Microwave-induced strength reduction and weakening mechanisms of basic rocks

Basic rocks are considered ideal materials for microwave breaking due to their high strength and high microwave sensitivity. However, the heating characteristics and weakening mechanisms of basic rocks under microwave irradiation have not been systematically investigated. In this study, the multimode microwave irradiation experiments were conducted on two types of diabase and three types of basalt with varying porosities to investigate the effects of microwave conditions and rock properties on the heating characteristics and weakening effects of basic rocks, respectively. The results indicate that all five basic rocks exhibited similar heating rates under microwave irradiation, and the porosity had a minor impact on the heating characteristics of basic rocks. Both cracking and spalling failure modes occurred in basic rocks under microwave irradiation. Specifically, diabase #1, basalt #1, basalt #2 and basalt #3 exhibited cracking failure. As the irradiation time increased, the highest surface temperature of the rocks, the number and width of microwave-induced cracks, the amounts of volume expansion, P-wave velocity reduction and strength reduction of microwave-treated rocks all progressively increased. Under the same microwave irradiation conditions, the failure of diabase was generally more prominent than that of basalt. Additionally, the weakening effects on basalt #1, basalt #2, and basalt #3 gradually diminish with increasing porosity. Diabase #2 exhibited spalling failure under a low microwave power and a short irradiation time, which is related to the rapid heating and chemical decomposition of iron oxides and carbonate amygdales filling the pores within diabase under microwave irradiation.