Self-healing concrete: A resilient material for life

Material degradation of our civil infrastructure is inevitable and consequently regular maintenance is required to mitigate against failure during the service-life. However, understanding and knowledge of composites is now leading to the creation of concretes with autonomic self-healing capabilities. This development will transform our infrastructure by embedding self-immunity and resilience so that structures evolve over their lifespan enhancing durability and
serviceability, improving safety and reducing maintenance costs. Research in the UK under the auspices of Materials for Life and Resilient Materials for Life has developed a suite of multiple-scale biomimetic self-healing concretes that have the ability to adapt and respond to damage without external intervention. This paper covers the latest developments in these technologies. It discusses the use of minerals and polymers that create hardened healing products with similar mechanical properties to that of the original cementitious matrix, and the continued development of the use of bacteria to precipitate calcite in cracks in concrete. Whilst bacteria-based healing is
possible through a number of pathways, it is only now that a better understanding is permitting the optimization of the process. Initial research investigating genetic engineering of bacteria for self-healing is discussed. The paper describes the potential of two key technologies for including healing agents in concrete: (i) microcapsules and (ii) vascular networks. Through emulsion polymerisation and microfluidics, microcapsules that survive mixing but are also brittle enough to break open at low tensile stresses have been developed. In contrast, vascular networks permit unlimited delivery of liquid healing agents to internal areas of damage throughout the life permitting repair on a reoccurring basis. Finally, the paper discusses the use of remotely activated shape memory polymers to assist in the healing of larger cracks, and permit autonomous healing functions to work more effectively.