Investigation of microwave-assisted concrete recycling using single-particle testing

► We examine the effects of rapid heating in a microwave cavity on concrete. ► We find concrete strength and stiffness decrease more the longer the exposure. ► Microwave exposure increases liberations of concrete components when comminuted. ► Changes in liberation are monotonic in respect to total comminution energy. Microwave heating stands as a strong candidate for selective liberation of multiphase materials like concrete. It takes advantage of the differences in thermal, dielectric and mechanical properties of each of the components to create stress gradients that can lead to grain boundary fracture and embrittlement. The work and results reported are concerned with selective liberation of concrete’s raw constituents for recycling by combination of microwave heating and comminution. A single particle testing approach is presented for detailed analysis of the process. Concrete particles 10mm in size are treated individually in a single mode cavity microwave (2.45GHz, 2kW) test apparatus. The microwave induced effects are quantified by single particle impact testing on a fast Hopkinson bar. Analysis of impact traces reveals a thorough embrittlement of concrete particles from microwave treatment and fragment analysis confirms the potential of microwaves for selective liberation of the raw constituents of concrete. These results validate that microwaves and comminution can be combined to liberate concrete’s raw constituents.