Material Properties and Triaxial Thermal Damage Evolution Mechanism of Limestone under Different Temperature and Standing Time

The mechanisms of changes in rock properties over time following high-temperature exposure are critical for evaluating the long-term stability of thermally damaged surrounding rocks. This study focuses on limestone from coal-bearing sedimentary strata, conducting high-temperature experiments to analyze the changes in its physical and mechanical properties. The evolution equation of thermal damage in rock over time is derived, and the microscopic mechanisms behind the evolution of thermal damage characteristics are revealed. The results show that (1) after high-temperature treatment, the density of limestone exhibits the greatest rate of change after 60 days of placement, while the wave velocity, resistivity, and hardness show the greatest rate of change after 100 days. The mechanical properties of limestone generally change the most after 40 days of placement, with a slight rebound thereafter, stabilizing after 60 days. (2) At 20°C and 200°C, the physical and mechanical properties of limestone change insignificantly over time; however, at 400°C, the properties deteriorate over time, while, at 600°C, self-healing properties are observed. (3) At 400°C, the damage values of limestone increase over time, while, at 600°C, the damage values decrease. (4) At 20°C and 200°C, microscopic cracks do not develop over time, and the mineral composition remains largely unchanged; at 400°C, cracks begin to form and expand over time, while minerals undergo complete decomposition. At 600°C, larger cracks form, but, over time, these cracks heal, with minerals fully reacting to form new substances that fill the cracks, demonstrating clear self-healing characteristics. These findings provide an important theoretical foundation for assessing the long-term stability of rocks in high-temperature environments, particularly for geothermal energy extraction, deep mining, and other related fields. The understanding of thermal damage and self-healing properties is of significant practical relevance.