Reflective Concrete
Portland cement
concrete is a workhorse of construction materials. A lesser known sustainable
benefit of concrete is its reflectivity.
Surface color of a
material affects how much of the sun's energy (heat) is absorbed. Darker
colored surfaces absorb more heat. In the past, this quality was referred to as
"albedo," but now, terms like "solar reflectance" or "solar reflectivity index"
have become common. A material that has a higher solar reflectance absorbs less
of the sun's energy. By virtue of its light color, concrete is naturally
reflective.
Wherever pavements and structures (especially those that are darker colored)
are clustered closely together, as in large cities, the mass of building
materials collects heat when warmed by the sun. This creates a microclimate
with temperatures measurably higher than in less developed areas-the urban heat island effect.
In turn, air conditioners must run longer and harder to keep people cool, which
further adds to the high temperatures. This is bad for the environment because
it wastes energy, which in turn increases carbon dioxide emissions. Effects of
urban heat islands are reduced by selecting lighter colored paving and roofing
materials, by situating buildings and parking lots to minimize their exposure
to the sun, or by establishing trees and other foliage that provide shade for
parking areas.
Concrete is a
mixture of cement, water, fine aggregate (sand), and coarse aggregate (rock or
stone). Cement and water form the paste that binds the ingredients into a
hardened mass. Most concrete is formulated with gray portland cement. This
results in a light gray colored surface, which is an advantage over darker
colored paving materials in terms of solar reflectivity. White cement is
chemically similar to gray cement, but contains a lesser quantity of the metal
oxides (iron & manganese) that impart portland cement with its
characteristic gray color. Concrete made with white cement is significantly
lighter in color than gray cement concrete, and therefore, more reflective.
