Abstract
Impact Elastic Wave Method is a non destructive test method for concrete structures. In Impact Elastic Wave Method, Fast Fourier Transform (FFT) has mainly been used for measuring the frequency with which elastic wave is reflected between the opposite su rfaces of a concrete plate, and if the velocity of elastic wave is known, the thickness of concrete plat e can be calculated by this measured frequency. In this paper limitation of measuring by using FFT is discussed and other frequency analysis method that uses cross-correlation function and FFT is studied. As a result, the attenuation of reflected elastic wave was found to be the major drawback to determination of the frequency. In concrete plate whose thickness is 2m or greater, the thickness of concrete plate can not be measured by using FFT. On the other hand, the cross-correlation function that is cal culated by the initial portion of the waveform relate to the arrival time of the reflected elastic wave without influence of the attenuation. It was concluded that the frequency analysis method using cross-correlation function and FFT can be an effectual method for measuring the frequency and the thickness of concrete plate.
