The Grouting Defect Detection Of Rebar Lapping In Grout-Filled Hole Based On The Impact-Echo Method

Prefabricated buildings are significant changes to the traditional construction pattern,they are an important measure for China to promote supply-side structural reforms and new urbanization.Prefabricated buildings have many advantages such as low energy consumption,low pollution,high efficiency and safety,and they are also it is also the development trend of the future construction industry.Rebar lapping in grout-filled hole connection is one of the main connection forms of prefabricated building components.It has the advantages of simple structure,reliable performance,construct simply and low cost,and the broad development prospects.The grouting quality of the ducts of the rebar lapping in grout-filled hole directly affects the mechanical performance of the joints and the overall stability of the structure.If there are grouting defects in the grouting ducts,the entry of water and air will cause corrosion of the anchor bar,resulting in a reduction in the anchorage quality,which will affect the durability and safety of the shear wall.In addition,grouting quality defects can also cause concrete stress concentration,and then change the force state of the design of the wall,thus affecting the prefabricated shear wall bearing capacity and service life.The grouting quality of rebar lapping in grout-filled hole directly affects the mechanical performance of joints and the overall stability of the structure.Therefore,it is necessary to detect and determine the compactness of duct grouting.Among the many existing non-destructive testing methods for judging the grouting quality of concrete,impact-echo method is considered as the most promising and most efficient method.In this paper,the application of this method to the detection of the ducts grouting density of rebar lapping in grout-filled hole is introduced from two parts of the indoor test and numerical simulation,and the numerical simulation is used to expand the research of different detection conditions.The main contents are as follows:1.Introduce the development course of the impact echo method and the application status in the actual project,and explain the feasibility of this method in non-destructive testing by analyzing its propagation mechanism.2.Carry out indoor test research and conduct impact echo detection with the prestressed concrete beam multifunctional detector(SPC-MATS)to arrange different grouting conditions in the prefabricated double-row duct concrete shear wall.Some measuring points are arranged equidistantly above the duct of the test piece.The echo signal is acquired by means of vibration and reception to detect the density in grouting duct of the rebar lapping in grout-filled hole.The internal defects of grouting ducts were made with foams,and the presence or absence of grouting defects in double row channels and examined and the accuracy of the method for the detection of rebar lapping in grout-filled hole grouting density.The results show that the compaction degree of the grouting in theduct can be detected intuitively,quickly and accurately using the impact-echo method and the results are in good agreement with the actual situation.3.The finite element simulation software ABAQUS was used to simulate the grouting compaction and different defect conditions.The simulation results were in good agreement with the experimental results.The simulation results for different working conditions show that when there is a defect in the ducts,the predominant frequency by numerical simulation analysis drifts to low frequency.The larger the same position defect,the more obvious the remarkable reduction in frequency;for defects with small dimensional changes,they cannot be identified at a certain resolution.This rule also applies to actual engineering inspections;for the case where the duct is not grouted,the drift of the frequency corresponding to the nominal plate thickness of the single row of ducts to the low frequency is smaller than the corresponding frequency drift of the double row of ducts,that is,the delay of the double row of channels is larger;when the depth of defect changes,the corresponding plate thickness frequency will also change.When the same size defect is located in the middle of the plate thickness,the delay of the stress wave is the largest,and displayed the symmetry trend toward both sides gradually decreases;when the test point is near the thickness range of 0.3 times of the test piece's free boundary,the predominant frequency drafts to the low frequency,and the delay occurs.4.Conduct a comprehensive summary of the experimental research results,numerical simulation results with the impact-echo theory,and conduct a preliminary discussion on future research directions.