Nitrate reducing CaCO3 precipitating bacteria survive in mortar and inhibit steel corrosion

Microbial healing of concrete cracks is a relatively slow process, and meanwhile the steel rebar is exposed to corrosive substances. Nitrate reducing bacteria can inhibit corrosion and provide crack healing, by simultaneously producing NO2− and inducing CaCO3 precipitation. In this study, the functionality of one non-axenic and two axenic NO3− reducing cultures for the development of corrosion resistant self-healing concrete was investigated. Both axenic cultures survived in mortar when incorporated in protective carriers and became active 3 days after the pH dropped below 10. The non-axenic culture named “activated compact denitrifying core” (ACDC) revealed comparable resuscitation performance without any additional protection. Moreover, ACDC induced passivation of the steel in corrosive electrolyte solution (0.05 M NaCl) by producing 57 mM NO2− in 1 week. The axenic cultures produced NO2− up to 26.8 mM, and passivation breakdown and pitting corrosion were observed. Overall, ACDC appears suitable for corrosion resistant microbial self-healing concrete.