White Concrete Guide

c r e a t i n g w h i t e c o n c r e t e f o r a l i g h t e r w o r l d

SnowcreteW H I T E C E M E N T

Yq2

Uniclass L621

CI/SfB

March 2007

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IntroductionContents

White cement – architecturalconcrete for a lighter worldWhite cement opens up a whole new world of possibilitiesfor designers. And Snowcrete white cement from LafargeCement UK is the product that can help turn architecturalvision into reality.

By mixing white cement with pure light coloured sand andlight coloured aggregates such as white granite, marble orcrushed calcined flint it is possible to create a pure whiteconcrete. This is in marked contrast to ordinary greyconcrete, in which ordinary Portland cement is mixed with naturally coloured sands and aggregates.

The colour and light-reflecting qualities of white concretegive it a highly distinctive appearance, differentiating itmarkedly from grey concrete. White concrete can beinstrumental in creating architecture of striking visualquality, with lightness, quality of finish, and dramaticinterplay of light and shade reflected to maximum effectthrough built form and imaginative detailing.

White concrete also enhances the effect of colour.Coloured pigmented concrete based on Snowcrete isespecially pure and vibrant compared with colouredconcrete made with grey cement. This exceptional purityof colour is also apparent when white cement is used formortars and renders.

The images throughout are just a taster of the incrediblevisual qualities of white concrete.

This guide describes and illustrates the applications,qualities and characteristic of concrete products madewith white cement. You will find detailed informationwithin clearly defined sections. After a generalintroduction, the guide looks in depth at the wide rangeof white cement based applications, which include:

• In situ concrete construction

• Precast building components

• Terrazzo

• Fibre reinforced concrete

and the many associated uses in, for example, paving,architectural facing masonry, tiles, renders, paints, mortars, etc.

There is a detailed section on concrete production, which covers everything from formwork, vibration andcuring to detailing and coloured concretes. Finally, there is a summary of relevant standards and references relevantto the use of white cement in the United Kingdom.

We hope you find this specifiers’ guide inspiring anduseful. Welcome to a new world of possibilities using Snowcrete white cement!

Introduction 2

White cement in concrete 4

Snowcrete 6

Applications 8

Cast in situ concrete 8

Precast 10

Terrazzo 12

Precast elements 14

Fibre reinforced concrete 16

Renders 17

Production of concrete 18

Formwork 20

Exposed surface finishes 22

Concrete vibration 24

Curing 26

Avoiding blemishes 27

Detailing 29

Coloured concrete 31

Standards and references 33

SnowcreteW H I T E C E M E N T

Elemental chlorine free

Woodpulp sourced from

sustainable forests

80%recycled fibre

NAPM approvedrecycled product

Printed on eco-friendly paper to protectour environment

At Lafarge Cement we are committed to playing our part in conserving the environmentand supporting sustainable development. That is why this publication is printed on papermanufactured without adverse environmentalimpacts.

Technical specification:

This publication is printed on papermanufactured from:

• 80% recycled fibre content – comprising 60%recovered from post-consumer de-inked pulpsources FSC (Forestry Stewardship Council)certified, and 20% recycled wood and fibre

• 10% of the virgin fibre FSC accredited and10% sourced from sustainable forests

Cover photograph ©Edmund Sumner/VIEW

80%

Cert no. TT-COC-002326

FSC Trademark © 1996 Forest Stewardship Council A.C.

This quality of paper helps us to maintain ourhigh presentational standards, while respectingour environment and promoting sustainability.’

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At present, less white cement is usedworldwide than ordinary grey Portland cement.However, with fast-increasing awareness of itsexceptional qualities, the use of white cementis growing by about 4-5% annually.

Snowcrete is a white cement. When used withlight coloured aggregates it creates a lightcoloured concrete. For truly white colouredconcrete white aggregates and pure light sandmust be used to create the distinctive purewhite, light reflecting finish. Although whiteconcrete is often characterised by great visualdelicacy, Snowcrete has a higher final strengththan ordinary Portland cement.

Visual appeal and functionalityThe effect of white concrete can be stunning,with surfaces that resonate with a continuouslychanging light and shade as the sun’s pathchanges. The desire for white concrete beganin response to the Bauhaus buildings of the1930s, which reflected the teachings of themovement on the importance of materials andthe characteristics of colour and form. Themove towards exposed concrete structuresallows architects to express the structuralquality of concrete in their designs, while whiteconcrete adds light and drama to structure andform in architecture.

Concrete structures are not only visuallyappealing they are also functionally effective.The thermal mass of an exposed concretestructure helps to even out daily swings intemperature, avoiding the need for airconditioning. The importance of utilising thethermal mass of concrete has become anincreasingly common theme in many recentbuildings. The dampening effect of the highthermal mass on peak summer temperatureshas enabled the use of natural ventilation toreplace what would previously have been airconditioned buildings. The use of exposedconcrete results in more sustainable buildings.

Where concrete is exposed, the use of whitecement to create a light coloured concretehelps to reflect a higher proportion of daylightinto the building, reducing the energy need for lighting.

SnowcreteW H I T E C E M E N T

Introduction

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6

Snowcrete

Product characteristicsSnowcrete is a Portland cement that isdesignated CEM I 52,5 to BS EN 197-1. It is aquality assured cement carrying CE Markingwith independent third party certification.

Concrete made with Snowcrete is rapidhardening and quickly gains high compressivestrength. Its ultimate strength is higher thanconcrete using ordinary Portland cement (CEM I 42,5). The inherently high compressivestrength is a direct result of the highproportion of strength developing calciumsilicate minerals present in white cement.

What makes the cement white? It is the presence of Iron Oxide (Fe2O3) that

gives ordinary Portland cement its grey colour.Every 0.1% of Iron Oxide reduces thereflectivity of the cement powder by about2.5%. So to produce a cement as white aspossible involves minimising the Iron content inany form (oxides or sulphates). Other heavymetal compounds also colour the cement, butare present in much smaller concentrations.

The potential whiteness of the cement isdetermined by:

• The raw materials

• The processing in the kiln

• The grinding of the cement clinker

The raw materialsSnowcrete is made from particularly pure whitechalk and finely ground silica sand, which islow in iron. The effect of small quantities ofcoloured substances that occur naturally in theraw materials are eliminated through the useof a special flame-cleaning technique. There iscontinuous monitoring of the raw materials toensure the iron content is less than 0.15%.

Kiln processingThe manufacturing process is very similar to theproduction of ‘grey’ Portland cement. However,in grey cement the iron content acts as the fluxwhen burning the ingredients to create theclinker that is then cooled and ground to makecement powder. As white cement has a verylow iron content, mineralisers are added to themix to aid burnability. Even with themineralisers, the kiln must be fired to highertemperatures than for grey Portland cement,typically to 1400ºC. This ensures full burning of the ingredients. Kilns for producing white

cement have more complex linings towithstand the greater temperatures andprevent colour contamination of the cement.To help maintain the whiteness of the cementfiring takes place in a slightly reducedatmosphere by close control of the combustionair to the main burner.

When the clinker from the kiln first cools, anyiron in the mix will oxidise, colouring thecement. To prevent this, the clinker is quenchcooled as soon as possible after passingthrough the burning zone. Quenching is bywater spray which cools the clinker to about800ºC. This is sufficient to maintain thewhiteness of the cement. Heat recovered fromthe subsequent cooling is used to preheat thecombustion air to 200ºC. This reduces fuelconsumption and stabilises the flame. Greatcare is needed to remove the superheatedsteam from the quenching process withoutcausing health and safety issues.

GrindingQuench cooling shatters the clinker making itfiner and easier to grind. The clinker is groundwith gypsum to produce the final cementpowder. Gypsum helps to control the settingtime of the cement. White gypsum is used tomaximise the whiteness. The finer the grindingthe brighter the whiteness. White cement isnormally ground finer than grey Portlandcement for this reason.

How is ‘whiteness’ measured?The ‘white’ quality of cement powder can bemeasured using a photometer. For consistentresults, the cement powder is compressed witha force of 50KN for 10 seconds and measuredwithin 10 minutes of pressing, as samplesdarken with time.

The results are usually expressed using theL*a*b* system which is universally used by all photometer manufacturers.

L* (luminance) black = 0, white = 100

a* = green-red axis (-=green, +=red)

b* = blue-yellow axis (-=blue, +=yellow)

The main emphasis for a white cement is onthe luminance value (L*). There is usually a low range of variation in the a* and b*measurements, with a tendency towards yellow.

The graph opposite compares the luminance ofvarious cements with their iron oxide content.

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Product data

Alkali content

The soluble alkali content of Snowcrete is only0.1 to 0.3%, making it a low-alkali cement.

Sulfate resistance

Snowcrete has a typical C3A content of

approximately 6%, providing a high level ofsulfate resistance.

Typical properties

1 day strength

2 day strength

7 days strength

28 day strength

Initial setting time

Expansion

Loss on ignition

Insoluble residue

Sulfate content SO3

Chloride

C3A

Alkali content

Water soluble chromate

Y-Reflection (DIN 5033)

Specific density

100

90

80

70

500 1 3 4 5

Lum

inan

ce(L

*)

White Portland cements

Cem I, II and IIIordinary Portland cements

60

2

Fe O content (%)32

Source: Lafarge Cement Division

Comparison of White and ordinary Portland cements

Chromate content

Snowcrete has a low soluble Chromium (VI)content of 2 ppm.

The table outlines the typical characteristics of Snowcrete.

Property Declared interval Requirement EN 197-1None

30MPa

None

52,5MPa

45min

10mm

5,0%

5,0%

4,0%

0,10%

None

None

None

None

None

18-24MPa

34-42MPa

55-67MPa

70-79MPa

85-130min

0-2mm

0-1.0%

0-0.3%

1.8-2.3%

0-0.02%

4-5%

0.2-0.3%

0-2mg/kg

85.0-89.5%

3120-3180kg/m3

≤

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Applications – Cast in situ concrete

Columns

Ceilings

Walls

Floors

Staircases

Facades

White cement is used as a construction cementthroughout the world for reinforced concretestructures of all types. For in situ work, thehigh reflectivity of white concrete enhancesstrong architectural forms, with dramaticcontrasts of brilliant light and shade. This isparticularly so where the white concrete finishis smooth when the contrast of dazzling whiteis particularly evident.

In situ concrete offers the designer wideopportunities for striking architecturaltreatment through structural form and a widevariety of surface treatments and textures. Snowcrete is ideal for in situ work because ofits high early and final strength. It can be usedin place of ordinary Portland cement for anystructure.

To fully exploit the special character of in situconcrete, careful selection and detailing of the formwork is required. The design of the formwork will be reflected in the finishedconcrete and will be more pronounced thelighter the colour of the concrete. Formclamps, the nature of the shuttering material,and joints between lifts will all be plainly visiblein the finished construction. These ‘workings’in the concrete add character and can be used to complement the form and shape of the structure.

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Applications – Precast

Decks

Pavements

Walls

Columns and girders

Facades

Opposite page, bottom, Jubilee Church by RichardMeier & Partners

White cement can be used to construct precastbuilding elements, both structural anddecorative. Precasting produces constructionalelements that do not require on-site finishing.

With precast concrete frames the buildingstructure is fabricated off-site. Used in this way,white concrete meets both structural andaesthetic design requirements. A wide range of mixes, colours and finishes is possible.

Precast cladding panels can be formed intovirtually unlimited configurations to createdistinctive modelling for buildings. Varied visualeffect is also created through many differenttypes of finish including acid etched, smooth or coarse ground, grit or sand blasted, rubbedor polished. Many effects can be achieved with different aggregates and the addition ofcoloured pigment. White cement can be usedin cladding panels to replicate a natural stoneeffect, including Bath stone, Portland stone andmarble. The finish can be natural, weathered orhighly polished.

Offsite prefabrication means faster programmetimes with no potential ill-effects from adverseweather or labour shortages. Offsite fabricationof structural components results in fast andefficient erection on site. Through off-sitemanufacture it is possible to achieve a finish onwhite concrete frames of an exceptionally highstandard that can be left exposed. Precastcladding also improves buildability because thedry envelope is completed quickly, enablingfollowing trades to begin work sooner.

Precast concrete panels are cast face-down inpurpose-built moulds, usually of timber or glassfibre. Different designs and surface effects canbe achieved in various ways. Template mats orrods inserted into the base of the mould cancreate intricate patterns or replicate joints. The benefits of offsite fabrication are beingextended to include other elements, such asinsulation and windows, during the manufactureof precast panels. After demoulding the surfaceof a precast panel can be treated in a variety ofways – acid-etched, smooth or coarse ground,grit or sand blasted, rubbed of polished.

SnowcreteW H I T E C E M E N T

Staircases

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Photograph ©Edmund Sumner/VIEW

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Applications – Terrazzo

The high reflectivity of white cement can createan exceptionally white terrazzo when combinedwith light aggregates. Snowcrete white cementis therefore the perfect binder for modern dayterrazzo applications, with a high strength thatadds to the naturally hardwearing nature ofterrazzo surfaces.

Terrazzo comprises up to 70% aggregate, and it is the aggregate therefore thatpredominantly determines the final finishedappearance. If a coloured concrete binder isused, white cement provides an ideal base forachieving clear sharp or translucent colours. A combination of pigment and differentcoloured aggregates can be used to createexciting finishes and patterns of almost limitlessvariety. In tandem numerous chemical cleanersand sealers have been developed to enhanceand preserve the beauty of terrazzo.

The term terrazzo derives from the Italian wordfor terrace. Terrazzo first appeared severalhundred years ago in Europe when Venetianworkers discovered a new use for discardedmarble remnants. A smooth surface wasachieved by hand rubbing with stones.Through experience, craftsmen discovered thatgoats’ milk enhanced and preserved the truecolour of the marble – perhaps the firstterrazzo sealer.

Terrazzo can be poured as a top coating over aconcrete base but it can also be cast. Althoughit is most often used for floors and stairs,Terrazzo can be used for façade facing,tabletops, vanitory units, washbasins, stairtreads, etc.

After pouring, the terrazzo surface is keptdamp for 2-3 days until it develops sufficienthardness. It is then coarse ground and treatedwith cement paste. After about 24 hours theterrazzo is finely ground until the surface issmooth and free from cement slurry.

Terrazzo is not only beautiful it is also anextremely practical, easy to clean andhardwearing surface. Research conducted in the USA by the National Terrazzo andMosaic Association has shown that the wholelife cost of terrazzo is extremely favourablein comparison with carpet, ceramic tile, vinyland other flooring materials.

Fittings andfurniture

Walls

Floors

Staircases

Facades

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Applications – Precast elements

Precast elementsWhite cement has been successfully used in theproduction of precast ornamental elements forbuilding and decorative reconstructed stone. It is also frequently used for applications suchas floor tiles, paving and edging stones, stairtreads and balconies, window casings and city furniture. White cement also finds uses in precast applications such as whitebriquettes, pressed bricks, concrete gratings,pool edgings, etc.

Artistic useWhite cement is widely used to produceconcrete statues, monuments, scarfito as well asin modern artistic applications and restorationsof archeological and ornate buildings.

The light-reflecting properties of Snowcreteimprove traffic safety when used to producekerbs, road-markings, safety barriers, tunnellinings and tunnel ramps.

Pavements

Urban spaces

Floors

Columns

Details

Blockwork

Traffic regulation

Footpaths

SnowcreteW H I T E C E M E N T

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Applications – Fibre reinforced concrete

Fittings andfurniture

Balconies

Refurbishment

Cladding panels

Details

White cement can be mixed with reinforcingglass and steel fibres to produce incrediblyslender yet strong concrete structures. Theexample on the right is constructed using ultrahigh strength Compact Reinforced Composite(CRC) with steel fibre reinforcement. The edgesof the steps are only 30mm thick. CRC wasdeveloped in Denmark and has recently resultedin an increasing number of innovative andpioneering structures such as this spiral staircase.

Adding steel fibres to high strength concretesadds ductility to what can otherwise be abrittle material. The usual applications forthese concretes in precast production are small slender elements such as balcony slabs,staircases, beams and columns.

Glass fibre reinforced concrete with Snowcretecan also be used to produce slender andelegant components. The white concrete finishemphasises the lightness and elegance of thefinished product.

Alkali resistant glass fibre adds the tensilestrength that concrete lacks. At low dosagerates, the fibres are used to control shrinkagecracking in normal concrete. A higher glassfibre content of 5-6% is used for spraying intomoulds. The finished thickness of precastcladding panels is only 10-15mm. GRC isparticularly suitable for delicate fine detailedconcrete, as shown below.

SnowcreteW H I T E C E M E N T

Staircases

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Applications – Renders

Walls

Facades

Snowcrete can be used in cement:sand rendersto provide either a clean white render or athrough coloured render.

The choice of sand should match the finishedcolour of the render as far as possible. This isbecause as the render is exposed over time thecolour of the aggregate material itself willbecome apparent.

White cement is recommended as the basis forrenders where the maximum light reflectance isrequired. The use of white cement ensureslong term colour fastness.

White cement is also the basis for clean, fresh coloured renders without the dullnessassociated with ordinary Portland cements. The use of coloured pigments can produce awide range of tints that help transform theappearance of a building.

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Production of concrete

Selecting the right ingredientsSnowcrete is used to produce white concrete bymixing with white aggregates, light colouredsand, water and admixtures.

Cement

Snowcrete can be supplied both bagged and inbulk. Due to the naturally low content of solubleChromium (VI) in white cement, there are nochromium related ‘shelf life’ issues. It can bestored for at least six months if kept in suitabledry conditions. Bagged cement should not bestored in direct contact with the ground, on aconcrete ground floor, or up against externalwalls. We recommend that bags are stored onpallets, to keep them off the ground, andprotected from the weather.

Water

The water used for mixing concrete and forcuring cast concrete must be clean, such asmains water.

As with any concrete, the water/cement ratio is critical in determining the final strength ofthe concrete.

Aggregates

The choice of coarse aggregate and its colour iscrucial to the final appearance of white concretethat has an exposed aggregate surface.Aggregates suitable for white concrete includewhite granite, white marble and crushedcalcinated flint.

For fair faced finishes, it is the choice of fineaggregate, especially the colour of the fillerparticles smaller than 0.25mm, that has moreinfluence on the whiteness of the concrete. Fillermaterial of white marble and feldspar make iteasier to achieve a consistent white colour to thefinished concrete.

In determining aggregate composition, it isimportant when making up facade concrete –whether for smooth-cast surfaces or exposedsurfaces – to keep to the narrow tolerance limits of the combined grading curve. It isrecommended that a tolerance of ±5% beapplied to screen meshes of 0.25mm and 4mm,and to the mesh corresponding to half the valueof the selected maximum grain size. If this is 16mm for example, the tolerance for 8mmscreen mesh applies.

The aggregate grading also influences thedevelopment of surface air voids (blowholes) inthe concrete. A well-defined grading curve witha suitable content of filler (<0.25mm) givesconcrete good compaction characteristics.Furthermore, it leaves little room for free waterand free air in the concrete, and so reduces therisk of air void formation. Experience shows thatthe content of filler for smooth-cast surfacesshould occupy between 5 and 10% of thegrading curve. Filler material should consist ofcubic and rounded grains.

The maximum grain size in aggregate and grainshape is also significant. The general rule is thatcoarse aggregate increases air void formation,compared with smaller grain size. Coarseraggregate materials with irregular shapes alsoabsorb far more air at the surface than natural,rounded, smooth aggregate.

All aggregates should be stored and used toavoid contamination so that the aestheticappearance of the concrete is not compromised.Extra care is also needed to ensure that the mixof aggregates is as constant as possible betweenbatches in order to avoid differences in shadingof the finished product.

Aggregate exposed bywashing

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Concrete composition

Surface Grading Cement Fine aggregate Coarse Fine/ Admixtures w/ckg/m3 kg/m3 aggregate coarse ratio

Exposed Gap graded 330-350 400-500 1350-1450 25-75% HRWRA, WRA 0.55colour (AEA)*

Smooth Smooth grading curve 330-350 650-800 1000-1150 40-60% WRA, AEA 0.55 moulded or slightly oversanded colour, HRWRA

Profiled Smooth grading curve 330-350 650-800 1000-1150 40-60% WRA, AEA 0.55or slightly oversanded colour, HRWRA

Smooth, profiled, Smooth grading curve 330-350 650-800 1000-1150 40-60% WRA, AEA 0.55 acid-etched or slightly oversanded colour, HRWRA

* It can however be quite difficult to mix air in exposed concrete, because of its composition.WRA = Water reducing agentHRWRA = High range water reducing agentAEA = Air entraining agent

100

90

80

70

60

50

40

30

20

10

064321684210.50.250.125

Perc

enta

ge

pas

sin

gth

rou

gh

mes

h(%

)

Screen mesh in mm

Filler Fines Coarse aggregate

100

90

80

70

60

50

40

30

20

10

064321684210.50.250.125

Perc

enta

ge

pas

sin

gth

rou

gh

mes

h(%

)

Screen mesh in mm

Filler Fines Coarse aggregate

Combined grading curve for acid etched finish

Combined grading curve for exposed aggregate finish

Coarse/fine 75/25%Coarse aggregate content 1400-1450kg/m3

Coarse/fine 60/40%Coarse aggregate content 1050-1150kg/m3

Admixtures

Admixtures are accepted as contributing to the production of durable concrete that is easierto handle, place and compact when fresh andreduces the permeability of hardened concrete.BS EN 934-2: 2001 covers the requirements foradmixtures in concrete.

All admixtures should be colourless. To ensure the desired white colour, it is alwaysrecommended to make trial mixes. Trial mixescan also help to establish the dosage necessaryto achieve the desired result.

Air entraining agents help to reduce thetendency of efflorescence and are particularlyrecommended in the colder months.

The use of water reducing/plasticising agents willallow a reduction in the water/cement ratio andproduce concrete which is more workable.Concrete with a relatively low water/cement ratioquite often requires strong compaction to achievea suitable density. Intense compaction by vibrationincreases the risk of large air bubbles forming. It istherefore advantageous to use additives that givebetter flow characteristics which in turn permit areduction in the use of intense vibration.

To avoid mottled discolouration, calciumchloride should not be used in white orcoloured concrete.

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Production of concrete – Formwork

Formwork must be able to resist thetremendous pressure exerted during placingand compaction.

Formwork and shutteringWhere an ‘as struck’ or ‘fair faced’ finish is specified, the choice of formwork for both in situ and precast concrete has asignificant affect on the appearance of thefinished concrete.

Where a smooth finish is required, there is a choice of three types of formwork:

• Film-faced plywood

• Steel formwork

• Plastic formwork

Film-faced plywoodFilm faced formwork plywood consist of a resin impregnated film which is bonded to the plywood under pressure. The resin finishmasks the natural grain of the plywood,producing a smooth uniform concrete surfacecolour and quality for each and every application.The durable surface finish is resistant to minordamage and minor scratches do not leave visiblemarks on the finished concrete.

These plywoods are used for multiple pourhigh quality concrete formwork and can offer40 or more concrete pours. The resin surfaceoffers easy separation from the concrete andeasy cleaning. Because the resin finish is hardand abrasion-resistant, film faced plywood isoften specified when the smoothest possibleconcrete finish is desired.

Most film faced plywood panels are suppliedwith edges sealed to inhibit moisture absorption.Panels should be cut with sharp tools and all cutedges sealed.

Damaged panels should be discarded ratherthan repaired, as materials used for repairusually have a different degree of moistureabsorption to the ply face and can result in achange in colour to the finished concrete.

Steel formworkSteel formwork is a good choice for theproduction of large, smooth surfaces. Itsrelatively high cost and durability make itsuitable where repeat usage is high. The hardsurface of steel means that formwork defectsare uncommon, however, the dense surfacetends to increase the number of blowholes inthe concrete surface.

Two samples made fromthe same concrete mix,but cast in differentformwork – timberboarding (top), film-faced plywood (bottom)

Plastic formworkPlastic formwork is particularly suitable forcreating complex shapes. Different types ofplastic formwork are used, but the omission offormwork oil is not recommended. Withrepeated use, increased wear can affect thefinished appearance of the concrete surface.Plastic formwork presents a similar risk ofsurface blowholes as steel formwork.

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Timber formworkWhere it is desired that the grain of the timber isexpressed in the finished concrete, particular careis needed to ensure a white finish is achieved.

For a uniform high quality finish, it is vital toobtain consistent surface texture and porosity.The timber grain can be enhanced by using asteel brush or sand blasting the surface of theboards. The joints between boards must beglued or otherwise sealed to prevent groutloss. Grout loss can result in the appearance of dark edges in the finished concrete.

To prevent moisture absorption by the timberand eliminate the transfer of wood sugars andresins into the concrete a water-based sealermust be applied to the formwork.

Good workmanship in the construction oftimber formwork is critical to the quality ofthe finished concrete.

Chemical release agent

These are a blend of fatty acids in anevaporative carrier. They provide a stain-freeconcrete finish and are usually the preferredoption for ‘as struck’ high quality concrete.

Chemical release agents are suitable for use on all impervious formwork surfaces. They areapplied as a fine film. After application they takeabout 12 hours to dry to a rain resistant, mattfinish on the formwork surface. The dry surfacereduces the pick up of airborne dust which canmar the appearance of fair faced concrete.

The agents are mildly acidic. They react withthe alkalinity of the concrete to form a soapthat allows clean demoulding, without leavingany residue on the concrete surface.

Mould oils

The big advantage these have over chemicalrelease agents is that there is no waiting timefor the release agent to dry. Mould oils aretherefore suited to precast plants where largevolumes are placed quickly.

Spray application is recommended for an even film thickness. Application of excessiveamounts of mould oil should be avoided.

Formwork release agentsThe choice of formwork release agent has a fargreater effect on surface quality than is oftenappreciated. The release agent plays anessential part in releasing the concrete from theformwork and minimising the risk of surfaceblow holes. In addition, a good release agent:

• Reduces the amount of cleaning necessaryand increases the number of times a mouldcan be used

• Avoids discolouration of the concrete

• Does not cause formwork to swell or shrink

• Leaves minimum residue

• Does not retard the concrete surface

Trial castings using different agents should bemade to check their effect on the colour of thefinished concrete.There are many products onthe market, the most suitable for use withwhite concrete are:

• Chemical release agents

• Mould oils

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Production of concrete – Exposed surface finishes

Exposed finishes involve the removal oflaitance, the very thin layer of fine aggregateand cement that forms on the surface of freshconcrete. A very wide range of surface finishesand textures can be achieved, options include:

• Acid etching

• Exposed aggregate surfaces

• Polishing and grinding

• Reconstituted stone

The surface texture has a significant effect onthe appearance of the building, especiallywhen viewed at close quarters.

Acid etchingMild acid etching of plane or profiled surfacesthe day after casting will remove cement pasteand leave a very finely textured, stone-likesurface. Acid etching is usually performedusing a 1:10 acid solution (30% commercialhydrochloric acid).

A retarder is often used in combination withacid etching. Retarding agents delay thesurface hardening of the concrete so that, after formwork stripping, the surface layer can be removed more easily. The retarder isapplied to the formwork in an even layer and is allowed to dry before casting.

It is important to thoroughly wet the concretesurfaces with water before acid etching toprevent the surface from absorbinghydrochloric acid. After acid etching, thesurface must be thoroughly flushed with water.

Normally, this form of treatment only exposesthe sand grains, so it is the colour of the sandand fines that largely determines the finishedcolour of the concrete.

Exposure of aggregateby flushing and brushingthe concrete surface.

Sand blasting to exposethe aggregate

Exposed aggregate surfacesDepending on the colour of the coarseaggregate and the method used to remove theouter surface of concrete, a wide range ofsurface textures can be achieved. The gradingof the aggregates can also influence thefinished appearance, especially where water isused to expose the aggregate.

Water and sand blasting are the two mainmethods used for exposed aggregate finishes.

A retarder is often used to delay the surfacehardening of the concrete and make it easierto remove the outer concrete paste with awater spray or jet and brushing. Whereaggregate is exposed by water, it retains its angular or rounded shape and naturalreflectivity.

Sandblasting is more commonly used onhardened in situ concrete. The surface is leftrough, but quite uniform.

Sand blasting must be carried out before theconcrete has hardened too much. So formworkshould be removed relatively early. The carefulplanning and control of hardening conditionsare therefore necessary.

Sandblasting is normally performed with quartzsand. The treatment is often carried out in twostages. Coarse-grained sand is used first, theday after casting for example, followed sometime later by fine-sand blasting to create aneven and uniform finished surface.

The object is to wear away the cement pasteon the surface so that the aggregate andcoarse sand grains are left in a relativelyuniform texture. With sand blasting, thenatural colour of the surface becomes slightlygreyish or matt.

Exposed aggregate, polished and acid etched – three different finishes from the same concrete mix

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If the concrete is sufficiently hard, the sandblasting will tear out sand grains andaggregate. If the concrete is allowed tothoroughly harden, costs will be high becauseof the time needed to expose the aggregate.

Dry sand blasting develops large quantities of dust and workers must use specialprotective clothing.

Polishing and grinding Polishing of precast facade units gives aterrazzo like finish. It is best carried out at afactory used to dealing with horizontal grinding.

Grinding is coarser than polishing and gives asimilar surface finish to acid etching. Grindingshould normally be carried out after 3-4 dayshardening time, otherwise there is a risk oftearing aggregate out of the concrete. Inplanning such work, it is imperative to takeaccount of the fact that the grinding processrequires the provision of a drain to take awaythe large amount of water involved. It is alsoimportant to use aggregate that is suitable forgrinding (marble, granite, etc).

Hammering and pick chisellingThis is a relatively expensive finishing methodthat is normally only used on in situ concrete.

A pneumatic bush hammer is normally used forhammering. This achieves a fairly modest depthpenetration. Ideally, formwork should containthe fewest possible joints.

A stronger effect can be achieved with a pickchisel bit. Surfaces become coarser and ingeneral the appearance is more uniform.Normally the intention is to create an

appearance similar to that of split granite. It is therefore an advantage to use granite in theaggregate when making up this type of concrete.

Account must be taken of the fact thathammering and especially chiselling removesubstantial amounts of material (with chisellingup to 2-3 cm). Sharp lines are very difficult toachieve. Thus, beams and column edges willappear a little uneven. This is why suchtreatment is often reserved for surfaces that areto be framed with smooth-cast concrete, sothat all corners and edges can be left untreated.

Hammering and especially chiselling requirestrong concrete and should not be started untila hardening time of about 14 days has elapsed.

Reconstituted stoneThis is a specialised form of exposed aggregate,in which the colour of the aggregate, sand andpigmented cement are all matched to give athrough colour to imitate a natural stone, suchas Portland or Cotswold. The finished surface isusually washed or sand blasted to expose thenatural colour of the aggregate.

Precast panels ofreconstituted stone togive the appearance ofPortland stone

Calcinated flint with a scraped finish Calcinated flint with a waterwashed finish

Hoveringham gravel, in greyconcrete with point tooled finish inupper photo and in white concretewith washed finish below

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Production of concrete – Concrete vibration

Good compaction is essential not only for the strength of the concrete, but also for itsappearance. Freshly poured concrete contains a large amount of entrapped air from themixing process and from placing in theformwork. To prevent pores forming at theconcrete surface, this air must be removed.

Vibration is used to remove air bubbles. The greater the distance the air has to travel to the surface, the more the concrete has to beworked. This is why it is more difficult to limitthe number of blowholes in walls and pillarsthan in floors. The upper parts of walls andpillars are normally where most blowholesappear and therefore these parts of theconstruction require special care.

In situ concrete The concrete should be poured continuously inlayers at an even rate. Pauses between layers cangive rise to discolouration and void formation. In general, the drop height for poured concretemust not exceed 1m. If this is exceeded, there isincreased risk of segregation.

For in situ concrete, the vibration poker shouldbe pushed down into the freshly pouredconcrete. The poker must be taken down intothe concrete rapidly, then, after allowing it tooperate for a short time at the deepest point,withdrawn slowly so that no cavities formbehind it. The whole process should take 15-30seconds. This helps the upward movement ofentrapped air bubbles. Experienced concretecasters are able to judge when concrete hasbeen sufficiently vibrated by looking at thesurface. It should be closed by cement slurry,with just an occasional air blister appearing.

When casting constructions of limited cross-sectional area, pillars for example, rapidinsertion of the vibrator is important. If it isallowed to operate for too long in the upperlayers the fine-grained constituents pack, soblocking the escape of larger air bubbles. This in turn leads to the formation of moreblowholes in the finished concrete surface.

Poker vibrators with a long drive shaft orvibrators with a built in motor and long cableare ideal where high, vertical walls and pillarsare involved. These vibrators can be insertedthrough ‘ports’ in the sides of forms. Uniformvibration throughout the entire height is aprecondition for a successful result and auniform concrete surface.

Ideally, concrete should be poured intoformwork in horizontal layers of equalthickness. Under no circumstances should any layer be more than half a metre thick. The aim is to cast the same layer thickness for the entire job.

Pouring and vibrating must be co-ordinated sothat the poured concrete becomes compactedcorrectly. Where there are strict surfacerequirements, the height of each pouring layershould not exceed 300mm.The vibrator mustalways be inserted to the same depth in theunderlying, already vibrated, layer. The insertionpoints should be in a regular pattern ofdistribution. It might be advantageous to use a poker with a diameter of 40mm.

Layer thicknesses greater than 500mm can be expected to result in an increased numberof blowholes. There is also a risk that layerdivision lines will be visible in the finishedconcrete. A reduced layer thickness can bedifficult to maintain, especially when thinwalling is being cast.

Vibration of in situ concrete with heavy reinforcement

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Example of blowhole formation from pouring & vibration

Contact between poker and reinforcement closeto shuttering can result in marks being left in theconcrete surface.

The poker vibrator must not be used to distributethe concrete as this will result in surface defects,and the concrete might segregate.

It is recommended that trial castings are made inorder to establish the most suitable method ofvibration and the correct concrete composition.

Self-compacting concreteThe use of self-compacting concrete (or SCC) is becoming increasingly widespread in precastconcrete applications. There are advantages for the producer in terms of reduced noise and vibration and the claimed improvements to surface finish. With careful selection ofmaterials and concrete mix design, whitecement can also be used in SCC.

Self-compacting concrete does not needvibration (either internal or external) to achievefull compaction or to move the concrete withinthe formwork. Indeed if vibration is appliedthere is a risk that the concrete may segregate.Specialist advice is available in the ConcreteSociety publication Self-compacting concrete – A review. Technical Report 62, 2005, 80pp.

When pouring floors, the poker vibrator shouldbe used at an angle. This compacts the concretebetter than a vertically inserted poker vibrator.For consistency, the angle and direction of thepoker vibrator should be maintained throughoutthe pour.

With reinforced concrete, it is important that thereinforcement be positioned to allow insertion ofthe vibrator at the correct distances. If very close-pitched reinforcement makes pouring in uniformlythick layers impossible, it can become necessary todistribute the concrete with the poker vibrator. Toprevent the relatively long vibration time giving riseto separation, each layer must here again be nomore than 500mm thick. The concrete must havea composition that gives ‘self-contained’ orcohesive flow without releasing water.

If pumped or liquid concrete is poured intonarrow forms with close-pitched reinforcement,the vibrator used must have a maximumdiameter of 40mm and the vibration time mustbe shorter than with stiffer concrete, ie, 10-20seconds per insertion. The precise sequenceshould be established by trial casting.

Precast concreteFor precast work, beam vibrators or formvibrators are used. These vibrate the wholeformwork unit. To ensure a minimum of airpores and to avoid ‘acoustic patterns’ it isimportant to aim at mounting a few largevibrators on a correctly braced form. Suchvibrators are usually mounted at form ends.

Potential problemsIncorrect vibration can cause honeycombing,extensive colour variations, and, with looseformwork, cement slurry leakage. With vibrationit is important to use formwork that is wellsecured so that it does not leak. The forcesgenerated by the pressure of poured concreteplus the vibration from vibrators can open joints.

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Production of concrete – Curing

To ensure a durable concrete, good curing isessential. A controlled loss of moisture fromthe concrete during hardening will also help to achieve a uniform colour.

Newly cast concrete should be prevented from drying out too quickly and protected fromfrost and large temperature swings. Protectionagainst rapid drying out is particularly vitalwithin the first 24-48 hours of maturity andthe first week of curing.

Drying out can be controlled by:

• Allowing formwork to stay in place

• Plastic sheet, impervious paper or similar covering

• Keeping the concrete surface wet

FormworkFormwork itself will prevent a certain amountof drying out. Formwork of lacquered or oiled plywood and steel are waterproof and non-absorbent and act in the same way as plastic film.

With ordinary wooden shuttering, the actualmoisture content of the wood affects the rateof curing. Ideally the shuttering should bewetted to prevent it drying out in hot weather.

PlasticPlastic film laid or fixed close to the concretesurface is an effective way of preventingevaporation. This however assumes that the formof the construction is regular without inwardprojections and corners, and that reinforcing barsdo not project from the concrete surface. Floorsand walls with substantial horizontal areas areideal for curing with plastic film.

It is important to ensure that film is held inposition and cannot be blown off or lifted infolds that might create a wind tunnel effect.For the sake of the final surface finish, it mightbe necessary to delay covering until theconcrete surface has gained a certain degree of strength and cannot be marked or deformedin any way by the application of plastic film.This problem can be avoided by using a sealing agent.

Preserving the surface appearance might alsomean laying the plastic film so that it is in closecontact with the concrete to prevent blotchesand discolouration arising because of non-uniform protection or condensation on theunderside of the film. However, a plastic filmlying direct on a wet/soft concrete surface

will often result in shiny, smooth patches. This problem can be eliminated by using, forexample, a covering of felt or geotextile beforelaying the plastic film.

Spray applied curing membranesCuring membranes are used primarily toprotect fresh concrete, but can also giveprotection when formwork is removed. Theyshould be applied by spraying in thin layers toprevent drips and uneven protection which canresult in permanent discolouration.

Curing membranes are becoming widely usedin the protection of fresh horizontal concretesurfaces. Their most obvious advantage is thatthey can be sprayed on without leaving marksin the hardening concrete. However, they dohave a tendency to produce various shades of discolouration if spraying is not uniform orthe concrete surface is uneven. Information onthe effectiveness of these materials should beobtained from the supplier before use. Inpractice, however, where large surfaces areinvolved, it can be difficult to ensure uniformand complete coverage without suitablespraying equipment.

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Plastic sheeting used to cure concrete can result inareas of varying porosity

Production of concrete – Avoiding blemishes

As most reinforced concrete is hidden fromview once a building is finished, a few blemishesin the surface appearance are not consideredimportant. However, white concrete is invariablyused as a face material and any surfaceblemishes will detract from its appearance.

Correctly specified and mixed concrete, whenwell compacted, will faithfully reproduce thesurface finish of the formwork. Where surfacetreatment, such as acid washing or sandblasting, are specified, many surface blemishescan be obliterated or successfully corrected by remedial measures. However, where largeareas of concrete are cast against smoothimpermeable formwork, any surface blemishesare obvious and remedial work is difficult toachieve without tell tale signs.

Viewing distanceWhen a building is completed, many parts will not be seen close up. This should beconsidered when setting standards for minorsurface blemishes. The demands for the verybest quality at close viewing should be reservedfor the entrance areas and surfaces wherepeople can regularly see the concrete close up.

Some of the most common blemishes andadvice on how to avoid them are given below.

Blowholes

These are individual small air pores usually onlya few millimetres across. They are created byair or water which adhere to the surface of theformwork during compaction. blowholes aremore likely to occur on vertical surfaces ratherthan horizontal surfaces.

Blow-hole formation can be caused by differentfactors. The fineness of the cement and thedispersal of cement paste have an influence onthe flow characteristics of the concrete. During

compaction, the cement paste acts as alubricant for aggregates so that they can bepacked and fill voids. The water/cement ratioalso plays a large role. Concrete with a highwater/cement ratio will separate if overvibrated, thus giving rise to a large risk ofwater pores on the surface against formwork.

The use of formwork with a hard smoothsurface contributes to the formation of blowholes. Lean concrete gives significantlymore blowholes than a rich concrete.

Prevention measures include ensuring:

• A thin, even coating of release agent

• Concrete with a good workability

• Adequate vibration

Honeycombing

This has the appearance of a coarse stonysurface with multiple honeycombing. It isusually a result of poor compaction orinadequate fines in the mix. To avoid:

• Check the sand and cement content is adequate

• Check the grading of the coarse aggregate

• Ensure adequate mixing and placing to avoid segregation

• Provide adequate vibration

Surface crazing

This consists of a network of fine cracks overthe whole of the surface. This is usually causedby shrinkage of the surface material after theconcrete has hardened.

Prevention measures include:

• Avoiding shiny, impermeable formwork surfaces

• Correct curing

Extensive blowholes and honeycombing indicate poorsite practice

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Blooming on coloured concrete

Blooming is the formation of whitish stains onthe concrete surface as a result of hydration ofthe concrete and the evaporation of salts in theconcrete. While these stains spoil the colour,they do not have any impact on the strength ofthe concrete.

In coloured concretes, the following measuresshould be taken in order to prevent blooming:

• During concrete production, maintain a lowwater-cement ratio

• Ensure the formwork is leak-free and theconcrete is well compacted to reduce thepermeability of the concrete

• Make sure that there are no salts in the mixwater, aggregates or water used for curing

• Use pusolonic additives in the concrete mix

Colour variations

These can occur for a number of reasons,including the different absorption or roughnesscharacteristics of adjacent sections of formwork,or uneven curing or exposure as a result ofdifferent drying conditions in adjacent castings.

Grout loss at joints in the formwork can alsocause a darkening of the concrete at joints.

Remedial work

It is virtually impossible to treat surfaceblemishes so that the repair is indistinguishablefrom the original concrete. Even where thesame concrete mix is used, a surface finishedby hand will never be as dense as a concretemechanically compacted against formwork andsubject to the pressure of concrete above.

Colour variation due to differences in formworktexture and absorption

The differences in density, surface texture andmoisture content tend to produce differencesin colour, with the repair usually appearingdarker. Any difference is likely to beexaggerated over time, as the more absorptiverepair surface collects and holds more dirt from weathering.

High standards of workmanship are requiredwherever high quality fair faced concrete isspecified. Concrete with an acid etched orlightly sand blasted finish is much moreforgiving of minor surface blemishes and any repair treatment that may be necessary.

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Production of concrete – Avoiding blemishes

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Production of concrete – Detailing

Creating a blemish-free white concrete is onlyone half of the design process. Where concreteis used externally, it must be detailed to takeaccount of weathering. In particular, the run-off of rainwater and the build-up of dirtparticles as the building ages.

It is important to understand that weatheringwill inevitably result in changes to theappearance of a building. The aim of thedetailing and design features should be, as far as possible, to achieve a controlled andgraceful ageing. This is particularly importantfor a building constructed of white concrete.

The following advice is intended as an aid inthe design, production and maintenance of in situ concrete structures and precast elements.

Shape and orientationThe overall shape and orientation of anystructure influences how different parts of thebuilding are affected by weather, the directionof the prevailing wind and the microclimate ofnearby structures.

This means that the various concrete surfacesare subjected to unevenly distributed amountsof water, sun and airborne particles for theirentire life. For example, a building in an urbanarea will be subjected to traffic-generated dustand dirt at its base but a cleaner, windier andwetter microclimate at roof level. The detailingof the building can be used to try and obscureor emphasise the boundaries between thedifferently affected parts of the building.

Polished concrete panels promote water run-offcombined with deep joints where dirt is deposited

Facade composed of large sloping sections – water willrun to the bottom of each section and deposit dirt alongthe edge, accentuating rather than obscuring the design

Dirty water running offthe roof and onto theconcrete facade

The wide overhang andguttering protect thisfacade from run-off

Different facades of the same building show how the same element is affected differently by rainwater run-offand dirt accumulation – the centre example is also affected by wind turbulence from an adjacent building

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DetailingThere are two objectives when detailing a concrete structure:

• Emphasising the desired architecturalexpression of the building

• Removing or distributing water in acontrolled way on the building surface

There are a whole array of architectural designfeatures that can be employed to managewater flow:

• Horizontal projections

• Surface texture

• Changes of plane

Horizontal projections, such as string coursesand sills, shelter the area below, particularly at lower levels. However, at roof level, smalloverhangs at copings do not offer the sameprotection because of local wind turbulence.Much larger overhangs are necessary at rooflevel to shelter the wall below.

From experience and observation, the threeways to avoid unsightly effects of rainwaterstaining are:

• Avoid concentrations of water flow

• Use overhanging details to throw as muchwater as possible clear of the wall surface

• Disperse the remaining flow as evenly as possible over the surface

TextureConcrete surfaces which weather mostsuccessfully in our damp climate are those whichare heavily textured, or are made up of relativelysmall units or a series of well defined areas.

Surface texture such as profiling or exposedaggregate invariably improves weatheringcharacteristics. Vertically profiled concrete isparticularly successful at concealing grimebuild-up, which tends to enhance the shadoweffect of the profile. With exposed aggregatefinishes water flow is impeded and dirt tendsto get deposited in the recesses, againemphasising the modelling.

With a flush sill, water running down the windowpicks up dirt and gets blown to one end of the sill bythe prevailing wind – dirt is deposited as the waterruns down the wall surface

The more shaded parts of a building receive less rainand therefore retain more dirt

Festoon staining ofconcrete is one of themost common defectson many modernbuildings with flush sillsand no drip projections

Surfaces with verticalstriations are the best at disguising theaccumulation of dirt.

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Production of concrete – Detailing

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Coloured concrete

Coloured concrete can be achieved by usingcoloured aggregates, pigments or colour stains.

Colour pigmentsThrough coloured concretes, mortars andrenders are achieved by adding pigments to BS EN 12878: 2005. As pigments are very finepowders, it is normal to use admixtures todisperse them. In practice, many proprietarycolouring agents already contain admixtures.

For extremely white concrete the white pigmentTitanium Dioxide may be added. However,because it is non-hydraulic, such ‘whiteners’should be applied with care.

Combining two or more pigments provides awide range of colour choices. Using whitecement intensifies the colour of pigmentedconcrete. White cement is particularly suitablefor use with yellow, green and blue pigments asthe finished colour is much cleaner and brighterthan with ordinary Portland cement, whichtends to mute the colour.

The following guidelines can be used to determine the intensity of colour:

• For light pastel colour based on Snowcrete,use 1-2kg pigment per 100kg of cement

• For middle colouring, use 3-5kg pigment per 100kg of cement

• For strong colouring,use 6-8kg pigment per 100kg of cement

It is recommended that the pigment is mixedwith the sand, aggregate and a small amountof water before adding the cement. Pigmentgranules require a minimum of moisture to befully dispersed. Only when the dry ingredientshave been thoroughly mixed should the mainwater content be added. These mixinginstructions will produce a uniform, brilliant and reproducible colour tone in the concrete or render.

It is best to make sure that the fillers, sandsand aggregates used have a colour as close aspossible to the pigment colour. Difficulties canarise if there are large colour variations inaggregates, especially when the constructionhas been exposed to normal wear. Initially, theouter layer of coloured cement paste covers allaggregate particles, but will in time be wornaway – thus allowing the colour of theaggregate material itself to become dominant.This condition will, primarily, concern thoseengaged in paving.

The architect John Outram is well known for his useof coloured concrete

Photograph ©Peter Cook/VIEW

Colour intensity depending on dosage quantity withassociated colour shade scale.

The sculptor Carole Vincent used coloured concrete tospectacular effect at the 2001 Chelsea Flower Show

Black

Brown

Red

Yellow

Blue

Green

1% 3.5% 5% 7% 9%

Coloured aggregatesA consistent concrete mix and exposuretechnique are essential where the aggregate is to be exposed. Although the colour of thecoarse aggregate will be dominant, the size,shape and grading will also affect the finishedtexture and appearance.

Colour pigments can be used in combinationwith coloured aggregate to further extend thevisual range. Pigments with a similar colour tothe aggregate can strengthen the overallconcrete colour. Alternatively, aggregates andpigments with extreme colour differences canproduce striking effects.

Colour stainsColour stains can be used to turn a plainconcrete surface into a decorative and stylishone. Colour stains are often used to imitate theappearance of traditional natural materials suchas marble and slate but at a realistic andaffordable price. Colour can also be used tocreate patterns in flooring to almost any design.

Traditional concrete stains are limited to apalette of eight colours and are acid based.However, modern stains are available in virtuallyany colour and are usually water based.

Although not suitable for every application,colour stains vastly improve the choices fordesigners when looking for a stained floor.Colour stains will leave a variegated finish toconcrete floors and are not designed for densesingle colours.

Coloured staining of concrete floors is widelyused in the USA and is also gaining interest inthe UK.

Alternative offer fromLafarge ReadymixLafarge Readymix, part of the Lafarge Group,exclusively offer Artevia® Colour, a range ofconcretes using liquid pigment technology toprovide unparalleled quality and consistency ofcolour and texture. Offering a wide range ofearthy tones designed to complement andenhance an area's appeal, you are sure to finda mix which suits your design. Alternatively,bespoke colours or special design mixes arealso available, just call Lafarge Readymix'sspecialist sales team on 0870 336 8256.

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Coloured concrete

Somerford Keyneslimestone, 1% yellow pigment

Criggion granite, 1%green pigment

Coloured concrete made with Snowcrete makes itpossible to add any colour anywhere

Artevia® colour uses specialist pigments to producerich, vibrant colours

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References

Cast in concrete II, Susan Dawson, BritishPrecast Concrete Federation, 2003

Written by an architect, this is an authoritativework on architectural precast concrete, itsnature, potential, use and advantages.Copiously illustrated with case studies, thebook covers design, structural and physicalproperties, manufacturing processes, surfacecolour and texture, transportability, weatheringand environmental issues. The history ofarchitectural precast concrete is also recountedwith reference to well-known historic buildings.

Precast concrete paving – A design handbook,C Pritchard, Edited by S Dawson, British PrecastConcrete Federation, 1999

Provides advice on aesthetics, in-depthinformation on technical and specification dataplus practical applications and detailing tipsand ideas. Clear diagrams aid understanding of the techniques and coloured photosillustrate the applications.

Appearance Matters 6 – The weathering ofconcrete buildings, W Monks, British CementAssociation, 1986

Describes the effects on well made concrete of natural forces such as rain and sunlight, and unnatural forces such as pollution. Givesadvice on the control of weathering. Contains30 illustrated study sheets on detailing to avoidweathering problems.

Design, manufacture and installation of glassreinforced concrete, Concrete Society, 1998

Produced by the National Precast ConcreteAssociation, Australia, this guide coversmaterials, GRC manufacture, curing, properties, quality control, strength, contractconsiderations, practical applications, surfacefinishes and concludes with a section onvibration-cast GRC. Basic concepts areillustrated using line drawings and graphs, to provide an ideal introduction to GRC.

GRC in action, Concrete Society, 2003

An illustrated introduction to the propertiesand applications of GRC. It aims to givearchitects and engineers an insight into thewide range of applications of GRC currentlybeing executed throughout the world.Download from: www.grca.org.uk

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SnowcreteW H I T E C E M E N T

References

British Standards Institution

BS EN 197-1: 2000 – Cement. Compositions,specifications and conformity criteria forcommon cement

BS EN 206-1: 2001 – Concrete Part 1:Specification, performance, production and conformity

BS EN 934-2: 2001 – Concrete admixtures –Definitions, requirements, conformity, markingand labelling

BS 8500-1 Concrete Complementary BritishStandard to BS EN 206-1, Part 1: 2002 Methodof specifying and guidance for the specifier.

BS 8500-2 Concrete Complementary BritishStandard to BS EN 206-1, Part 2: 2002Specification for constituent materials and concrete.

BS 8500-1 covers all the information needed inthe UK to specify concrete, whilst BS EN 206-1and BS 8500-2 contain information required byconcrete producers.

BS 8110 – Structural use of concrete,Part 1: 1997, Code of practice for design and construction

BS EN 12620 – Aggregates for concrete(supersedes BS 882)

BS EN 12878 – Pigments for colouringbuilding materials based on cement and lime – Specifications and methods of test(supersedes BS 1014)

BS EN 13139: 2002 – Aggregates for mortar(supersedes BS 1199 and BS 1200)

BIP 2001: 2004 – Standards for fresh concrete

British Cement Association (BCA)

Appearance Matters 1 – Visual concrete:design and production, W Monks, 1988

Appearance Matters 3 – The control ofblemishes in concrete, W Monks, 1981

Appearance Matters 6 – The weathering ofconcrete buildings, W Monks, 1986

Appearance Matters 7 – Textured and profiledconcrete finishes, W Monks, 1986

Appearance Matters 8 – Exposed aggregateconcrete finishes, W Monks

Appearance Matters 9 – Tooled concretefinishes, W Monks, 1985

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Lafarge Cement UKManor Court, Chilton, Oxon OX11 ORN

For further information:

Technical helpline 0870 609 0011

E-mail [email protected]

Customer services 0870 600 0203

E-mail [email protected]

Facsimile 01635 280250

Website www.lafargecement.co.uk

Lafarge Cement reserves the right to change content within this publication without notice, owing to a policy of continuous development and improvement