Effects of rapid cooling treatment on heated sandstone: a comparison between water and liquid nitrogen cooling

Rock mass is frequently subjected to rapid cooling in many temperature-dependent engineering applications. In this paper, to understand the effects of water and liquid nitrogen cooling treatments on heated sandstone, P-wave velocity and uniaxial compression tests, Brazilian test, and fracture toughness tests were carried out to evaluate variations in physical and mechanical properties. The microscopic morphology of the thermally treated sandstone was also obtained by scanning electron microscopy (SEM). Test results reveal that the P-wave velocity, uniaxial compressive strength, Young’s modulus, tensile strength, and fracture toughness of the sandstone after heating and cooling treatment decrease continuously with increasing temperature. Compared to the water cooling treatment, the liquid nitrogen cooling treatment caused much more damage to the heated sandstone. The ductility of the thermally treated sandstone increased with increasing heating temperature, which was evidenced by the stress–strain response in uniaxial compression tests. The transition from shear-dominant fracturing to complex fracturing of the failure mode demonstrated that damage of sandstone induced by heating and cooling treatment increased with increasing temperature. Based on the SEM observation, the increase in heating temperature and cooling rate can weaken particle cementation and promote the generation and propagation of the micro-cracks in sandstone, and the generation of inter-granular cracks caused the reduction of tensile strength and fracture toughness of sandstone. In addition, the tensile stress caused by the thermal shock during rapid cooling treatment is the main reason of cracks growth in sandstone specimens, and the tensile stress is positively correlated with the temperature difference and the heat transfer coefficient.