Infrared thermography detection of grouting defects in post-tensioned tendon ducts under active thermal excitation

Abstract

The efficacy of employing infrared thermography (IRT) for concrete bridge deck inspection has been well established. Although an IRT detection method during construction stage under hydration heat excitation had been proposed in old works, it is also essential to be applicated in the existing large amounts of bridges in service, while it can be challenging due to factors, such as the substantial depth of the ducts and the variation in duct materials. Therefore, this study presents an IRT detection method for grouting defects in post-tensioned tendon ducts under the stimulation of a shortwave infrared heater. The investigation explores the influence of different factors, such as duct depth, length, grouting compactness level, and duct material, on the detection results and the corresponding heating durations required. Results indicate that with a thermal radiation intensity of approximately 550 W/m2 with a heating duration of 45 mins and followed by a cooling period of 90 mins to 130 mins, the detection of fully grouted void defects within 350 mm long ducts made of polyvinyl chloride (PVC) at burial depths of 50, 70, and 90 mm is feasible. For the best detection results, grouting void defects buried at a depth of 50 mm should be detected after a maximum heating duration of 75 mins and 90 mins corresponding to the PVC ducts and metal ducts. The detection effectiveness is higher for PVC ducts than for metal ducts. Furthermore, an environmental impact analysis should be carried out in the future to make this method into practice.