Factors influencing self-healing mechanisms of cementitious materials: A review

The increasing awareness of climate change and global warming has pushed industries to be more conscious of their environmental impact, especially in the construction industry with the main contributor being concrete. Concrete is a material that is in very high demand in the construction industry for structural applications. However, it's a material with a major concern with the challenges of microcracking. New technology has seen the development of self-healing material, using novel techniques to bring cementitious materials back to its original state. This paper reviews and evaluates the novel techniques adopted by the researchers in the field to achieve a self-healing material, with the main focus being on the factors influencing the mechanisms of autogenous healing and bacteria-based healing. Various parameters including bacteria type, pH, temperature, nutrient, urea, and Ca2+ concentration, bacteria concentration and application, pre-cracking, healing condition, cement type, and crack width are all important for healing efficiency, although the use of water to facilitate both autogenous and ureolytic bacteria healing mechanism is paramount for the triggering of healing processes. This study thoroughly presents various factors and their correlation to the healing mechanisms of autogenous healing and ureolytic bacteria healing. Further studies are identified to better understand the exact mechanism taking place and which healing process contributed to how much of the healing, and this review could serve as an informative platform for these pursues.