Physicochemical characteristics of crack mouth solution in microbial self-healing mortar

Aiming at the problem of only shallow layer repair of microbial self-repairing cement-based materials, the effects of crack width, cracking age and crack depth on the physicochemical characteristics of the crack mouth solution were explored, and the reasons for shallow repair were explained. The pH value of the crack mouth solution was measured by pH test paper and pH meter. The determination of Ca2+ concentration in the solution was achieved by a calcium ion meter and an ethylene diamine tetraacetic acid(EDTA) titration method. And the CO3 2- concentration of the solution was measured by a micro-plate reader. Thus, physicochemical characteristics of the crack mouth solution in microbial self-healing cement-based materials were determined. The results show that in the closed environment, the pH value in the crack mouth solution is about 13.3; with the cracking age of the specimen increased from 3 to 56 d, the Ca2+ concentration in the crack mouth solution gradually increases from 140 to 350 mg/L. In the atmospheric environment, the pH value of the surface layer 3mm crack mouth solution is relatively low, and gradually increases along the depth of the crack, and then stabilizes at about 13.2; the Ca2+ concentration in the crack mouth gradually increases along the depth direction and tends to be stable; the CO3 2- concentration in the crack mouth solution gradually decreases in the depth direction and tends to be stabilized at about 1.5 g/L. After the addition of microorganisms in the crack mouth solution, the CO3 2- concentration in the surface layer increases, and the CO3 2- concentration in the depth direction does not increase significantly. The lower concentration of carbonate ions in the depth of the crack is the main cause of the shallow repair of the crack mouth. It can be seen from SEM and XRD that the mineralized product is mainly calcium carbonate in calcite-type in the crack mouth solution and the mineralized product under the action of microorganisms is gelatinous and has certain cohesiveness. © 2020, Editorial Department of Journal of Southeast University. All right reserved.