance,
refitting and refuelling of the UK submarine fleet
including the Vanguard class submarines. To
provide the facilities for the Vanguard class
submarines and to enable continuation of use of
the submarine docks in the Submarine Refit
Complex it was necessary for the existing docks
and ancillary facilities to be upgraded and
enhanced.
It should be recognised that the Devonport site
is unique within the UK in that it accommodates
both a privately owned commercial dockyard,
owned by Devonport Management Ltd (DML)
involved in the refit, repair and maintenance of
nuclear powered submarines as well as an
operational submarine base, owned by the
Ministry of Defence (MoD).
Award of contractThe contract for the facility redevelopment
programme, known as the D154 Project, was
agreed in March 1997 between the MoD and
DML. The works essentially comprised the
upgrading of:
• 14 and 15 Docks within the Submarine
Refit Complex (which were originally
constructed in the early 1970s) to
accommodate the Swiftsure and Trafalgar
classes of submarines without precluding
the future Astute class of submarines
• 9 Dock, which was originally constructed
during the period 1896-1904, to
accommodate the Vanguard class of
submarines
• Provision of a new low level refuelling
facility to accommodate new and used
nuclear fuel
• Ancillary buildings
• A new seismically qualified railway system.
The upgrade of 9 Dock had to be completed
to accommodate HMS Vanguard by February
2002. 15 Dock’s upgrade had to be completed
by June 1999 to accommodate HMS Trenchant.
14 Dock’s upgrade had to be completed for the
defuel of HMS Valiant in May 2002. All of these
targets were achieved.
Whilst 15 Dock was being upgraded, refitting
of a nuclear submarine in 14 Dock was
undertaken and similarly, when 14 Dock was
being upgraded, 15 Dock was occupied by a
nuclear submarine undergoing refit.
Figure 2: Plan of 5 Basin
6161
To ensure the timely success of the project
required the mobilisation of diverse UK
engineering skills and this was achieved by DML
creating an alliance partnership with:
• Kellogg, Brown & Root (KBR)
(management services and design of
buildings and infrastructures)
• Rolls Royce (nuclear fuel handling
equipment and nuclear power process)
• Strachan & Henshaw Ltd (reactor access
house to facilitate refuelling, and
seismically qualified submarine support
cradles)
• BNFL Engineering Ltd (safety case
production and design of low level
refuelling facility)
• Babtie Group Ltd (civil design and building
services design).
At its peak, in August 2001, the D154 project
employed 2865 personnel on site. It is estimated
that, at various stages, more than 100 separate
contractors and 40,000 people were involved in
turning the facility proposal into timely reality.
The upgrade works had to be carried out in the
confines of an operational dockyard where
nuclear safety remained paramount.
SAFETY CASE REQUIREMENTThe design and construction of the upgraded
docks were subject to rigorous reviews and
checking due to their safety significance - each
dock effectively supported a nuclear reactor.
The site was subject to regulation by two
organisations:
• HM Nuclear Installations Inspectorate (Civil
Regulator)
• Chairman, Naval Nuclear Regulatory Panel
(MoD Regulator).
The consequences of failure were viewed from
the perspective of any design being inadequately
conceived and executed. The level of scrutiny of
designs and construction methods were,
therefore, commensurate with the consequences
of failure.
The dock structures thus fell into the highest
safety category and their designs had to be
robust against extreme loading conditions, of
which seismic loading generally proved to be the
most onerous. The docks had to withstand a
seismic design basis event (DBE) with a return
period of 10,000 years. A site-specific seismic
hazard assessment was undertaken which
determined that the magnitude of such a return
period seismic event would have a peak
horizontal ground acceleration of 0.25g with a
vertical component of two-thirds of this value. It
was also a requirement to check that there would
be no cliff-edge effects immediately beyond the
DBE and to satisfy this, the designs were checked
at DBE + 40% ie, 0.35g earthquake.
To provide the necessary ductility in the
concrete structures significant amounts of
reinforcing steel had to be utilised.
Figure 3: 14 Dock, showing floor construction
6262
PRINCIPAL QUANTITIESOverall, some 195,000 m3 of concrete has
been used within the various facilities of which
150,000 m3 were supplied from a dedicated on-
site batching plant operated by RMC Readymix
South West. The volumes of concrete and
reinforcing steel used in each of the dock
structures were as Table 1.
The low level refuelling facility which
accommodates the new and used nuclear fuel
was constructed on an island site within 5 Basin.
The island, 47m x 26m in plan, was constructed
from the rock surface of the basin floor using
mass concrete, which was placed under water
using tremie tubes to form a platform 10m above
the basin floor. 11,000 m3 of mass concrete were
required to be placed in this way. Placing
concrete under water is not new but is unusual
on such a large scale and where quality standards
are so demanding. A paper describing this work
was published in Concrete Engineering, Summer
2001 [1].
The new railway system (1.8km long) was
constructed comprising tram lines at standard
gauge set into a 0.5m thick reinforced concrete
slab overlying a 0.5m thick mass concrete
foundation. Because it is used to transfer fissile
material between the nuclear facilities it, too, had
to be seismically qualified; the first seismically
qualified railway in the UK. Some 8,100 m3 of
concrete were used in its construction.
CODES AND STANDARDSThe principal code used for the design of the
reinforced concrete structures was ACI 349-85
"Code Requirements for Nuclear Safety Related
Concrete Structures", including amendment of
March 1st 1990.
During the design and construction period, the
code underwent a significant revision and was re-
issued as ACI 349-97 in 1998 with an additional
chapter (Chapter 21) which addressed ductility
requirements. In particular, it defined additional
confinement reinforcement to be provided in the
form of ties and links.
15 Dock had already been designed to ACI
349-85 and its construction was nearing
completion by the time the new code became
available.
9 Dock’s construction had commenced but had
to have additional reinforcement fixed to meet
the requirements of ACI 349-97.
14 Dock’s design fully embodied the
requirements of ACI 349-97.
The change of the Code ensures ductility
beyond the design basis earthquake (DBE). The
designs for the 9, 14 and 15 Dock structures have
been undertaken and detailed so that they will
Facility Concrete Rebar Dowelsm3 tonnes No.
9 Dock 73,000 15,000 600
14 Dock 28,885 5,000 6,000
15 Dock 27,174 5,000 6,000
Figure 4: Low level refuelling baseconstructed using tremie concrete
Table 1
Figure 5: Nuclear transfer route(railway) under construction
6363
behave elastically to DBE plus a 40 percent
margin. The effect of the code change means
that beyond DBE plus 40 percent 9 and 14 dock
structures will behave in a ductile manner
whereas this is not assured for 15 Dock.
Early age thermal cracking was checked
against BS 8007 used in conjunction with
Department of Transport Publication BD 28/89
"Early Thermal Cracking of Concrete", 1987.
Although an American code was used for the
design, the concrete materials used were to
British Standards:
Ground granulated
blastfurnace slag BS 6699
Portland Cement BS 146 or BS 4246
Concrete Testing BS 1881
Statistical monitoring of cubes BS 5328.
The design of reinforced concrete was based
on 50N/mm2 concrete.
CONCRETE MIX DESIGN AND BATCHINGDue to restricted working areas and to avoid
significant drop heights (9 Dock is about 14.25m
deep and 14 and 15 Docks are each about
13.75m deep), pumped concrete was generally
adopted
A typical C50 concrete mix comprised:
As noted earlier, the majority of the concrete
was supplied from a dedicated concrete batching
plant operated by RMC Readymix South West,
which was established at Weston Mill Lake within
the dockyard. On occasions, it was necessary to
undertaken large pours of the order of 1,000m3
in one day. To ensure the timely supply of
concrete, as well as ensuring back-up, concrete
was also provided by RMC’s Saltash and Plymouth
depots.
Table 2
Materials Dry batch
weights (kg/m3)
Portland Cement Blue Circle - Hope P C-RM 235
GGBS Civil & Marine - Western 235
Sand Bardon Aggregates, Moorcroft 790
10mm limestone Bardon Aggregates, Moorcroft 285
20mm limestone Bardon Aggregates, Moorcroft 665
Water reducing agent Grace WRDA 2820(ml)
Water Free water/cement ratio 0.42
Note: Air entrainment was not beneficial for C50 mixes.
Figure 6: 15 Dock under construction
6464
MONITORING OF CONCRETE Quality sampling of concrete was undertaken
in accordance with the requirements of BS1881:
Part 101 at the following rates with a minimum
of three cubes per set:
Size of Pour (m3) Rate of SamplingNo. of sets of cubes
Less than 50 1 per 18 m3
Greater than 50 1 per 30 m3
Each load of concrete was subjected to a
workability test. The rejection rate was 1%.
Figure 9 indicates a typical graph for monitoring
7 and 28 day cube strengths. None of the test
results fell below the minimum strength
requirements.
During the progress of the works, there was a
period in mid 2001 when there was a noticeable
reduction in concrete strength, albeit that the
minimum specified acceptable strength was
always achieved. The problem was traced to the
use of weak cement.
Monitoring of concrete temperatures was
required when the thickness of the concrete
sections was greater than one metre or the
volume of concrete placed was greater than
20m3. A typical temperature-time graph (Figure
10) is shown for 14 Dock floor slab (2.20m
thickness) which indicates that the temperature
differential across the section was below the
specified maximum differential of 25°C.
THE DOCK STRUCTURESFigures 11, 12 and 13 show typical cross
sections through 9, 14 and 15 Docks respectively.
The design philosophy for each was different and
determined from detailed value engineering
studies which considered a range of attributes
such as nuclear safety, buildability, ease of design
justification, programme and cost.
9 DOCKThe existing mass concrete dock floor and
upper sections of the mass concrete dock walls
(which were lined with granite sets) were
demolished and a new reinforced concrete
structure provided. The floor of the dock was
provided with an extensive underfloor drainage
system which is fully accessible. The design of
the dock, and hence its safety case, is reliant on
this underfloor drainage system to avoid the
build-up of uplifting hydrostatic pressure acting
on the dock structure. 9 Dock was upgraded
during the period 1998-2001.
Figure 7: On-site batching plant sitedat Weston Mill Lake
Figure 8: 9 Dock before commencementof construction
6565
Figure 9: 14 Dock upgrade – C50/20, 15mm slump concrete. 7 & 28 day cubestrengths
Figure 10: 14 Dock upgrade. Dock floor G/L 4.2-7 concrete pourthermocouple readings
6666
Figure 11: Section through 9 Dock
Figure 12: Section through 14 Dock
6767
Figure 14: 9 Dock during construction
Figure 15: 9 Dock near end ofconstruction
15 DOCKThis was the first dock to be upgraded (1997-
1999). It was not feasible to provide an
accessible underfloor drainage system and so the
dock structure was designed for full hydrostatic
and hydrodynamic uplift forces. A total of 206
number 75mm Macalloy bar anchorages were
installed in the dock floor. Any beneficial effects
of the existing rock anchorages and underfloor
drainage system installed in the 1970s
construction were ignored.
The west and east walls were tied to the new
reinforced concrete lining of the dock by means
of dowels which were grouted in place. Cement
grout was found to be better than epoxy since it
was less problematic to mix, more user-friendly
and equally reliable, whilst the epoxy appeared to
soak into the concrete leaving little available to
bond to the dowel itself. The design took
account of the mass of the original west wall and
for the east wall it was conservatively assumed
that 50 percent of the existing reinforcement was
effective.
The design of the dowels was undertaken in
accordance with the requirements of ACI 349 for
calculating shear friction resistance. In shear
friction, the applied shear is resisted by friction
between the interfaces of old and new concrete
and the dowel action of the reinforcement across
the interface.
Figure 13: Section through 15 Dock
6868
The existing concrete surfaces were required to
be roughened to ensure that the necessary shear
friction component between the concrete
interfaces would be attained. The code required
the surface to have an amplitude of 5mm but did
not indicate at what wave length. Discussions
with the authors of the code indicated the wave
length was typically 100mm.
When trial panels were produced it was found
that shot blasting and water jetting did not
produce the desired roughness and, instead,
ended up polishing the surface due to the
aggregates and cement matrix having the same
hardness. Scabbling also proved not to be
entirely satisfactory and due to the large surfaces
to be prepared (some 2,500 m2) it would have
been both time consuming and expensive. After
many trials, the roughness was achieved by
providing grooves in both directions on a 100mm
x 100mm grid using grit blasting.
14 DOCK14 Dock was the last of the three docks to be
upgraded. Work commenced in November 2000
and was completed by December 2001. The
design principle for this dock was very similar to
that for 15 Dock, saving that the majority of rock
anchorages were installed in the east dock wall
(94 No.) with only 50 No. installed in the floor to
ensure that there would be no uplift and
consequent "chatter" of the floor during a
design basis earthquake.
An optimisation study was undertaken with
the Building Research Establishment to re-
examine the shear friction dowel arrangement
which concluded (and quantified) that the
roughening of the concrete surface need only be
local to the dowels.
With the improvement in jetting equipment
and technology between the start of 15 Dock in
1997 and 14 Dock in late 2000, further trials of
water jetting were undertaken and by careful
adjustment of pressure and flow through the
water jetting nozzles it was possible to achieve
the specified roughness of the existing concrete
surface within 14 Dock without the need to
Figure 16: Reinforcement in 15 Dock floor slab (note pockets for rock anchorages)
Figure 17: 15 Dock, showing drilling fordowels on the prepared surface
6969
provide a grid of grooves. The specification
required a clean, rough, uniform face which,
when measured over a representative portion of
the prepared face, a profile drawn on a pair of
1200mm long straight lines, forming a
horizontal/vertical cross, showed one of the
following characteristics:
• that there exists a minimum of 24
individual indentations (measured peak to
valley) of amplitude 5mm or greater
• or that over the same distance there are a
minimum of 40 individual indentations of
amplitude 4mm or greater
• or that the sum of individual indentations
3.5mm or greater in amplitude over the
1200mm length totals at least 150mm.
Checking that the required roughness profiles
were achieved was done by comb survey; see
Figure 19.
CAISSONSThe design of the dock closures (concrete
caissons) proved to be particularly challenging
since they had to:
i) Resist a drop load of 10t from a height of
+25.0m AOD. (ie, a total drop height to
bottom of caisson of about 34m);
ii) Remain stable and maintain the seal to
the dock when subject to an impact of a
20,000t vessel travelling at 0.4 knots;
Figure 18: 14 Dock, showing drilling fordowels on the prepared surface
Figure 20: 14 Dock at completion of construction
Figure 19: Comb survey
7070
iii) Maintain the seal to the dock when
subject to a reverse hydrostatic head of
6.1m in conjunction with a seismic event
which had a return period of 100 years.
The co-efficient of friction between the
underside of the caisson and the cill was
taken as zero to cater for mollusc
infestation.
Value engineering studies identified the best
option to be a multicellular reinforced concrete
structure, the principal dimensions of which are
as follows for each of the docks.
To counteract a reverse head with zero friction,
a spigot/socket shear key running across the
width of the caisson is provided. The shear key is
2.5m in width and 300mm high.
Figure 22 shows typical details of the caisson
for 14 Dock. The construction of the caissons
was carried out in an available dry dock using
conventional formwork techniques. It was the
original intention to construct the new 14 and 15
Dock caissons together in 9 Docks prior to its
upgrade works commencing. Site investigations
of the dock indicated that its floor was sound.
Problems were, however, encountered for the
14 Dock caisson which was sited further into the
dock than the 15 Dock caisson, which was close
to the entrance. Investigations revealed that the
granite floor sets embedded into the mass
concrete of the dock had separated and arched
upwards from the underlying mass concrete by
some 75mm due to hydrostatic uplift (see Figure
23). The casting of the 950mm thick base slab of
the caisson provided sufficient mass to depress
this, resulting in a bow shaped base slab. The
base slab had to be scrapped and, due to
programming requirements, arrangements had to
be made to use another dry dock for its
construction. The construction of 15 Dock
caisson proceeded as there was no separation of
the granite floor sets from the underlying mass
concrete.
Figure 21: General view of caisson
Figure 22: 14 Dock caisson
Overall Wall Thickness BaseDock Number Width Length Height External Internal thickness
of cells m m m mm mm mm
9 12 26.7 18.0 14.9 700 550 900
14/15 9 20.5 18.0 14.9 700 550 900
Table 3: Dock dimensions
7171
CONCLUDING COMMENTSThe construction of the upgraded facilities to
support the Royal Navy’s nuclear submarine fleet
within the confines of a working dockyard proved
to be challenging within the timescales set to
ensure minimal disruption to the submarine refit
programme and the need to maintain the fleet in
an operational state.
Although concrete, in itself, is a brittle
material, extensive use throughout the upgrade
works in conjunction with carefully detailed
reinforcement provides robust structures which
can behave predictably when subjected to seismic
loading.
REFERENCE
1 Concrete Engineering, Summer 2001.Construction Beneath the Waves. DaveCullen, Rob Williams and Jon Knights.
Figure 23: 9 Dock before start of construction
Figure 24: 15 Dock caisson underconstruction in 9 Dock and 14 Dockcaisson being demolished in theforeground.
Figure 25: HMS Vanguard in 9 Dock
7272
73
Andrew Bourne, over the past
21 years, has been responsible
for the concrete for many
major projects, including the
M25, Thanet Way, Bluewater
Park and now the Channel
Tunnel Rail Link, as Technical Manager for Brett
Concrete Limited. He has a first degree in
geology and a masters in environmental earth
science.
ABSTRACTThis paper discusses various aspects of
concrete supply to the Channel Tunnel Rail Link. It
concentrates on the contracts supplied in part or
whole by Brett Concrete, however the comments
are also applicable to other Projects. Supply
solutions in terms of concrete mix design, as well
as plant and equipment options are examined.
KEYWORDSChannel Tunnel Rail Link, Concrete
Specification, Oxygen and Chloride Diffusion,
Ground Granulated Blastfurnace Slag (GGBS),
Shotcrete Concrete, Polypropylene Fibres, Steel
Fibres, Concrete Segments, Partnership,
Teamwork, Communication
INTRODUCTIONThe Channel Tunnel Rail Link has been a very
visible feature of construction in the South East of
England since 1998. Since that time it has been
one of the major if not the major construction
project in Europe.
The whole project is due for completion in
2007 although Phase 1 is due to open to rail
traffic in September of this year.
The scale of the project has posed many
challenges to suppliers and contractors alike,
particularly in terms of resource provision from
the skills, personnel and materials perspectives.
The ready-mixed concrete industry has
sometimes been accused of being inflexible and
unable to respond to changing circumstances,
however the range of concrete types that have
been supplied to the Channel Tunnel Rail Link
proves the opposite and highlights that suppliers
are able to work in conjunction with contractors
and clients to satisfy the most demanding of
requirements.
Brett Concrete has now supplied concrete to
four major contracts and has worked in
partnership with contractors and client Rail Link
Engineering (RLE), as well as being suppliers
CONCRETE SUPPLY SOLUTIONS
TO THE CHANNEL TUNNEL RAIL LINK
Mr. Andrew Bourne BSc(Hons), MSc, AMICT
Brett Concrete Ltd
Figure 1: The route of the Channel Tunnel Rail Link
74
either solely on contracts or in conjunction with
other suppliers as part of a joint venture
operation.
At the present time Brett Concrete Ltd has
supplied in excess of 600,000m3 since
commencing supply in the autumn of 1998 with
the prospect of approximately another
100,000m3 to be supplied to complete current
commitments.
The approach of Brett Concrete to supply on
this overall project has encompassed several
fundamental tenets namely: exploring
partnerships, engendering a positive proactive
approach, utilising teamwork and clearly
communicating in a consistent manner with all
involved in the supply chain.
The overall length of the link is 113km of
which 25% will be in tunnel.
Phase 1: Channel Tunnel Terminal to Fawkham
Junction is 74km long and
construction commenced in 1998.
Phase 2: Ebbsfleet to St Pancras Station is
39km long and construction
commenced in 2001.
Ultimately 8 Eurostar trains per hour will use
the Rail Link travelling at speeds of up to
300km/hour.
The travel time for passengers travelling to
Paris from London will be cut by 45 minutes from
3 hours to 2 hours 15 minutes.
The budget cost for construction of the link is
£5.2 billion.
Phase 1 of the link contained 6 major civil
engineering contracts and is at the current time
some 95% complete and due to open to fare-
paying customers in September 2003.
To date, in excess of 25million man-hours have
been worked on the project. Some 11,500 piles
have been placed together with in excess of
550,000m3 of structural concrete.
The total volume of concrete supplied is
difficult to estimate but can safely said to be in
excess of 800,000m3
Construction of phase 2 began in July 2001. In
excess of 50% (20km) of this phase is in tunnel;
nominally twin bored tunnels of 7.15m internal
diameter.
Phase 1 Phase2Channel Tunnel to Fawkham Junction Fawkham Junction to St Pancras
1998 Critical design work completeCritical contracts let or firm bids receivedConstruction commences
2001 Track laying commences Critical design work completeCritical contracts let or firm bids receivedConstruction commences
2002 Track work and most fixed equipment Boring of London and Thamesinstallation completed Tunnels commencesTesting and commissioning commences
2003 Testing and commissioning complete Boring of London and ThamesPermit to use issued Tunnels commencesRailway Open
2004 Track laying commencesTunnel boring complete
2006 Track work completeTesting and commissioning commencesSt Pancras station completedFixed equipment installation complete
2007 Testing and commissioning complete Permit to use issuedRailway Open
Table 1: The CTRL Work Programme - some dates, overall statistics & interesting facts
75
The first tunnel drive on Contract 320
(Thames Tunnels) is now complete.
This phase also includes the construction of
two new international stations, at Stratford and
Ebbsfleet.
Contract 310 at Thurrock takes the railway
over the Dartford Crossing approaches and under
the Queen Elizabeth Bridge, between two of the
piers.
THE CONCRETE SPECIFICATIONThe concrete specification is extensively based
on the Department of Transport Specification for
Highway Works with contract-specific
amendments as appropriate and required.
Structural and piling concrete is essentially
Grade 40 with specific durability requirements
depending on the contract conditions. Concrete
in the ground has had a range of Class 1 to Class
4 sulfate conditions to be met.
Compliance is based on means of 4 analysis
with the familiar moving margin depending on
the standard deviation of the previous 40 results.
The overriding requirement within the
specification is for all concrete in contact with
ground or air to be in compliance with the
oxygen and chloride diffusion characteristics
detailed below and in reality it is this requirement
that has been the main driver in terms of mix
design characterisation.
The parameters within the structural concrete
specification were as follows:
• Chloride diffusion coefficient shall be less
than 1x10-12m2/s
• Oxygen diffusion coefficient shall be less
than 5x10-8m2/s.
At the commencement of the contract only
limited knowledge was available to us about the
mix parameters that would satisfy the
requirements of the specification; however,
greater knowledge as a result of testing enabled
us to significantly improve our understanding of
these parameters and to refine mix designs
accordingly.
Concrete Supplies to Phase 1Brett Concrete was involved in two major
contracts with differing supply characteristics.
Contract 430On Contract 430 (Ashford town centre to
Lenham Heath) Brett Concrete entered a formal
partnership arrangement with the contractor
(Skanska Construction UK Ltd) and the project
manager (Rail Link Engineering). This
arrangement meant that we were fully involved in
developments on the supply front and were able
to contribute fully to the decision making
process. The partnership also meant the
development of a pricing formula based on
material price and production cost declarations.
In relation to this contract, the initial
considerations concerning supply concentrated on
the provision of sustainable sources of materials.
The initial tender volumes of approximately
285,000m3 meant that the supply of marine
gravel aggregate concrete was not feasible due to
constraints on the availability of coarse
aggregates. The company sourced a sustainable
source of Glensanda granite coarse aggregate
from Foster Yeoman at the Isle of Grain, which
was used in conjunction with marine sand landed
at wharves in Kent.
Concrete mixes were optimised for
performance in conjunction with Skanska.
As a means of getting away from the usual
discussions about the workability of concrete, all
structural concrete was designed with a target
workability of 100mm and as pump mixes; a
philosophy that was readily embraced by Skanska
and RLE.
All concerned with the supply of concrete
appreciated the costs of unnecessarily rejected
concrete and the difficulty of disposing of such
material on site. To overcome this, a
comprehensive water addition procedure was
developed and used with the assistance of the
project manager and contractor for both piling
and structural concrete options.
This procedure detailed the process for initial
testing at site and the exact methodology to be
followed if water was to be added, including the
compulsory taking of extra cubes for strength
Figure 2: The Ashford Viaduct
76
testing. The procedure was distributed to all
drivers, plant staff and representatives of the
independent test house employed to carry out
the compliance testing on site. Similar
procedures, fundamentally based on the original
generic procedure, have been used on all of our
supply contracts since.
A range of mix design options were developed
and offered to the contractor and RLE to optimise
the commercial benefits available. In respect of
the piling concrete, four options of GGBS
replacement level were offered, with a range of
50%-80% GGBS being available. Each of the
different mixes attracted a different price and the
contractor was able to take advantage of the
price differences to suit particular circumstances.
In cases where piles were to be in the ground
for a number of months before further work,
higher replacement levels of GGBS were used; in
fact almost all of the piling concrete was
ultimately placed with 70% or 80% replacement.
All of the mix options were trialed through
the formal trial mix procedure prior to being
accepted as available approved options for use on
site.
Structural concrete was similarly offered with a
range of GGBS options at 50%, 60% and 70%.
This range of options had the benefit of allowing
large pours, e.g. bases and pile caps, to be placed
with a low heat option to minimise heat
generation and limit the possibility of thermal
cracking and permitted the placement of slender
elements or elements where a rapid formwork
turnaround was required to be placed with the
50% option.
This approach to mix design has had the
benefit of maximising the returns available to the
contractor and project manager and has enabled
the most economic options to be assessed and
used for each particular situation.
Consideration of the batching plant to supply
such contracts is also of prime importance; in this
case two site plants were commissioned: a
Steelfields Major 60 wide-line plant with a 3m3
capacity pan mixer, which was supplemented
with an Elba 60 Plant with a 1m3 capacity pan
mixer. In addition, the local static plant in Ashford
was upgraded so that it could support the
supplies of concrete to the project. All plants
supplying the project were equipped with the
latest computer controlled batching system,
supplied by Command Alkon.
Workability control through the pan mixer
was achieved via an ammeter fitted in the batch
cabin. Control of concrete produced through the
dry batch process was controlled visually and by
the use of truck-based workability meters. These
proved to be extremely successful.
All of the structural and piling concrete
contained admixtures and these were stored on
site in bulk double-bunded storage tanks in
volumes of up to 10,000 litres; delivery was
typically via tanker direct to site.
Haulage for the project was provided by a
contract haulier who provided a truck-base fleet
with additional support depending on the
programmed quantity of concrete to be delivered
in any period.
All trucks were equipped with regularly
calibrated (every 3 months) water meters, so that
if water needed to be added on site then the
exact amount discharged was known and could
be recorded easily.
At the end of 2002 the project was awarded
the accolade of Major Project of the Year at the
Annual British Construction Industry Awards. The
New Civil Engineer and the Daily Telegraph
sponsor these awards.
A letter received in recognition from the
Project Director noted…
"To win this award is a real achievement and
as such recognises the hard work carried out by
everyone on the contract. It is also recognition of
the quality of the work carried out and the team-
working that helped the project to be completed
on time.
Brett Concrete played a major role in this
achievement, producing and supplying quality
concrete throughout the project to enable the
works to be completed on programme,
supported by a first class team who worked
extremely closely with Skanska…"
Contract 420On Contract 420 (Boxley to Lenham Heath)
the company led a consortium that was put
together to supply both the aggregate and
concrete requirements of the project. The
company - KCML (Kent Construction Materials
Ltd) was a joint venture between Brett, Hanson
and RMC.
Brett Concrete project managed the supply
and as the liaison and contact point between the
contractor and supply consortium; taking the lead
in regular progress meetings on site as required,
we were then able to liaise with the other
suppliers as appropriate.
77
The consortium appointed a project manager
and shipper who were based on site in the main
project office. They formed the primary day-to-
day link with the contract and were able to bring
in specialist support as required.
Up to 7 supply plants were made available by
the consortium. All of the plants used marine
aggregates and we were able to justify that the
sources of aggregate available were all
demonstrably similar to QSRMC requirements.
Part of our approach was to ensure that all plants
carried the same admixtures and cementitious
materials and, where necessary, supply sources
wee changed to meet this requirement.
All of the plants were able to use a single
consistent mix design for each of the mix options
developed. Formal plant trials were carried out on
each plant for the piling and structural mix
options.
The project benefited from having the
resources of three major suppliers at their
disposal with a single point of contact to ensure
consistency of approach.
Concrete Supplies to Phase 2Supplies to the second phase of the project
have, in may ways, been more challenging than
on Phase1, essentially due to the different nature
of the concrete mixes required, over and above
the more normal structural and piling options;
these include, steel fibre-reinforced shotcrete
supplies and segment concrete.
Steel Fibre-reinforced ShotcreteSupplies were required for temporary works to
allow construction of the foundations associated
with a major bridge slide on the North Kent
railway line forming part of the Ebbsfleet
Contract 342 works.
Initial indications were that a total volume of
400m3-500m3 was required. To date in excess of
1500m3 has been supplied, essentially due to the
ground conditions encountered in the chalk spine
that has been excavated.
The mix design was essentially "Prescribed"
with 430kg/m3 CEM I, approximately 60%fines
content (marine sand), a maximum aggregate size
of 10mm and the use of crushed rock (granite)
aggregate. The mix had to be set-retarded for in
excess of 12hours with Delvocrete stabiliser and
was required to contain 40kg/m3 of steel fibres.
The supply required the installation of a
stainless steel admixture pump and special lines
as the stabiliser has a pH value of 2.
Haulage was supplied under a contract
between the contractor and the site-based
haulage subcontractor; this enabled the
contractor to have trucks available for 24 hours
per day.
Steel fibres were imported from Germany in
20 kg boxes and transferred into a dispenser,
which then "blew" them into the truck-mixer.
Other plant constraints meant that the concrete
had to be dry batched with an extended mixing
time of 30-45 minutes to ensure the elimination
of cement or fibre balls. Workability control was
also critical with a target of 175mm slump
± 25mm.
Yet again the importance of understanding a
contractor’s needs and discussing all details of the
supply on a regular basis cannot be
overemphasised.
Segment ConcreteThe volume of segment concrete on Contract
320 for the Thames Tunnels Contract is
approximately 45,000m3.
Hochtief Murphy has constructed a purpose-
built factory on site solely for the purpose of
supplying this element of the contract. It consists
of a single carousel system, which is capable of
producing up to 140 segments per day.
The specification for the segment concrete
contains requirements in respect of the following
parameters: compressive strength, tensile
strength, first-crack flexural strength and residual
flexural strength. Additionally a measurement of
the distribution of steel fibres was also included.
In addition to steel fibres the mix also was
Figure 3: Concrete segment for use inthe Thames Tunnel
78
designed to contain monofilament polypropylene
fibres for fire protection purposes.
As ever with a precast operation, efficiency in
the turnaround of moulds is paramount and the
de-moulding strength of 18N/mm2 was required
to be achieved at 6-hours or earlier age (albeit
after steam curing). The use of hot water at
55°C, when necessary, has facilitated stripping of
moulds at 5 hours age; the strength being
assessed from cubes passed through the curing
process alongside the segment moulds.
Target workability for the mix was required to
be in the range of 20-30mm slump, this being to
facilitate finishing of the extrados of the
segments prior to steam curing, which typically
commences at approximately 1 hour after the
mould is filled with concrete and vibrated.
Ground conditions necessitated compliance
with Class 4 sulfate conditions and hence the use
of a PFA blended cement to achieve the early
strength, stripping times and specification
durability requirements.
Brett Concrete invested in fibre handling and
transfer devices to facilitate the loading of the
steel and polypropylene fibres; both devices were
linked to the plant’s batch computer to ensure
consistent accuracy of weighing and autographic
recording of all materials in each batch of
concrete. We further arranged for bulk deliveries
of steel fibres in 24 tonne containerised deliveries
from Germany in 400kg bags and for the bulk
delivery of polypropylene fibres to be in 250kg
size boxes to facilitate loading into the bulk
dispenser.
The whole supply operation depends greatly
on a proactive approach with suppliers, customer
and project manager alike. There is no doubt that
the process has been time consuming and often
frustrating; however, the successful placement of
segments in the tunnel certainly brings sufficient
reward to those involved.
The compliance requirements for this mix are
onerous and influenced by many factors beyond
the control of the concrete producer. These
factors have been discussed in two recent papers
published in Concrete magazine.
By developing an understanding of the
difficulties involved in the production of the
concrete for this critical phase of the project we
were able to negotiate a position whereby the
risk for the factors beyond the control of the
concrete producer were accepted by the
contractor; another example of a close working
relationship.
CONCLUSIONSThe Channel Tunnel Rail Link has been a major
feature on the construction landscape since 1998.
The project has been demanding for concrete
suppliers and the approach that has been
employed to meet the challenges has required
the application of a flexible approach to
traditional and new methods of work, embracing
teamwork and partnering principles and
techniques as well as continued close-knit
communication between supplier, contractor and
client.
ACKNOWLEDGEMENTSThe author would like to express his
appreciation to members of the Rail Link
Engineering staff in particular Peter Shuttleworth
for his helpful and thoughtful assistance
throughout the length of the contract.
In addition, he also thanks the publicity
department of Union Railways for permission to
see the information included in this paper.
FURTHER READING
1. BOURNE, A. Precast segments on theThames tunnels, CONCRETE, April 2002Vol.36 No.4, pp.32-33.
7979
Ross Dimmock is Technical
Director of Master Builders
Technologies’ International
Underground Construction
Division. His main activities are
the development of permanent
sprayed concrete linings for use in underground
structures. The focus of his company’s business is
on providing the industry with the whole system
from equipment to waterproofing and fire
protection systems. Ross is also the Technical
Chairman of the EFNARC (European Federation of
Producers and Applicators of Specialist Products
for Structures) European Technical Committee for
Sprayed Concrete and is involved in the EFNARC
Fire Protection for Tunnel Linings team.
ABSTRACTThe paper gives an overview of the
improvements in sprayed concrete technology
that have occurred rapidly over the last 10 years,
allowing the industry to consider sprayed
concrete as a "permanent" structural support for
urban tunnels. Consequently, its implementation
as a support system has increased dramatically
worldwide. The developments have been focused
on attaining high quality, homogeneous,
environmentally safe sprayed concrete via the
adoption of the wet-mix process using robotic
spraying techniques coupled with advances in
sprayed concrete mixture proportions, particularly
operator- and structure-friendly liquid
accelerators.
As highlighted in the paper, emphasis within
the industry now needs to be given to a more
holistic approach to creating durable sprayed
concrete structures using the modern application
systems described. With a construction method
whose success is fully dependent on human
influence, the paper provides an overview of
critical elements such as contractor and designer
experience and site control systems. Furthermore,
the need for modern, up-to-date specifications to
reflect current technology are suggested, coupled
with the industry-wide need for relevant
nozzleman training and recognised certification
schemes.
KEYWORDSAlkali-free accelerators, Durability, Fibre
reinforcement, Fire protection, Permanent,
Specifications, Sprayed concrete, Waterproofing.
MODERN SPRAYED CONCRETE FOR URBAN TUNNELS
Mr. Ross Dimmock BSc(Hons)
Master Builders Technologies
Figure 1: Factors that significantly determine the durability of a sprayed concrete structure
8080
INTRODUCTIONThe durability of a tunnel lining should be such
that the lining remains safe and serviceable for
the designed life, without the need for a high
degree of maintenance expenditure. To attain
durability, the designer needs to assess the
exposure environment of the structure during
both construction and operation, as structural
degradation normally occurs with unforeseen
environmental changes.
With this in mind, the term durability may be
related to structures that are designed to resist
loads during a construction period before a
secondary lining is placed. However, more often,
with the use of sprayed concrete for permanent
single shell linings, the durability of the concrete
should consider a design life of 100 years or
more. It is this latter case that is the focus of the
presentation and paper.
As can be seen from Figure 1, the durability of
a sprayed concrete structure is established via a
total of many possible parameters. In sprayed
concrete construction, not only correct concrete
mixture proportions and cover to reinforcement
as with traditional cast concrete is sufficient. The
main reason behind this is that the material is
spray applied, and consequently the quality is
significantly reliant on human skills and spray
equipment performance. Some of the main
durability issues listed in Figure 1 are briefly
discussed in this paper.
BUILDABLE DESIGNSWith respect to existing concrete tunnel
structures, the major durability problems are not
directly related to the concrete itself, but more
often to the corrosion of steel reinforcement
elements that have been insufficiently protected
against water ingress or humidity. Tunnels
constructed with permanent sprayed concrete
create other durability concerns, particularly in
terms of providing the required material
properties such as compaction, and with the
unknown stability concerns associated with the
necessary amount of admixtures used for modern
wet-mix sprayed concrete application methods.
To address the durability requirements, a
holistic approach to the design and construction
of durable sprayed concrete tunnel linings is
required. In essence, the sprayed concrete lining
method is heavily reliant on human competence
during construction and therefore the design
should reflect this by considering the
"buildability" of tunnels using sprayed concrete.
Designing "buildability" ensures that safety and
durability critical elements are either designed
out, or simplified for ease of construction on the
job site.
To facilitate this goal, design teams should be
aware of the limitations of modern sprayed
concrete construction processes and be familiar
with the likely material performance. They also
should have a strong site presence to ensure that
the critical safety and durability features are
constructed in accordance with their design.
SPECIFICATIONS AND GUIDANCEUnfortunately, too often in the sprayed
concrete industry, specifications and guidance
documents tend to be "cut and pasted" into new
contracts year after year, without much in depth
research as to the current advanced state of the
sprayed concrete industry. The recent increase in
wet-mix sprayed concrete has provided an
opportunity to re-examine the "old"
specifications and now new documents are
emerging which reflect the current state-of-the-
art in sprayed concrete technology.
These modern sprayed concrete specifications
now specify permanent, durable sprayed concrete
for the first time as a construction material. They
address the issues of achieving a quality
controlled modern mixture proportions, providing
guidance on promoting and testing for durability
and effective execution of the spraying processes.
As an example, the new European Specification
for Sprayed Concrete (1996) produced by
EFNARC, provides comprehensive systems to
attain permanent sprayed concrete. This
specification has been the basis for new project-
specific specifications worldwide and for the new
European Norm Sprayed Concrete Specification.
Furthermore, the EFNARC Sprayed Concrete
Specification is the first document to address
issues such as national nozzleman training and
accreditation for high capacity, mechanised
robotic spraying. The Specification also sets out
systems for contractors and specifiers/designers to
consider, prior to construction, the sprayed
concrete structures they are to build, so as to
adapt the sprayed concrete system and mixture
proportions accordingly.
CONSTRUCTION COMPETENCEThe construction team should be made aware
of the design elements that are key factors in
determining the safety and durability of the
8181
tunnel structure. To ensure that the quality of the
concrete lining is achieved, quality review systems
should be adequate to control the production. It
is of paramount importance that the
communication link between design and
construction teams should be maintained from
pre-design stage to project completion so that
the above processes are promoted.
Nozzlemen should have previous experience in
the application of sprayed concrete and have
knowledge of the sprayed concrete process to be
adopted on the specific project. It is
recommended that an operator be able to
demonstrate his experience either as a holder of a
certificate from previous work, or required to
demonstrate his competence in a non-works
location.
Prevailing regulations place added
requirements on the people doing the spraying
work to have technical knowledge of concrete,
particularly with sprayed concrete. Present
requirements have led to better training of the
personnel involved. The result of this is an
improved quality of work. The number of special
contractors who are working with sprayed
concrete has increased over the last few years,
which has globally raised the quality of
application.
SPRAYED CONCRETE MIXTURE PROPORTIONS
The main factor that determines the durability of
a concrete structure is achieving a low permeability,
which reduces the ingress of potentially deleterious
substances, thereby inhibiting chemical reactions
such as those involving the cement and thereby
preventing chemical changes. Low permeability is
achieved in sprayed concrete applications by the
following means:
• A well graded material suitable for the
sprayed concrete application system in
terms of pumpability, workability, rebound
reduction and good compaction. All
aggregates should be checked for alkali-
silica reaction
• Adequate cementitious content, typically
400 to 500kg/m3. The cement content
should not be less than 350kg/m3
• Low, pre-defined W/C less than 0.45,
achieved using water reducing agents /
superplasticisers. Modern superplasticisers,
referred to as "hyperplasticisers", can
provide W/C between 0.35 and 0.4, whilst
maintaining a slump of 200mm
• Use of pozzolanic materials such as silica
fume and fly ash. Silica fume has a
definite filler effect in that it is believed to
distribute the hydration products in a
more homogeneous fashion in the
available space. This leads to a concrete
with reduced permeability, increased
sulphate resistance and improved freezing
and thawing durability
• Control of micro-cracking to 0.2mm by
fibre reinforcement instead of mesh,
thereby allowing autogenous healing
• Controlled, low dosages of alkali-free
accelerators for reduced reduction in final
strength compared to the base mixture,
significantly reduced leachates, reduced
rebound and dust, and most importantly,
to provide safe working conditions
• Hydration control admixtures to prevent
premature hydration of the concrete
mixture before it is applied to the
substrate. Pre-hydration may cause
significant deleterious effects to the
hardened physical properties of the
sprayed concrete, such as low strengths
and densities, and increased permeability.
NEW "ALKALI-FREE" ACCELERATING ADMIXTURES
Of late, safety and ecological concerns have
become dominant in the sprayed concrete
accelerator market, and applicators have started
to be reluctant to apply aggressive products. In
addition, requirements for strength and durability
of concrete structures are increasing. Strength
loss or leaching effects suspected to be caused by
strong alkaline accelerators (aluminates) has
forced our industry to provide answers and to
develop products with better performances.
Due to their complex chemistry, alkali-free
accelerators are legitimately more expensive than
traditional accelerators. However, accelerator
prices have very little influence on the total cost
of in-place sprayed concrete. Of much larger
consequence are the time and rebound savings
achieved, the enhancement of the quality,
durability and, most importantly, the provision of
a safe working environment.
The increasing demand for accelerators for
sprayed concrete termed alkali-free always
contains one or more of the following issues:
• Reduction of risk of alkali-aggregate
reaction, by removing the alkali content
8282
arising from the use of the common
caustic aluminate based accelerators
• Improvement of working safety by
reduced aggressiveness of the accelerator
in order to avoid skin burns, loss of
eyesight and respiratory health problems.
The typical pH of alkali-free accelerators is
between 2.5 and 4 (skin is pH5.5)
• Environmental protection by reducing the
amount of aggressive leachates to the
ground water, from both the in situ
sprayed concrete and rebound material
deposited as landfill
• Reduced difference between the base
concrete mixture and sprayed concrete
final strength compared to older style
aluminate and waterglass accelerators that
typically varied between 15 and 50%
dosage.
The focus within different markets, regarding
the above points, is variable. Where most sprayed
concrete is used for primary lining (in design
considered temporary and not load bearing), the
second and third points are the most important.
When sprayed concrete is used for permanent
structures, the first and last items become equally
important.
As a result of the above demands, in excess of
25,000 tonnes of alkali-free accelerator has been
used worldwide since 1995. From MBT’s
perspective, this accelerator type is considered
state-of-the-art, and as a result is currently
producing it in 18 countries.
In terms of sulphate resistance, a number of
tests have been carried out by SINTEF, Norway
and the results are summarised in Table 1, with
"High" denoting excellent sulphate resistance.
A number of comments can be made
regarding these results:
• Alkali-free accelerators can be used to
produce sulphate resisting sprayed
concrete up to dosages of 10%
• Alkali-free accelerators perform better
than modified sodium silicate accelerators
with normal Portland cements
• The use of 6% silica fume provides
comparable sulphate resistance with
normal Portland cement as with sulphate
resisting cement (SR). This is important as
it is preferential to use normal Portland
cement rather than SR cement in sprayed
concrete due to the faster setting and
early strength development
• The lower the water-cement ratio, the
higher the sulphate resisting performance.
It is recommended to have a W/C below
0.45, and preferably with the aid of new
hyperplasticisers, attain a W/C of less
than 0.4.
APPLICATION REQUIREMENTSQuite often, the benefits of well-engineered
mixture proportions to achieve the durability
requirements of the structure are negated by
poor application processes.
It is strongly recommended that only the wet-
mix sprayed concrete process be used for the
construction of durable linings. The wet-mix
process is currently the only viable method to
achieve quality, particularly with respect to
controlling the water cement ratio that is vital for
concrete durability and long term strength.
Additionally, the wet-mix process has also
demonstrated significant economical benefits
over the dry-mix process.
Table 1: Sulphate resistance of sprayed concrete (SINTEF, 1999)
Cement Type OPC OPC OPC OPC SR
Aggregates: alkali-silica reactivity reactive reactive non-reactive non-reactive slightly reactive
Microsilica 0% 6% 0% 6% 0% and 6%
w/c ratio 0.45 0.47 0.52 0.48 0.45 to 0.48
Accelerator & Dosage
Modified sodium silicate 5% moderate high none high high
Modified sodium silicate 10% none high none high high
alkali-free 5% high high none high high
alkali-free 10% moderate high none high high
none (no resistance) : greater than 0.1% expansionmoderate resistance : between 0.05% and 0.1% expansionhigh resistance : less than 0.05% expansion
8383
Many of the factors that cause high rebound
values, poor compaction, loss in structural
performance and hence increased project costs
are attributed to the performance of the
nozzleman, particularly that of the hand held
nozzle systems using the dry-mix process.
The advent of modern admixtures applied to
wet-mix sprayed concrete has reduced these
problems significantly by enabling the placed
concrete to be initially plastic in nature. For some
minutes after application, new sprayed concrete
can be absorbed and compacted more readily
than very fast, or flash setting materials. This
approach reduces rebound significantly and
allows steel encapsulation to be achieved more
readily.
Problems relating to nozzle angle, nozzle
distance and achieving the correct compaction
with the required air volume and pressure have
been facilitated by the use of robotic spraying
manipulators, particularly in large diameter
tunnels. The MEYCO Robojet spraying
manipulator is controlled by a remote-control
joystick by the nozzleman to allow the nozzle to
be spraying at the correct distance and angle at
all times (Figure 2). This, coupled with the
required air volume and pressure, ensures low
rebound and well-compacted sprayed concrete.
Good surface finishes can be achieved by
selecting the automatic oscillating movement of
the nozzle mode as indicated in Figure 2.
STEEL AND HIGH PERFORMANCEPOLYMER FIBRE REINFORCEMENT
From experience, water ingress is associated
with sections of the sprayed concrete lining that
contain large diameter steel reinforcement, such
as lattice girders, lattice girder connection bars,
and excessive overlaps of steel reinforcement.
Therefore the emphasis should be to minimise the
quantity of steel reinforcement by:
• Optimisation of the tunnel cross-sectional
profile to reduce moment influences
• Increasing the thickness of the tunnel
lining to maintain the line of thrust to the
middle third of the concrete section
• Where structurally possible, using the
more favourable option of fibre
reinforcement.
Steel fibres have been used successfully in
permanent sprayed concrete tunnel projects to
reduce cracking widths to 0.2mm to produce
watertight, durable tunnel linings. The advantage
over conventional anti-crack reinforcement is that
the fibres are randomly distributed and
discontinuous throughout the entire tunnel lining
structure, allowing uniform reinforcement that
evenly re-distributes tensile loads, producing a
greater quantity of uniformly distributed
microcracks of limited depth. Steel fibres also
transforms the concrete from a brittle into a
highly ductile material, giving the lining a higher
load bearing capacity, post initial cracking
through the effective redistribution of load,
thereby increasing the safety of the structure
during construction. More recently, HPP fibres
have been introduced, having the added benefit
of being corrosion resistant, whilst offering similar
performance to steel fibres.
With all fibre-based concrete mixtures, care
should be taken to match the fibre strength to
the tensile strength of the concrete, as high
strength concrete with normal tensile strength
fibres may still produce a brittle material. As
fibres are added during the batching process, this
removes the timely operation of welded mesh
installation from the construction cycle.
If conventional reinforcement is required for
structural purposes, then the reinforcement
Figure 2: MEYCO Robojet spraying manipultor - correct angle and distance forreduction in rebound and enhanced quality
8484
should be designed with the installation method
in mind, and be evenly distributed. The
reinforcement arrangement should be such that
the nozzleman can facilitate full encapsulation of
the bars, and the construction sequence can
allow sequential installation of the reinforcement.
Under no circumstances should sprayed concrete
be applied through full reinforcement cages or
excessive overlaps of mesh. Attention should also
be paid to avoiding flash sets from high dosages
of accelerating admixtures, as this inhibits the
fresh concrete from behaving plastically and
moving around reinforcement immediately after
spraying.
ACHIEVING WATERTIGHTNESS VIA SPRAYABLE MEMBRANES
With the advent of permanent sprayed
concrete linings, there has also been a request by
the industry to provide watertight sprayed
concrete. This is of particular importance with
public access tunnels and highway tunnels that
are exposed to freezing conditions during winter
months, and also electrified rail tunnels. It has
been shown that most permanent sprayed
concrete exhibits an extremely low permeability
(typically 1 x 10-14 m/s), however, water ingress
tends to still occur at construction joints, at
locations of embedded steel and rockbolts.
Traditionally, polymer sheet membranes have
been used, where the system has been shown to
be sensitive to the quality of heat sealed joints
and tunnel geometry, particularly at junctions.
Furthermore, when sheet membranes have been
installed with an inner lining of sprayed concrete,
the following adverse conditions can occur:
• As the sheet membranes are point fixed,
sprayed inner linings may not to be in
intimate contact via the membrane to the
substrate. This may lead to asymmetrical
loading of the tunnel lining
• To aid the build of sprayed concrete onto
sheet membranes, a layer of welded mesh
is used. Due to the sheet membrane being
point fixed, the quality of sprayed
concrete between the mesh and the sheet
membrane is often inferior and may lead
to durability concerns
• The bond strength between sprayed
concrete inner lining and sheet membrane
is inadequate and leads to potential de-
bonding, particularly in the crown sections
of the tunnel profile. This is a detrimental
effect when constructing monolithic
structures
• As there is little bond strength at the
concrete/sheet membrane interface, any
ground water will migrate in an unlimited
manner. Should the membrane be
breached, the ground water will inevitably
seep into the inside tunnel surface at any
lining construction joint or crack over a
considerable length of tunnel lining.
Figure 3: Spray applied waterproofing membrane for complex undergroundstructures
85
To combat these problems, MBT have
developed a water based polymer sprayable
membrane, Masterseal® 340F.
This sprayable membrane has excellent double-
sided bond strength (0.8 to 1.3 MPa), allowing it
to be used in composite structures, and thereby
effectively preventing any potential ground water
paths on both membrane/concrete interfaces
being created. Masterseal® 340F also has an
elasticity of 80 to 140% over a wide range of
temperatures allowing it to bridge any cracks that
may occur in the concrete structure. Being a
water-based dispersion with no hazardous
components, it is safe to handle and apply in
confined spaces. The product can be sprayed
using a screw pump and requires two operatives
to apply up to 50m2/h, particularly in the most
complex of tunnel geometries, where sheet
membranes have always demonstrated their
limitation, as shown in Figure 3.
As presented in Figure 3, in single shell lining
applications, Masterseal® 340F is applied after the
first layer of permanent fibre-reinforced sprayed
concrete, where the sprayed surface should be as
regular as possible to allow an economical
application of membrane 5 to 8mm thick (all
fibres are covered also). A second layer of
permanent steel fibre reinforced sprayed concrete
can then be applied to the inside. As the bond
strength between the Masterseal® 340F and the
two layers of permanent sprayed concrete is
about 1MPa, the structure can act monolithically,
with the sprayable membrane resisting up to
15bar. As this application considers no water
drainage, the second layer of sprayed concrete
must be designed to resist any potential
hydrostatic load over the life of the structure.
PROVISION OF FIRE PROTECTIONIn recent years, the tunnelling industry has
been shocked by the rapid devastation, and in
some cases loss of life, caused by very notable
fires, such as the Channel Tunnel, Mont Blanc
and more recently, tunnels in Austria.
Whilst systems are being developed to further
secure the safety arrangements of passengers and
operatives of tunnels during tunnel fires, clients
are increasingly requesting that structural tunnel
linings remain fire damage resistant.
Currently, a common form of fire protection in
new-build concrete lined tunnels is through
modification of the concrete mixture proportions
with the addition of monofilament polypropylene
fibres in both precast and in situ concrete linings.
This approach offers defences against explosive
spalling but may not offer adequate thermal
protection in high energy fire scenarios, such as
with petrol tanker fires, and, consequently, steel
reinforced concrete sections will have limited, if
not no, tensile strength during such fires, leading
to collapse.
Master Builders Technologies has addressed
the issue by developing a relatively thin (30 to
50mm) thermal barrier system referred to as
MEYCO® Fix Fireshield 1350. The philosophy
behind MEYCO® Fix Fireshield 1350 is to provide
a passive fire-protective layer to any underground
85
Figure 4: Sprayed application of passive fire protection layer to structural sprayed orcast concrete tunnel lining
86
structure using a rapid robotic spray application
process, as indicated in Figure 4. Furthermore, the
protective layer should be as thin as possible to
reduce effects on the required operating
structural envelope. If attacked by fire, the
underlying structural concrete would be protected
for temperatures up to 1350ºC. Repair is simply
completed by local removal of the damaged
protection layer and re-sprayed with a new
application.
The performance of such passive fire
protection systems is currently evaluated at the
TNO Test Centre for Fire Research, Delft,
Netherlands. To simulate a petrol tanker fire in a
tunnel, the Dutch RWS fire curve is currently
specified for testing fire protection systems for
underground structures. Apart from the
temperature being above 1200ºC for two hours
and a maximum temperature of 1350ºC, the test
also puts the system under immediate thermal
shock. See Figure 5 for time-temperature curve of
furnace temperature and corresponding curve for
interface temperature between fire protection
and structural concrete sample.
Testing of MEYCO® Fix Fireshield 1350 at the
TNO Centre has shown excellent results with a
layer thickness of between 40 and 55mm,
producing very low interface temperatures of
below 225ºC at 50mm thickness and below
400ºC at 40mm thickness. No spalling was
observed on any of the test panels. TNO consider
a temperature of 225ºC as the most onerous
maximum permissible interface temperature
requirement to date.
CONCLUSIONSTo achieve durable sprayed concrete linings,
the development of the concrete mixture
proportions is but one facet that needs to be
accomplished. The production of durable sprayed
concrete is significantly reliant on human skills
during spraying and on equipment that is fit for
the purpose.
The designer also has a key role to play. The
important issues in this case are to understand
the sprayed concrete application process and not
to over-specify material properties. The key to
achieving durability is through "buildable" by
keeping details as simple as possible.
Wet-mix sprayed concrete applied using
modern, high performance, environmentally safe
admixtures and equipment equips the tunnel
industry with an economical tool to construct
permanent, durable single-shell linings. The
construction process has become highly
automated thereby significantly reducing the
degree of human influence that has, in the past,
prevented clients from considering sprayed
concrete as a permanent support.
Modern sprayed concrete specifications now
address the issues of achieving quality controlled
modern mixture proportions, providing guidance
on promoting durability and effective execution
of the spraying processes. As an example, the
new European Specification for Sprayed Concrete
(1996) produced by EFNARC, provides
comprehensive systems to attain permanent
sprayed concrete.
With the increased use of durable sprayed
concrete linings, new technologies to promote
and maintain their use have entered the market
recently. These systems enhance watertightness
and provide high performance fire resistance.
Further implementation of durable sprayed
concrete for tunnels and other civil engineering
structures is increasing, with a marked change
during the mid 1990s. This trend is set to increase
further as design and construction teams become
more familiar with modern sprayed concrete
technology, and the durable concrete that can be
produced.
FURTHER READING
1. ALDRIAN, W., MELBYE, T. & DIMMOCK, R.2000. "Wet sprayed concrete –Achievements and further work"; FelsbauPublication. Vol 18, No.6 Novr 2000. Pp16-23.
2. DIMMOCK, R. & GARSHOL, K.F. 2002."Robotic application of high performancethermal barriers in tunnel linings"; Concretejournal published by the Concrete Society,UK. April 2002, Vol 36, No4, pp12-13.
3. EFNARC. 1996. The European Specificationfor sprayed concrete. Published by EFNARC,Hampshire, UK.
4. MELBYE, T.A., DIMMOCK, R. & GARSHOL,K.F. 2001. Sprayed Concrete for RockSupport. 9th edition. Published by MBTUGC International. Switzerland, December2001.
5. KORTEKAAS & VAN DEN BERG 2001."Determination of the contribution of acoating MEYCOFix Fireshield 1350 to thefire resistance of tunnels". Published byTNO Building and Concrete Research,Centre for Fire Research. Report No 2001-CVB-R03026, March 2001.
86
The Concrete Centre has been established tochampion the benefits of concrete construction.
Formed by the major UK cement and concretecompanies, with the aim of helping designers and
constructors to get the best out of this unique material,The Concrete Centre provides a vital new resource to the
£5 billion concrete sector.
Working closely with industry partners, specifiers, contractors, clientsand the Government, The Concrete Centre’s prime goals are to
communicate the benefits of concrete across all sectors and to make itsbusiness case in new and robust ways.
For more information on The Concrete Centre, and to find out how it can help you to better design and construct in
concrete, visit www.concretecentre.com or call 01344 762986
INFORMATION • EDUCATION • TRAINING • RESEARCH MANAGEMENT • MARKET DEVELOPMENT • PRODUCT INNOVATION
THE INSTITUTE OF CONCRETE TECHNOLOGY
A web-based course is due to be available from June 2004.For details, contact Dr J B Newman, Imperial College, London, SW7 2BU
E-mail: [email protected]
Residential courses are held in the UK, Ireland and South Africa.
ADVANCED CONCRETE TECHNOLOGY DIPLOMA COURSES
The ACT Diploma is the principal entry qualificationfor Membership of the Institute.
For further details contact: ICT Secretariat, P.O. Box 7827, Crowthorne, Berks. RG45 6FRTel: +44(0)1344 752 096 E-mail [email protected]
O S C R E T E
O S C R E T E
• range of admixtures for concrete and mortar
• Water repellents• Super plasticisers• Accelerators• Plasticisers/process aids for semi dry production
• Retarders• Air entrainers• Mould release agents
is the brand name of ADMIXTURES manufactured and distributed by:
Christeyns UK LtdRutland Street, Bradford, West Yorkshire, BD4 7EA, UKTel: 01274 393286 Fax: 01274 309143
The
FM 09569
Densities between 2400kg/m3 and 5950kg/m3
achievable with the versatility of our product
range. Suitable applications include:-
Coastal Protection
Counterweights
Pipecoating
Offshore Ballasting
Scour Protection
Ground Stabilisation
Worldwide group, Minelco, has recently acquired the Fillers & MineralsDivision of the Frank & Schulte Group. This includes UK basedcompanies Fergusson Wild Ltd and Quay Minerals Ltd, which in Jan2004, will unite with Minelco Ltd to become Minelco Minerals. Thisenables Minelco to offer a wide range of quality minerals to bettermeet the specialised needs of the construction industry.
High Density Concrete & Ballast
MagnaDense
minerals customised for industry
Tel 01673 861951
Fax 01673 862707
e-mail: [email protected]
www.minelco.com
Full technical service is available to all customers offering advice onaggregate suitability, mix design and specific concrete requirements.
MAKING THE FUTURE TAKE SHAPE.Few products are helping to shape the future of Britain more so thanthose from Lafarge Cement UK. Thinkof some of the highest profile civilprojects in the UK and you’ll find thatour bulk supplied cement has turnedthem into stunning reality... theFalkirk Wheel,
as seen in the illustration above, the Canary Wharf development, theChannel Tunnel, the Tay Bridge andCardiff’s Millennium Stadium. Our most powerful ingredient is 100years of leadership in cementtechnology. Rely on our dedicatedtechnical sales team
and world-beating products to helpshape your ideas for the nextcentury.
Need technical advice?Call 0870 600 0203
www.lafargecement.co.uk The cement technology leaders
A leading companyand a leadingbrand
GROUP PLC
TELEPHONE: 01707 364500 WEBSITE: http://www.john-doyle.co.uk
CONSTRUCTION
BLYTHEWOODPLANT HIRE
MG Associates is a small consultancy dealingwith the investigation and testing of buildingsand structures, advice and project managementand supervision of repairs.
Non Destructive Testing
Forensic Investigations
Laboratory Testing
Fire Damage Appraisal
Abseiling Surveys
Core Drilling and sampling
Training in Concrete, Inspection and Repair.
MG Associates Construction Consultancy Ltd.11 The Quadrant, Manor Park CrescentEdgware, Middlesex. HA8 7LUTel: +44 (0)20 8381 1429Fax: +44 (0)20 8381 1425E-Mail: [email protected]: www.concrete-testing.com
MG AssociatesTHE INSTITUTE OF
CONCRETE TECHNOLOGY WOULD LIKE TO THANK
ALL THE COMPANIES AND ORGANISATIONS
WHO HAVE ADVERTISED IN THIS YEARBOOK
PLEASE SUPPORT THEM.
DATE FOR YOUR DIARY
THE ICT 2004 CONVENTION will be held at the
RENAISSANCE HOTELDERBY/NOTTINGHAMON 22-24 MARCH 2004
Ready Mixed ConcreteWhich third party scheme will yourely on for EN206-1 certification?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 together industrybest practice and customer requirements in a scheme designed to meet theneeds of all sectors of the construction industry.
Demonstrate product conformity with the most widely specified and the only UK Certification Body dedicated to the supply of ready mixed concrete
To find out more about the benefits of QSRMC certification contact:
The Quality Scheme for Ready Mixed Concrete, 3 High Street, Hampton. TW12 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 system is thatthe system, the relationship between members of the family and the functioning of the system areapproved and regularly audited by a third party certification body that has expertise in concretetechnology and production." (CEN REPORT CR 13901 – ‘The use of the concept of concrete families forthe production and conformity control of concrete’)
One designed specifically to meet the requirements of concreteproducers, purchasers and specifiers?
Adding Value to Concrete
MBT Admixtures, Albany House, Swinton Hall Road, Swinton, Manchester M27 4DT
Tel: +44 (0) 161 794 7411 Fax: +44 (0) 161 727 8881
e-mail: [email protected] www.mbtfeb.co.uk
Our daily challenge is to push the limits to find unusual solutions. We do it by applying our innovation
potential and our understanding of the market. Using this combination, we get more out of concrete.
We are constantly creating new and better properties for concrete, expanding its field of application.
That means added value for everyone in the project.
Limits are ourChallenge.
87
ADVANCED CONCRETE TECHNOLOGY DIPLOMA:
SUMMARIES OF PROJECT REPORTS 2002
The project reports are an integral and important part of the ACT Diploma.
The purpose of the projects is to show that the candidates can think about a topic or problem in alogical and disciplined way. The project normally spans some six months. Significant advances can bemade and several of the projects have evolved into research programmes in their own right.
Summaries of a selection of projects submitted during the 2002 - 2003 course are given in thefollowing pages.
PROJECT TITLE: AUTHOR:
NON-DESTRUCTIVE TESTING FOR CRACKING AND DE-BONDING Jannes BesterOF SURFACE REPAIRS ON CONCRETE STRUCTURES
THE EFFECT THAT MANUFACTURED SAND AND COREX SLAG HAS ON THE Jaco CokartWORKABILITY, WATER DEMAND, COMPRESSIVE STRENGTH AND THE COST OF READYMIX CONCRETE
THE INFLUENCE OF SAND GRADING ON THE AIR VOID SYSTEM OF Harry CorporaalFRESH MASONRY MORTAR
THE SENSITIVITY OF THE MICRO-CONCRETE HALF-SLUMP TEST, Santie GouwsAS INFLUENCED BY CEMENT CHARACTERISTICS
THE SALT SCALING RESISTANCE OF SELF-COMPACTING CONCRETE Esa Heikkilä
INFLUENCE OF TEST AGGREGATE ON THE COMPRESSIVE STRENGTH OF Kevin MacleodPORTLAND AND PORTLAND FLYASH CEMENTS
ALKALI-SILICA REACTION IN KWA ZULU NATAL Wayne Milligan
THE EFFECTS OF FINER GROUND SLAG ON WORKABILITY Robin Page
A PRELIMINARY INVESTIGATION INTO THE EFFECT OF DRUM COLOUR Zoë PerksON CERTAIN FRESH AND HARDENED PROPERTIES OF CONCRETE
THE FEASIBILITY OF USING RHEOLOGICAL TEST METHODS TO DEVELOP Christopher RigbyMIX DESIGNS FOR FLOWING SELF-COMPACTING CONCRETE
SELF-COMPACTING CONCRETE AT REDUCED LEVELS OF POWDER CONTENT Andrew Rogers
THE INFLUENCE OF BINDER TYPE ON EARLY AGE CRACKING IN CONCRETE Ebrahim Yusuf Seedat
THE EVALUATION OF NEW GENERATION SOUTH AFRICAN CEMENT Clive SofianosEXTENDERS: A CONTRACTORS VIEWPOINT
BOND STRENGTH ACROSS JOINTS IN A ROLLER COMPACTED Yvette StaplesCONCRETE DAM
POTENTIAL USE OF SANDSTONE AND/OR NATURAL SAND AS SOURCE OF Tente TenteFINE AGGREGATES FOR CONCRETE PRODUCTION AT FUTURE MASHAI DAM
A full list of earlier ACT projects, dating back to 1971 when the individual project was introduced as 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 Concrete Information Ltd (CIL) Libraryand these can be made available on loan. Subscribers to the CIL’s information service, Concquest, may obtaincopies on loan, free of charge. Requests should be addressed to: Concrete Information Ltd, Century House,Telford Avenue, Crowthorne, Berkshire RG45 6YS.
ICT members may address their requests to: The Executive Officer, Institute of Concrete Technology, P.O. Box 7827,Crowthorne, Berkshire RG45 6FR. Copies can then be obtained from CIL free of charge.
8888
SUMMARYIn South Africa a shortage of good quality
sand, stockpiling of crusher fines and concernsabout alkali silica reaction have led ready mixcompanies to consider ways of incorporating thecrusher fines into their mixes and finding newways to combat ASR. In this investigation theperformance of concrete mixes containing crushersand and Corex Slagment were evaluated againstcost and durability requirements. The parametersinvestigated included: workability, water demand,compressive strength and cost. The concretesinvestigated had a water/binder ratio of 0.70 anda constant water content of 180 litres.
It was found that the fines content, quantityand shape play a large role in determining watercontent, workability, density and strength. Whenfines (<0.075mm) are increased above set limitsthere is a detrimental effect on water contentthat necessitates an increase in cementitiouscontent leading to increased costs and, for 70%slag mixes, increased bleeding. For 70% slagmixes longer curing periods should be used.
On the other hand, if fines are increased from5.70% to 11.20% the density of the concreteincreases from 2450kg/m3 to 2550kg/m3. Thiscould mean the difference between passing orfailing on compressive strength and/or durabilityindices.
Even though the best densities and strengthperformance were achieved with the highestamount of slag replacement, the achieved settingtimes and demand by contractors mean that theslag replacement should be kept between 20%and 50%.
Overall it was found that concrete stability:workability, surface finishing, permeability andcompressive strength can be increased byinclusion of optimal amount of fines in theconcrete.
THE EFFECT THAT MANUFACTUREDSAND AND COREX SLAG HAS ON THEWORKABILITY, WATER DEMAND,COMPRESSIVE STRENGTH AND THECOST OF READYMIX CONCRETE
By: Jaco Cokart
NON-DESTRUCTIVE TESTING FORRACKING AND DE-BONDING OF SURFACE REPAIRS ON CONCRETESTRUCTURES
By: Jannes Bester
SUMMARYThis project was concerned with repairs to
concrete and was aimed at determining whetherthe incidents of follow-up repairs could be avoided.
The problems associated with concrete repair atthe Rand Afrikaans University (RAU) stimulated thework. Inadequate concrete cover (12 mm against arequired 25 mm) was regarded as the cause ofdeterioration.
It would seem that concrete repair is a verycompetitive market with low profit margins. As aresult there is a reluctance to perform re-hashrepairs and therefore some means of determiningthe quality and effectiveness of patch repairs tobegin with is desirable.
Two techniques were used namely:
• Ultrasonic pulse velocity - (TICO) • Rebound Hammer (DIGI - Schmidt 2).
The two techniques were used together withultrasonic pulse velocity determining cracking anddebonding and the rebound hammer to determineuniformity of the repair.
The background to concrete deterioration isgiven, together with details on both techniques.Particular reference is made to Rilem Publication:Materials and Structures, 1993, pp43-49.
The aims of the laboratory work were:
• To determine the effect of concrete strengthon pulse velocity
• To determine the effect of moisture contenton pulse velocity
• To determine the effect of path length onpulse velocity
• To determine the effect of reinforcement onpulse velocity
• To determine the effect of reinforcementdiameter on pulse velocity
• To establish the conditions of debonding ofthe repair material from the substrate
• To establish the cause of cracking of therepair material.
It was found that cracking of the repair was notnormally preceded by debonding. The ultrasonicpulse velocity method did indicate when hydrationwas poor.
The laboratory work was not extended toevaluate actual fuelled repair situations so it is notpossible to judge the potential capability of the twotechniques when used together in a fieldapplication.
Five appendices are given covering:
• Corrosion inhibiting reinforcement primer• Reprofiling polymer modified mortar• Rapid setting mortar• Digi-Schmidt 2• TICO UPV equipment.
8989
THE INFLUENCE OF SAND GRADING ONTHE AIR VOID SYSTEM OF FRESHMASONRY MORTAR
By: Harry Corporaal
SUMMARYMasonry mortar is important in contributing to
strength as well as durability. The workability ofmasonry mortar is equally important if thebricklayer is to make good masonry brickwork.Good workability is achieved by a combination ofmix design, flow characteristics and a stable airvoid system.
The air content in masonry mortar has alwaysbeen an important parameter because the airgives the mortar its cohesiveness and consistency.The use of air-entrainment means that less wateris needed for the same flow capability. Less waterleads to better stability in that there is lessbleeding.
Up to now only total air content has beenmeasured. With the availability of new measuringtechniques such as the Air Void Analyser itbecomes possible to explore the complete air voidsystem of the mortar. The size of the formed airbubbles becomes pertinent because the moresmaller air bubbles (less than 300 microns) actinglike fine sand will give a better workability of themortar.
In this project the influence of sand grading onthe air void system in masonry mortar has beenstudied. Three sand gradings are defined as –low, mean and high. The difference betweenthese gradings is the amount of fines (less than250 microns) in the sand. It can be concludedthat the sand grading does have a significantinfluence on the resulting air void system inmasonry mortar. That categorised as meanproduces the most small air bubbles, which resultin a good workability for the mortar. More or lessfines in the sand (low or high) leads to fewersmall air bubbles.
A knowledge of the air void system ratherthan total air content may be a better indicator ofperformance. The Air Void Analyser would allowsuch a measure at early ages and permits theassessment of air-entrainer efficiency.
Optimising mix design and in particular finesaddition, content and shape, including cementcontent is desirable.
Other factors such as type of mixer, mixingtime and temperature all affect the air voidsystem.
SUMMARYThe objective of this work was to establish a
method of determining the effect of a number ofparameters on the workability of concretewithout having to use concrete as the testmaterial. Such tests are regarded as costly.
A simple ‘micro-concrete’ or mortar was usedwith a half-slump cone test. A link between themini-slump test and changes to concretecomposition was determined.
Such changes as cement fineness, gypsumcontent and its chemical form, together with freelime content was studied.
In order to limit the number of samples to betested, two levels of the above variables wereused in the programme. A half-factorialexperimental design was used.
The outcome can be expressed as:
• the micro-concrete half-slump shows goodpotential to be used as a tool to predictbehaviour of cement in concrete
• the micro-concrete half-slump testperformed on a modified EN 196 mortarshows good potential to be used as acontrol test in cement factory laboratories,and gives a better indication of cementperformance in fresh concrete than otherroutine cement control tests used in theselaboratories
• the micro-concrete half-slump test shouldonly be used to assess the performance ofcement in well-proportioned concretemixes. Harsh, stony mixes do not givegood correlation with concrete slump
• the micro-concrete half-slump test gives agood indication of slump retention
• concrete slump of cement from the samesource is only significantly affected bychanging the gypsum from dihydrate tohemi-hydrate.
Changes in specific surface area of cement andincreasing temperature up to 70˚C as well asincreasing the SO3 content up to 3% and freelime to 2.7% had no significant effect.
It is recommended that repeatability andreproducability tests be performed together withfactory produced cements using a wider range ofslump rather than the 25-85 mm used in thiswork.
THE SENSITIVITY OF THE MICRO-CONCRETE HALF-SLUMP TEST, ASINFLUENCED BY CEMENTCHARACTERISTICS
By: Santie Gouws
90
SUMMARYThis investigation was prompted by the
unexpectedly high compressive strengths given byPortland flyash cements when tested in laboratorygravel concrete. These results were notconsistent with feedback from the fieldconcerning the relative performance of plainPortland and Portland flyash cement.
The project investigated the 28-daycompressive strength achieved in laboratoryconcretes and mortar made with 3 Portlandcements and 3 Portland flyash cements from thesame 3 cement plants. The concrete mixescontained granite, flint gravel, and quartziticgravel aggregate. The strengths achieved in EN196 mortar were also tested.
It was found that the main factor affecting thestrength ranking of the cements is the amount ofentrained/entrapped air within the concretemixes. Therefore concrete manufacturers who useaggregates that have a tendency to retain airshould find that Portland flyash cement performsrelatively well compared with PC. Concretemanufacturers who use aggregate that does nothave a tendency to retain air within the mixshould find relatively poorer performance withPortland flyash cement.
A key aspect affecting the amount ofentrained air in the gravel concrete is the largequantity of the sand particles in the size range300 – 600 μm.
INFLUENCE OF TEST AGGREGATE ONTHE COMPRESSIVE STRENGTH OFPORTLAND AND PORTLAND FLYASHCEMENTS
By: Kevin MacleodSUMMARYThe aim of this work was to establish the role
of air entrainment in self-compacting concreteand its effectiveness in resisting freeze-thawattack.
The durability of concrete against repeatedfreezing and thawing cycles is one of the majorfactors affecting the durability and service life ofan outdoors concrete structure in Finland andother northern countries.
To make freeze-thaw durable concrete, airentraining admixtures are used. Their pedigreehas been well established in normal concretes.However, their role in self-compacting concrete isless clear since this concept is also relatively new.Self-compacting concrete moves and compactswithout vibration, under its own weight. The self-compactivity is achieved using polycarboxylate-type superplasticisers in conjunction with viscositymodifying agents based on polymerizedmelamine sulphate. In addition, a high finesmaterials content is used. The superplasticiser andworkability of concrete have a large effect on thestable air entrainment of concrete.
Three different mixes were tested containinggranulated blastfurnace slag, limestone filler andmicrosilica. The cement used was rapid hardeningCEM II/A-LL 42.5R. The aggregate was granite-based sand and gravel covering the range fromfiller to 16 mm.
In this study four different self-compactingconcrete mixes were tested. It was found that air-entrainment has the greatest effect on the salt-scaling resistance of self-compacting concrete. Airentrained self-compacting concrete with slag,limestone filler and micro-silica additions willresist against surface scaling in salt water.
The effect of air content is similar to the effecton concrete with normal workability. However,the loss of entrained air is greater in self-compacting concrete than in normal workabilitymixes. This effect has to be taken into accountwhen measuring the air content of air-entrainedSCC at the mixing plant.
Making durable self-compacting concreteseems to be a prospect when using slag,limestone filler or silica-fume additions togetherwith an air-entraining admixture.
THE SALT SCALING RESISTANCE OF SELF-COMPACTING CONCRETE
By: Esa Heikkilä
91
SUMMARYThe aim of this Project was to compile a
comprehensive survey of the alkali reactivity ofaggregates from commercial quarries in Kwa ZuluNatal by petrographic examination and anaccelerated mortar test programme to identify thepotentially reactive aggregates. Once these hadbeen identified, to ascertain their alkali reactivitywith two cements (CEMI 42.5N) with differentalkali levels, and then determine at what level ofground granulated blastfurnace slag (GGBS)replacement this reaction could be controlled.
In the initial survey 23 aggregates were tested,22 local and a known reactive aggregate from theCape Province (hornfels). The test method usedwas the accelerated mortar bar method (SABS1245:1994) in which mortar bars are stored in 1NNaOH at 80˚C. Initial tests used a CEMI 42.5cement with a Na2Oeq of 0.52%. These testswere repeated on selected aggregates using aCEMI 42.5N cement with a Na2Oeq of 0.86% andwith replacement levels of 15, 20, 30 and 50%slag.
It was found that alkali-silica reaction could bea potential problem in Kwa Zulu Natal with nineof the aggregates being classified as "slowlyreactive" and five being classified as"deleteriously reactive or rapidly expansive".
The adverse effect of the increase of the alkalicontent of the cement from 0.52% to 0.86%Na2Oeq was confirmed although the increase inexpansion was relatively small.
The addition of ground granulatedblastfurnace slag significantly reduced thereaction and at the 30% replacement theexpansion cased by alkali-silica reaction fell belowthe 0.1% which is accepted as innocuous.
ALKALI-SILICA REACTION INKWA ZULU NATAL
By: Wayne Milligan
THE INFLUENCE OF SAND GRADING ON THE AIR VOID SYSTEM OF FRESHMASONRY MORTAR
By: Robin Page
SUMMARYIn South Africa, the fineness of ground
granulated blastfurnace slag (GGBS or SL) istypically 3600 cm2/g (Blaine). The producers arenow looking at finer ground slags, 5000 cm2/g.to improve the strength performance.
In this investigation, the strengths of concretemixes of similar workability made with variousbinder contents and binder proportions werecompared. Various methods of measuringworkability were used, including rheology testing.
Four binder types were investigated; PortlandCement (CEMI), GGBS (3600), GGBS (5000) andpulverized fuel ash (PFA). To eliminate the effectsof aggregates on workability, it was decided touse only binder pastes, where possible, fortesting. The blending proportions adopted arecommon ratios used in practice. The PFA wasincluded in the programme to provide anotherreference and an indication of the sensitivity ofthe test methods.
The comparative tests carried out on thebinder pastes were:
• Standard Consistency
• Flow Table
• Viscosity over Time (Single Speed)
• Rheology of Mortar - Variable SpeedViscometer.
The results showed that the use of GGBS(3600) improved the workability of the mix, butnot as much as PFA. However, the finer GGBS(5000) resulted in a similar or worse workabilitycompared with CEMI mixes.
The variation in water demand for theconcrete mixes correlated well with the yieldstress of the relevant pastes (determined with thevariable speed viscometer). A large percentagedrop in yield stress (47%) for the PFA pastesrelated to a high water reduction (18 litre). Onthe other hand the percentage change in yieldstresses with the GGBS pastes were a lot less(10%), whilst the yield stress and the viscosity ofthe pastes with the finer ground slag increasedwhen compared with the CEMI mix.
Therefore, overall, it is concluded that theincreased water requirement will have a negativeimpact on the initial idea to improve the earlystrengths of concrete by using a finer groundslag.
92
A PRELIMINARY INVESTIGATION INTOTHE EFFECT OF DRUM COLOUR ONCERTAIN FRESH AND HARDENEDPROPERTIES OF CONCRETE
By: Zoë Perks
SUMMARYTemperature rise during mixing and making
can affect compressive strength at later stagesand also cause slump loss. Long journey timesand high ambient temperatures can exacerbatethese effects. However, there appears to be nodefinite literature quantifying the effect of drumcolour on fresh and hardened concrete properties.
The work concentrated on what effect darkdrum colour has on the temperature within thedrum and any resulting changes of the concrete.
A water reducing admixture was usedthroughout the test.
Durability assessment was also incorporatedinto the programme, covering oxygenpermeability, water absorbtivity and chlorideconductivity.
Good correlation was obtained betweenconcrete mixing temperature and differences incompressive strengths. The effect on durabilityparameters was less conclusive.
Changing drum colour to white could not bejustified at this stage.
THE FEASIBILITY OF USINGRHEOLOGICAL TEST METHODS TODEVELOP MIX DESIGNS FOR FLOWINGSELF-COMPACTING CONCRETE
By: Christopher Rigby
SUMMARYThis project consisted of:
• A review of literature on rheology, mortar,self-compacting concrete and admixtures
• An investigation into admixturesdeveloped by the RMC Group for use inself-compacting concrete
• An investigation of the relation betweenfine mortar viscometry tests and concreterheology measurements.
Seven different admixtures were assessed usingviscometry and workability tests and the mostsuitable admixture and dosage for use in theRMC branded self-compacting concreteestablished. Using this admixture and dosage, acomparison was made between the Haake VT500viscometer and the Tattersall two pointworkability machine.
It was found that mortar trials do not predictthe behaviour of fresh concrete well. However, itwas possible to confirm the optimum dosagelevel from the viscometry results. This wasconfirmed by the Tattersall machine, which gavegood correlation with the viscometry data. Thedata from both tests show that the mortar andconcrete conform to the Casson and Binghammathematical models.
Overall the project showed that proposed mixdesigns in flowing, self-compacting concrete canbe assessed using fine mortar tests to predictplastic viscosity.
93
SELF-COMPACTING CONCRETE ATREDUCED LEVELS OF POWDER CONTENT
By: Andrew Rogers
SUMMARYThe potential benefits in using self-
compacting concrete (SCC) are many. Recentdevelopments in admixtures have resulted in apotential for reducing the high powder contentscommonly regarded as necessary for satisfactorySCC. This report examines that potential byassessing changes in SCC as powder content isreduced and admixtures are used to maintain thedesired properties. SCC is characterised by:
• filling ability – the property of flow permittingthe complete filling of spaces withinformwork by the concrete’s own weight
• passing ability – flow through gaps betweenreinforcement and formwork withoutblocking
• resistance to segregation – retaining uniformcomposition during the placing stage.
An impediment to using the SCC is the addedcost and that in turn is due to the higher cementcontents used and added admixture costs relatingto higher cement contents.
A series of trials have been carried out at theRMC Readymix Central Laboratory in Chertsey toinvestigate the feasibility of producing SCC withcharacteristic compressive strengths in the range30 MPa to 50 MPa. The work involved the use ofaggregates representative of those readilyavailable in the UK with partial cementreplacement materials, limestone flour and PFA.
An iterative approach to gradually reducingpowder content was adopted, initially withoutviscosity modifying admixture and then repeatedwith them. It was found that:
• production of true self-compacting concretewas possible using gravel and limestoneaggregates incorporating partial replacementwith limestone flour
• incorporation of a viscosity modifying agentas well as a superplasticiser was essential atthe lower powder contents, in order tostabilise the concrete, to which additionalwater was added
• the sensitivity of the lower powder contentmixes to small changes in water content islikely to give difficulties. Full-scale conditionscannot exercise the same level of control usedin these trials. For practical reasons thereforetarget powder contents should be no lowerthan 400 kg/m2 unless close control ofaggregate moisture contents can beguaranteed
• the use of PFA as cement replacement caused‘frothing’ of the fresh concrete
• formwork design needs consideration butdesign on full hydrostatic head is thought tobe pessimistic.
Trials showed that satisfactory SCC couldindeed be produced in the laboratory at totalpowder contents of 350-400 kg/m3.
SUMMARYThis investigation explores the influence of
binder composition on early age cracking inconcrete, with particular reference to conditions inthe Middle East. It also investigates the effect ofthe different binders on the engineering propertiesof concrete made at elevated temperatures.
Four binder compositions were assessed: OPC(100%), OPC/GGBS (50:50), OPC/FA (70:30) andOPS/FA/SP (70:25:5), with total cementitiouscontents of 380kg/m3. Concrete specimens werecast and temperature-matched cured to a profilepreviously determined for these mixes.Compressive and tensile strengths, shrinkage andexpansion were measured.
The results confirmed the beneficial effects ofcement extenders on long term strength gain andreduced temperature rise. The FA and FA/SP mixeshad higher early tensile strengths and lower earlyshrinkage strains, suggesting that that these mixeswould be less prone to early age cracking. TheGGBS mixes had moderate shrinkage values butlow early age tensile strengths, indicating a lowerability to withstand early age thermal stresses. TheOPC mixes had higher early age strengths but thehigher temperatures reached by these mixesproduced lower long term strengths. These highearly strengths and high modulus of elasticity arelikely to result in temperature-related cracking.
THE INFLUENCE OF BINDER TYPE ONEARLY AGE CRACKING IN CONCRETE
By: Ebrahim Yusuf Seedat
94
SUMMARYThis investigation sets out to provide
conclusive evidence of the most effective methodof preparing the surfaces formed at coldhorizontal joints in Roller Compacted Concrete(RCC) dams. Roller compaction became acceptedas a sound and cost-effective method of damconstruction during the latter half of the 20thcentury. An ongoing debate, however, has beenhow to prepare the horizontal surfaces formed atcold joints to ensure adequate bond across thejoints.
Five test scenarios: no preparation, severegreencutting, greencutting to laitance removalonly, mechanical brooming and sandblasting, allcommonly-used methods of surface preparation,were investigated on a RCC dam currently underconstruction. Each of the scenarios tested werealso modelled in cubes prepared in the sitelaboratory. Cores were drilled from the in situ testsections as well as from the laboratory cubes.These were used to compare the effectiveness ofeach type of surface preparation by subjectingthe samples to direct tensile tests and waterpermeability tests.
The investigation showed that some form ofsurface preparation definitely improves the bondstrength across horizontal cold joints in RCCdams. The smooth failure plane across the jointseen in the tensile tests of in situ cores supportsthis conclusion. This finding supports a recurringobservation in the literature study that laitanceremaining on the surface has a weakening effecton the bond. However, the method of surfacepreparation applied does not have a significantinfluence on the performance of the joint and thechoice of method can safely be left to thecontractor.
BOND STRENGTH ACROSS JOINTS IN AROLLER COMPACTED CONCRETE DAM
By: Yvette Staples
THE EVALUATION OF NEW GENERATIONSOUTH AFRICAN CEMENT EXTENDERS:A CONTRACTORS VIEWPOINT
By: Clive Sofianos
SUMMARYThe effects on concrete of the new generation
cement extenders available in South Africa wereinvestigated.
"Fly Ash", "Superpozz", "Condensed SilicaFume" and "Ground Granulated Corex Slag"blends with a standard CEMI; 42.5 cement and awater reducing admixture were assessed usingmixes typically specified for aggressiveenvironments.
Both plastic and hardened properties weremeasured in terms of practicality of batching andcompacting as well as the short to medium termengineering properties. Slump retention, settingtime and floor finishing (floating and cutting) andthe effects of curing were evaluated.
The assessment was carried out both underlaboratory conditions and in the field for practicalapplications.
This investigation has shown that there aredefinite technical and economic benefits in usingthese extenders.
Fly ash can be used at large replacement levels(up to 65% in dam construction), and still producesound, fit-for-purpose concrete. It is practical towork with and the relatively large replacementlevels are easy to measure, batch and mix into thefresh concrete.
Condensed silica fume is expensive to transportover a long distances because of its relatively lowbulk density and requires a greater degree ofcontrol regarding weighing, batching andthorough mixing to ensure a homogeneous endproduct. The engineering benefits obtained usingblends of condensed silica fume are welldocumented, but are obtainable at a premiumprice.
Ground granulated corex slag is practical towork with and has all round technical benefit inconcrete, particularly with regard to compressivestrength development. However, it is important toensure that minimum cementitious contents areadopted where durable concrete is required.
Superpozz is used at small replacement levels(between 5 and 15%), which requires a greaterdegree of control. It is likely that superpozz will beused for special applications and mining projects,competing with condensed silica fume.
Overall, this investigation highlights theimportance of selecting an extender, not only onits technical benefits, but also on its merits withregard to practicality of storing, weighing, mixing,placing and finishing. Proper curing techniquescannot be overemphasised.
95
POTENTIAL USE OF SANDSTONEAND/OR NATURAL SAND AS SOURCE OFFINE AGGREGATES FOR CONCRETEPRODUCTION AT FUTURE MASHAI DAM
By: Tente Tente
SUMMARYThe work concerned obtaining a suitable sand
for concrete production. In particular withdetermining whether replacing crushed basalt bycrushed sandstone was feasible in order to giveeconomic benefit on the Mashai Dam project(phase 2 of the Lesotho Highland Water Project).
The concrete specification was used as aguideline in judging the performance of concreteproduced from these sands. Acceptance criteriafor concrete aggregates addressed 14characteristics. The only research variables werethe type and source of fine aggregates.
A total of 11 trial mixes were cast and theircompliance with the specification requirementsfor fresh properties were assessed. Out of 11mixes, 8 were tested for compliance withhardened concrete requirements. The results weresatisfactory and indicated that substantial savingscould be made by eliminating the need to crushbasalt to sizes passing a 7 mm sieve.
Crushing of the sandstone could also beachieved using a simple driven roller and passingthrough the requisite sieves.
It was concluded from the performance of theconcrete produced from both crushed sandstoneand natural aggregates that, despite theirshortcomings, these sands have a strong potentialfor replacing crushed basalt sand duringconstruction of the Mashai Dam with substantialbenefits to the overall project.
Further work is recommended on also usingthese derived sands as fine fillers.
96
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 MANUFACTURERSWellington StRipleyDerbyshire DE5 3DZTel: 01773 746111
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 CENTRECentury HouseTelford AvenueCrowthorneBerkshire RG45 6YSTel: 01344 762676www.concretecentre.com
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 MATERIALSMINERALS & MINING1 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
97
Published by:THE INSTITUTE OF
CONCRETE TECHNOLOGYP.O.Box 7827Crowthorne
Berks RG45 6FRTel/Fax: 01344 752096Email: [email protected]
Website: www.ictech.org
ICT YEARBOOK 2003-2004
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.
Professional Affiliate
Yearbook: 2003-2004
CONCRETE TECHNOLOGYINSTITUTE OF
The
The I
NSTI
TUTE
OF
CO
NC
RETE
TEC
HN
OLO
GY
- Y
earb
oo
k:
2003-2
004
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.