Post-tensioned Concrete Construction Research Articles

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

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.

Enhancing radiographic imaging of cementitious materials in composite structures with photon attenuating inclusions

ABSTRACTThis article investigates the use of photon attenuating inclusions (PAI) for enhancing radiographic imaging of cementitious materials in composite structures. By targeting characteristic high attenuation regions in the photon energy spectrum, PAI can improve void detection in the parent material by increasing contrast in radiographic images. Radiographic imaging of cementitious grout specimens with 5% and 15% weight fractions of candidate PAI materials (Fe, BaCO3, BaSO4) was performed to characterize X-ray attenuation. Virtual radiography simulations were then conducted to evaluate the application of PAI to grout void detection in post-tensioned concrete construction. The simulations demonstrate that grout void detection is most effective when the high energy region of the emission spectrum is near the K-edge of the PAI material.

The Pitan Bridge, Taiwan

To alleviate traffic congestion near Taipei, in 1985 the Taiwan Area National Freeway Bureau planned the construction of the 108 km long Northern Taiwan Second Freeway. The majority of the Second Freeway’s alignments are on grade, on embankments, in tunnels, or on viaduct structures. At several locations however, obstacles were identified that required special bridges. The Pitan Bridge spans one of these areas. The Pitan Bridge, actually two nearly parallel bridge structures, is located about 15 km south of Taipei. It connects typical low-level viaducts to a tunnel. Both bridge units have total length of approximately 800 m, a 750 m radius curvature and a slope of approximately 1%. The structure as designed and built makes use of the well-established economy of a segmentally erected post-tensioned concrete box girder bridge, adapted for the site with the innovative use of delta-shaped piers of post-tensioned concrete construction.

Grouts for Bonded Post-Tensioned Concrete Construction: Protecting Prestressing Steel From Corrosion

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An approach to the evaluation of stress-corrosion of high strength steels

Experiments have been conducted on high strength prestressing and bridge wires (zinc-coated) to assess their susceptibility to stress-corrosion cracking (SCC). The wires were subjected to various stress levels and corrosive environments. Loss of ductility and reduction in the ultimate strength of these materials are determined. A criterion is then proposed to evaluate the susceptibility to stress-corrosion by means of an index based on the observed mechanical properties of the wires. Further experiments were carried out on another high-strength bridge wire to validate the proposed approach.Based on the experimental and field observations, the proposed method could be applied to select the type of wire used in pre- or post-tensioned concrete construction or in other applications to ensure better protection against SCC.