Heat Island Impact of Chip Seals

Chip seals are a common pavement preservation technique for maintaining an acceptable roadway condition for vehicles. Chip seals applied in urban areas can alter the optical and thermal properties of the pavement, which affects the Urban Heat Island (UHI). Four field cores were extracted from chip seal roadways that were 6–12 months old and their thermal and optical properties were measured to quantify the impact on UHI. The thermal properties were measured using a transient plane source (TPS) technique for the asphalt substrate layer as well as the combined asphalt and chip seal structure, with similar values found for both sets. Measurements with the combined structure had a higher standard deviation as compared to the asphalt only condition, indicating a higher percentage of air voids in the chip seals. The optical properties were measured only for the chip seal surface. The albedo of the chip seal ranged from 0.04 to 0.06, as compared to 0.15 to 0.20 for typical asphalt that is at least a year old. The emissivity of the chip seal averaged 0.92, as compared to 0.83 for asphalt concrete reported in literature. The UHI impact was quantified in terms of the global warming potential (GWP) as well as the hourly average net surface heat flux and surface temperature. Given the measured optical and thermal properties of field cores, chip seals were found to increase the UHI effect of flexible pavements by a small amount.