Microbial nitrate reduction induced autonomous self-healing in concrete

Concrete is the most widely used construction material in structures such as tunnels, bridges, car parks etc. Since concrete is a relatively weak material under tensile stresses, to achieve a durable structure concrete is usually combined with the steel reinforcement bars. However, in service, due to the physical and chemical factors, micro-cracks occur on concrete which enable aggressive substances to reach steel rebars causing corrosion. Therefore, regular monitoring and repair of the concrete cracks are necessary. In order to minimize the external maintenance services and related expenses, researchers focused on mechanisms triggering self-healing of these cracks. Microbial induced CaCO3 precipitation (MICP) can be mentioned among the investigated mechanisms. Basically, in MICP, the CO2 produced by the bacteria precipitates in the form of CaCO3 inside the concrete cracks and fills them up. This study presents the use of NO3- respiring bacteria to develop microbial self-healing concrete. In the context of the study, individual cultures (Pseudomonas aeruginosa and Diaphorobacter nitroreducens) were tested for their CaCO3 precipitation yields and their performance inside the mortar. Different protective carriers were used to incorporate these bacteria in mortar. Additionally, a self-protected culture in granular form was tested. As a result, cracks up to 500 µm crack width could be sealed. Water permeability of the cracked mortar specimens decreased 85 % following microbial healing of the cracks.

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