1THE IMPACT-ECHO METHOD: AN OVERVIEW by

The impact-echo method is a technique for flaw detection in concrete. It is based on monitoring the surface motion resulting from a short-duration mechanical impact. The method overcomes many of the barriers associated with flaw detection in concrete based on ultrasonic methods. The purpose of this paper is to provide an overview of the technique and to discuss the important parameters involved in this type of testing. One of the key features of the method is the transformation of the recorded time domain waveform of the surface motion into the frequency domain. The impact gives rise to modes of vibration and the frequency of these modes is related to the geometry of the test object and the presence of flaws. The principles involved in frequency analysis are discussed. The importance of the impact duration in relation to flaw detection and other factors affecting the smallest flaw that can be detected are also reviewed. The paper concludes with a summary of the ASTM standard governing the use of the impact-echo method for measuring the thickness of plate-like structures