Application Of Impact-echo Method In Testing Grouting Density Of Prestressed Concrete

The prestressed concrete structure has the advantages of small self-weight,stable compression members,and good fatigue resistance.In modern bridges in China,most of them are prestressed concrete structures,and their quality is particularly important.In practical engineering,the grouting of the hole is not compacted due to the grouting process,grouting material or human neglect,and so on.Therefore,the quality testing of the hole grouting is an important research topic.This paper mainly studies the application of impact-echo method in the test of the grouting density of prestressed concrete tunnels,and carries out the following research work:Firstly,the background,the status,and the main contents of impact-echo method are expounded.Secondly,starting from the basic theory of elastic waves,the classification and propagation characteristics of elastic waves are described.The basic principle of impact-echo method for detecting internal defects under different grouting conditions is described in detail.Thirdly,the finite element analysis software ABAQUS is used to simulate the impact-echo detection process,and the time-history data extracted by ABAQUS is converted by the fast Fourier transform using Matlab software to obtain the frequency spectrum map,and then the different influencing factors are analyzed for the impact-echo method,and the influence of the material of the tunnel,and the influence of the spacing of the bellows:?1?The ideal distance between the receiving point and the impact point of the impact-echo signal is 4⁸ cm.?2?When the slab thickness of the concrete is determined,the frequency of thickness is different in different grouting conditions.The more dense the grouting,the higher the frequency of thickness.?3?The concrete slabs of 20 cm,30 cm,40 cm,50 cm,and 60 cm are simulated respectively.According to the finite element simulation results,a linear fitting method is used to obtain a fitting curve of the compaction density and thickness frequency,y=?-36.835H+2 481.8?x+10 678e^-0.024H,where H is the thickness of the concrete;x is the density of grouting;y is the thickness of the plate thickness.The formula is suitable for quantitative inspection of grouting density of prestressed concrete pavement with C50 strength of concrete.Finally,the engineering application of shock echo method to detect the compactness of grouting is mainly introduced.The methods and principles of detection,qualitative detection and positioning detection methods are expounded.The relationship between grouting density and plate thickness frequency is emphatically utilized to quantitatively test the compaction degree of grouting in prestressed concrete tunnels in practical engineering,which can determine the degree of defects in various locations of the hole.