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Improperly constructed cold joints lead to poor water tightness. Water, chloride ions, and other harmful substances can therefore enter through the joint, causing the accelerated corrosion of steel bars. In this study, the surface wave group velocity profile, which can identify velocity at variant depths beneath concrete surfaces, was used to determine the interfacial condition of a cold joint. The proposed test method performed a single test with one impacting source and one receiver placed on a concrete surface across the joint. The short-time Fourier transform (STFT) and the reassignment technique were used to process the received signal and obtain the image of the group velocity spectrogram. The surface wave group velocity profile was then extracted from the spectrogram. A 0.4 m-thick reinforced concrete wall containing a cold joint was constructed for the experimental studies. The experimental results revealed a sudden decrease in wave speed for wavelengths larger than 0.2 m: the Rayleigh wave speed dropped from 2,000 m/s for normal concrete to 1,300 m/s for concrete including a cold joint. These results suggest that the rebars near both sides of the wall surface constrained the joint from separating up to the depth of 0.1 m; however, a poor interfacial condition was found near the center of the wall.

Quantitative assessment of interfacial condition of cold joint using surface wave group velocity profile