Cracking Behavior and Mechanism of Igneous Rocks Under Open-Ended Microwave Irradiation

Motivated by the potential field application of microwave-assisted rock breakage in rock engineering, microwave irradiation tests with open-ended applicators (hereafter surface irradiation) have been comprehensively carried out. In the present study, three kinds of igneous rocks were selected to conduct tests under different microwave conditions. The heating characteristics and cracking behaviors of the rocks under surface irradiation were obtained and the influences of rock and microwave conditions were analyzed. Furthermore, numerical simulations were conducted using COMSOL Multiphysics to obtain the temperature and stress distribution inside the rock. The results show that the highest surface temperature and the number, total length and maximum width of the cracks of igneous rocks increase with the microwave power level and duration. Under the same microwave condition, the diabase has the best heating characteristics and cracking behaviors, followed by quartz monzonite, and then alkali-feldspar granite. Dense crack zones within the irradiation area and radial cracks extending to the sample edges can be observed under surface irradiation. The dense crack zone is formed due to the differential expansion between minerals, while the generation of radial cracks is related to the circumferential tensile stress caused by the thermal expansion of the rock center. Highlights Conducted surface irradiation on three kinds of igneous rocks. Analyzed the influence of rock and microwave conditions on cracking effect. Simulated the temperature and stress distribution inside the irradiated rocks. Revealed the cracking mechanism of rock under surface irradiation.