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March 14, 2012

Porous Asphalt Pavement Temperature Effects on UHI


Recently, the NCE completed a study for the Asphalt Pavement Alliance (APA) on asphalt pavement temperature effects on overall Urban Heat Island (UHI) with focus on characterizing porous asphalt mixtures. A paper summarizing the study was presented at the Transportation Research Board meeting in January 2012. Excerpts of the study are presented as follows. Please contact the NCE to obtain a copy of the report or paper.

Rapid urbanization requires an increase in pavement surface area, which contributes to UHI due to unfavorable heat retention properties. In recent years, the use of alternate pavement designs has become more common in attempt to mitigate environmental impacts of urbanization. Specifically, use of porous pavements is gaining popularity in the paving industry due to attractive storm water mitigation and friction properties. However, little information is available regarding thermal behavior of these materials.

This study explored the extent to which porous asphalt pavement influenced pavement temperatures and investigated the impact on UHI by considering the diurnal temperature cycle. A one-dimensional pavement temperature model developed at ASU was used to model surface temperatures of porous asphalt, dense graded asphalt and Portland cement concrete pavements.

Several scenarios were considered to include variations in pavement thickness, structure and albedo. In addition, thermal conductivity testing was performed on porous asphalt mixtures to obtain values for current and future analysis.

In general, porous asphalt exhibited higher daytime surface temperatures of the three pavement types because of the reduced thermal energy transfer from the surface to subsurface layers. In comparison, porous asphalt showed the lowest nighttime temperatures when compared to other materials with similar or higher albedo. This trend can be attributed to the unique insulating properties of this material due to a high air void content. As anticipated, the outcome of this study indicated that pavements impact on UHI is a complex problem and needs to consider important interaction between influencing factors such as pavement thickness, structure, material type, and albedo.