In this study, FT-IR analysis was performed by exposing cement paste to high temperature in order to characterize the change of hydration behavior of concrete structure damaged by fire accident. As the holding time increased, the Al-O vibration region increased due to the increase of Si-O symmetric Ca₂(SiO₄) and Brownilerite, and the OH stretching region tended to increase due to thermal decomposition of Ca(OH)₂.