Ultrasound Monitoring and Microwave Self-healing of Top-Down Cracks in Asphalt Pavements

Surface-initiated cracking with top-down propagation (TDC) is one of the most frequent and important failure modes of asphalt pavements. In order to achieve long-lasting pavements, it is necessary to control the evolution of these cracks and so repair them before they become deeper and deteriorate the lower layers. Self-healing of asphalt mixtures is possible if the temperature is raised near the softening point of the binder, thus allowing the fusion of the cracks. For this purpose, conductive additions can be used to promote induction heating when applying electromagnetic fields. This laboratory work shows the self-healing results of TDC on bituminous mixtures after microwaves exposure. Different mixtures (semi-dense asphalt concrete AC-S, gap-graded asphalt concrete for very thin layers AC-VTL and porous asphalt PA) with diverse types, sizes and proportions of metallic additions from industrial waste were tested. Three aspects were studied: (a) analysis of the type, particle size and content of each addition on the heating speed; (b) temperature increase with the specific energy; (c) monitoring of the healing process by using ultrasounds. Microwave exposure allowed the total closure of cracks using an industrial waste, with reduced exposure times and applied energies. The results validate the microwave healing capacity, as well as the use of ultrasounds for tracking the crack depth.