Self-healing properties of cement-based materials in different matrix based on microbial mineralization coupled with bimetallic hydroxide

Self-healing properties of cement-based materials in different matrix based on microbial mineralization coupled with bimetallic hydroxide were systematically studied. Firstly, the self-healing macroscopic properties of cementbased materials in different matrix were studied. The area repair rate of cement paste early crack was better than that of mortar and concrete, which showed that self-repairing agent also had excellent repair properties in the early stage. With the extension of the curing time, the repair effect was significantly enhanced; The repair effect was basically the same when the curing time was 28 d. After curing for 28 d, the resistance of the three matrix to water permeability were basically restored to intact. At each curing time, the ultrasonic propagation velocity in concrete was the largest, and that in cement paste was the smallest. Secondly, the composition and microstructure of the mineralized products were analyzed by XRD, SEM, EDS and TGA. Additionally, the pore size of the product was also tested. The characteristic peaks of XRD were consistent with the products of the target design, corresponding to the formation of calcium-aluminum bimetallic hydroxide and calcium carbonate. Mineralized products were mainly composed of two forms of inorganic minerals, one was bimetallic hydroxide with lamellar structure, and the other was CaCO3; Moreover, the quantity of calcite was much higher than that of bimetallic hydroxide. Finally, the principle that ultrasonic velocity differently after repair in different matrix was explained, and the mechanism of microbial mineralization coupled with bimetallic hydroxide to repair crack was revealed. The bimetallic hydroxide could fix the hydroxide ion, chloride ion and sulfate ion, which not only improved the repair efficiency, but also reduced the corrosion.