Effects of Long-Term UV Exposure on the Performance of Cement Plasters Integrated with Thermochromic Paint and PCMs for Building Facade Applications

The exterior finish layer in building facades is exposed to considerable environmental loads, which can reduce the service life of the materials, increasing the need for replacement. New climate challenges impose to look more carefully at the long-term performance and durability of building components and materials. Thermal stresses due to daily temperature fluctuations and UV exposure can significantly damage facades and degrade their performance. This research measures the long-term performance of a responsive cementitious finish plaster. The developed cement plaster is combined with phase change materials (PCMs), and thermochromic (TC) pigments to control solar radiation and surface temperatures dynamically on the exterior façade year around. The main objective of the study is to quantify the effect of long-term UV exposure on the optical performance of the cement plasters. PCMs with three different melting temperatures of 18°C, 24°C, and 28° C were combined with two different colors of blue and red TC paint with a transition temperature of 31°C. Accelerated UV aging of the samples was performed using lab tests to simulate exposure to UV radiation for two years. The solar reflectance of the samples was characterized before and after the accelerated UV aging tests. The results of the aging tests revealed that UV exposure impacts the solar reflectance of the finish material based on the method of integrating the TC paint to the cement plaster. In the case of TC paint applied to the surface, the solar reflectance of the plasters with only the TC is reduced by 15% after aging, while the ones combined with PCMs have a similar solar reflectance value after aging.