Preparation And Properties Of Self-healing Recycled Aggregate Concrete Based On Microbial Mineralization

Recycled aggregate concrete is an environmentally friendly and sustainable green concrete that the country strongly advocates for development.However,compared to natural aggregates,the quality of recycled aggregates is often poor,leading to a decrease in the performance of recycled aggregate concrete,which limits the promotion and application of recycled aggregate concrete.In this paper,microbial mineralization technology is used to improve the performance of recycled aggregate,and recycled aggregate is used as a microbial carrier to achieve self-healing of cracks in recycled aggregate concrete,so as to improve the performance of recycled aggregate concrete.Firstly,the microbial loading and mineralization strengthening processes and effects of recycled aggregate were studied.On this basis,the selfhealing recycled aggregate concrete was prepared by replacing the natural aggregate with bacteria loaded and mineralized recycled aggregate(the replacement rate was 50%and 100%),and introducing the mineralized substrate required for microbial mineralization to repair cracks.The workability,mechanical properties,durability,and self-healing behavior of recycled aggregate concrete were studied,and the mechanism for improving the performance of recycled aggregate concrete was explored.The main research conclusions are as follows:(1)The vacuum adsorption method can effectively load bacteria into the recycled aggregate,and the quality of the recycled aggregate after the microbial mineralization strengthening treatment is significantly improved.Compared with the untreated recycled aggregate,the apparent density of the recycled aggregate is increased by 1.9%,the water absorption rate is reduced by 13.9%,and the crushing index is reduced by 15.3%.Moreover,the mineralized sediment formed by the strengthening treatment can further protect the microorganisms loaded in the recycled aggregate.(2)Compared to ordinary recycled aggregate concrete,the self-healing recycled aggregate concrete has significantly improved its crack self-healing effect.When the replacement rate of recycled aggregate is 50%,for cracks with a width of about 0.4mm,compared to ordinary recycled aggregate concrete(RAC50 group),the self-healing recycled aggregate concrete(mRAC50 group)has increased the crack width healing rate,crack area healing rate,and impermeability repair rate by 50.3%,29.9%,and 32.6%after 56 days of repair,respectively.When the replacement rate of recycled aggregate is 100%,for cracks with a width of about 0.4mm,compared to ordinary recycled aggregate concrete(RAC 100 group),the self-healing recycled aggregate concrete(mRAC 100 group)has improved the crack width healing rate,crack area healing rate,and impermeability repair rate by 61%,38.2%,and 78.9%after 56 days of repair,respectively.(3)When the replacement rate of recycled aggregate is 50%,compared to ordinary recycled aggregate concrete(RAC50 group),the compressive strength of the self-healing recycled concrete(mRAC50 group)after 28 days has increased by 6.9%,and a significant improvement in workability and resistance to chloride ion penetration.When the replacement rate of recycled aggregate is 100%,compared to ordinary recycled aggregate concrete(RAC 100 group),the compressive strength of the self-healing recycled concrete(mRAC 100 group)after 28 days has increased by 16.6%,and the workability and resistance to chloride ion penetration have also been significantly improved.(4)XRD,TG/DTG and SEM-EDS test results show that the self-healing product on the crack surface of self-healing recycled aggregate concrete is calcite,and pits similar to bacteria are found in the microscopic morphology of self-healing product,indicating that bacteria participate in the repair process,thus forming more healing products.The SEM test results indicate that there are multiple interface transition zones in recycled aggregate concrete,including the new interface transition zone formed by the combination of recycled aggregate and cement slurry,as well as the old interface transition zone formed by the combination of the aggregate part of recycled aggregate itself and the mortar attached to its surface.The thickness of the interface transition zone is a key factor in reducing the mechanical properties and durability of recycled aggregate concrete.The interface transition zone of self-healing recycled aggregate concrete prepared from the recycled aggregate strengthened by microbial mineralization becomes more denser.The improvement of the performance of self-healing recycled aggregate concrete is the result of the combined effect of the improvement of the quality of recycled aggregate itself,the improvement of the microstructure of the interface transition zone,and the empowerment of crack self-healing function.