Seminar

It is well documented that increasing temperature to 400 ℃ or above can significantly lower rock strength due to the corrosion by thermal decomposition and disintegration by thermal cracks. However, the phenomenon of strength increase with elevated temperature between room temperature and 400 ℃ has also been reported in a number of studies. To explore the causative factors of thermal strengthening, we carried out triaxial compressive tests on Sichuan marble specimens, which were heated to different elevated temperatures. In total, eight real-time heating groups (25-200 ℃ with an increment of 25 ℃) and one thermally treated group (175 ℃) were tested. In the former, the mechanical loading was exerted to the specimens which had been heated to and maintained at the designated temperatures, while in the latter, the mechanical loading was applied to the specimens which had been first heated and then naturally cooled down to room temperature. Thermal strengthening was observed in the real-time heating groups but not in the thermal-treatment group. The pre- and post-loading EDX, SEM examinations revealed that the thermal decomposition of the minerals and the development of thermal cracks were limited. Thermal dilation, which leads to a tighter grain-grain contact, is the most plausible factor leading to thermal strengthening. To our best knowledge, this study is the first to explicitly confirm the phenomenon of thermal strengthening and comprehensively investigate the underlying mechanism. The findings provide an in-depth understanding of the thermal effect on rock strength in the moderate temperature range with implications in geological engineering practices. 

Additional information: Mr. CUI Xin, u3005741@hku.hk