The Application Study Of Impact-echo Method In Nondestructive Testing Of Prestressed Concrete Structures

In recent years,the post-tensioned prestressed concrete structure plays an important role in bridge engineering with its unique advantages.However,due to the fact that the prestressed pipe grouting is not dense in the actual engineering,it will lead to the corrosion of the prestressed steel easily,the resulting structural security problem has become increasingly prominent.In addition,as an important indicator of the evaluation for structural quality,the traditional testing methods of concrete strength include core drilling method and rebound method,the core drilling method has some damage to the concrete structure and the rebound method has large error.Based on these issues,it is necessary to find an accurate and convenient nondestructive testing method to measure the grouting quality of prestressed pipe and concrete strength in practical engineering.Impact-echo method is a nondestructive testing method based on stress wave,based on this detection method,the experimental research and engineering application of the grouting quality of prestressed pipe and concrete strength and elastic modulus are studied in this paper.The main work and conclusions are as follows:(1)The finite element method is used to simulate the impact-echo method,the results show that the ideal distance between impact point and signal receiving point is 5cm-8cm.Simulation of grouting defects with different sizes,the results show that the impact-echo method can not locate the defects when the defect size is less than 1cm,the impact-echo method can locate the defects accurately when the defect size is more than 2cm.The simulation analysis is carried out by changing the offset distance of the impact point relative to the internal defect.The results show that the impact-echo method can be used to locate the grouting defects when the offset distance of impact point is not more than 0.8D(D:size of internal defect).(2)Based on the analysis of the characteristic frequency spectrum of the prestressed channel in different grouting conditions,draw the conclusion:the reflection frequency of the plate thickness has a tendency to increase when the grouting defect exists in the prestressed channel,the impact-echo method can be used to locate the grouting defects accurately in the experiment.Research findings the material quality of corrugated tube has little effect on the detection results by comparing the characteristic frequency spectrum of prestressed channel made of different materials.So,the effect of material quality of corrugated pipe can be ignored in practical engineering testing.It can be used to judge the grouting of prestressed channel is dense by the conclusion that the test characteristic spectrum of prestressed channel grouted dense and dense concrete plate is the same.The detection results of prestressed reinforcement grouting hole in the roof of box girder show that the impact-echo method can detect the grouting defects accurately.(3)The velocity of stress wave of concrete with different strength and different aggregate types is obtained by analyzing the characteristic spectrum of different concrete specimens.The basic formula of stress wave velocity and compressive strength or elastic modulus of concrete are established.The relationship of stress wave velocity in concrete with different aggregate under the same strength:stress wave velocity of ordinary concrete>stress wave velocity of concrete made by coral aggregate>stress wave velocity of concrete made by ceramsite>stress wave velocity of ECC.The application of the basic formula of wave velocity and compressive strength show that the basic formula can calculate the compressive strength of concrete structure accurately and the test error is less than 7%.