| Civil engineering materials are the material basis of civil engineering infrastructure construction,which are required to be sufficiently sturdy and durable.While microorganisms can carry out biomineralization to induce calcium carbonate,which can strengthen and improve the performance of cementitious materials.In this study,an alkali-resistant urease microorganism,Bacillus cereus,extracted from concrete,was added to cementitious materials,and the effect of this microorganism on the performance of cementitious materials,namely,net cement paste,cement mortar and concrete was investigated.The main contents of the study are as follows.(1)Biomineralization was simulated in a conical flask,and by detection and analysis,it was found that the composition of the Biomineralization product was calcium carbonate.The survival of the microorganisms in the simulated pore solution of the cementitious material was examined,and it was found that the microorganisms could survive in the pore solution of simulated cementitious material at p H 12.8.(2)Effect of microbial admixture on the mechanical properties of microbial cement net paste was investigated.Experimental results show the microbial cement net paste test specimen of OD value of 1,the 28-day compressive strength increased by 13.7% and the28-day flexural strength increased by 23.5%.Addition of urea and calcium lactate has a positive effect on the mechanical properties of microbial cement net paste,and the optimal addition amount is 0.3 mol/L for urea and 0.075 mol/L for calcium lactate.(3)Mechanism of the effect of microorganisms on cement net paste was analyzed by microscopic means.Firstly,it was found that the early hydration of cement net paste was promoted by the addition of microorganisms and the addition of urea and calcium lactate in addition to microorganisms,and the hydration heat at 72 hours was increased,and the results of 3 day infrared spectroscopy showed consistency with the heat of hydration.Then,by rheological tests,it was found that the addition of microorganisms and the addition of urea and calcium lactate in addition to microorganisms increased the yield stress and apparent viscosity of the cement net paste.Finally,the 28 d cement paste was analyzed by thermogravimetry and XRD,and it was found that the addition of microorganisms promoted the increase of calcium carbonate and calcium silicate hydrate content.(4)Mechanical properties of mortar and concrete were significantly improved after incorporation of appropriate amount of microorganisms.When the OD value of microbial suspension was 0.5,and 0.3 mol/L urea and 0.075 mol/L calcium lactate were added,the mechanical properties of mortar and concrete were optimal,and compared with the blank control group,the 28-day compressive strength and flexural strength of mortar increased by45.8% and 36.8% respectively,and compared with the blank control group,the 28-day compressive strength,flexural strength and splitting tensile strength of concrete increased by32.2%,24.3% and 32.2% respectively.It was observed by transmission optical microscopy that the microorganisms were adsorbed on the surface of mortar particles and survived well.It was observed by scanning electron microscopy,remarkable biomineralization was carried out by microorganisms,making the cement matrix of the concrete more dense.(5)More dense microbial concrete interior and surface made the water absorption and permeability height reduced after the addition of appropriate amount of microorganisms.The water absorption of microbial concrete group with OD value of 0.5 and 1 was the lowest,which was 27.8% lower than zero group.M0.5U2C2 group of concrete,mixed with the microbial suspension OD value of 0.5,0.3 mol/L urea,0.075 mol/L calcium lactate,was22.2% lower than zero group.M0.5U2C2 group concrete had the lowest permeability height,which was 29 mm lower than the zero control group.The surface tension of the microbial suspension was lower than water,which reduced the shrinkage of the concrete mixed with microbial suspension. |
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