Analysis of the recovery effect and mechanism of microwave responsive microcapsules on aged bitumen performance

As one of the repair methods for microcracks in bitumen materials, microcapsules can repair internal microcracks in bitumen materials. However, they are essentially passive repair, and there is insufficient research on the recovery of aged bitumen performance after core release. To achieve the active response of microcapsules and the recovery of aged bitumen performance, a novel microwave responsive microcapsule, namely carbon black microcapsules (CM), was prepared in this work. Under microwave irradiation, the core material release characteristics of traditional microcapsules and CM were compared. The recovery effect of the released core material on aged bitumen performance was systematically studied. The results show that CM has good morphological structure and stability, with an increase in wall thickness and surface carbon content of 27.94% and 4.89%, respectively, compared to traditional microcapsules. Based on the release behavior of the core material, it is recommended that the microwave radiation time be 180 s; After microwave radiation, the aging recovery rates of complex modulus, phase angle, creep stiffness, and m value of aged bitumen containing CM were 69.86%, 53.83%, 39.96%, and 40.38%, respectively. Meanwhile, the aging recovery rates of carbonyl index, sulfoxide index, and macromolecular content were 77.78%, 59.57%, and 88.28%, respectively, which were closer to the pre-aged state. This work not only provides a novel technical route for the active release of microcapsules, but also effectively restores the aged performance of in-service bitumen materials, laying a solid foundation for the intelligent development of road engineering.