A method to measure retro-reflectance and durability of retro-reflective materials for building outer walls

Abstract

A method of determining the retro-reflectance of retro-reflective materials used for building coatings is proposed in this article. In addition, the durability of retro-reflective materials over long-term outdoor exposure is also estimated. Retro-reflective materials are currently limited to use in specific purposes, such as road traffic signs in Japan. To consider their application as a building coating, it is also necessary to examine the thermal performance and durability of retro-reflective materials. We proposed a method of determining the retro-reflectance of retro-reflective materials (capsule retro-reflective material and prism retro-reflective material were used in this experiment) by experiment. To explore the durability of retro-reflective materials over long-term outdoor exposure, we measured the changes in solar reflectance and retro-reflectance of retro-reflective materials exposed to the outdoors over about 25 months. The solar reflectance of capsule retro-reflective material decreased from 0.69 to 0.51 and that of prism retro-reflective material decreased from 0.83 to 0.81. The retro-reflectance of capsule retro-reflective material decreased from 0.18 to near 0 (0.0072) and that of prism retro-reflective material decreased from 0.44 to 0.42. At the end of the test period, we cleaned the surface of the retro-reflective materials. Both of the retro-reflective materials recovered about 50% of the lost solar reflectance by cleaning. The retro-reflectance of capsule retro-reflective material increased by about 0.08 (46% recovered) by cleaning and that of prism retro-reflective material increased by only 0.01 (with 50% recovered) by cleaning. We concluded that the durability of prism retro-reflective material is better than that of capsule retro-reflective material for use on building coatings.