Experimental investigation on the macro- and micromechanical properties of water-cooled granite at different high temperatures

Abstract To investigate the influence of high-temperature and water-cooling treatments on the macro and micro-mechanical properties of granite, uniaxial compression tests were conducted on the treated samples using the MTS815.04 testing system. Simultaneously, acoustic emission signals were collected, and micro-mechanical experiments were performed using a nanoindenter for further analysis. The results revealed that (1) with increasing temperature, the peak strength and elastic modulus of granite decreased, leading to a deterioration in mechanical properties, with a pronounced degradation trend observed after 400–500 ℃. (2) The ringing count of acoustic emission exhibited a similar trend over time within the range of 25–400 ℃, with an increasing proportion of active period I and a decreasing quiet period. The quiet period disappeared at 500 ℃, indicating a significant increase in the influence of high temperature and rapid cooling on internal rock damage beyond 500 ℃. (3) When the temperature is below 500 ℃, the slow decline in the macroscopic mechanical properties of granite is attributed to the differences in the thermophysical properties and content of minerals. However, the rapid decline in the microscopic mechanical properties of the minerals and the generation and propagation of microcracks may be the primary factors contributing to the deterioration of the macroscopic mechanical properties of granite above 500 ℃. (4) The water-cooled granite's uniaxial damage mode changed from tensile damage to tensile‒shear composite damage at 400 ℃ and finally to shear damage at 800 ℃.