抄録
Though the impact echo method is commonly used for thickness measurement of plate concrete structures, the method to detect the internal defects in concrete structures is still not clearly established. Basically the impact echo technology is used to obtain the resonant frequency of flutter echo between the measuring surface and the opposite surface of a concrete plate. The thickness can be calculated by dividing the elastic wave speed of the concrete by twice the measured dominant frequency. By this method, if the thickness of the plate is known, the wave speed of the flutter echo can be calculated. We found out that the travel path condition of the wave affect the wave speed. The wave speed is almost always reduced if there is defected area on the path. In case the cross section of defect is circular, higher harmonic frequencies are generated near the direct top surface of the defected areas. From these observations, distribution of the flutter echo's wave speed on the measuring plane shows the location of the projection area of the defect. The results of the experiments using concrete plate with voids show that the location of the voids are indicated by the area where the wave speeds of the flutter echo are slower than the areas with no voids. Also the method and the results for location detection and degree of filling of the actual PC bridge sheaths are shown in this paper.
