Preparation And Characterization Of Self-healing Cement-based Materials Based On The Mechanism Of Microbial Mineralization

As the most widely used artificial construction material in the world,concrete has many advantages such as high strength,good durability,and low cost,but the lower tensile strength makes concrete prone to different degrees of microcracks,which reduces the durability of concrete.The application of microbial induced calcium carbonate precipitation（MICP）technology can effectively fill the cracks and prevent their further expansion.Although there is more research on MICP,further research is needed on how to effectively incorporate bacteria into concrete to maintain the economy and not affect the strength of concrete;in addition,there is a gap in bioremediation for engineering cementitious composites（ECC）.In the context of the national“double carbon”strategy and“new infrastructure”strategy,this paper presents a study on the preparation and characterization of bacterial self-healing concrete based on the mechanism of MICP,and then the development of bacterial-ECC materials.The main studies are as follows:（1）By testing the mineralization ability of 11 kinds of Bacillus,the best alkaline resistant S.pasteurii was selected and visually characterized,and finally the optimum temperature and p H required for the growth and reproduction of S.pasteurii were obtained.Comparative analysis of a variety of Bacillus and OD₆₀₀showed that S.pasteurii had outstanding alkali resistance and could survive in the medium with p H of 9～11.The ability of mineralization was tested.SEM,EDS and XRD showed that the precipitate was aragonite like calcium carbonate with good crystallinity;The three-dimensional morphology shows that it is difficult for bacteria to survive in the micro pores of concrete;Green fluorescent labeling of S.pasteurii was carried out to provide a technical method for subsequent experimental observation;Finally,the effects of temperature and p H on its growth,reproduction and mineralization were explored.The experiment showed that the optimum temperature was 30℃and the optimum p H was 9.（2）The effect of mechanical properties and crack repair effect of self-healing concrete was investigated by using bacterial concentration and air-entraining agent admixture as variables.The three-point bending experiments showed that the flexural strength of the concrete cured and repaired was more significantly improved;the concrete crack healing rate increased with the increase of bacterial concentration and air-entraining agent admixture;under the comprehensive consideration of repair efficiency and strength recovery,the optimal bacterial concentration was suggested to be 2×10⁶cells/m L and the air-entraining agent admixture was 0.01%of the mass of the cementitious material;finally,the physical phase analysis was conducted to verified that the crack filler was calcium carbonate.The bonded repair between fiber/matrix resulted in improved bending strength after recovery,and the repair mechanism of fiber concrete was summarized.（3）Based on the ECC design principle,S.pasteurii was incorporated into ECC to explore the alteration of bacterial-ECC mechanical properties.The results of the mechanical tests showed that the incorporation of bacteria had some positive effects on the compressive strength,tensile strength and tensile strain capacity of the ECC specimens.The ECC specimens with preload-unload-reload showed better recovery of ultimate strain capacity under the repair effect of bacteria,and the ECC matrix properties were changed with a decrease in crack width and an increase in the number of narrow cracks,indicating better durability.At the microscopic scale,the interfacial chemical bond G_d decreased,the friction bond strengthτ₀and slip hardening coefficientβincreased,and bacteria were found to repair the interfacial region between the fibers and the matrix,allowing ECC to maintain a higher tensile strength while restoring some deformation capacity.