Moist curing increases the solar reflectance of concrete

Most people are dwelling in cities, which contain a high density of buildings constructed of concrete or similar materials. Conventional grey-colored concrete is absorptive to solar radiation and discharges the absorbed heat to the air as sensible heat, contributing to the development of urban heat island. While existing studies have attempted to find high-reflective concrete by varying the components of the concrete mix, the influence of cured conditions on the albedo of concrete samples is still unknown and has not been reported. Here we first prepared 120 cement pastes with different water-to-cement ratios and different cementitious materials, and then cured the pastes in an indoor environment and a moist chamber, respectively. After cured in a moist chamber for 28 days and then cured in the air for 365 days, the spectral reflectance of all the pastes was tested. Experimental results indicated that the pastes cured in a moist chamber have an albedo that is 0.01–0.10 greater than those of the pastes cured in an indoor environment, with a greater albedo difference at relatively higher water-to-cement ratios. The results also revealed that when concrete productions, such as concrete roof tiles and concrete paver blocks, are prepared, it is practical to cure such productions in a moist environment to get a high albedo