Experimental investigation on the degradation of coating on concrete surfaces exposed to accelerated and natural UV in chloride environment

This paper aims to investigate the degradation of coating materials on concrete surfaces exposed to accelerated and natural ultraviolet (UV) rays under a chloride environment for two years. Two types of coating materials, epoxy (EP) and cementitious-based waterproof (CW) were studied. The surface of cement-only concrete was coated by the coating materials. The UV radiation sources for inducing degradation of the coating materials were natural sunlight and accelerated UV in the laboratory. The intensity of the accelerated UV was about 4–5 times higher than that of the sunlight. The wet/dry cycles (1 week per cycle with 3 days wet and 4 days dry) were applied to concrete specimens during the tests. The specimens were exposed to the chloride solution during the wetting period and UV radiation during the drying period. At the end of each specified cycle, visual inspection and measurement of chloride contents in the concrete specimens were conducted. From the experimental results, it was found that UV radiation significantly degraded the coating materials. The degradation of the surface coating materials depended on the intensity of the UV. The chloride penetration resistance of the coated concrete with EP was considerably higher than that coated with CW after 107 cycles of the wet-dry test (two years of exposure).