Detection of internal defects of concrete structures based on statistical evaluation of healthy part of concrete by the noncontact acoustic inspection method

摘要

A noncontact acoustic inspection method was developed to perform measurements from a long distance (usually about 5 to 7m but even over 30 m) and detect internal defects (up to 10 cm in depth) of concrete structures using a long-range acoustic device and a laser Doppler vibrometer. An algorithm was also proposed to detect internal defects of concrete by combining two acoustic features, the vibrational energy ratio and spectral entropy obtained by our measurement. However, in actual concrete structures, it is difficult to distinguish a boundary between a healthy part and a defective part owing to influences such as the shape of internal defects, age-induced deterioration, and the surface condition of concrete. Therefore, we propose a method to statistically evaluate the distribution of the healthy part of concrete and extract the healthy part to identify the defective part. By this proposed method, the actual concrete floor slab bridge was measured from 33m away and some internal defects were detected and visualized. Furthermore, a result for a railroad tunnel was compared with the Schmidt hammer rebound value and elastic wave velocity to verify the validity of the proposed method. (C) 2018 The Japan Society of Applied Physics.