The Application Of Impact-Echo Method On Nondestructive Testing For Concrete Structures

The applications of impact-echo method on nondestructive testing for concrete structures are researched in this paper.Firstly, the principles of the impact-echo method are described in details. The dominating relation in the impact-echo method , i.e. ,the relation among frequency, speed and thickness, is discussed. It is theoretical foundation for testing in field.The other nondestructive testing methods are not suitable to measure the thickness of concrete structures with one surface on which stress wave is generated by impact. However, the impact-echo just be suited. Combining the technique of measuring P-wave speed with impact-echo methods, the procedure for measuring thickness of concrete pavement accurately, two-step test procedure , is designed. The results on measuring thickness of concrete pavement show that the accuracy is satisfied.The effects of scattering and absorbing for stress wave in concrete structures are overcome, as the frequencies of stress wave generated are relative low. And the diffractive P-waves are received by two transducers. Therefore the aim of measuring the depth of surface-opening crack, including perpendicular, inclined and curved, is achieved. The measuring results in field show that the impact-echo method is effective in measuring the depth of surface-opening crack.According to the engineering characteristics of the impact-echo technique and the grouted tendon duct, the test procedure for voids in post- tensioned grouted metal ducts is designed. The testing results shown that the technique can locate the voids in ducts effectively. After the ducts were cut open for inspection, the results are coincident.Finally the applications of the impact-echo on measuring the thickness of concrete structures with one surface voids, the depth of surface-opening crack and locating the voids in post- tensioned grouted, are concluded in this paper. The problems need to research in further are brought.