Factors Affecting the Release Behavior and Sustained Repair Effect of Self-Healing Microcapsules Encapsulating Rejuvenators in Asphalt Mastic

Microcapsule technology is a promising approach for enhancing the self-healing ability of asphalt pavements. In this study, the self-healing behavior of melamine-urea-formaldehyde (MUF) microcapsules was investigated. The microcapsules were synthesized using an in situ polymerization method. The proposed healing indicators, combined with fluorescence tracing technology, were used to evaluate the release behavior and sustained repair effect of the microcapsules at different damage levels, healing intervals, aging degrees, and healing temperatures. The results showed that most microcapsules survived at low damage levels, whereas larger microcapsules were more likely to rupture and release the rejuvenators. The sustained self-healing effect of the microcapsules could effectively repair internal damage within the asphalt pavement over an extended service life. Aged asphalt was particularly susceptible to the activation of microcapsules, leading to increased self-healing and the provision of additional rejuvenators for damaged asphalt mastic. Additionally, the self-healing of asphalt mastic with microcapsules had a critical temperature threshold. Microcapsules could enhance the fatigue and self-healing performance of asphalt mastic only when the healing temperature was below a certain value; otherwise, they may lead to adverse effects. The critical healing temperature threshold for thin-film oven testing (TFOT)-aged asphalt increased from approximately 30°C to about 45°C after PAV aging. This study provides a better understanding of the self-healing behavior of microcapsule asphalt, as well as the factors affecting the release behavior and sustained repair effects of the microcapsules. These results can be used to optimize the design and implementation of microcapsule technology to enhance the durability and sustainability of asphalt pavements.