Abstract
The defect in the concrete structure can be detected by using the resonant frequency of elastic wave measured by impact acoustic method. The resonant frequency is, however, dependent on the water content of concrete. To investigate the effect of water content on the resonant frequency, the deflective and longitudinal resonant frequencies were measured for the concrete having the various water contents in the laboratory. It was found as a result that the deflective resonant frequency reduced by 2-4 % for 1% reduction of water content, and the longitudinal one reduced by 1-2%. Moreover, the dependency of the resonant frequency on the water content was different between drying and seeping processes. The longitudinal wave velocity could be modeled by geometric mean for drying process and by harmonic mean for seeping process. Therefore, it was inferred that the zone near surface of the concrete, which had high water content at the seeping process, had a low elastic wave velocity and the resonant frequency became low as a consequent.
