Influence of concentration and proportion prepared bacteria on properties of self-healing concrete in sulfate environment

Self-healing of concrete is significance to regain the performance of concrete because cracking is unavoidable by the use of the bacteria to produce calcite precipitate which can fill the cracks. This study investigated the relationship between the proportions of nutrient, bacteria, and the bacterial concentration on properties of the self-healing concrete where there is no standard for the mixing ratio of bacteria and nutrients. Also, the current study aimed to study the change in compressive strength on exposure to sulfate attack. Two types of bacteria Sporosarcina pasteurii DSM 33 and Bacillus sphaericus DSM 396 were introduced into the concrete. Two concentrations of bacteria 2 × 10 9 and 2 × 10 10 colony-forming units per milliliter and four proportions of bacteria 0.5, 1, 4, and 10% of cement weight were selected for the study. In addition, calcium lactate was used at 0.25, 0.5, and 1% of cement weight as nutrition of bacteria. Tests were performed for compressive strength, water permeability, rapid chloride permeability, SEM, EDX, and XRD. The results show a tremendous development in the compressive strength of concrete especially with 10% bacterial proportion with 1% nutrient, and this can be attributed to the filling of cracks in concrete by calcite which was confirmed by SEM and EDX. Also, the results confirmed that bacteria reduce chloride penetration into the concrete and improved the resistance to sulfate ingress.