Non-Destructive Technique of Evaluating Defects on a Concrete Plate by an Acoustic Impact Method *

摘要

It is very important to assess component materials such as concrete structures with non-destructive techniques. An acoustic impact method takes advantages of an easy handling and low costs in many other non-destructive techniques. Fourier spectrum, which was obtained by a fast Fourier transform of detected waves was examined for the evaluation of artificial defects formed on the square concrete samples. The effects of a striker and a detector on the Fourier spectrum were discussed to detect defects and their positions in the specimen. Vibration mode analyses were attempted to clarity the cause of the many peaks of frequency in the Fourier spectrum. It is found that the peak frequency, its amplitude and half-power bandwidth of the frequency spectrum can be indicators for detecting the artificial defect. The results suggested that this acoustic impact method using a steel ball as a striker and a microphone as a detector was fairly useful as one of non-destructive techniques for the assessment of concrete structures.