Experimental Study On The Performance Of Microbial Cement Grouting Anchoring Steel Bars

The prefabricated concrete structure has the advantages of energy saving and environmental protection,fast production cycle and labor saving.At present,the vertical members of the structure are generally connected by grouting sleeves.However,in actual engineering,this connection method is prone to the situation that the grouting material is not completely filled and the internal space is emptied,thereby reducing the anchoring performance of the grouting material to the steel bar,thereby affecting the integrity of the structure.Microbial cement provides a new idea for the reinforcement and repair of defective grouting sleeve connections due to its strong fluidity and green environmental protection.In this thesis,in order to study the mechanical properties of microbial cement grouting anchored steel bars,three sets of single-variable experimental studies were carried out.The test parameters include different calcium source concentrations(2 mol/L,1 mol/L,0.5 mol/L),filling of different particle sizes in the grouting pores(quartz sand particle size is 0?0.5 mm,0.5?1 mm,1?2 mm)and different shapes of steel bars(smooth round steel bars and ribbed steel bars),etc.After each round of grouting,a set of specimens were reserved for the pull-out test of the anchoring steel bar.In addition to recording the calcium carbonate deposition on the surface of the steel bar,the ultimate pull-out bearing capacity of the steel bar,the load-displacement curve and the stress-load curves of the steel bar were also tested.Based on the experimental phenomenon and data arrangement,the mechanism of microbial cement grouting anchoring steel bars was revealed,and the bearing capacity calculation formula was proposed.The main conclusions of this thesis are as follows:(1)The more grouting cycles,the more uniform the distribution of calcium carbonate on the outer surface of the steel bar;the failure modes of the tensile specimens are all steel bar pull-out failures.(2)The lower the calcium source concentration of the grouting solution,the more grouting rounds are required to achieve the best anchoring effect,the denser the calcium carbonate precipitate is,and the stronger the anchoring ability to steel bars.Among them,the specimen with the calcium source concentration of 1 mol/L,after 5 rounds of grouting,the anchoring and pull-out bearing capacity of the steel bar reaches 687.76 N,which is the maximum value in the control group.(3)The anchoring capacity of the steel bar is greatly improved after filling the voids of the grouting channel with quartz sand and other media,and the anchoring force of the steel bar of the specimen with a medium particle size of 0.5-1 mm reaches the maximum value of 18890 N.(4)The anchorage performance of the ribbed steel bar is higher than that of the smooth round bar.Anchoring properties of steel bars.(5)After the load-displacement curve of the specimen without medium reaches the ultimate bearing capacity,the plastic deformation is about 3-4 times that of the elastic stage;the specimen mixed with the medium shows obvious stress softening phenomenon after reaching the ultimate bearing capacity.(6)It can be seen from the strain-load curve of the steel bar that under the action of the pulling force,the anchoring force of the steel bar near the grouting mouth is exerted first,and the anchoring force of the steel bar is gradually transmitted from the tension end to the distal end.Based on the experimental data,the mechanism of microbial cement grouting anchoring steel bars is revealed: the anchoring steel bars go through three stages: bonding stage,slip stage and softening stage during the pull-out process.With the increasing tensile load,the bonding force gradually weakens and degrades,and the friction force between calcium carbonate and quartz sand on the steel bar is gradually mobilized.On this basis,a formula for calculating the bearing capacity of microbial cement grouting anchored steel bars is proposed.The research results provide theoretical support for the application of microbial cement grouting to anchor steel bars.