Influences of permeable pavements with different hydraulic properties on evaporative cooling and outdoor thermal environment: Field experiments

Permeable pavements have great potential to mitigate urban heat through evaporative cooling and are widely applied in urban construction. The effectiveness of evaporative cooling depends on the availability of surface water, influenced by the hydraulic properties of the pavement materials, particularly permeability and water absorption. In this study, three commonly adopted materials, i.e., porous asphalt (PA), ceramic permeable bricks (PB), and pervious concrete (PC), were investigated through field experiments. Permeability was assessed using the infiltration rate, while water absorption was evaluated through the capillary absorption coefficient and capillary moisture content. Results indicate that higher permeability reduces surface water retention, while higher absorption coefficients and capillary moisture content prolong the duration of evaporation. PB presents an optimal material choice that combines these properties well. Additionally, irrigation reduces the surface temperature of permeable pavement by over 10 degrees C, thereby cooling and humidifying the air, particularly within 30 cm of the surface, by converting convective sensible heat into latent heat. This increase in latent heat is positively correlated with the capillary moisture content of pavements. As a result, Irrigation significantly improved the thermal comfort of PB, reducing the average UTCI difference between PB and impermeable brick pavements by 0.4 degrees C compared to dry conditions. In contrast, PA and PC, which prioritize permeability, showed no notable improvement in the thermal environment. To effectively improve thermal comfort in urban pavement applications, both permeability and evaporative cooling effects should be considered, along with a thorough evaluation of permeability and water absorption properties.