Revolutionizing concrete durability: Case studies on encapsulation- based chemical (autonomous) self-healing techniques and future directions – A critical review

There are growing concerns surrounding the premature degradation of concrete structures worldwide. Undesirable cracks provide pathways for moisture and aggressive chemicals to penetrate, leading to further deterioration of the concrete and the corrosion of steel reinforcements. This issue incurs substantial maintenance costs, with billions spent annually on repairs in countries like the United States and Canada. Efforts to enhance concrete durability have led to the development of self-healing approaches, both autogenous and autonomous, as alternatives to traditional crack repair methods. Autogenous self-healing relies on the natural properties of concrete materials, while autonomous self-healing involves the use of capsules containing healing agents that are released when cracks form. The growing interest in self-healing concrete is evident from the increasing number of publications on the topic in recent years. Through a synthesis of multiple case studies, it examines the realm of chemical self-healing in concrete, with a specific emphasis on capsule-based methods. It explores various capsule materials, healing agents, geometric shapes, and trigger mechanisms. Furthermore, an assessment of the different test methodologies has been conducted, and a particular focus has been placed on the mechanical and durability properties regained by the self-healing process. The paper not only discusses existing capsule-based chemical self-healing concrete attributes and evaluation methods but also presents current undertakings in developing novel self-healing concrete using machine learning techniques. It also proposes recommendations for further research and applications in the realm of self-healing concrete.