Effect of microwave pretreatment on mechanical behavior of concrete and aggregate recovery

Microwave heating has exhibited remarkable potential for concrete aggregate recovery due to selectivity and high efficiency. The paper aims to investigate the effect of microwave on mechanical behavior of concrete and aggregate recovery after mechanical crushing. The variations of compressive strength, elastic modulus and brittleness for concrete under different heating parameters were investigated from the macroscopic point of view and of porosity and microstructure were analyzed from the microscopic point of view. Further, the concrete fragmentation and aggregate liberated rate were evaluated following crushing. The experimental results show that hot spots occur in the central region due to the convergence of electric field in the multimode cavity. Microwaves deteriorate the microstructure of mortar and induce the growth and penetration of pores as a consequence of thermal effect and athermal effect, leading to an increase in porosity. Microwave heating results in weakened mechanical properties of concrete, including compressive strength, elastic modulus and brittleness, even at very low energy consumption. Microwave pretreatment facilitates concrete fragmentation and aggregate liberation after crushing based on the increase of mortar porosity and the weakening of interfacial transition zone. In particular, microwave power has an obvious effect on these phenomena mentioned above, and high power will promote the recovery of aggregate and fine powder. Microwave-assisted concrete recycling can be considered as an effective technique to improve the quality and recovery efficiency of aggregate.