Using 3-D velocity contour plots to detect voids in grouted tendon ducts in post-tensioned concrete construction: Fid-Bau Portal

Using 3-D velocity contour plots to detect voids in grouted tendon ducts in post-tensioned concrete construction

Cheng, Chia-Chi / Lin, Yung-Chiang / Ke, Ying-Tzu / Ke, Fong-Jhang

Highlights • Using 3-D velocity contour plots to detect voids in grouted tendon ducts. • Dispersion curve obtained by a receiver and a small instrumented hammer. • Low velocity at wavelengths twice the duct’s range indicates the existence of void. • Latticed grid test quickly detects probable voids without knowing ducts’ location. • Grouting conditions can be detected using vertical grids directly above the ducts. • Provide wave velocity reduction for different grouting conditions and cover.

Abstract 3-D velocity contour plots are constructed to detect voids in grouted tendon ducts by a stress-wave test method requiring a receiver and a small instrumented hammer. Each time-domain waveform due to hammer impact is processed using the short-time Fourier transform to obtain the spectrogram (frequency-time relationship), which is enhanced using the reassignment method. The reassigned spectrogram is used to obtain the dispersion curve (velocity-wavelength relationship). The results from all test points are assembled to develop wave-velocity contour plots at different wavelengths. A wall specimen containing ducts with five different grouted conditions was constructed. Two types of test grids were used, namely latticed grids covering the entire wall surface and vertical grids directly above the ducts. For the former method, 3D contour plots of a large area can be constructed with few testing lines. For the latter method, the wave velocity contour plots can distinguish different grouting conditions. Finally, the wave velocity reduction to be expected for different grouting conditions and cover depth is provided.