Microwave heating could increase the efficiency of eliminating mortar in recycled concrete aggregate and improving recycled concrete aggregate quality. A 2D finite element model of microwave oven and concrete particles was established to study the distribution and evolution law of thermal stress field in concrete particles. In this model, influences of power, time, aggregate radius, and mortar thickness were considered. Results showed that the temperature and stress of concrete particles in a microwave field are in approximately symmetric distribution. The maximum stress of mortar is on the interface between mortar and the recycled concrete aggregate. The maximum tensile stress of mortar and recycled concrete aggregate was proportional to microwave power and irradiation time but inversely proportional to aggregate radius. The maximum tensile stress of mortar and recycled concrete aggregate initially increased and then decreased with increased mortar thickness. Given the same energy consumption, higher microwave power led to stronger tensile stress of concrete particles and higher energy use. With reasonable irradiation time, the mortar produced cracks, whereas the recycled concrete aggregate remained integral.

Microwave-assisted rock breaking can effectively improve rock breaking efficiency, decrease energy consumption, and promote the development of miniaturized and lightweight rock breaking equipment. This study uses rock mass with structural surface as the research object and analyzes the representative volume element of rock mass at varied temperatures. The general expression of rock mass strength is first obtained. The analytical formula of rock mass strength under microwave irradiation is then derived on the basis of temperature rise features under microwave irradiation. The analytical formula is verified by the experiment. Finally, the variation law of rock mass strength is studied. Results show that microwave irradiation effectively decreases rock mass strength. A longer microwave irradiation time corresponds to high microwave power density and low rock mass strength. Rock mass strength decreases linearly when microwave irradiation time and microwave power density increases. The reduction of the rock structural surface is greater than the rock mass strength under the same microwave irradiation.