Study On Self-repairing Cement-based Materials Based On Bacteria Immobilized In Shale Pottery Sand

Microbial self-healing cement-based material is an interdisciplinary study of mineralization in the field of biology and civil engineering.It uses the unique metabolic and deposition mechanism of biological bacteria to intelligently repair cracks to achieve self-perception and self-healing of cement-based material,which is an environmentally friendly material in line with the future development trend.Calcium sources play an important role in the microbial mineralization deposition products and the repair effect of materials.At present,the commonly used calcium sources in microbial self-repair are mainly calcium chloride,calcium nitrate,calcium lactate and calcium acetate,which are used in self-repair cement-based materials with problems such as steel corrosion,low toxicity,high price and large dosage.In this study,a series of studies were conducted on the feasibility of calcium formate as a microbial self-healing calcium source in order to expand the selection range of calcium sources for microbial mineralization and deposition,starting from the condition that calcium formate has early and strong effect on cement and has become a calcium source.Four calcium sources(calcium formate,calcium lactate,calcium acetate and calcium chloride)including calcium formate were selected to compare their effects on compressive strength and microbial mineralization ability of mortar.The alkaliresistant microorganisms and the corresponding nutrients were determined through the tests of alkali resistance,alkali acclimation and nutrient compatibility of microorganisms to prepare self-healing granules with shale pottery sand as the carrier of microbial self-healing agent.Calcium source and self-healing particles were used to prepare microbial self-healing cement-based materials to explore the effects of microbial incorporation,microbial species,calcium source content and proportion of self-healing particles on mechanical properties and self-healing effect of cracks.The results show that :(1)Compared with the control group,the 28-day compressive strength of mortar specimens mixed with calcium formate is increased by 12.58 %,and the mass of precipitate in the mineralization reaction of calcium formate and Bacillus pasteurii is12.2 g,By XRD phase analysis,it is determined that most of the precipitates are calcite,which is an ideal calcium source in line with the test expectation.(2)B.Pasteurella has stronger alkaline tolerance and can grow and reproduce in an environment with p H ≤ 13.The direct incorporation of microbial nutrients into mortar will lead to slow setting of mortar and reduce the strength of mortar.Therefore,Bacillus pasteuris and its necessary nutrients were mixed into microbial self-healing agent,which was immobilized in 0.3 – 4.75 mm shale ceramic sand by vacuum impregnation method to prepare microbial self-healing particles.(3)Adding microorganism can improve the crack self-healing effect of mortar specimen.Adding microorganism self-healing agent in the form of self-healing particles can effectively reduce its adverse effect on the compressive strength of mortar.The 28-day compressive strength of mortar with Bacillus subtilis group was lower than that of mortar with Bacillus subtilis group.(4)The compressive strength of self-healing mortar increases first and then decreases with the increase of calcium formate content.When calcium formate is used as calcium source for microbial mineralization,the crack repair effect of self-healing mortar is positively correlated with calcium source content.The compressive strength of the self-healing mortar specimen with 2 % calcium formate is the highest.After 28 days,the maximum crack repair width of the specimen can reach 1.135 mm,and the crack area repair rate is > 80 %.(5)With the increase of the proportion of microbial self-repairing particles,the strength of cement-based materials generally decreased,but the self-repairing effect of cracks increased.When the proportion of self-repairing particles is 40 % and 60 %,the compressive strength of self-repairing mortar specimens is > 50 MPa,and the cracks below 0.7 mm can be completely repaired.Overall,the crack self-healing effect of mortar is better than that of concrete,and its average and maximum crack repair width are larger than those of concrete specimens.