Nitrite producing bacteria inhibit reinforcement bar corrosion in cementitious materials.

Chemicals and synthetic coatings are widely used to protect steel against corrosion. Bio-based corrosion inhibition strategies can be an alternative in the arising bioeconomy era. To maintain the good state of steel reinforcement in cracked concrete, microbe-based self-healing cementitious composites (MSCC) have been developed. Yet, proposed strategies involve reasonably slow crack filling by biomineralization and thus risk the possible rebar corrosion during crack healing. Here we upgrade the rebar protection to a higher level by combining MSCC with microbial induced corrosion inhibition. Presented NO3- reducing bacterial granules inhibit rebar corrosion by producing the anodic corrosion inhibitor NO2- and meanwhile heal a 300-µm-wide crack in 28 days. During 120 days exposure to 0.5 M Cl- solution, the rebars in cracked MSCC keep showing open circuit potentials above the critical value of -250 mV and they lose less than 2% of the total rebar material which corresponds to half the material loss in cracked plain mortar. Overall, the obtained rebar protection performance is comparable with that of uncracked mortar and mortar containing chemical inhibitor, hence the microbe-based system becomes an alternative to the traditional methods.