Study On Nondestructive Testing And Mechanical Properties Of Sleeve Grouting Joint Defects

Prefabricated construction(PC for short)generally produces and processes the components required by the project in advance in a prefabricated component processing plant,and then sends the completed components to the site for operation.With the continuous advancement of my country’s construction industrialization,prefabricated concrete buildings have developed rapidly.Compared with the traditional construction model,PC has obvious advantages in terms of resource consumption,waste generation,improvement of construction production efficiency,civilized construction,safety management,and environmental protection.In most of the prefabricated concrete buildings in our country,the connection method of the nodes is connected by sleeve grouting,and the steel bars are restrained by the sleeve and grouting material to realize the reliable transmission of force.Therefore,the compactness of the grouting in the sleeve will directly affect the safety and durability of the fabricated structure.If the grouting is not dense,the joint working performance of the sleeve,steel bars,and grouting material will be greatly reduced,and the force transmission will be affected,making the overall performance of the structure difficult to meet the requirements of the structure using cast-in-place,and there is a huge safety hazard.Moreover,the sleeve grouting construction is a concealed project,and it is difficult to scientifically and effectively judge the construction quality after the grouting is completed.Therefore,it is necessary to study the mechanical properties of sleeve connectors and nondestructive testing of their grouting quality.This article summarizes the predecessors’ research on the mechanical properties of sleeve grouting connectors and their non-destructive testing methods.Through the experimental research on the mechanical properties of sleeve connectors,based on shock echo method and pre-hole endoscope Method through theoretical analysis,experimental research,numerical simulation and actual engineering inspection,in order to combine the two inspection methods to quantitatively analyze the defects of sleeve grouting.The main work and conclusions of this paper are as follows:1.Through on-site investigation of the project,participation in grouting operations,comparison of the advantages and disadvantages of grouting methods,influence of grouting time,etc.,various defects in the grouting process and the reasons for the formation of defects are given.It is found that at present,the grouting method and the connecting cavity are mainly used for grouting.The internal defects of the sleeve during grouting are mainly divided into the conditions of no grout from the grout outlet,backflow of the slurry after grouting,corrosion of the sleeve,and reduced fluidity of the grout.2.Considering different positions and lengths to place defects in the sleeve,a total of 72 full-grouted sleeve connection specimens containing defects,carry out mechanical performance tests,and explore what kind of damage and defects occur to the connectors at different positions and lengths.The impact on the mechanical properties of connectors.Through the experiment,it is found that the failure modes of the sleeve grouting connector mainly include the fracture of the reinforcing steel connecting the sleeve,the shearing of the slurry in the sleeve,and the sliding of the reinforcing steel.When the defect is located in the middle of the sleeve,the effect is greater than when the defect is at the end of the sleeve.The strain value in the middle of the sleeve is the maximum before the steel bar yields and after the specimen is damaged.3.Summarize the start and application of the shock echo method,analyze the classification and propagation characteristics of elastic waves on the basis of the existing shock echo theory;carry out the feasibility of using the shock echo method to detect the compactness of sleeve grouting Discussed.4.According to the actual situation of arranging the sleeves on site,make threesided shear wall specimens.The sleeves are arranged in single-row,plum blossom,and double-row symmetrical arrangements.The grouting density is set to 40%,and the grouting density is 40%.For sleeves in four working conditions of 60%,80% and 100%,the impact echo method and the pre-hole endoscopy method are used to detect the degree of grouting of the sleeve as the compactness.The results show that: when there is only one row of sleeves in the shear wall,whether it is aligned or arranged alternately before and after,the shock echo method can largely find grouting defects,but for the shear wall,there are two rows at the same time.When the sleeve is used,this method cannot effectively identify the defects of sleeve grouting.The endoscopic method can image and quantitatively analyze the grout defect at the grout outlet.5.In order to better study the characteristics of elastic waves and the propagation laws in concrete,ABAQUS is used to establish shock wave models,and the influence of different receiving positions on the signal,the influence of steel bars on the propagation of shock signals in concrete,and the difference in concrete are simulated and discussed respectively.The relationship between the diameter defect and the impact signal,and the influence of the sleeve on the impact signal propagation in the concrete.It is found that it is most appropriate to collect and extract signals at a distance of 4-6cm from the excitation point;steel bars have almost no effect on the propagation of elastic waves in concrete;the shock echo method can accurately identify defects with a diameter of 1-30 mm in concrete members.When the defect diameter exceeds 35 mm,the reflected signal is not obvious,and the frequency tends to move to low frequency as the defect increases in thickness.6.Using "impact echo + endoscope" to inspect the grouting sleeves in the shear wall of an actual project,use the shock echo method to conduct a general survey of the sleeves arranged in single row and quincunx,and check the problematic sleeves.The tube is drilled at the pulp outlet for quantitative analysis with an endoscope.The doublerow symmetrical arrangement sleeve adopts the pre-hole endoscopic method to detect the compactness.The overall quality control method of sleeve grouting connector is proposed,aiming at problems such as the degree of corrosion inside the sleeve,the accumulation of debris in the sleeve,the length of the steel anchored in the sleeve,the corrosion degree of the steel anchored in the sleeve,and the compactness of the sleeve grouting.Perform inspection and analysis.The results show that the "impact echo +industrial endoscope" method can fully and effectively control the quality of sleeve grouting connectors,and can be effectively applied to the quality control of on-site sleeve grouting connectors,and solve problems for actual projects.