Analysis And Application Of Echo Signal On Elastic Solid

The impact echo method for evaluating concrete cast quality has been the key issue in the civil engineering field at the present.The issue urgently needs to be solved but has not yet been well resolved.In this paper,based on the analysis and application of echo signals in elastic solids,a study was conducted on detecting pre-stressed duct grouting quality and the quality defect of cast-in-steel part.According to the fluctuation characteristics in elastic solid and elastic layered systems,the analysis method and evaluation rules of defect information are established.It is expected that the accurate evaluation of concrete placement quality defects in the two types of structures which is of great significance to the reliable evaluation of the actual construction quality.The main research work of this article includes:(1)Wave theory in elastic solids.The wave equation in elastic solids is deduced from the calculation model of elastic uniform half-space body subjected to plane uniform load.According to the characteristics of the fluctuating effect in the elastic layered system,the key issues that need to be paid attention to in signal excitation and acquisition in shock echo testing are summarized.(2)The evaluation of grouting debonding defects and voiding defects in pre-stressed holes.Through setting the interfacial agent on the inner wall of the corrugated pipe,the expansion agent in the slurry,and the curing method of grouting as parameter,three different conditions for debonding the interface were prepared and the foam plate was embedded in the inner wall of the corrugated pipe to make grouting emptying defects.Five pre-stressed grouting specimens were tested for five consecutive days.With the increase of pulp age after grouting,the grouting debonding defect and grouting vacant defect can be easily distinguished.The measurement was based on the change rule of the measured main frequency and frequency spectrum.Then,according to the time-frequency characteristics of the signal at each test time,the evaluation rules for grouting debonding defects and voiding defects of pre-stressed holes were established,and a single impact echo test evaluation for two types of grouting defects was achieved.(3)The impact-echo signal's spectrum characteristics of echo test in steel-concrete composite structures are summarized.Through the impact-echo test of steel-concrete composite specimens,the effects of the material of vibrated surface and the steel-concrete interface are take into consideration.The test result show that,echo wave will be reflected at the boundary position of the structure while the interface existed,instead of the steel-concrete interface.Therefore,the interface have no effects on the domain frequency of the impact-echo signal.In addition,the second frequency peak with a higher amplitude as a direct result of the material of vibrated surface.(4)Evaluate the concrete defects of steel-concrete joint successfully.Through the concrete quality evaluating experiment on steel-cell model specimens and steel-concrete joint by impact echo method.The concrete defects in steel-concrete composite structure can be assessment by the characteristics which are the time domain,frequency domain,time-frequency and power spectrum curve of the impact echo signal.It provides a reference for the elastic echo theory to distinguish the two defects which are void-existed defect and hollowing defect.