Cracking is the primary pathway through which water, chlorides, and carbon dioxide enter cementitious structures, accelerating the corrosion of steel reinforcement and shortening the service life of the concrete on which most civil and geotechnical infrastructure depends. A biological alternative, in which bacteria precipitate calcium carbonate inside cracks as they form, offers autonomous and durable sealing (Achalet al., 2011).

This study evaluated a self-healing system based on an alkali-tolerant, ureolytic and denitrifying bacterial strains. To shield the cells from the high alkalinity and mechanical stresses of the fresh matrix, spores were encapsulated together with a calcium source and immobilised before being added to mortar and concrete specimens. When cracking exposed the encapsulated agent to moisture and air, the germinating cells hydrolysed urea, raised the local pH, and precipitated calcium carbonate that progressively bridged the crack walls (Wang et al., 2014). Healing was assessed through visual crack closure, water permeability, recovery of compressive strength, and mineralogical characterisation of the sealing product.

Specimens containing the encapsulated bacterial agent sealed surface cracks up to about 0.4 millimetres wide within twenty-eight days of water exposure, whereas comparable cracks in bacteria-free control specimens remained largely open. Water tightness improved substantially in the healed specimens, and a considerable part of the strength lost to cracking was regained. Mineralogical analysis confirmed that the sealing material was predominantly calcite of biological origin. Encapsulation proved decisive, because unprotected cells lost viability in the fresh matrix and produced little healing (Fang & Achal, 2025).

These results show that bacterial carbonate precipitation can give concrete a self-activating repair capacity that extends service life and lowers the maintenance burden and carbon emissions of infrastructure exposed to increasingly severe climatic loading. The strategy is particularly valuable for geotechnical structures such as retaining walls, tunnel linings, and coastal defences, where limited accessibility makes autonomous healing especially attractive.

References 

Achal, V., Mukherjee, A., & Reddy, M. S. (2011). Microbial concrete: Way to enhance the durability of building structures. Journal of Materials in Civil Engineering, 23(6), 730-734.

Fang, C., & Achal, V. (2025) Enhancing engineering properties of cement mortars through microbial self-healing and community analysis. Construction and Building Materials, 462, 139934.

Wang, J. Y., Soens, H., Verstraete, W., & De Belie, N. (2014). Self-healing concrete by use of microencapsulated bacterial spores. Cement and Concrete Research, 56, 139-152.