Investigation of thermally-induced separation in mortar-aggregate under microwave irradiation

Recycled aggregate demand is growing worldwide owing to the rapid development of public infrastructure. This paper aims to investigate the effect of multi-field coupling on the separation of mortar and aggregate based on theoretical analysis and numerical simulation, and the reliability of the models is verified by microwave heating experiment. The results indicate that the electric field intensity and temperature in mortar are greater than that in aggregate. The electric field is continuous at the interface, but there are jumps in temperature and stress. In the wave propagation plane, there are two neutral axes located respectively in mortar and aggregate. The neutral axis in mortar gradually moves towards the interface with heating time, resulting in the increase of tensile stress on mortar surface. As the tensile stress exceeds the critical strength of mortar, microcracks are appeared on the surface and then gradually propagate towards the interface. The mortar is removed from the aggregate surface as the cracks propagate to the interface. Moreover, during the heating process, dehydration of hydrous minerals and moisture migration in mortar also affect the separation of mortar and aggregate. This provides insight into the efficient separation of mortar and aggregate.