Research On Surface-opening Cracks Of Concrete Based On Impact Echo Method

Nondestructive testing is a very important and difficult research lesson about the defect of concrete structures. This paper mainly measures the stress waves conveying in concrete structures and the depth of surface-opening cracks in concrete plates by using impact echo method after carefully reading a lot of articles about the state and the abroad of concrete nondestructive in the field and incorporating the special conditions on the laboratory.Firstly, this paper synthetically introduces the state and the abroad of concrete structures about nondestructive testing, in particular examining flaws in concrete structures by using impact echo method, gets at the problem existing at present and clarifies the direction and the content of research lesson in the field.Secondly, according to the theory of impact echo method examining flaws, the road surface and the bridge surface are aimed as study targets, four concrete plates are made with differently deep surface-opening cracks. Using the experimental system of impact echo method made by Sansalone etc., this paper measures the stress waves velocity conveying in concrete plates by using one transducer or two transducers, and measures the depth of surface-opening cracks in concrete plates by using two transducers, and then the important data are attained.Thirdly, through assaying the error generated during measuring data, the result manifests: 1) The location installed of the transducer and the point thumped affects the experiment result to some extent. If surface-opening cracks is deeper, the location of the transducers installed and the point thumped should be further away from the location of surface-opening cracks. 2) When the depth of surface-opening cracks is near to 50mm, it is very difficult to measure the depth of surface-opening cracks because the depth of R_wave conveying in concrete plates from the different small ball bringing forth exceeds 50mm.3) It is clear from the experiment result, the influence isn't big for the diameters of small balls to measure the data while the time interval between two transducers touched firstly has very big influence on the result.Fourthly, respectively using cross correlation method for estimation of time delay, phase spectrum method for estimation of time delay and high order spectrum method for estimation of time delay, this paper measures time delay estimation of the data obtained because time delay between two signals has big importance on thetesting result. Through comparing three results, accurate time delay is obtained under their own different circumstances.At last, base on the Windows2000 operation system, the soft wrap of impact echo examining system is explored by using the language Matlab6.1.The soft can achieve some function, including calculating the velocity of P_wave in concrete plates by using one transducer or two transducers, amounting the depth of surface-opening cracks in concrete plates by using two transducers and measuring the depth of highway. The whole system has friendly human_computer interface. It is easy for the users to operate, it is straight and quick for the users to calculate and it is clear for the users to observe.