Reflectivity and Sustainability
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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.
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| 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.
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| 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.
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| 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.
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| 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.
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