CONCRETE ELEGANCE 2004

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FOREWORD

'The Concrete Elegance lecture series is a ConcreteCentre initiative in collaboration with The BuildingCentre Trust. The series has become a firm favouritewith a regular audience of Architects and Engineers,eager to learn more about the ways in which concretecan be used to achieve elegant designs.

David Bennett, the series organiser and resident guru,has devised an excellent mix of projects which haveformed the backbone of the talks by designers andspecialists. Concrete has for many, been discovered asa versatile material suited to a wide range ofapplications from small scale artefacts and sculptures,domestic scale architecture through to multi-storeybuildings and landscapes where the current generationof concretes offer greater potential than ever.

This publication documents the 2004 series. FutureConcrete Elegance lectures are planned to includeEuropean architectural projects, smaller domestic worksand, more art based projects, revealing both passionand commitment to the imaginative use of concrete

We are confident that the chosen topics featured here,will inspire and renew interest in concrete’s dynamicvisual qualities’

See you at the next series

Allan Haines

Education and Training Manager, The Concrete Centre.

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ACKNOWLEDGEMENTS

The Concrete Centre wish to thank all the speakersfor their contribution to the success of the 2004series, for helping with the supply of images andassisting with notes for the drafting of text.

For further information on future ConcreteElegance programmes see the back cover for details.

Written and Edited by David Bennett,David Bennett Associates

Booklet Designed by Kneath Associates

© The Concrete Centre 2005TCC/06/03

ISBN 1-904818-21-8

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CONTENTS

01 2004 Overview

02 Precast ‘Prefabulous’ TechnologyThe Canongate Wall of The Scottish Parliament BuildingDavid Shillito, Malling Products and Gary Lucas, Patterns and Moulds

03 Spiral Dreams CRC Challenges Metal for Slimness

Bendt Aarup of CRC Technology, Hans Exner of Ramboll Engineers

04 Residential DelightsElegant Concrete Houses

architects Alex de Rijk of dRMM & Ferhan Azman of Azman Architects

05 Sculptural Inspirations Concrete as Art :

sculpture Carole Vincent & artist David Undery

06 Prefabricated Perfection The Bridge of Peace in Seoul :

Mouloud Behloul of Lafarge DUCTAL®

CONCRETE ELEGANCEIS A SERIES OF

ARCHITECTURALPRESENTATIONS GIVEN

AT THE BUILDINGCENTRE BY LEADING

DESIGNERS,INNOVATORS AND

MANUFACTURERS OFCONCRETE. THESE

WERE THE THEMES ANDSUBJECTS OF THE

2004 SERIES.E

CONCRETE ELEGANCE//OVERVIEW 01

Concrete as an architectural and structural material

has gone through many changes and evolutions in

its development over the years, but probably none

more so than in the past decade. There is renewed

interest in concretes plastic and aesthetic qualities

in architecture today helped and encouraged by the

expressive way that two young architectural

practices highlighted in this review have exploited

its self finished quality and form with great success.

Both projects demonstrate that standard truck

mixed concrete and the right selection of formwork

and placement techniques can produce award

winning architecture at affordable prices. What is

also a revelation is that both architects have never

designed or used exposed concrete before. What

they did discover is that there is a wealth of

knowledge within the concrete industry to tap into

to give them the confidence and encouragement to

realise their ambitions.

Concrete as a structural material has had to be

redefined in recent years with the introduction into

the world market of two new ultra high performance

concretes - CRC and Ductal®. These products

have set new performance standards and new

thinking on how such materials can be engineered

and prefabricated to produce pencil thin, light

weight structures that compare with structural steel.

The case studies of the stunning Spiral Staircase in

Copenhagen and taut concrete arch of the Seonyu

Bridge in Seoul highlighted in this review, show the

range and potential of these new concretes in

building and civil engineering applications. What is

so disappointing is that we have yet to see a

structure exploiting these new concretes in the UK.

Art and sculpture reflect the changing patterns of

social culture, scientific advancement and

intellectual thinking through mankind’s history,

expressed as paintings on canvas, castings in

bronze or toolings in marble. Photography, screen

printing, video recording, steel plate, industrial

plastic, animal carcasses and hum-drum every day

objects in recent decades have replaced canvas

and bronze to communicate modern art. Carole

Vincent has been exploiting concrete colour,

texture and geometric forms in sculpture for many

years from her studio in Boscastle. Thanks to her

many commissions and international reputation,

concrete is fast becoming a material for artist

OVERVIEW

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expression appealing to potters, sculptures and

painters alike. Alongside Carole Vincent’s silky

smooth, conical sculptures, the work of the young

concrete artist David Undery’s enamelled abstract

paintings are highlighted to show just how

expressive and sensuous etching, pigmenting and

lacquering concrete can be. Such creativity can be

an inspiration for façade panels on buildings,

making insitu kitchen worktops and casting

concrete floors.

Art has been expressed in architecture over the

centuries, often as figures carved in stone, stained

glass in windows, statues placed on cornices,

frescos painted on plaster and mosaics on the

floor. Rarely has the structure or the shape of the

external fabric of a modern building been

consciously derived from artistic motivation. With

the completion of the new Scottish Parliament

Building in Edinburgh art has become the focus for

the design of the precast boundary walls along

Canongate and the west elevation of the MSP

Office Building. The making of the master moulds

and of the liner for casting each bespoke panel

was solved by using a special computer guided

routing tool that came from the aerospace industry.

Malling Products in partnership with Patterns and

Moulds made the world’s first bespoke precast

panels requiring no labour or carpentry skills in

mould making, drastically reducing the cost and

time for forming bespoke precast concrete.

The technology and the process on how this was

achieved are highlighted in this review. The images

of the Canongate Wall and the MSP Office

boundary wall tell their own story.

In the presentations for the Concrete Elegance

series for 2005 we will be covering self compacting

concrete, glass reinforced cement, innovative use

of concrete on small projects and taking a look at

the precast architecture in Northern Europe.

For more details of these and other related events

contact The Concrete Centre.

We hope that this booklet will renew your interest in

concrete in all its many forms and expressions and

inspire you with new challenges and possibilities.

David Bennett,

December 2004

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CONCRETE ELEGANCE//PRECAST PREFABULOUS 02

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THE CANONGATE WALL OF THE SCOTTISH PARLIAMENT BUILDINGDavid Shillito, Malling Products and Gary Lucas, Patterns and Moulds.

This lecture was also part of ‘The Fabricator’ series given at theBuilding Centre by material specialistswho can turn concepts into reality andsolve the challenges set by designers.

The Scottish Parliament Building hasbeen the most challenging andarchitectural complex structure to bebuilt in the UK in the past fifty years.The exceptional complexity and artisticcreativity of the precast panels thatcloak the Canongate Wall, could onlybe solved using robotic technologycommonly deployed in Formula Oneracing and the aerospace industry. Ithas enabled Malling Precast tobecome the market leader in bespokeprecast cladding in Europe.

We were involved in the Scottish Parliamentbuildings through Laing O’Rourke who had won thecontract for building the concrete frame. We are asubsidiary company within Laing O’Rourke and werealready working on ideas of how to incorporate asmuch precast elements into the frame because thefinished quality had to be very good. We resorted toinsitu concrete construction where it was notpractical or possible to precast.

We were given one drawing for the Canongate Wallfrom which to evolve the precast panels and thefinishes. The drawing was a combination of a roughsketch, a montage of images that had been cut outof magazines or from photos taken of thesurrounding landscape…. and some poetry! Itfrightened the living daylights out of us when we firstsaw it and were asked to comment on theprecasting possibilities. We invited Gary Lucas ofPatterns and Moulds to join us at the nextconstruction meeting in the hope that we could find asolution to the problem. His company make a lot ofspecial precast moulds for Malling. We did not wantto say yes straight away and find out later that it wasimpossible to precast.

We were already working with Patterns and Mouldstrying to find an economical way to make latex

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moulds for the unique bamboo pattern relief on theflat panels for the MSP boundary walls. Thechallenge was not how we cast or finished theconcrete but how we could make bespoke mouldswhich were curved along an asymmetric axis andindented with large and small pockets in a randomorder to receive pieces of natural stone. Usingconventional methods of mould making andemploying teams of carpenters it would have takenfive times longer than the robotic router method thatPatterns and Moulds invested in. The cost of thefinished concrete using the robotic router wasaround £1000/m

2. It would have cost at least

£6000/m2

using traditional methods and taken atleast three weeks to make each master mould.

The CNC (Computer Numeric Controlled) Routerhas been used in the aerospace and carmanufacturing industry for many years. They areprogrammed to cut and accurately form threedimensional shapes. An identical copy of themachine is in the Jordan Formula 1 factory. Therewas a specialist company in Loughborough who hada CNC machine and who Patterns and Moulds hadhired to cut out the bamboo motifs on MDF boardfor the special MSP precast walls. So when thesketch for the Canongate wall was further developedby RMJM into a CAD model, we knew that the

master mould could be made using upgradedsoftware to drive a CNC machine which waspurchased by Patterns and Moulds for this project.

The 3D model of the each panel was generated inAutoCAD by the architects. The CAD image had tobe transposed to a CAD/CAM system or MC9file forit to be read by the machine’s software. The actualprecast panels were 3m by 4.5m in size, but as themachine can only tool or cut mould sizes of notmore than 3m by 1.5m we had to split the 3D imageinto thirds to tool the whole panel. The information inthe MC9file tells the CNC machine what cutterdiameter is required, the depth and curvature to cutand the line to follow. To programme the CNCmachine it takes a technician about four days sittingin front of a computer.

The biggest bug bear of the system is the qualityand accuracy of the AutoCAD drawing that is sent tous. The information input for a CNC machine worksto an accuracy of five decimal places, so if adjoininglines on the CAD image is out by less than half amillimetre the machine will not function and throw upan error. The software produces the tool path to drivethe cutter and sends it positioning code signals similarto that of a stereoscopic image of contour lines on anOS map. The cutter has directional information along

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the x, y and z axis and plus the B and C rotationalaxes. B axis is rotary on plan and C is rotational onelevation. In this way we can programme the machineto cut a perfect sphere if required.

To begin the process a 50mm deep, 3m by 4.5mMDF panel is placed below the router head. Therouter cuts to a depth of 25mm into the MDF to formthe patterns. The router starts by cutting the first 3mby 1.5m section in 14hrs. It can take up to 2days tocomplete the whole panel. The cutting head rotatesat 25,000rpm and the cutting tool is changeddepending on the stage of the process .The firststage is the rough cut using 16mm to 25mm cutterdiameters, when a large amount of material isremoved. When the router gets down to thefinishing stages, the machine makes hundred ofpasses over the panel to bring the cut surface to asmooth finish, using ball-end cutter heads.

The completed MDF panel is waterproofed andvarnished and set in a boundary frame. A latexrubber solution which is a two part thermo-settingpolymer resin, is poured over the MDF. It has theconsistency of treacle and fills all the depressionsand comes to level across the boundary frame.When it has hardened it is lifted out and sent toMalling Products at Grays. The latex rubber mould is

placed in the precast mould frame and a releaseagent applied. The small stones that appear in therecesses and windows in the panels are then placedin position. Some of the stones were recovered fromthe old brewery that once occupied the site. Everypiece of stone had to be carefully cut to size andshape and placed in the correct recess in the panelbefore concreting. The very large stones arepositioned by crane into the recesses once the panelis in position on site. The Scottish Parliamentconcrete mix was poured into the mould and left toharden. The mix was a pale grey concrete usingOrdinary Portland cement and crushed Derbyshirelimestone fines.

The 250mm thick precast panel which wasreinforced with mesh was left to cure in the mouldfor 24hours. When the panel was removed somesurfaces had to sand blasted and others left with alightly polished finish. We had to mask all the fair-face non blasted surfaces with plastic insulating tapeand fill up the stone rebates with weak mortar sothat during blasting it would not get eroded , but waseasy to remove afterwards. That was the mostdifficult part of the precasting work at Grays.

An important issue on the Scottish ParliamentBuilding and all precast work is the surface quality

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and preciseness of panel construction. Many of thepanels had patterns on the surface that werecontinued onto adjacent units. If we worked to thetolerances we are allowed to use (i.e. +or-10mm forfixing tolerance, plus + or - 6mm for manufacturingtolerances which is collective of +or- 12mm,) we canhave ugly edges of discontinuity as wide as 15mmto 20mm which are permissible. With the CNCrouted moulds we achieved a manufacturingaccuracy to within one millimetre of exactness.Although the panels on the Canongate Wall wereheavy- some of them were 18 tonnes - and therewas deflection in the cantilever steel supportingframe as they were positioned; we ended with apositional tolerance of only +or- 2mm which isphenomenal.

When you invest in a CNC machine you have tothink about recovery of the capital cost within a fiveyear period. By that time the machine will beobsolete and you will need to invest in the latestmodel. The efficiency you gain and the reduction inlabour cost you save must be offset against theinvestment of £140k for the machine and £25k forthe software we had to purchase. We can say withconfidence it was well worth the savings it made onthis project alone, never mind the next five years!

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The staircase is located in Tuborg 15 buildingwhich is along Tuborg Boulevard in the newurban quarter of Tuborg Havn in Hellerup.

The area was a run down industrial zone onlya few years ago, since then it has changedinto a vibrant new commercial district ofCopenhagen. Tuborg 15 is a purpose builtfour storey office building that is leased bythree software companies. The focal point ofwhich is the open staircase that spirals downthe east elevation of the atrium – a piece ofsculptural art. Connected to the floor divisionsat landing level only, it is a completely selfsupporting structure.

CONCRETE ELEGANCE//SPIRAL DREAMS 03

THE DESIGN OF SPIRAL STAIRCASE IN TUBORG 15 BUILDING, HELLERUP

Hans Exner of Ramboll Engineering andBendt Aarup of CRC Technology.

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STRUCTURAL CONSIDERATIONS

Hans Exner, Rambol

When we first thought about the spiral staircase wehad never heard of CRC and intended to scheme itin steel or reinforced concrete. It was only by chancewhen reading a design journal that the architectsArkitema came across CRC. It is a fantastic product.We met with Bendt Aarup from CRC Technology andthe spiral staircase evolved.

The architect wished to design the staircase with adouble balustrade and no columns and all in whiteconcrete. We persuaded them that it was betterstructurally to have a column and only an interiorbalustrade. The column support was necessary asthe precast beams at the edge of the building floorwere neither robust enough nor thick enough to carrythe landing loads from the staircase when weassessed the structure. We could not fix nor tie thebalustrade walls to the building floor without having todo some strengthening work to the entire edge of thefloor beam. This would have been disruptive, costlyand quite unsightly. It should be noted that thestaircase was included after the main building hadbeen designed and building floors had beenconstructed. We also felt that the double balustradewall would not look as pleasing as it blanks out thetransparency and lightness of the staircase.

We proposed a column with an interior balustradewall acting as a beam from which the steps cantilever

out. The leading edge of the steps can be made verythin as there was no force acting on it. The architectaccepted our ideas and incorporated that into thefinal design. However the column was made as acurved segment of a circle, wider at the base andtapering towards the top and an integral part of thebalustrade. It supports the spiral beam and thelanding and carries the loads to the foundations. Thebalustrade beam spans from floor to floor, betweenthe columns. The column restricts the bending andtorsion in the balustrade beam. Each staircase stepcantilevers as an independent element – we did notallow for any interaction or restraint from the adjacentsteps or for the spread of load in our calculations. Inreality the steps and risers help each other andensure an exceptional rigidity of the construction,resulting in zero deflection at the edge under theworst loading conditions. We designed the floorloading as 2.5kN/m

2or the equivalent of ten cement

bags per square metre across the steps. Thelandings are connected to the building floor andprovide the lateral stability of the staircase structure.

Every element of the spiral staircase is precast with100Mpa CRC. The flights - which comprise thebalustrade beam and cantilever steps - are cast infour sections and stitched together with insituJointCast CRC on site. The joints between flights are

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nominally 80mm wide as the JointCast has anexceptional high bond strength which reduces thejoint width. The upper balustrade section connectsover the top of the column and links with the landingsection. The first flight structure is carefully proppedbefore the upper column element is put in positionand the joints then filled.

The design rules for the CRC staircase were takenfrom standard design rules for reinforced concretespiral staircases in our codes of practice. The maimdifference between CRC and conventional concreteapart from the increase in compressive and tensilestrength, is the superior bond strength andanchorage length that we can work to. We candesign with very short lengths of starter and lappingbars, only one fifth of the bond length required fornormal concrete. The most critical section was theanchorage length of 100mm required for the rebar ofthe cantilever steps. Allowing for tolerance and coverthis required the balustrade wall to be 150mm wide.The reinforcement takes all the cantilever momentand transfers it to the balustrade beam. Perhaps wecould have made the balustrade beam as thinas100mm and used U bars to develop the anchoragefor the steps, but that would have made the jointdetails with the interconnecting bars of the balustradebeam too complicated. In any case we felt we

needed the150mm thickness to cater for the bendingand torsion in the beam.

When we first proposed a column supporting thebalustrade beam we suggested it should be square.The architect came up with the idea of making it150mm thick the same as the balustrade and tocurve its width to maintain the curvature of thebalustrade. That was a very elegant solution whichwe then detailed.

In all our design work using CRC we had to justifyour calculations and assumptions to the checkingauthorities. We showed them the long term testresults on durability, bending, anchorage, fatigue etcthat CRC Technology had undertaken over fifteenyears That was sufficient to satisfy them. As regardsfire risk, the staircase is not the fire escape stairs forthe building and therefore required only a half hourfire rating. The concrete cover to the bars was 15mm(10mm for cover and 5mm tolerance) and we haveused 8mm diameter bars in the steps and 16mmbars in the balustrade wall and column.

We did not prepare the staircase prefabricationdrawings, we only prepared the reinforcementarrangement drawing and sent them to the architectwho pulled all the information together and sent themto the contractor.

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High Strength or High Performance Concretes(HSC or HPC) are used increasingly for a range ofstructural applications, and standards in a numberof countries are being revised to accommodatethese improved materials. Often, however, HSC ismore brittle than conventional concretes, which canlead to problems in failure mode as well as underservice conditions. One way of overcoming thisproblem is to provide ductility by incorporating steelfibres in the matrix. Fibre Reinforced Concretes(FRC) have mostly been used in non-structuralapplications such as slabs-on-grade, floors andarchitectural concrete and where less than 1% byvolume of fibres are used.

CRC is a special type of Fibre Reinforced HighPerformance Concrete developed in 1986 byAalborg Portland in Denmark which incorporatesfibre contents of 2 to 6 % by volume correspondingto between 150 and 475 kg of steel fibres per m

3of

concrete. In addition to this, the matrix has a verylarge content of microsilica, plus water/binder ratiosof typically 0.2 or lower. This composition makesCRC very dense and well suited for structuralapplications with a typical mean compressivestrength of 150 N/mm2, high tensile strength, good

durability and a high ductility. It is thus possible toutilise reinforcement much more effectively withouthaving large cracks under service conditions. AsCRC is quite different from conventional concrete ithas been necessary to provide extensivedocumentation on the properties of CRC before thematerial could be considered for structuralapplications. CRC has been the subject of anumber of research projects dealing with structuralproperties, but also with aspects such as durabilityand fire resistance.

With the high fibre contents that are somewhatdetrimental to workability, CRC is especially suitablefor precast applications, but a special type of CRCcalled CRC JointCast - a mortar with 6% of fibres(475 kg/m

3) – is used for in-situ cast joints between

structural members of ordinary concrete. TheBuilding Research Establishment at Watford hasinvestigated this type of application in a project oninnovative joints under a DETR FrameworkProgramme. For precast applications a specialCRC-binder is sold and the production plants arethen given advice on casting, which aggregates touse etc. CRC JointCast is supplied as a dry-mortar– mainly to improve quality control as CRC

CRC (COMPACT REINFORCED COMPOSITE) FOR PRECAST APPLICATIONS

Bendt Aarup, CRC Technology

IMAGES REQUIRED

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JointCast is typically used on site. Due to the lowwater content, CRC has to be protected fromevaporation shortly after casting, and the highcontent of super plasticizer means that at normaltemperatures (20 0C) it takes up to 16 hours beforeelements can be removed from the moulds. Typicalstrength at 1 day is 80 N/mm

2.

Typical applications for precast work are small andslender elements such as balcony slabs, staircasesand small beams and columns. While strength andductility is much better than for conventionalconcrete, stiffness is only slightly higher, whichmeans that deformations is one of the aspects thathas to be considered carefully in design – especiallyas CRC is always used in very slender designs.Allowance also has to be made for shrinkage ofCRC due to the large binder content. This is usuallyhandled by incorporating additional reinforcement.

The CRC binder is more expensive than cementand the steel fibre content also leads to a higherprice for CRC. On the other hand elements aretypically one third the volume of conventionalconcrete. This means that on the types ofapplications that have been used in Denmark –typically balcony slabs and staircases – the price for

CRC has been equivalent to alternatives in steel orconcrete. Obviously in cases where the architectchooses very special solutions this also requires ahigher price, but in these cases it has little to dowith the price of materials, but more to do with priceof formwork and production costs. In a number ofcases CRC has been chosen for applications simplybecause the price was lower than alternatives insteel or concrete. In these cases the engineer orarchitect has usually chosen a different supportingsystem for CRC, such as replacing concretebalcony slabs supported on columns withcantilevered CRC slabs.

This challenge of utilising a different type of materialin a manner that leads to savings in the total priceand at the same time produce a spectacular designis a challenge that has been met by a number ofDanish architects leading to several interestingprojects just like the spiral staircase at Tuborg 15and increasing interest from architects abroad.

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Centaur Street was conceived asan ‘inside-out’ building. Internallythe walls are of texturedconcrete, and externally they areover clad with a chocolate-brownconcrete graduated ‘timber’rainscreen. The building consistsof four apartments, each enjoyinga dynamic interior organised as alarge, open double-height livingspace, interpenetrated byadjacent enclosed bedroomsand stairs which form a buffer tothe viaduct.

CONCRETE ELEGANCE//RESIDENTIAL DELIGHTS 04

ONE, CENTAUR STREET, WATERLOO

Alex de Rijke, De Rijke Marsh Morgan Architects

The brief was to create an experimental housingtype which examined and exploited the potential ofdensity on small gap sites. The Eurostar viaductwas an unlikely genus loci, but its close proximitygenerated a clear zoning of the plan; a powerfulentry route, with stairs and services, and finallyliving space, all arranged as parallel strips. Theaccommodation is varied, intimate and prioritisesspace and light.

We have been interested in all building materialsand the art of construction, working entirely withstandardised materials that we find in catalogues.Yet we try to create non standard architecture bycarefully assembling the components. The clientRoger Zogolovitch came to us with a proposal todesign an entirely insitu concrete building, whichwas quite a challenge as we had never designedwith concrete before. It was to be exposedinternally and clad externally which is odd becausethere seems to be a precedent for it to be the otherway round in the UK. This project was more abouttexture and surface quality than composition orcolour. It was achieved internally by the process ofcasting and forming the walls, the floors and theroof. We had a site into which we simply pouredconcrete right up to the boundaries and to the

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rooftops. Had we had more time to reflect andfreedom to consider our options we might haveelected to go with precast concrete for thestaircases. But we had a client who was completelyin love with insitu concrete ‘the grey gold’ as hewould affectionately brand it. He wanted a joint-less, seamless building and I quite understand why.The contractor was not completely equipped orexperienced to form it to the standard we hadexpected, but they made an honest and diligenteffort and after the surface was lightly sand blastedwe were very satisfied with the resulting cave- likequality. There is something wonderful about thismaterial - it is the structure and architecture it is notstitched together, bolted or nailed. We can designdouble height load bearing walls, overhangingcantilever slabs and neo Georgian steps inconcrete.

Our working relations with the client who was anarchitect, was both open and exacting and astrange intense process. It was the paradox ofhaving an architect commission you to design hisown building but he trusted us enough to let usbring our ideas forward and infuse them into thedesign. We had board marking on some wallsmaking it in softwood and flat finish in the

bedrooms using phenolic resin overlaid plywoodpanels. We enjoyed the illusion of wood that theinternal concrete conveys. On the outside we hadfibre- cement board marked panels, pretending tobe wood very effectively and maintenance free. Itwas an Eternit product that was developed forweather boarding on seaside chalets but not on abuilding. Since we have adapted it as a rainscreenon our building, we see it copied everywhere.

This building is didactic, the cladding does notcover up the weather tight insulation behind it, andthe insulation does not hide the load bearingstructure nor the structure hide the finishedarchitecture. It’s a layered composite design likethe vest, shirt and jacket of clothing that you cansee at the edges. I think building architecture goesdown hill once the main structure is covered up likethe upholstery of a furniture frame. I hate the notionthat you need five trades to make a wall – studframe, plaster board, insulation, plaster and paint.Concrete is the perfect medium for houseconstruction - it has character, it can support itself,it is self finished and is one process.

We introduced recycled materials from theconstruction into introduced them in the furnitureand flooring of our new office in the ground floor

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apartment. The ply which had a phenolic resinoverlay and which was used for the floor slabs, weused for the bookshelves. The rough boardedtimber laths that formed the board marked wall, weused new panels to make into a sliding door. Wetried to limit the palette of materials by using theformwork that cast the concrete. The glass parqueton the ground floor was recycled from the glassthat was supplied incorrectly for the louvers on thestairwell and the window box on the east elevation.I could not bear to see such beautiful glass throwninto a skip. We retrieved them and had the sheetscut into 300mm squares with bevelled edges.However to lay the glass parquet on a fire-retarded, Styrofoam substrate has proved atechnical nightmare. A self levelling screed waspoured over the existing floor which was not flatenough for the styrofoam. The styrofoam hasrouted ducts for running the computer cables andfor sleeving the under floor heating pipes and oncethese were in position, we placed an acrylic sheetover the support ridges to distribute the load and tobed the parquet to the foam substrate. The glasspanels are held down by double sided adhesivetape and the joint edges sealed with glass glue. Wefound the glue was too brittle and de-bonded withthe slightest movement, so we replaced it with

silicone that seems to work well.

The spatial organisation of the interior is based onthe Raumplan principle pioneered by Adolf Loos.The double height central space has a tightmezzanine floor slotted into it with smaller selfcontained rooms leading off to the sides. This wasnot to be a static event with rooms assembled inrows around a central staircase, like a terracedVictorian house. Here the smaller rooms wrappedaround the large void and were interconnected byseries of discrete stairs. It is a hybrid of the openplan European apartment and the English verticalterraced house and it works well.

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ABERDEEN LANE, ISLINGTON

Ferhad Azman, Azman Architects

This new build house for afamily of six is located on anunadopted lane dominatedby workshops, studios, andlight industrial sheds.

The site backs on to anestablished residentialneighbourhood. This trendsetting modern house inIslington is a statement inwall to wall insitu concrete. What is so surprising aboutthe concrete is its marblesmooth finish, its flawlesslyclean surface and seamlessappearance.

The focus of the brief was to create a house withsufficient space and comfort for a family of four. The site is bordered by a detached house on the westside, terraced mews houses on the east side and agarden wall at the rear. The starting point of theconcept was the decision on the orientation of thehouse. The decision to face the house inwards tocreate a courtyard rather than face the lane wasfollowed by a series of decisions that lead to the choiceof materials and method of construction. It was decidedthat the north and south walls to the house (the wallsfacing the lane and the house at the rear) would betreated as solid without many openings, in order tomaintain a definitive edge to the lane and avoidoverlooking. The other instrumental parameter was thedepth of the mews house at the east side of the site.With these two critical decisions the house wasdesigned as two interlocking cubes of internally andexternally exposed reinforced concrete walls. Thechoice of concrete was driven by the desired solidnessof the north and south walls. We wanted these walls tobe seamless planes and proposed concrete to theclient. The house was designed like a dolls house witha west facing ‘courtyard’ façade left transparent withlarge panes of glass in timber framing. This respondsto the clients’ brief for the house accommodatingvarying needs of a large family. Timber louvers are

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installed at first floor level for a degree of privacy.

We chose to use the same materials throughoutthe house internally and externally, which arelimited to concrete, limestone, timber and glassapart from the quaint guest bathroom built instainless steel with a red rubber floor.

Aberdeen Lane in Islington is a bit off the beatentrack, along a dirt road, past a collection of singlestorey warehouses, back gardens and drab garagelots. Why build something so ultra modern andspanking new stuck down a long uninvitingindustrial lane, in the shadow of a 1920s brick builtmansion. For the client this site was perfect – it’s afive minute walk from the tube station, a ten minutecar ride into the city; it’s in a very sought afterlocation, but more to the point it was a plot of landwithin their budget. The client thought the siteinteresting and private. The location gave us theopportunity to create something dramatic andmonolithic in appearance - there were no buildingsclose by to relate to. Instinctively our thoughts wentto insitu concrete and when we suggested it to theclient they were surprised but not shocked. Whatwas causing the greatest anxiety to both architectand client was finding a contractor who would pricethe job within budget and also execute the concrete

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beautifully; a notion that many designers think aremutually incompatible objectives. VarbudConstruction in Perivale had worked for thearchitects before on refurbishment projects - theymade furniture, fitted out retail units, builthandmade kitchens , did all the plastering ,plumbing and brickwork, even cast concrete floorsand walls and were always very competitive ontheir pricing. They were keen to take on AberdeenLane and we trusted their integrity knowing howcarefully they work, but fair-face insitu concretewas going to be a new challenge for them. Thisbold project was going to establish their reputation

The double skin concrete walls of the box structureact as bookends, retaining the open glasselevations that look westwards over the courtyardgarden , the large ash tree, the iroko panelledtimber garage and garden room. The concrete inner walls support the concrete firstfloor slab, the flat roof and staircase. The livingspaces are all on the ground floor - the kitchen,lounge, TV room and dining area - with thebedrooms on the first floor. They are accessed viaan open plan precast staircase that runs along thedouble height east wall, whose roof light floods thestair case in day light. Single skin block work walls

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divide the internal spaces of the house into theirfunctional uses – bedrooms, bathrooms, walk-inwardrobes and so on. All the 200mm thick innerload bearing concrete walls, and the floors werecast ,before the 150mm outer skin of the concretecavity walls, were constructed. The finishedconcrete surface is marble smooth to touch, lightgrey in colour and full of subtle abstract flecks andvariations depending on the angle of the light. Howwas it achieved? After the contractor hadcompleted the sample panels to check theefficiency of different release agents, they machinecut the large birch faced ply sheets in theirworkshops and prepared the surface by sanding itdown, then coating it with two coats of lacquer.

Once on site the birch faced panels were lightlyoiled with a high performance chemical releaseagent manufactured by Nufins, before they werescrew fixed to the backing ply. They were notallowed to screw fix on the fair face side of the ply.Everything had to be screwed from the back of thepanels. In addition, the strongbacks and waling tosupport the forms were designed with no tie-boltsover the body of the formwork. A–Plant whosupplied all the props, had never designed

temporary works with quite this degree ofsophistication and control, but it worked verywell. The push pull props in the mid-span, theclose centred walings over the lower half andthe double row of strong backs, kept theshutters rigid and true under the 3m head ofliquid concrete. The concrete walls are asstraight as a pole, perfectly plumb, with nolipping or bowing over their height. WackerUK Ltd arranged a training workshop to showthe concrete ganger how to use theirconstant amplitude pokers effectively. Wewere supplied with the best concrete wehave ever seen for consistency of mix andworkability by Hanson Premix. Their serviceto the site has been first class.

We wanted a smooth- faced, light greyconcrete that would not get dirt encrusted orstained. What has been achieved has comeup to all our expectations. The surface issensual, cool and very tactile and makes astrong contrast with the limestone groundfloor tiles, the wooden framed windows, andthe elm covered first floor panels.

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CONCRETE ELEGANCE//SCULPTURAL INSPIRATIONS 05

CONCRETE AS ART

Carole Vincent, Sculptress

Carole Vincent is the Britain’sforemost artist working inconcrete. She is a painter andsculptor by training who lives inBoscastle, Cornwall.

Her large scale commissionshave included the award winningsundial and fountain in Plymouthtown square, ‘The Pedestrians’ inDevon, Quartet in Glasgow andColloquy Two in Singapore toname but a few. The Bude Lightin Cornwall and The Blue CircleGarden at the Chelsea FlowerShow, both of which receivedCertificates of Excellence from theConcrete Society, are her morerecent major works.

Carole Vincent wrtes:

Boscastle with its harbour and surrounding clifflandscape has been a major influence on my workin sculpture and in painting for over forty years. Ilive at the top of the village in an old stone cottagewith roses round the front door. It has a galleryupstairs, a converted piggery as one studio and apurpose built studio for working in concrete Andthen I have an acre of garden , developed from afield and divided into three distinct areas of cottagegarden, a wild wood and concrete garden.

Concrete has always been a significant part of mylife. My fathers building firm had a small concreteworks and I remember making concrete blocks asa child. I only began to realise concretes sculpturalpotential in 1982 when I was asked to make thesculpture ‘Reunion’ for my former headmistress . Itwas too large for carving in stone and too bulky forcasting in bronze. A chance meeting with aprofessional plaster mould maker showed me how Icould work in clay, make a plaster mould and thenfill it with concrete. It was not very good concrete atfirst because I used recipes provided by artists andnot those in the precast industry. When I designedthe piece ‘One and All’ I sought advice from theprecast company Minterstone who were verygenerous in providing materials and recipes. Moresmall works followed

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and the concrete finish became better polished withdifferent aggregates making changes of colour. TheArmada Dial in 1988 which comprises a sundialand fountain in Plymouth City Centre gave me thebreak that every artist dreams of . A major work ona scale that was not possible to cast in the studio. I produced the maquettes , drafted the sundialspecification and the fountain design and acontractor built it

Several commissions followed – the Pedestrians,Quartet, Colloquy and Les Jonglers in Jersey. Myconcrete vocabulary changed from theapproximations of a builders yard to the precisionand controlled output of a scientific laboratory. Ibecame obsessed with particle size, the grading ofaggregates, their natural colours and the water-cement ratio of the concrete. Surface grinding,polishing and lacquering techniques wereperfected. Before 1992 all my work was withnatural aggregates - stone look-a likes - but in thesummer of ‘92 I had a chance to experiment withcolour and pigments . I knew that earth colouredpigments existed, the red and yellow oxides plusback and cyanine blue. If I could have blue Ithought, why not a spectrum of red, yellow, greenand purple, its been used in pottery for centuries?

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Again a serendipitous meeting led me to sourcetrue primary pigments for colouring concrete. Many,many experiments allowed me to sort out thosepigments that were compatible with concrete.Architects, engineers, contractors and precastmanufacturers were sceptical with my approach.They argued that pigmented colour in concretefades, the colours are unstable and who wantscolour anyway? I did and wanted to cast pictureswith coloured concrete mortars. A still life, a potand a bowl, a sundial and other pieces followed.They were different, they were multi-coloured, theydid not fade and I had created my new concrete artform. The Jonathan Ball practice worked with meand Anthony Fanshawe to produce the Bude Lightsculpture in 2000, a tribute to the inventor of theBude Light , Sir Goldsworthy Gurney, and a clearstatement of what you can do with pigmentedcolour in concrete.

It was becoming apparent to me that sculpture andthe environment were synonymous, as Sir FredericGibberd had concluded many years ago when hedesigned his wonderful garden in Harlow. Mygarden has also proved its possible to combinehardscape and sculpture with plants. In thesummer of 2000 Elwen Balfour of the Brunswick

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Group was sitting in my garden and said “ Thisgarden must go to Chelsea – I’ll see what I cando.” Blue Circle Cement agreed to be the sponsorsof a show garden of my creativity at Chelsea – itwas called the Blue Circle Garden and earned abronze medal from the RHS. The large sphere inthe garden has fibre optical lighting. Before castingthe piece, dozens of fibres were threaded throughthe fibre glass mould, bunched together into acable that comes out of the base and leads to theprojector. The problem was filling the mould with acats cradle of fibres inside.

In January 2001 I was talking to Ian Hart of Pieri,now part of Grace Products and he told me what Ireally wanted was a concrete mix that I could pourlike plaster into a mould that did not requirecompaction. He said “Have you heard of self-compacting concrete- SCC for short?” It’s producedwith carefully selected and blended fine aggregatesand cement, plus superplasticisers and a viscosityagent. It makes free flowing concrete with lowwater /cement ratios that do not need vibration orcompaction. It carries the aggregates to allsurfaces and produces a hard, compact surfacevirtually devoid of air bubbles and voids. It soundedwonderful! No more ramming and the potential to

cast intricate shapes with holes.

As a sculptor I work on very small scale projects.All my experiments with concrete were done in aKenwood Mixer with 1500grammes of concrete. Aconventional concrete slump test would not work,so I converted to using yoghurt pots and mademixes that achieved a 175mm flow on the tablewhen they were poured out of the pot. It worked. Isoon discovered that certain aggregates werebetter than others, that every pigment has adifferent workability and required differentplasticiser dosages. The stiff mixers that I had usedpreviously were not as sensitive, but they had to berammed and compacted in the mould in layers andthis produced bands of colour. The flowing SCCmixes produce fluid patches of colour that are sodifferent and exciting, like patches of paint on thesurface yet they retain their crisp colour edge .Without SCC I would not have been able to fill themould of my latest sculpture ‘Houmet Florains’.This building like sculpture is based on anabstraction of the ruin of a Victorian Fort atAlderney built in 1850. I made one in white and onein black and hope to use it for a memorial in Jerseyfor Pat Carter who founded the Jersey PublicSculpture Trust.

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CONCRETE AS ART

David Undery, Artist

After graduating from SouthamptonInstitute with a Fine Arts Degree in1997, David Undery wasted no time indeveloping his ‘concrete’ fine art careerwith exhibitions in a number of artgalleries across the UK.

He describes his work as abstractpaintings in concrete even thoughsome of the work is highly sculptural.His work crosses the boundariesbetween painting and sculpture tocreate wall hangings that combinelustrous colours with satin-soft or highlypolished surfaces. Through his owndedicated passion for concrete, hetransforms the material into a trulyunique, aesthetic art form.

David Undery explains:

I started off as a figurative painter at art schoolworking in oils and painting portraits. After a year Ibegan an interest in painting cityscapes , inspiredby the building and architecture of Southamptonand concrete pavement slabs that I walked onevery day. Many of the buildings were precastparticularly near the railway station and were verydominating structures. The weather patterning andtexture on the concrete surfaces was intriguing,particularly the markings on pavement slabsabsorbed from rain water run off, spillage of drinks,the resin stains from leaves and other detritus. Thecityscapes I was painting were based on concretecolours and I thought it would be fun to add someneat cement in with the oils when I painted on thecanvas. I started by sprinkling cement dust on theoils over the hardscape areas which became moreintense towards the base of the canvas. Thecement caused the surface to become lumpy andflake away. I then thought of washing the canvaswith cement slurry over the bottom third to createthe hardscape colour then continue with oils abovethat. I added a poly-vinyl-acrylic(PVA) to the wateras a bonding agent to help the cement adhere tothe canvas. Some parts of the picture would be oilpaints and others neat cement and I found that thebigger the painting the better the cement slurry

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worked with the oil as a composition. When Iattempted to lift the canvas, bits of cement mortarwould crack and fall out because the canvas was soflexible. So I started using hardboard to lay thecement mortar on and worked on 12ft wide by 6fthigh compositions consisting of nine separatepanels 4ft by 2ft. The bottom three panels weremade of cement mortar cast on hardboard intowhich I had inserted pipe work and bits of glass likean abstraction of building materials. The panelsbecome very heavy; some were more than 50mmthick. They were paving slabs with a hardboardbacking! It was by chance when I had taken downthe upper panels from the wall of the art room andhad just the three concrete ones left on view, that Irealised what I liked most about the composition – it was the concrete panels. So from that day on I started to concentrate on painting with concrete panels.

The technology of concrete mixing and makingdurable concrete was new to me. I found out thehard way that you must not add too much water tothe mix that you can’t use poster colours forpigments, that reinforcement is required for tensilestrength to reduce the thickness of the panel and toensure it will not break when lifted. I had learnt

about water/cement ratios by the time I had finishedmy degree but had not discovered the world ofconcrete pigments and colour. The college tutorshad not much knowledge of concrete and what Iknew was self taught. I had only beenexperimenting using grey monochrome concrete,tooling and etching the surface by the time I left art school.

I discovered concrete pigments when I went to abuilders merchant to buy cement and also notedthat you can get white and grey cement. Walkingpast construction sites I observed they were usingreinforcing bars to strengthen concrete slabs not thesmall bore metal pipes that I had been trying. Next Idid some research on concrete mixes andpigments, surface texturing and profiling usingreference books and publication on architecturalconcrete that I found in the library. I found out aboutchemical stains and dry shake pigments fromsuppliers Hatfields in Yorkshire. I did try anexperiment with powder paints as used in postercolours instead of concrete pigments, but thecement never hardened. When I approached agallery in Southampton who were keen to displaymy art, they were genuinely concerned about thedurability of the panel whether it would last more

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than a year if it was made with cement. I reassuredthem that it outlast the life of the buyer.

With my concrete canvas the whole surface wasdifferentially pigmented and varied in texture andsurface appearance, unlike traditional precastpanels or paving slabs which have the sameunifying surface colour or texture throughout.Combinations of natural materials like wood andstone even copper are inserted into the concretecanvas whose colour is as rippled and layered as aveneer of beautiful rosewood and cherry wood. Thelustre of the surface finishes are brought about bycoating the hardened concrete with special clearlacquers. This intensifies the base colour pigmentsand heightens the minute particles of sand grainsand micro- pores that appear on the surface asthough carried on a lava-like flow. It reminds me ofa star cluster or a nebula gas cloud in the MilkyWay. The lava or toffee effect of colour on thesurface is created by tilting the panel slightly whenthe cement has just set and pouring a small amountof acid etch on one corner and watch it mingle,disturb and dissolve the surface colour slowly into apaste that trickles down the face. I sometimesintroduce copper as this patinates with the acid etchto release a turquoise green into the colour flow.

When the concrete has fully hardened I applydifferent textures by further acid etching or addingchemical stains which react with the free lime to dyethe substrate terracotta, black or green. Many of mycompositions have elliptical motifs and colour bandsthat add emphasis to the shape and textures that Ihave created. I have recently started to experimentwith polishing and abrading the surface with discs toexpress the aggregates, cutting into the panel,forming drifts and strata of colour moving away fromsurface colouring and highly glazed pieces. This ismy new concrete stone effect paintings that maylead me on to sculptural art one day. There seemsno end to concrete’s versatility, plasticity andcreative possibilities.

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CONCRETE ELEGANCE//PREFABRICATEDPERFECTION 06

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The Seonyu footbridge links the maintown of Seoul to Sunyudo Islandacross the Han river.

The footbridge, which was built intime for the World Cup in 2000 wascalled ‘The Bridge of Peace’ when itwas opened but has since revertedto its official name. It consists of twosteel approach spans and a centralarch of 120m made of Ductal, a newultra high performance concrete.Before describing how we were ableto precast the bridge segments andbuild this very slender concrete arch,let me first explain what Ductal is andhow the material differs fromconventional concrete.

DUCTAL® - A NEW ULTRA HIGH PERFORMANCECONCRETE AND THE BRIDGE OF PEACE, SEOUL

Mouloud Behoul, Lafarge, France

WHAT IS DUCTAL

Ductal is a concrete composed of cement particles,fibres, special fillers and plasticisers that is able tofully hydrate with the minimum of added water. It hasa water/cement ratio of just 0.20. It belongs to aspecial group of ultra high performance fibrereinforced concretes, referred to as UHPFRC. Ductalis the outcome of over ten years of collaborativeresearch between Lafarge the matériel manufacturer,Bouygues the contractor and Rhodia, a chemicalmanufacturer. Through intensive research anddevelopment work, the material has been patented,refined and commercialised. Fifteen universities andsix testing laboratories in different countries havealso contributed to the research effort.

In May 2002 design guidance rules and materialrecommendations were formulated in France for theuse of Ductal in structural applications. Theserecommendations were established by a workinggroup comprising representatives from leadingconstruction companies, building control agencies,suppliers, certification authorities and coordinated bySETRA (Road and Traffic Government Agency)

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The material consists of cement and cementitiousfillers carefully blended and graded, with a particlesize distribution ranging from a maximum of 600 µm(0.6mm), down to less than 0.1 µm to obtain thedensest packing with the minimum of void spaces. Ithas no sand fines or coarse aggregates. It is a superhigh strength concrete mortar with the minimum ofinternal and external imperfections such as micro-cracks, air voids and pore spaces. This enables thematerial to achieve a greater percentage of itsultimate load carrying capacity and enhances itsdurability properties.

The material has a compressive strength rangingfrom 200Mpa - 350Mpa, but has not sufficientlyductility. The inclusion of steel fibres drasticallyimproves the tensile strength and provides asubstantial level of ductility. The various formulationsand applications of Ductal that we havecommercialised, are based on an optimisation of thematerial composition with steel and organic fibres.For example to enhance its structural performancesteel fibres are included and the material is also heattreated to reduce creep and shrinkage strain. Forevery application the technology can be adjusted toachieve the optimum performance required.

For structural grades, Ductal®-FM is prescribed, for asmooth decorative material that can be handledDuctal®-FO is prescribed which has organic fibres,and while for enhanced fire resistance Ductal® AF isprescribed which has a combination of steel andorganic (polypropylene) fibres.

The fresh mixing of these materials with the controlsthat we have introduced makes it relatively easy tohandle in terms of flow and self-compaction. Withminor adjustments, most conventional concretebatching equipment is suitable for mixing Ductal. TheDuctal matrix gives a very fine ‘bone china’ surfacefinish that can be moulded to replicate any kind ofprofile or intricate pattern. By using adequatepigments a range of coloured concretes can beachieved for architectural and decorativeapplications. .

Ductal®-FM, with a compressive strength of 180Mpawas specified for the Seonyu bridge where highbending and direct tensile strengths are required.These mechanical properties are achieved byintroducing short steel fibres 13-15 mm in length witha diameter of 0.2 mm at a dosage of 2% of the mixvolume. The application of heat treatment after themix sets in the mould, eliminates drying shrinkageand greatly reduces creep.

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A typical load–deflection curve for Ductal under athree point loading test is shown below. The materialexhibits linear elastic behaviour up to first crack andhas considerable ductility thereafter until the ultimateflexure load is reached, where upon it begins to yieldwith plastic failure until rupture. It has an ultimatebending strength which is over twice its first crackstress and more than ten times the ultimate stress ofconventional mortars. With such high strength andductility Ductal allows us to design structures withoutany secondary passive reinforcement and no shearreinforcement.

The main properties of the Ductal that was cast in thebridge sections in Seoul, is given in table 1.

THE DUCTAL ARCH

The 120m arch is connected at each end to massivereinforced concrete foundations which are 9m deep.These foundations are designed to absorb thehorizontal thrust of the arch. The arch consisting of aribbed upper deck slab (the walkway) and two girderbeams in a double T configuration. The width of deckslab is 4.3m and the beams are 1.3 m deep. Thedeck slab has a 30mm topping with transverse ribs at600mm centres that are 150mm deep. The deck slab

is supported by the two 160 mm thick girder beams.The shape of the girder beams and deck slabgeometry was chosen for easy demoulding of thesection.

The ribs of the deck slab are prestressed by either oneor two 12.5mm diameter monostrands. Speciallyadapted small anchors were used to transfer theprestressing forces from the strands to the ribs. Eachgirder beam is prestressed longitudinally by threetendon clusters which are sleeved through metal ducts.There are nine strands in each of the clusters in thelower two ducts and 12 strands in the upper duct. Thetendons of the beams are stressed once the segmentsare in place on the supporting scaffold towers. Aftercompletion of the stressing phase, the tendon ducts aregrouted. Two temporary monostrands are cast intoeach segment in the lower part of beam to cater forstresses during lifting and placing operations as eachsegment in positioned onto the scaffold towers thatwere built across the river.

The arch is composed of six segments. Thesesegments are prefabricated in an area next to thefinal location of the arch. Diaphragms are added atthe ends of each segment. The diaphragms on theend segment spreads the compressive loadsimpacting on the foundation concrete, while those

Table 1. Properties (typical values) of Ductal® with steel fibres and after heat treatment.

Density 2500 kg/m3

Compressive strength 180 MPa

Tensile strength 8 MPa

Post-peak strength in tension 5 MPa

Young modulus 50 000 MPa

Poisson ratio 0.2

Shrinkage 0

Creep factor 0.2

Thermal expansion coefficient 12.10-6 m/m

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over the central arch are for jacking the two halves ofthe arch.

The segments are 20-22m long and curved. Theslope at the extremities is more than 8%. The volumeof Ductal in a segment is 22.5 m

3. The total mixing

time to fill the metal mould for each segment was fiveand a half hours. The mould is filled using eightinjection points positioned midway along the internalsurface of the beams. During the casting operations,the fluidity of the Ductal mix is constantly checkedand controlled .

After casting a segment, it is cured in the mould at35°C for 48 hours. A spreader beam is used to cranelift the segment from the casting area to a heattreatment chamber. The segment is then steamcured at 90°C for 48 hours.

The six segments - three on each half of the arch -are positioned in sequence on the scaffold towers bya crane, mounted on a river barge. The segments oneach of the half spans are stitched together, thenprestressed before the tendon ducts are grouted up.The two half spans are finally joined together bycasting the short insitu crown or key segment stitch.Before casting the insitu stitch a precompressionforce of 2300 kN is applied to each half span using

hydraulic jacks. The key segment stitch is then castand when the Ductal in the stitch has reached astrength of 85 MPa, the jack loads are removed andthe force transfers back into the arch, to maintain thearch in precompression. This is good for stability androbustness.

This is the first time in the world that an ultra highperformance concrete, reinforced with steel fibreshas been used for a span of 120m. The properties ofDuctal have made it possible to design a veryslender arch with thin sections, giving the footbridgeelegance. Other footbridges have been constructedusing Ductal they are the Sakata Mirai in Japan, theSermaises in France, the Sherbrooke in Canada andanother one is under construction in Japan.

The use of this concrete-like material has almostunlimited possibilities of appearance, texture andcolour. It has excited architects by giving themaccess to an unexpected new world of shapes andforms. Ductal has been used in architecturalapplications like the bus shelters in Tucson (USA),flower pots in Rennes (France), façade panels inMonaco and the Kyoto clock tower in Japan.

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The Concrete Centre

Riverside House4 Meadows Business ParkStation Approach, BlackwaterCamberley, Surrey GU17 9AB

t: +44 (0) 700 4 822822www.concretecentre.com

The Building Centre Trust

26 Store StreetLondon WC1E 7BT

t: +44 (0) 20 7692 6208e: events@buildingcentretrust.org

Help and advice on concrete matters telephone the helpline on +44 (0) 700 4 500 500 or visitwww.concretecentre.com

All Concrete Elegance events are free of chargeand take place in the Building Centre in theevenings. To attend any event or to find outabout current and future programmes pleasecontact The Concrete Centre or the BuildingCentre Trust

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