Experimental study on response characteristics of micro–macroscopic performance of red sandstone after high-temperature treatment

The macroscopic responses to the progressive process of thermal damage of sandstone, as well as its micro-damage mechanisms, were obtained by measuring the macroscopic physical–mechanical properties and the microscopic properties of red sandstone that were heated at various temperatures up to 800 °C. The experimental results showed that the red sandstone sample had a critical damage threshold near 400 °C. When the heating temperature exceeded the threshold temperature, new fractures developed gradually, while the original fractures expanded rapidly. Some chemical reactions occurred in the minerals, i.e., decomposition, dehydroxylation, and fusion. These reactions resulted in the gradual damage of the mineral crystals and the microstructure. The response characteristics of the macroscopic physical–mechanical properties to the microscopic damage within this temperature range were intense. The damage mainly manifested as the rapid decrease in compressive strength, elastic modulus, tensile strength, P-wave velocity, and thermal diffusivity, and as the rapid increase in the strain and mass loss rate. The results are of great significance for understanding the mechanisms of rock thermal damage, as well as the study of the physical and mechanical properties of the deep rock mass.