Autonomous healing in concrete by bio-based healing agents - A review

Crack formation in concrete structures is inevitable due to deterioration throughout its service life due to various load and non-load factors. Therefore, repair and maintenance operations are needed to prevent cracks from propagating and decrease the structures' service life. However, accessibility to cracked zone may be difficult; besides such operations require capital and labor and contribute to pollution due to anthropogenic activities and usage of more repair materials. Self-healing may be a possible solution to reduce manual intervention. Autonomous crack sealing by bacteria induced carbonate precipitation is an environmental friendly mechanism which is studied intensively by many researchers worldwide. This review focuses on evaluation of crack healing by bacteria when it is added directly to the concrete or added after encapsulating it into a protective shell. Four key aspects that determine effectiveness of bacterial self- healing have been highlighted and discussed; they are capsule material and encapsulation of bio-agents, survival of capsules during concrete mixing, effect of addition of bio-agents or capsules on concrete properties, and sealing ability and recovery of mechanical and durability properties. Finally, research gaps and scope of future research work are identified and discussed.