Laboratory-simulated investigation on thermal behaviours of permeable concrete pavements

Abstract

Impermeable pavements are recognised as one of the biggest contributors to the urban heat island effect, because they not only increase local temperatures through additional heat storage in the paving materials, but also reduce evaporative cooling on the ground surfaces. Therefore, permeable pavements are considered an effective solution for mitigating the thermal discomforts in hot climates. In this study, the thermal behaviours and performances of permeable concrete pavement were investigated with a series of simulation experiments in the laboratory. For comparison purposes, traditional Portland cement concrete (PCC) and Portland cement porous concrete (PCPC), which are commonly used in municipal pavements, were considered for the study. The thermal properties of those materials and their thermal impacts on the surroundings were discussed with specially designed tests. It is verified that the laboratory simulation tests and corresponding analysis methods proposed in the study could be utilised to characterise the thermal behaviours of pavement materials effectively. The testing results showed that the surface temperature of PCPC was higher than that of PCC under the same thermal conditions, which indicates that permeable concrete pavements usually absorb more heat from solar radiations and present higher surface temperatures than those of traditional concrete pavements. Due to the relatively higher density, thermal conductivity, and specific heat capacity, the PCC specimen stored more thermal energy in the material during the temperature-rise period and dissipated more heat back to the ambient environments during the temperature-fall period, which is considered one of the negative contributions of PCC pavements to the thermal environments of residential districts. In addition, under windy conditions, the differences between impermeable and permeable concrete were more significant. Compared to the PCC, the surface temperatures of PCPC increased more slowly and decreased faster under windy conditions, and the higher the speed of wind, the more apparent differences could be observed. This indicates that thermal evaporation of permeable pavements is the main function in abating their thermal impacts on environments.