コンクリート中を伝ぱするアコースティック・エミッションの減衰特性

抄録

The damping characteristics of acoustic emission propagating through concrete were examined experimentally in order to establish the method of acoustic emission source wave analysis. The items chosen in the investigation were the effect of holding technique of sensor (Experiment-I), the effects of shape and size of specimen (Experiment-II), the effect of degree of heterogeneity of material (Experiment-III), and the effect of the degree of accumulative damage of specimen (Experiment-IV), respectively.
The main results obtained in the present study are summarized as follows:
(1) The frequency characteristics of acoustic emission picked up by the sensor were remarkably affected by its holding technique and the passing time after the sensor was held to the specimen, independently of the frequency characteristics of sensor or the degree of source acoustic emission.
(2) The acoustic emission propagating through concrete diminished with increasing the length and the sectional area of specimen. The damping of the frequency components higher than 200kHz and 100kHz became more significant with increasing the propagating distance of acoustic emission and the sectional area of specimen, respectively.
(3) Cement paste and mortar had the similar frequency characteristics of acoustic emission in the frequency range lower than 300kHz. In mortar, however, the frequency components higher than 300kHz diminished more than those of cement paste. On the other hand, the acoustic emission propagating through concrete diminished more remarkably in the whole frequency range than that of cement paste or mortar.
(4) The frequency components of acoustic emission in the range of 100∼200kHz were prominent in undamaged concrete. But the frequency components in this range diminished gradually with the progress of accumulative damage of concrete by loading, and the low frequency components became prominent and the power of acoustic emission propagating through concrete decreased.