Study on the effect of high-temperature combustion on damage evolution and mechanical properties of rock-like materials

In addressing the frontier issue of high-temperature damage mechanisms in underground engineering fires and their impact on lining concrete and surrounding rock mechanical properties, this study focuses on C35 concrete as the primary subject of investigation, with granite from tunnel sections in the Sichuan-Tibet region serving as a reference. The research analyzes the evolution of damage and mechanical responses of rock-like materials after exposure to high-temperature fire. The findings indicate that under high-temperature conditions, granite and concrete experience increased cross-sectional porosity due to factors such as cementitious material failure, mineral expansion, and decomposition. This porosity exhibits temporal and spatial characteristics, increasing logarithmically with exposure time and decreasing linearly with specimen height from the heated surface. As the high-temperature test time increases, the peak stress of granite and concrete specimens gradually decreases, and the rate of decrease gradually increases.The maximum peak stress reduction rates of the three strain rates were 80.49 %, 82.68 % and 59.42 % for granite specimens, and 47.48 %, 51.68 % and 50.98 % for concrete specimens. The compressive strength shows a negative correlation with exposure time, accompanied by a transition from brittle to ductile failure characteristics. These research conclusions hold significant theoretical importance for understanding the evolution of damage and changes in mechanical properties of surrounding rock and lining concrete after high-temperature fires in underground engineering, providing fundamental data for post-fire safety assessments.