Quantification of thermal damage and dynamic tensile behaviors of hard rock under microwave irradiation: an experimental investigation

Microwave-assisted hard rock breakage is a potential solution for exploitation of deeper resources. A series of ultrasonic non-destructive tests and NMR tests were conducted to quantitatively characterize the thermal damage of granite. The effects of temperature, microwave power, and loading rate on the dynamic tensile behaviors of granite were investigated by the SHPB tests. Results indicate that, when the temperature is higher than 400 °C, the ultrasonic velocity of microwave-treated granite samples significantly decreases, and the dynamic elastic modulus is more sensitive to temperature than microwave power. The microwave heating promotes the simplification of pore structure of granite, which manifests as the conversion of the pore size distribution from bimodal to trimodal and the decreases of fractal dimension of macropores. The dynamic tensile strength increases as the increasing loading rate and decreases as the increasing temperature and power. Under dynamic tensile stress, the microwave treatments weaken the brittleness of granite and the dependence of the dynamic tensile strength on the loading rate. The investigation of rock damage and dynamic tensile strength in this study provides guidance for optimizing microwave-assisted rock breakage technology.