Self-Healing Performance of Microencapsulated Asphalt Mixtures Enhanced with Nano-SiO2–Modified Microcapsules

It is well known that microcapsule technology is considered to be an effective means to improve the self-healing performance of asphalt mixtures. Clarifying the self-healing behavior of microencapsulated asphalt mixture and quantitatively evaluating its self-healing effect is the premise of further practical application of microcapsule technology. In this study, the three-point bending intermittent fatigue test was used to investigate the influence of asphalt binder types, microcapsule content, healing time, healing temperature, and healing environment on the self-healing performance of microcapsule asphalt mixtures. The ratio of the extended life of beam after healing to the average fatigue life was used as the healing index. Secondly, the self-healing process of microcapsules was observed based on the fluorescence microscope to reveal its self-healing mechanism. The results indicated that the self-healing performance enhancement of microencapsulated matrix asphalt mixtures is superior to that of microencapsulated SBS-modified asphalt mixtures. The self-healing performance of microencapsulated asphalt mixtures is gradually improved with the increase of microcapsule content, healing time, and healing temperature. When the microcapsule content increased from 0% to 12%, and HI of two asphalt mixtures increased by 4.3 times and 1.98 times, respectively. When the healing time increased from 0 to 6 h, the HI of two asphalt mixtures increased by 2.56 times and 1.83 times, respectively. When the healing temperature was raised to 50°C, the HI of two asphalt mixtures increased by 16.1 and 1.99 times, respectively. Microencapsulated asphalt mixture in a saline-alkali environment shows better self-healing performance compared to immersion and acid environments. The microscopic self-healing mechanism of microencapsulated asphalt mixtures is that the microcapsules rupture under the stress at the crack tip, and the regeneration agent is released, which flows, spreads, and gradually fills the microcracks under the capillary action to repair the microcracks.