Self healing of early age cracks in cementitious materials

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Concrete, the world's most used construction material, is susceptible to cracking that tends to compromise its structural integrity and durability. Traditional concrete repairs have failed in part to mitigate the problem because, in most cases, damage is only detected after concrete deterioration has already progressed. The implications have been economically, socially, and economically disastrous owing to a deteriorated built infrastructure that is costing Canada about $10 billion annually of public funds to repair or replace. The American Society of Civil Engineers estimated $2.2 trillion are needed to repair and retrofit the infrastructure over 5 years. As a result, a need exists to develop a new concrete that is either crack free or can heal itself in the event of cracking. Hence, self-healing concrete has emerged as an alternative and sustainable solution by emulating nature's time-tested strategy. Accordingly, this study aims to develop a cementitious mortar that can self-seal when cracking occurs. The long-term objective is to develop specifications and tools for designing and printing autonomic self-healing cementitious material. The self-healing mortar utilizes encapsulated healing agents that are not intrinsic to concrete. The healing agents are released when cracks cross the capsules and react and bind the cracked faces together. The efficiency of the autonomic self-healing mortar depends on the survivability of the capsules during mixing, mechanical compatibility of capsules and mortar, capsules bond strength, healing agents flow properties, and distribution of the capsules. Accordingly, experimental and analytical programs were developed to 1) quantify the likelihood of a 3-D crack intersecting capsules and self-healing in cementitious material, 2) investigate analytically the mechanical interaction between capsules and mortar as the mortar hardens and shrinkage cracks develop, 3) determine experimentally the capsules' properties necessary to survive during mixing and placing of mortar, and 4) study experimentally the efficacy and durability of capsules as mortar hardens and shrinkage cracks develop. This research is novel in many ways. It provides a holistic approach to study the mechanical and chemical aspects of self-healing mortar which includes cementitious material, polymeric capsules and healing agents, and their interactions. This research which addresses major areas of self-healing mortar that lack quantitative knowledge and measures, will yield analytical models and test methods for evaluating the performance and durability of self-healing mortar, and quantification tools for reliably and effectively designing self-healing mortar. In the long-term, translating and mobilizing the generated knowledge will significantly improve our understanding of the performance and durability of concrete, and ensure sustainable Canadian concrete infrastructure that will endure for many generations and provide economic growth to Canada.