Investigating the electrothermal self-healing bituminous composite material using microcapsules containing rejuvenator with graphene/organic hybrid structure shells

Self-healing bituminous material has become a hot research topic in self-healing materials, and this smart self-healing approach is a promising a revolution in pavement material technology. The aim of this work was to investigate the electrothermal self-healing bituminous composite material using microcapsules containing rejuvenator with graphene/organic. The microcapsules owned electric conductivity capability because of the advent of graphene, and realized the self-healing through the two approaches of heat induction and rejuvenation. Microcapsule shells were fabricated using a strength hexamethoxymethylmelamine (HMMM) resin and graphene by a two-step hybrid polymerization. Experimental tests were carried out to character the morphology, integrity and shell structure. It was found that the electric charge balance determined the graphene/HMMM microstructure. The graphene content in shells could not be greatly increased under an electrostatic balance in emulsion. XPS, EDS, TEM and AFM results indicated that the graphene had deposited on shells. TGA/DTG tests implied that the thermal decomposition temperature of microcapsules with graphene had increased to about 350 °C. The thermal conductivity of microcapsules had been sharply increased to about 8.0 W/m²·K with 2.0 wt% graphene in shells. At the same time, electrical resistivity of microcapsules/bitumen samples had a decrease with more graphene in bitumen. The self-healing efficiency of composite samples was evaluated by a beam on elastic foundation (BOEF) mechanical process including loading-unloading-reloading cycles under temperature of 0 °C. It was found that the samples had an enhanced self-healing capability because of the electrothermal self-healing mechanism. The crack surfaces of bitumen were softened under electrothermal effect. Moreover, the released rejuvenator diffused into aged bitumen with a faster rate under the help of heat energy.