Experimental Study On Microbial Induced Calcium Carbonate To Repair Concrete Cracks

Concrete is the most widely used building materials in the field of civil construction.Concrete structures are easily cracked during use,and cracks seriously affect the usability and safety of building structures.Therefore,the repair of concrete cracks has become the focus of academic and engineering.Based on the theory of calcium carbonate precipitation induced by microbial decomposition of urea,this paper uses urease microorganisms isolated and screened from soil to carry out relevant research on concrete crack repair.Four strains of ureolytic microorganisms were isolated and screened from the soil by using the selective medium,and the microorganisms were identified by molecular biology.The four strains were identified as follows:the#1 strain is Enterprise sp,the#2 strain is Flavobacterium sp,and the#3 and#4 strains is Alcaligenes faecalis.After that,The effects of temperature,pH,glucose addition method and glucose concentration on the growth of microorganisms were studied,the following conclusions were drawn:the appropriate culture temperature for microorganisms is 20～30℃,the appropriate culture pH is 7～8,and the culture time is 24～36 h;under medium and strong alkaline conditions,the addition of appropriate amount of glucose to the culture solution is beneficial to the growth of microorganisms.The effects of temperature,concentration of gelled solution,ratio of bacterial solution to gelled solution,glucose concentration in gelled solution and pH on microbial induced calcium carbonate precipitation were studied,and the working characteristics of microorganisms in soil were verified.The following conclusions were drawn:the#4 strain was the dominant strain;In the process of microbial induced calcium carbonate precipitation,the concentration of gelling liquid should be 0.5 mol/L,and the ratio of bacterial liquid to gelling liquid should be 1:5～2:5;In the medium and strong alkaline environment,adding a proper amount of glucose to the gelling solution is beneficial to increasing the precipitation amount of calcium carbonate;ureolytic microorganism in soil has high activity and good quality.Sand solidification tests were carried out.After solidification,the compressive strength of sand column reached 1 MPa and the permeability coefficient decreased by 2 orders of magnitude.The relationship between compressive strength of sand column and calcium carbonate content and distribution uniformity of calcium carbonate was analyzed.It was found that the higher the content and distribution uniformity of calcium carbonate in sand column,the better the curing effect.XRD and SEM microscopic analysis results show that the precipitation product induced by microorganisms is calcium carbonate,and the crystal type is mainly stable calcite.Carry out concrete crack repair tests.Firstly,the repair effect of cracks under different conditions was studied.The results show that the repair effect of continuous perfusion method is better than that of static injection method.Adding glucose to gelling fluid can optimize reaction conditions and improve crack repair effect.The crack width is less than 0.5 mm,depending on calcium carbonate induced by microorganisms,the crack can be completely repaired,the crack width is greater than 1.0 mm,and the effect of repairing wide cracks can be improved by pre-filling sand particles in the crack.After that,irregular cracks are repaired,and the repair rate of crack area reaches above 95%.The permeability coefficient of the sample reduced below10^-7 cm/s.The strength recovery rate reached 30%～40%.