SEGJ Technical Conference

Study on non-contact acoustic exploration method for non destructive inspection -Study on the defect detection in the concrete from a long distance-

Abstract The hammer method is widely used for the inspection of concrete surface of tunnels or bridge girders. With this method, however, it is difficult to inspect the places where people cannot reach. Therefore, we propose a new non-contact acoustic imaging method for nondestructive inspection using as a Scanning Laser Doppler Vibrometer (SLDV) and a Long Range Acoustic Device (LRAD). In this method, the vibration speed of concrete surface, which is excited by air- coupled sound, is measured using the SLDV. The LRAD, which have high sound pressure and a sharp directivity, is used as a vibration source. We carried out experiments to confirm the effectiveness of our proposed method using a concrete test-piece. As an experimental result, it became clear in having the detection of the square-shaped defect in the depth of 50mm from separation of 10m distance.