Comparison of Microwave- and Thermal-Assisted Rock Fragmentation Methods at Different Temperatures and Loading Rates

Understanding the effects of microwave irradiation and thermal treatment on the dynamic compression and fragmentation properties of rocks is essential to quantify energy consumption in rock engineering. In this study, Fangshan granite (FG) specimens were exposed to microwave irradiation and heat treatment. The damage of FG specimens induced by these two methods was compared using X-ray CT scanning and ultrasonic wave method. The temperatures of FG after microwave irradiation and thermal treatment were effectively evaluated using a newly proposed technique. A novelty method for precisely determining the geometric features of fragments is developed to estimate the fragmentation energy. Thus, the dynamic uniaxial compressive strength (UCS), the dynamic fragmentation characteristics, and the fragmentation energy of FG after these two pretreatment methods can be reasonably compared. The noticeable distinction of loading rate effect on the dynamic UCS of FG between these two pretreatment methods is first observed. A relationship is established between the dynamic UCS and the damage induced by microwave irradiation and heat treatment. Moreover, fragmentation energy fan analysis is introduced to accurately compare the fragmentation properties of FG after two pretreatment methods in dynamic compression tests.