In recent years, microbial repair materials have received widespread attention for their advantages such as stable products and good compatibility with cementitious materials. However, the current construction process of microbial repair materials is mainly by immersion, which limits the more widespread application. Therefore, this study proposed a coating construction process with sodium alginate as the carrier. The effects of sodium alginate concentration and dosing on the fundamental properties of microbial repair materials (CaCO3 content, mechanical properties, water absorption ratio, and heating shrinkage rate) and their effects on mortar repair effects (macroscopic morphology and surface water absorption ratio) were investigated. The repair effects were further verified by combining thermogravimetric analysis of repair products and scanning electron microscopy. The results showed that 1) the microbial repair material had better basic properties when sodium alginate solution with a mass concentration of 1.5% was used, and its solution-to-bacterial solution volume ratios were 8:2, 7:3, and 6:4; 2) using the coating technique, the microorganisms were fixed in the cracks on the mortar surface by using sodium alginate as the carrier. Only twice of repair could generate a mixture of calcium alginate and calcium carbonate crystals in the cracks by close adhesion. The surface water absorption of the repaired specimens was 67% lower than before the repair, which is a significant effect of the repair.
In response to the shortcomings of traditional concrete crack repair materials, a new generation of repair materials has been developed - a microbial repair material based on sodium alginate modification. The method adopts a brushing technique to fix the microorganisms on the cracks to be repaired so that they can deposit calcium carbonate in situ to repair the cracks. This paper carried out a study of the fundamental properties of the repair material, as well as studied the macroscopic morphology and surface water absorption of its specimens before and after repairing mortar cracks, and analyzed the material changes and microstructures of the repair products. The results showed that: (1) the CaCO3 content, water absorption ratio and heating shrinkage rate of the microbial repair material modified with sodium alginate were better than those of the repair material without microorganisms; (2) the microorganisms were fixed in the cracks on the surface of the mortar using the brushing technique with sodium alginate as the carrier and were able to adhere tightly to the cracks after only two repairs to produce repair products, which were mainly calcium alginate and calcium carbonate, and the surface water absorption rate was reduced by about 65% compared to that before the repair.
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