Co-Surface Three-Electrode Capacitive Sensoring Method for Prestressed Tendon Positioning in Grouted Duct

The grouted duct is an important part of the bridge, and its quality and safety are closely related. The prestressed tendon is the crucial part of the grouted duct, and the positioning of the prestressed tendon in the grouted duct is a prerequisite for quality evaluation. Based on the capacitive sensing technology, the three-electrode co-surface capacitive sensor is designed for the positioning of the prestressed tendon and compared with the dual-electrode structure. The sensitivity of the three-electrode structure is about twice that of the dual-electrode structure. The sensor performance was evaluated by finite-element simulations and experiments. This study analyzed the differences between simulation and experimental results through six grouted ducts. For a grouted duct with an inner diameter of 80 mm and a prestressed tendon with a radius of 8 mm, the three-electrode sensor can localize the angular and radial position of the prestressed tendon. The sensor can distinguish the radial position change of the prestressing tendon at 10-mm intervals. The precise positioning of the prestressed tendon is affected by factors, such as the structure of the sensor, the material properties of the concrete, and the degree of corrosion of the prestressed tendon. The difference between the experimental and simulation results does not affect the conclusion. The three-electrode co-surface capacitive sensor can be used for detecting the angular and radial position of the prestressed tendon in the grouted duct.