Self-healing of microcapsule-based materials for highway construction: A review

Maintaining the health and reliability of civil facilities is of strategic importance. In highway engineering, pavement cracking impairs the road service and travel comfort level, while structure cracking can cause catastrophic damage. Microcapsule-based self-healing materials offer solutions to auto-recovery micro-cracks and maintain structural health. Such solution has become available by laboratory synthesis and proved effective in addressing the cracking problem during long-term mechanical, thermal, and hydraulic conditions. However, full-scale applications of this technique are not prevalent, showing its potential limitations in highway engineering. Crack healing in highways is a big topic, therefore, this review has two insertion points. (1) We focus on the cracking issues on two specific materials: asphalt and concrete, which account for the vast majority of all the materials used in pavement and structures in highways. (2) Instead of the laboratory studies, we pay more attention to the practical applications, the meaning of healing performance, and the adverse effects of microcapsules to the main structural components (i.e., tunnel lining, bridge piers and beams) and pavement in highways. The practical significance of self-healing materials in highway projects was discussed from the three aspects: strength, durability, and stress redistribution. The difficulty in applying this new technique is also discussed from economic perspective. For future-proofing, a material evaluation system that fits the load condition is required. The self-healing technique brings