2021 Volume 19 Issue 4 Pages 301-320
Self-healing cement composites are considered to be an effective solution towards the enhancement of sustainability and service-life of cement and concrete structures, as well as the reduction of repair and maintenance cost. Among the several self-healing technologies, encapsulated healing agents present benefits that include healing of larger cracks and timeless healing potential upon damage. This paper presents a critical overview of the progress made in the development of encapsulated healing agents, along with the main achievements related to their integration in the cement mixtures. Encapsulated healing agents were classified according to their size in two main categories: (i) spherical microcapsules up to 1 mm, and (ii) macrocapsules that include larger spherical capsules (>1 mm) and/or tubular capsules up to 100 millimeters long. The review emphasizes on the performance characteristics of the shell material and the capsule system that are necessary in order to protect the different types of healing agents in the long-term, to provide even distribution and survivability and finally, to ensure efficient triggering and release of the healing agent during crack propagation. The relevant literature is analyzed and discussed according to the above thematic priorities, aiming to locate research gaps and best practices and thus, to enable and facilitate the development of effective encapsulated healing agents that could be scaled-up. To this end, particular emphasis is given on the effect of capsules integration on the properties of both fresh mixtures and hardened cement specimens.
