Ultrasonik Yöntemler ile Çelik-lif Takviyeli Betonda Eğilme Çatlaklarının Derinlik Tayini

Estimation of the depth of surface-breaking cracks caused by bending in concrete has crucial importance in order to predict the remaining load capacity of a structural member. In practice, ultrasonic tests are the most commonly used non-destructive methods to assess the condition of concrete. However, the commercial ultrasound-based methods focus on the estimation of thickness of the structural element rather than the crack depth. The cracks cause dispersion and attenuation in the propagating waves, and thus by monitoring the changes in these wave characteristics, diagnostic indexes correlated with the crack depth can be defined. This paper explains this approach through the tests performed on seven laboratory-scale steel-fiber reinforced concrete beams (50x10x10 cm3). The beams are loaded under the crack-controlled three-point bending test until a specific crack depth is reached. These beams are then subjected to ultrasonic testing to acquire the propagating surface waves. The recorded signals are analysed by utilizing signal processing techniques, including discrete wavelet transform and frequency-wavenumber analysis in order to extract two diagnostic features, namely, material attenuation coefficient and dispersion index. It is shown that both diagnostic features are able to detect the crack and estimate its depth.