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CONCRETE APPEARANCECONCRETE APPEARANCEDoes it matter?

Neil CrookThe Concrete Society Advisory Service

1st July 2010

cbdg annual conference– 1st July 2010

Structural or Appearance?

• Structural– Functionality– Structural capacity– Durability

• Appearance– Does it look nice– What will it look like in 20, 50 or 100 yearsy


Structural failureStructural failure


Visual Concrete

• Planning and assessment• Finishes• Control of blemishes• Weathering, stains & efflorescence


Planning and assessment

• Different levels of visuality‘hi h t’– ‘high art’

– Normal (grey/white) exposed but not colouredCoated e g painted– Coated e.g. painted

– Limited visual exposure• Not one size fits all• Not one size fits all• Perfection is not achievable nor should it

be expectedbe expected• Surface never completely uniform


Large scale structures



• SpecificationsBS 8110 Structural use of concrete (withdrawn in 2010)– BS 8110 Structural use of concrete (withdrawn in 2010)

– BS EN 13670 Execution of concrete structures– Highways Agency, Specification for Highway WorksHighways Agency, Specification for Highway Works– National Building Specification– Civil Engineering Specification for the Water Industry– National Structural Concrete Specification for Building

Construction

• ‘Fair faced’ is meaningless• Fair-faced is meaningless• Specification appropriate to the end use


Cracking


iJoints


Rebate feature


Rebated joints



• Formwork– Many systems– Many form face materials– All with give a different appearance


Formwork typesyp


Panel System finishes y



• Form faceSt l GRP Li CPF Ti b– Steel, GRP, Liners, CPF, Timber

• Release agentsOil Ch i l VERA– Oils, Chemical, VERA

• ConcreteC t A t S ifi ti– Cement, Aggregate, Specification

• ConstructionT i l l S W h Pl i– Trial panels, Spacers, Weather, Placing, Vibration, Remedial work


Line and block spacers effect of finish



• Assessment– Age, Lighting, Distance

• Bridges – from carriagewayB ildi• Buildings –– external – 3m– internal – 1minternal 1m


Finishes

• Formed and Unformed


Board marked


Ribbed –hammered,

it bl t dcbdg annual conference– 1st July 2010

grit blasted

Form liners


Dream


Tamped Brush Turf dragged

TiTine

Textured roller

cbdg annual conference– 1st July 2010 Burlap dragged

Pattern imprintedPattern imprinted


Exposed and washedExposed and washed aggregate


Abrasive blasting


Di d i dDiamond grind

Diamond groove


Dry shake and power trowelled


Polished


Stained, stencilled and blasted


Control of blemishes

• Defects• Blemishes

– Avoidable– Unavoidable


Natural variation


Blow holes

Aggregate bridgingbridging


Rust staining


Water lossLift lines

SScourPoker burns


Plastic shrinkage

i dRain damage


Frost damage


R i f t i lReinforcement ripple

Crazing

Delaminationcbdg annual conference– 1st July 2010

Delamination

Weathering, stains & efflorescence

Weathering affects all buildings


Weathering, stains & efflorescenceCleaningCleaning



Orientation



Surface Permeability



Surfaces intended to remain dirty – Bold profile



Details to controlcontrol weathering should be bold not subtle



Diagonally ribbed surfaces affect the flow of water in ways that are difficult to predict and control


Weathering, stains & efflorescenceQuality and detailingdetailing



Quality and detailing –exposed coarse aggregateexposed coarse aggregate



Only pyramids will be y pywashed clean on all faces



Uncontrolled water flowUncontrolled water flow



Gutters need notGutters need not necessarily be connected to rainwater pipe systems


p p y


Stains – Bitumen, rust, graffiti, litchen



Cleaning – water jet, acid grit blastingacid, grit blasting



Lime bloom, Lime weeping, e weep g,Salt crystallization


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