A systematic review of sustainable bacteria-based self-healing concrete using fly ash waste

Infrastructure development requires the amalgamation of different functional constituents on a scale sufficiently capable of driving global economies towards the achievement of advanced levels of civilization. One such essential component of the construction and development process is cement, which forms an indispensable part of concrete. As a result, cement represents one of the highest production and consumption statistics worldwide. However, cement production results in extremely vast amounts of carbon dioxide emissions every year, which is detrimental for the environment in terms of both short- and long-term consequences. Thus, considering the immense carbon footprints introduced into the environment annually and the current considerable emphasis on sustainability under the sustainable development goals (SDGs), replacing portions of cement with different waste materials for the preparation of concrete has been evolving rapidly as a novel construction paradigm. One such waste material widely used for this purpose is fly ash, a waste product of coal combustion produced in significant quantities by electric and steam generating plants. This practice will substantially reduce the amount of cement required for concrete production and also cut down the amount of unused fly ash. Further, inclusion of different bacterial species in the concrete mix results in microbial-induced calcite precipitation (MICP), thus orchestrating the healing of cracks formed in the concrete due to external factors like excess load and environmental conditions. This review discusses the developments that have taken place in relation to fly ash-based bacterial self-healing concrete, with emphasis on critical details that underline the possible deployment of such heterogeneous mixtures in the current construction scenario.