An experimental study on the physico-mechanical properties of two post-high-temperature rocks

• 600 °C and 800 °C are critical temperatures of granite and sandstone stress–strain curves.
• Damage of granite appears negative at 100 °C.
• UCS of sandstone does not obviously change from room temperature to 800 °C.
• Temperature effect on physical property is more intense than mechanical property.

Using a hydraulic servo pressure testing machine, we investigated physical and mechanical properties of granite and sandstone samples after high-temperature treatment. Variations in apparent form, density, longitudinal wave velocity, damage, stress–strain curve, compression strength, peak strain, and elastic modulus with temperature are analyzed. We explored the differences in temperature effects on the physical and mechanical characteristics. Granite samples begin to gradually change from taupe to gray above 600 °C and sandstone samples start to gradually change from gray to brownish-red above 400 °C. 600 °C and 800 °C are respectively the brittle–ductile transition critical temperatures of granite and sandstone stress–strain curves. Rock density generally shows a gradual decreasing trend with temperature increasing. The influence of high temperature on sandstone density is much greater than granite. The decline rate of longitudinal wave velocity in granite is much greater than sandstone. Overall, damage increases gradually with temperature, but granite appears to suffer negative damage at 100 °C. Granite sample compression strength generally decreases with increasing temperature, while sandstone compression strength does not show obvious change between room temperature and 800 °C, but begins to decline rapidly above 800 °C. Peak strain increases with temperature and the increase rate of granite is similar to that of sandstone. Elastic modulus decreases with increasing temperature and decline rate of granite is much greater than sandstone. In addition, the temperature effect on the physical properties is much more intense than the effect on the mechanical properties of these two rock types.