Materials, Theories and Experiments of Microcapsule Self-Healing Method — A Review

The construction of tunnels is booming in China in recent decades. However, the degradation of concrete lining in tunnels seems inevitable, and the challenges in the repair and maintenance in urban metro structures confront engineers daily. The concept of self-healing in concrete was proposed over a decade ago. Concretes with microencapsulated healing agents are very appealing due to the advantages of self-healing, adaptivity to concrete, and the potentiality of controllable, quantifiable healing. The focus of this paper is to summarize the motivation of using self-healing materials and to classify the investigations on the microcapsule-enabled concrete in terms of its components and properties. Relative materials, experiments and theories have been reviewed. Some important factors of microcapsule-enabled, self-healing, underground concrete in urban metro structures are discussed too.