Thermal and optical characterization of asphalt field cores for microscale urban heat island analysis

Abstract

Pavements contribute significantly to the development of Urban Heat Islands (UHIs). The impact of pavements on UHI depends on multiple material factors, including its thermal and optical properties. Field cores from asphalt concrete (AC) pavements from four locations in Illinois and one in Indiana, USA, were used to evaluate the optical and thermal properties of the corresponding pavements. Thermal conductivity ranged from 1.0 to 3.0 W/mK (average of 2.2 W/mK), diffusivity 0.6–2.0 mm2/s (average of 1.5 mm2/s), and heat capacity 0.7–3.0 MJ/m3K (average of 1.5 MJ/m3K), which differ significantly from values typically recommended in pavement design. The same cores were used to calibrate a simplified bilinear aging albedo model, with the asymptotic albedo and at-construction albedo being largely within the expected range of 0.10–0.20 and 0.05–0.10, respectively. The emissivity was found to be between 0.70 and 0.90, which agrees with values reported in the literature. These properties were used to evaluate the local pavement Radiative Forcing (RFp) and Global Warming Potential (GWP) as well as the diurnal net surface heat flux and surface temperature of the pavements. The RFp varied depending on aging albedo and emissivity, while surface temperature and net surface heat flux also depended on thermal properties.