Degradation of unsaturated polyester and aggregate, both of which are constituents of artificial stones, was investigated in terms of temperature and alkaline solution based on the environmental condition in the construction site, to elucidate the cause of yellowing of artificial stone under light-shielded and sealed conditions. The artificial stone, which was obtained from a non-discolored portion in the construction site, was examined by air exposure test, water immersion test and alkaline solution immersion test at 20℃ and 60℃ for 14 days. The artificial stone was discolored to yellow after immersing into alkaline solution at 60℃ for 14 days, while it didn't change after being immersed into alkaline solution at 20℃ and water at 20℃ and 60℃. As for the discolored stone attenuated total reflection FTIR measurement revealed that the unsaturated polyester was degraded to possess carbonyl groups as a chromophore and hydroxy groups as an auxochrome on its surface, although EPMA, WAXD and UV-vis measurements demonstrated no degradation on the aggregates and antioxidants. Degradation of the unsaturated polyester was also found for the artificial stone, which was obtained from a discolored portion in the construction site, but not for the aggregates and antioxidants. As a result, the yellowing of artificial stone was attributed to the degradation of unsaturated polyester as a constituent of the artificial stone.
