Microcapsule-based self-healing concrete was used in a tunnel engineering project in the Qianhai area, Shenzhen and the concrete performance was investigated using laboratory and field tests. The physical properties of the microcapsules and the microstructure of the self-healing concrete were experimentally investigated. The effects of the microcapsules on the strength, permeability, and long-term shrinkage of the self-healing concrete were also investigated. The self-healing efficiency was evaluated using a compressive strength test and a rapid chloride migration (RCM) test. The results indicated that the selfhealing functionality of the concrete containing 10% microcapsules gradually increased over time. The microcapsules had both positive and negative effects on the microstructure of the self-healing concrete. The use of the microcapsules resulted in a significant increase in the long-term shrinkage but the amount of shrinkage is acceptable for practical applications. No significant difference of the strain evolution was observed between the experimental and control groups in the field test, indicating that the use of microcapsule-based self-healing concrete is feasible and promising to improve the durability of concrete structures, especially in coastal civil engineering.

Introductions

The main cause of deterioration in concrete is the appearance of cracks, which threaten the safety, durability, and the functionality of concrete structures [1–۳]. In general, cracking inevitably occurs when the concrete structure is subjected to a variety of mechanical and environmental actions. In order to reduce the repair and maintenance costs of concrete infrastructure, multiple studies [4–۷] have been conducted in the past twenty years to develop techniques to prevent concrete from cracking. Over the years, mineral additives have received much attention due to its physicochemical properties, which reduce the cracking risk by minimizing the early cracking susceptibility of concrete [8,9]. However, this enhancement may only improve the durability of the concrete for a limited period rather than lengthen the service life of concrete structures in a smart way from long-term point of view. In addition, due to the fact that micro-cracks formed in the concrete matrix are invisible and their locations are usually difficult to determine, this method cannot be applied to prevent micro-cracks caused by loads or environmental conditions in the later service stages.