Effect of Temperature on Macroscopic and Microscopic Properties of Sandstone From Qidong Coal Mine

Heat from gas explosions affects the physical and mechanical properties of rock and reduces the stability of tunnels, such as in coal mines. This paper mainly studies the physical and mechanical properties of sandstone after heating and investigates the influences and mechanisms involved. Acoustic emission (AE) monitoring, X-ray diffraction (XRD), scanning electron microscopy (SEM) and polarized light microscopy are used to show that the uniaxial compressive strength (UCS) and peak strain of sandstone change significantly with temperature. In particular, the UCS decreases rapidly at 500 similar to 600 degrees C due to a transition from alpha-quartz to beta-quartz. The XRD analysis shows that the physical and mechanical properties of sandstone are affected by its mineral composition, as physical and chemical reactions of quartz, muscovite and kaolinite at high temperatures weaken the sandstone. The AE signals increase with temperature and correspond well with observed loading stages, as they reflect the spatiotemporal evolution in internal micro-cracks. The degree of crack opening is low at low temperatures, then cracks become connected with increasing temperature, further explaining the changes in mechanical properties. Polarized light microscopy shows that grain size and pore characteristics are related to mechanical strength; generally, higher strength is associated with smaller grains with a less even size distribution. In addition, thermal and mechanical damage were quantitatively characterized by deriving thermal, comprehensive and dynamic damage factors. The results provide a theoretical reference for mining engineering in high-temperature environments.