Physicochemical and mechanical characteristics of concrete exposed to high temperature

In order to understand the degradation mechanism of concrete structures in the Fukushima Dai-ichi nuclear power station during severe accident, the mechanical test, ultrasonic test and XRD analysis was conducted on concrete samples after subjected to different temperatures up to 800^oC. The results showed that the ultrasonic velocity and strength of concrete sharply decreased with increasing temperature above 400^oC. Between 600^oC to 800^oC, the change in strength was not significant. Additionally, the XRD studies clearly indicated the decomposition of Ca(OH)₂ and C-S-H structure above 400^oC and 600^oC, respectively. The results of XRD analysis were consistent with the changes in physicochemical and mechanical properties of heated concrete. (author)