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Cool Pavements
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definition
There is no official standard or labeling program to designate cool paving materials, and research in this area is in an early stage.
While studies show that pavements can affect the urban heat island and resulting air quality, results are complicated by several factors. These include the impact of shadows from nearby structures; changes in pavement characteristics over time; and the absorption by buildings of solar radiation reflected from the pavement surface.
There are situations, however, where communities interested in reducing heat island effects can choose paving materials that lower surface temperature and achieve related objectives. Large parking areas, terminal facilities, airfields, or urban roadways with large expanses of paved surface are examples where cool pavements may be most practical.
Investigations of cool paving materials have focused
on two mechanisms – surface reflectivity and
permeability. Pavements with higher
solar
reflectance
are cooler in the sun, holding other factors constant.
Porous, or permeable, pavements benefit from the
cooling effect of evaporation. To ensure high-level
performance, proper design and construction are
essential in applying either cool pavement
technique.
Other factors affecting performance, cost, and benefit must also be considered when selecting paving materials. In fact, the best solutions may occur where multiple benefits are obtained from a paving approach (e.g., porous pavements may help with storm water runoff as well as provide a cooler surface).
Cool pavement solutions are available for conventional materials such as asphalt and concrete, and for unpaved surfaces:
- Asphalt and concrete pavements can have higher
reflectance with the use of lighter-color aggregate,
provided it is locally available. Both asphalt and
concrete pavements can be built with porous or
permeable designs for lighter-duty applications.
- Other techniques can be applied to meet special
pavement needs while promoting cool pavement
objectives. Examples include roller compacted
concrete where a strong, economical pavement is
needed in locations where speed and smoothness are
not critical; and asphalt chip seals using
light-colored aggregate, which can improve
reflectance while extending asphalt pavement life and
improving skid resistance on lower volume roads.
- Permeable surfaces can also be constructed using lattices filled with soil, gravel, or grass.
The Los Angeles, CA, zoo uses a reflective paving product.
EPA has commissioned a report to capture the state of knowledge and activity on cool pavements (PDF, 72 pp., 581KB). This report is intended to present straightforward information to help decision-makers – to the degree possible – select the best pavements for their current needs. Further, this document is meant to help advance the issue by presenting information on research needs and next steps.