Biochar from waste biomass as hygroscopic filler for pervious concrete to improve evaporative cooling performance

Abstract

Pervious concrete is regarded as a contributing material to reduce surface runoff, purify water pollution, and mitigate the urban heat island. However, the poor water absorption and retention capabilities of it could not meet the need of evaporation. To prolong its evaporative cooling effect, this study introduces a modified method of incorporating biochar (BC) particles into pervious concrete as hygroscopic filler. The albedo, emissivity, porosity, microstructure morphology, water absorption, and evaporation of pervious concrete that was prepared by replacing the cement in weight, by 5.0% of BC particles were investigated. It was found that the BC addition had little impact on the emissivity and porosity of pervious concrete, while significantly reduced the albedo. Contributing to the abundant micro-pores and higher specific surface area of carbonaceous particles, they would significantly enhance the water absorption and retention capability of pervious concrete. Using 5.0% pulverized BC as the admixture maximally increased the total water absorption of pervious concrete from 100 ± 2 kg/m3 to 117 ± 8 kg/m3. During the evaporation process, the water absorption increment could effectively decrease the surface temperature by up to 3–6 °C, with an extra cooling period of 6 h, compared to conventional BC-free pervious concrete. Based on the findings, we conclude that replacing a small quantity of cement by pulverized BC in conventional pervious concretes could effectively improve the evaporative cooling performance.