Porous Asphalt Pavement Temperature Effects for Urban Heat Island Analysis

Increased nighttime temperatures caused by retained heat in urban areas is a phenomenon known as the urban heat island (UHI) effect. Urbanization requires an increase in pavement surface area, which contributes to UHI as a result of unfavorable heat retention properties. In recent years, alternative pavement designs have become more common in an attempt to mitigate the environmental impacts of urbanization. Specifically, porous pavements are gaining popularity in the paving industry because of their attractive storm water mitigation and friction properties. However, little information regarding the thermal behavior of these materials is available. This paper explores the extent to which porous asphalt pavement influences pavement temperatures and investigates the impact on UHI by considering the diurnal temperature cycle. A one-dimensional pavement temperature model developed at Arizona State University was used to model surface temperatures of porous asphalt, traditional dense-graded asphalt, and portland cement concrete pavements. Scenarios included variations in pavement thickness, structure, and albedo. 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 than the other pavements because of the reduced thermal energy transfer from the surface to subsurface layers. However, porous asphalt showed the lowest nighttime temperatures compared with other materials with a similar or higher albedo. This trend can be attributed to the unique insulating properties of this material, which result from a high air void content. As anticipated, the outcome of this study indicated that pavement impact on UHI is a complex problem and that important interactions between influencing factors such as pavement thickness, structure, material type, and albedo must be considered.