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It can be important to maximise the light reflectance from an exposed surface, for example to reduce the artificial lighting requirement. An as-struck smooth grey Portland cement surface may have a reflectance of 40% (CIBSE) although this will reduce if the surface is mottled or discoloured. A textured surface, such as board marked, may only produce 25% reflectance. Greater reflectance of a plain concrete surface can only be achieved with careful selection of constituent materials, particularly the cement, and adherence to good concreting practice. The use of Portland cement with ggbs is at the higher end of expectations compared to just Portland cement. The use of white cement should provide slightly in excess of 50%. A higher surface reflectance of can be achieved up to, say 70%, if the surface is coated with a white emulsion or similar.
Acknowledgement: Concrete Society
Other references:Chartered Institute of Building Services Engineers. Code for interior lighting, CIBSE,1994.
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