A study on the durability of a glass bead retro-reflective material applied to building facades

Heat from buildings contributes about 1/2 of the city's anthropogenic heat to the urban heat island (UHI). The ratio of heat emitted from building external walls occupies about 1/3 of the anthropogenic waste heat total in Japan. Retro-reflective (RR) materials applied to building facades instead of highly reflective (HR) materials for UHI mitigation are being studied. Glass bead RR material is one of the main RR material types. In this study, several glass bead RR materials with different refractive indices and different color reflective layers were developed. The long-term change in solar reflectivity and angular distribution of reflection intensity for these glass bead RR materials was evaluated for purpose of durability verification. The result showed that both the solar reflectivity and angular distribution of reflection intensity for these developed glass bead RR materials almost have no significant change after 368 days of exposure in the outdoor environment. Moreover, it is shown that the glass bead RR material with a refractive index of 1.9 has much better RR performance, compared to that with a refractive index of 1.5.