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How can I obtain a concrete mixture that has high albedo or reflectance, so that I can obtain a LEED site credit for reflective pavement?
The "Sustainable Sites Credit 7.1" in the LEED green building criteria gives 1 point if at least 30% of the (non-roof) paved surfaces have reflectance or albedo greater than 0.3. Normal concrete mixtures usually have reflectance of 0.3 to 0.5. Asphalt is typically 0.05 to 0.10.
First, pick a materials testing lab that has the capability to perform the reflectance test (see below) in addition to the concrete mixture design & testing, so that you can choose a concrete mixture that will get you above the 0.3 LEED requirement. Most "normal" concrete mixtures should get you above 0.3, but this may vary according to cement manufacturer & type, coarse aggregate type/source, fine aggregate type/source, admixtures, use of slag or fly ash, etc.
Lighter colored aggregates, use of ground granulated blast furnace slag, and light colored cements will brighten the concrete. Fly ash will typically darken it, so be careful when trying to add this recycled material to get the recycled content credit for LEED (Materials Credit 4).
The recommended test method for measuring reflectance/albedo of pavements is ASTM C 1549. Other test methods for reflectance that are not recommended for pavements are ASTM E 903 and ASTM E 1918.
For more information on reflectivity and albedo of pavements, click here.
For more information on how concrete can help achieve LEED credits, click here
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