Fullness Detection And Mechanical Properties Of Grout Sleeve For Rebar Connection

With the rapid development of China’s prefabricated construction,grout sleeve connection has been widely used for the rebar connection of precast concrete components.This connection method has the advantages of simple structure,convenient construction,and stable connection performance,especially suitable for the rebar connection in core joints.However,the quality of grouting sleeve connection has a significant impact on the bearing capacity,stiffness,and stability of the structure.Therefore,a reasonable and effective grouting guidance scheme and an accurate grouting sleeve filling degree detection method are the key to ensuring the construction quality of prefabricated concrete.By using reasonable experimental and numerical simulation methods,analyzing the influence of grouting defects on the stress performance of grouting sleeve connection is the theoretical basis for guiding actual engineering construction.Based on this,a series of studies have been carried out from the aspects of sleeve grouting process flow analysis,grouting sleeve quality detection method,stress mechanism,and failure mode of grouting defects.The main work and research results are as follows:(1)A flow state analysis was conducted for the grouting process of a sleeve using computational fluid dynamics simulations on three sets of single-sleeve models and three sets of interconnected chamber models.The variable for the single-sleeve models was the spacing between the rebar and the inner wall of the sleeve,while the variable for the interconnected chamber models was the layout of the rebar and sleeves.The variable for the single-sleeve model was the distance between the rebar and the sleeve inner wall,while the variable for the connected cavity model was the arrangement of the rebar sleeve.We studied the flow pattern of the grout inside the models,as well as the trends in fluid velocity and pressure.Based on the grout pressure on the sitting grout layer wall in the fluid simulation,we calculated the thickness of the sitting grout layer wall theoretically.The results showed that during grouting construction,defects in grouting are more likely to occur on the sleeve inner wall and the upper wall of the sitting grout layer.Additionally,there is a risk of grout leakage along the longitudinal wall of the sitting grout layer.(2)A non-destructive electrical resistance testing method based on the reaction of charged ions in grout material was proposed for detecting grout defects.Eight grouted sleeve specimens with different defect locations and defect amounts were tested using the non-destructive electrical resistance method.The test results showed that non-destructive resistance testing is effective for detecting insulated grouted sleeve specimens,with a 100% detection accuracy rate for upper defect specimens.Through analysis and theoretical resistance calculation of insulated and non-insulated sleeves,it was found that this testing method is effective for detecting insulated sleeve specimens,but the detection sensitivity for non-insulated sleeve specimens still needs to be improved.(3)Mechanical performance tests were conducted on grouted sleeve specimens with defects,with three different defect locations(upper,middle,and lateral)and their corresponding defect amounts as variables.Thirty-three grouted sleeve specimens with defects were subjected to uniaxial tensile tests.The test results showed that lateral defects had the greatest impact on the specimens,while middle grouting defects had a greater impact than upper grouting defects.When the middle defect was 4 times the diameter of the rebar(4d),the failure mode of the specimen changed from rebar rupture to rebar pullout.(4)A numerical simulation study was conducted to investigate the mechanical performance of grouted defect sleeves,whereby 66 models of such sleeves were subjected to nonlinear numerical simulations.The purpose of this research was to analyze the sleeves’ mechanical behavior under varying loading conditions and to identify potential failure modes.The non-linear numerical simulations were conducted on 66 grouted sleeve models,with a focus on the selection of the grout constitutive model in finite element simulations.The results showed that the specimens with optimized concrete plastic damage models for the grout had higher computational accuracy,and could simulate all the failure modes observed in the experiments.This conclusion provides important evidence for the refined finite element simulations of grouted sleeve defects.(5)The analysis of the mechanical mechanism of the grouting sleeve test piece was conducted,and a mechanical model of the cross-section of the grouting sleeve was established.The initial stress of the sleeve was derived,and the bonding and sliding formula of the grout was optimized.Meanwhile,the Mander restrained concrete calculation model was cited to theoretically derive the axial compressive bearing capacity of the grout sleeve constrained by the sleeve,and the calculation method of the transverse stress in the original equation was optimized.The core code of the grout bonding and sliding formula and the grout dosage prediction program was written in Python and visualized.By comparing the design strength,standard strength,and ultimate strength of the rebar through theory and program,it was finally discovered that when the actual anchoring length of the rebar is greater than 6d(d is the diameter of the rebar),the rebar will not experience bond pull-out failure;between 4d and 6d,the failure mode is in a transitional stage.When it is less than 4d,the rebar experiences pull-out failure.