Microwave assisted concrete breakage: The viewpoint on analysing concrete thermal and mechanical behaviour

Effective concrete breaking is a challenge for concrete recycling engineering. Macroscopic and microscopic tests were conducted to explore the thermal damage evolution of concrete under microwave irradiation in this paper. Uniaxial compressive strength test was employed to investigate the impact of microwave irradiation on concrete macroscopic mechanical. Concurrently, scanning electron microscopy test, X-Ray diffraction analysis, and computed tomography scan test were utilized to investigate microstructure evolution and chemical content variation. The results show that the response of basalt aggregate to microwaves was stronger than that of the mortar, resulting in thermal gradient stress between them, leading to interface debonding and concrete damage. Within the temperature range of 100°C–300°C, the water liberated by AFt (Ettringite) hydrolysis evaporated in conjunction with the free water within the concrete, leading to the increment of porosity and rapid growth of cracks. Within 300°C–500°C, CH and C-S-H decomposed, which causes internal crack propagation. A main fracture zone was formed in concrete after sufficient power input, creating a zone of concentrated damage. The fracture mainly occurred and propagated at aggregate–mortar interface. The study can provide a reference for the application of microwave-assisted concrete breaking.