Self-healing approach for micro-defects in 3D printed concrete:Microbial communityOA

Interlayer gaps and shrinkage cracks have significant impact to negate the mechanical properties,especially durability,of 3D printed concrete,which registers a lasting challenge hindering practical engineering application of 3D concrete printing technology.To this gap,this study translates the microbial-induced calcium carbonate precipitation(MICP)for casted concrete into a novel microbial community self-healing agent with high calcium carbonate deposition performance for 3D printed concrete.Under microaerobic conditions,the mineralization performance of the microbial community is 3.63 times that of commonly used self-healing bacteria B.pasteurii.The microbial community structure demonstrated that Pseudogracilibacillus is the dominant genus in both aerobic and microaerobic conditions.Under micro-oxygen conditions,relative abundance of unclassified_Bacillaceae_2 increases sharply to 32.08%–57.11%,registering the dominant genus to jointly promote mineralization.Addition of a microbial community self-healing agent will increase the flowability and setting time of 3D-printed concrete,and thus improving its cracking resistance.The total porosity,including interlayer gaps,is measured to be 0.72%at 1 day curing,which is one-third that of the control group.Compared to the counterparts in control group without the microbial community,the air voids and microcracks,mesopores,and macropores,decrease by 40%,14%,and 72%,respectively.Among all the different crack depths observed,for cracks with an opening width of approximately 1 millimeter,the repairing area reachs 100%within 7 days of curing.Given the efficient metabolism of facultative bacteria under microaerobic conditions,the average depth of crack repairing is 30 mm,and the maximum depth can reach even 38 mm.It can be stated this research promises to resolve efficiently the long standing micro-defect problem of 3D-printed concrete.