Experimental Study On Shear Properties Of Microbial Mineralized Morta

Masonry structure,as a traditional structural form,occupies an important position in the field of ancient architecture.However,its masonry mortar is mostly mixed with lime and clay,which has the problems of low mortar strength and poor seismic performance.Some traditional seismic reinforcement methods will cause a certain degree of damage to the original structure,and will change the original style of ancient buildings.Microbial mineralized mortar(referred to as "microbial mortar")not only has high strength,but also has little disturbance to the original structure,which provides a new idea for strengthening the masonry structure of ancient buildings.The application of this technology is limited due to the unclear mechanical mechanism of mortar and the lack of material constitutive relationship model.Based on the microbial induced calcium carbonate deposition technique,9 groups of single variable comparative tests were carried out to generate microbial mortar with high shear strength and deformation ability,which could also be used for full-section replacement.Test parameters include particle size distribution(good gradation,fine sand,coarse sand),mortar joint thickness(6mm,8mm,10mm),grouting method(bidirectional grouting,unidirectional grouting),calcium source concentration(1mol/L,0.5mol/L),grouting sequence(bacterial solution-urea mixed solution first and then calcium source solution,bacterial solution first and then urea-calcium source mixed solution),placement of bricks(horizontal,vertical),etc.For each group of specimens,the calcium carbonate generation was weighed,the compressive strength was detected by penetration method,and the double-sided shear test was carried out.Based on the test results,the calcium carbonate yield of each group of specimens was explored,the shear stress-strain curve of microbial mortar was analyzed,the deformation characteristics of microbial mortar were studied,and the shear strength growth mechanism of microbial mortar was revealed.The failure modes of twin shear test are mortar layer failure and interface failure,and the shear stress-load displacement curves correspond to strain softening and strain hardening respectively.The shear strength of interface failure is lower than that of mortar layer failure.There is an approximate linear correlation between shear strength and secant modulus of elasticity.The effects of different test parameters on the test results are reflected in the following aspects:(1)The smaller the thickness of the mortar joint,the more the amount of calcium carbonate generated in the specimen,and the higher the compressive strength and shear strength of the mortar.(2)The amount of calcium carbonate produced in coarse sand is greater than that in well-graded sand,and the amount of calcium carbonate produced in fine sand is the least.The compressive strength and shear strength of mortar are the highest for the well-graded sand specimens,followed by the coarse sand specimens,and the fine sand specimens are the lowest.(3)The yield of calcium carbonate,compressive strength and shear strength of bidirectional grouting specimens are higher than those of unidirectional grouting specimens.(4)The amount of calcium carbonate in the low concentration calcium source group is slightly lower than that in the high concentration calcium source group,but its mortar compressive strength and shear strength are higher than those in the high concentration calcium resource group.(5)Compared with the specimen which was first filled with bacteria solution-urea mixture and then filled with calcium source solution,the specimen which was first filled with bacteria solution-urea mixture and then filled with calcium source solution had a significant increase in the amount of calcium carbonate formation,compressive strength and shear strength.(6)The amount of calcium carbonate,mortar compressive strength and mortar shear strength of the specimens placed vertically are higher than those of the specimens placed horizontally.It can be concluded that reducing the thickness of ash joints and vertical placement of bricks can reduce the influence of gravity on the vertical inhomogeneity of calcium carbonate,while reducing the concentration of calcium source and two-way grouting can slow down the deposition of calcium carbonate and block the grouting path,and improve the horizontal uniformity of calcium carbonate.Good gradation of packed sand is an effective measure to improve the bonding efficiency of calcium carbonate.These measures not only increase the production of calcium carbonate,but also obtain higher compressive and shear strength.Based on the experimental data,the shear strength formula suitable for microbial mortar was obtained by fitting.Based on the above research,it is feasible to use microbial mineralized mortar to strengthen masonry,which can solve the problems of low mortar strength and poor seismic performance,and has important practical significance for the development of repair and reinforcement technology of historical buildings.