White Cement Concrete Reflects Sustainability

Portland cement concrete is a workhorse of construction materials. For structures large and small, underground, submerged, on the ground, or soaring to great heights, concrete's strength and versatility can't be matched. Yet these qualities would be less attractive if its life cycle were not measured in decades, centuries, and even eons; concrete's durability establishes its dominance among building materials, and demonstrates one aspect of why it is a sustainable product. A lesser known sustainable benefit of concrete is its reflectivity. Applications where reflectivity is beneficial include interior floors, roof tiles, and pavements—including flatwork, streets and roads, and highways.

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.

White cement powder is light colored and this leads to highly reflective concrete surfaces.

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.

There is an environmental advantage to using concrete to reduce heat gain of exposed surfaces. This was demonstrated by a 2007 study of various concrete mixtures by measuring their solar reflectivity index (SRI). The report documents the additional benefit gained by using concrete formulated with white cement (PCA report SN2982). Other concrete ingredients were considered, too; to a lesser degree, fine and coarse aggregate also affect the SRI of concrete.

At left is a concrete specimen was made with a gray cement on the right is a specimen made with white cement. PCA SN2982. States, that, "Generally, the higher the solar reflectance of the cementitious material, the higher the solar reflectance of the concrete. The solar reflectances of the ordinary cements (other than the white cement) range from 0.36 to 0.47. … white cement has the highest solar reflectance, 0.87. PCA SN2982.

Standard concrete has a relatively good SRI, certainly greater than dark colored paving or roofing materials. Concrete is well suited to paving and roofing applications because it is durable, heavy duty, and in the case of roof tiles, its weight can be advantageous in windy exposures like hurricanes or tornadoes; tiles are less likely to be ripped off the structure by strong wind forces.


Pale by Comparison—And Why That's a Good Thing

As discussed above, concrete absorbs less energy from the sun and moderates temperatures, reducing urban heat islands. Lighter colored surfaces reflect more light (from artificial sources) when used as flooring surfaces indoors or at night in exterior parking applications. One study showed concrete pavements require less lighting than asphalt pavements for the same amount of visibility (Stark 1986). The study concluded the same lighting standard could be met with a smaller investment in equipment, so it was less costly to place, operate, and maintain light fixtures, saving taxpayers money.

White cement concrete floors offer many benefits in interior spaces for commercial, industrial, and manufacturing facilities. They are durable, low maintenance, and reduce lighting requirements.

Lighting efficiency: Light colored interior floors require fewer light fixtures to provide the same amount of visibility as darker floors. Fewer fixtures save energy for lighting and reduce the lighting heat load, thereby reducing the need for air conditioning, saving building owners and operators money.

Safety is improved with lighter colored surfaces by reducing shadows, which is beneficial for industrial and manufacturing environments. Some studies of retail properties have shown that better lit interiors are more inviting and lead to improved sales. Light colored floor surfaces such as exposed white concrete can help achieve that.






Paving: Outside, properties with lighter colored surfaces are more inviting and can increase safety at night. With fewer shadows and dark areas, parking lots and walkways are safer for pedestrians and drivers. And as noted earlier, fewer lighting fixtures are needed to provide the same or better visibility, resulting in lower operating costs.

Parking lots of portland cement concrete are better lit with the same amount of lighting, making the property safer and more inviting.

The Future for Concrete Looks Bright

Color plays a part in the environmental performance of paved areas and roofing. Lowered heat gain, lowered energy requirements, and improved safety are associated with lighter colors. Concrete made with gray cement provides all these benefits, and white cement further increase concrete's surface reflectivity. Wherever property is being developed or improved, portland cement concrete, both the gray and white variety, offers sustainable benefits.

Reference

Stark, Richard E., "Road Surface's Reflectance Influences Lighting Design", Portland Cement Association RP269 , Skokie, Illinois, 1986, 7 pages. Reprinted with permission from Lighting Design + Application, April 1986.