Efficiency of NDT techniques to detect voids in grouted post-tensioned concrete ducts

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Abstract
Variations in the design requirements of prestressed concrete girders lead to variations in their geometry and section profile, thereby influencing the characteristics of the waves which form the working principles of the various NDT techniques, and thus possibly shield the presence of air void. Thus, an experimental plan was adopted to study the effect of the changes in parameters like the cover to the duct, the material of the duct, the number of strands, and diameter of the duct on the efficiency of Ultrasonic Pulse Velocity (UPV), Ground Penetrating Radar (GPR) and Infrared Thermography (IRT) (active and passive) to detect a simulated void in a grouted duct. Seven 150 × 150 x 750 mm specimens were prepared with duct embedded in concrete. Both steel (inner diameter 106.6 mm) and plastic (inner diameter 105 mm and 86 mm) ducts were used. Three specimens had 3 strands, three specimens had 5 strands, and one specimen had 8 strands. It was found that the efficiency of GPR increased with the increase in the number of strands and duct diameter. Active IRT is highly efficient for the detection of voids than Passive Thermography. The presence of steel strands influenced UPV results.

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