Grouting monitoring of post-tensioning tendon duct using PZT enabled time-reversal method

The post-tensioning method, which involves the post-tensioning tendon duct (PTTD), is often used to reinforce concrete beams. An important procedure of the post-tensioning method is to fill the tendon duct with grout to protect the prestressed reinforcement from moisture and air. The grouting quality has a great impact on the corrosion prevention for the prestressed reinforcement and the bearing capacity of the concrete structures. In this paper, a method using Lead Zirconate Titanate (PZT) enabled time-reversal method to monitor the grouting quality is proposed. PZT is a commonly used piezoceramic material with strong piezoelectric effect. In the proposed method, one PZT ring installed on the prestressed reinforcement is used as an actuator to generate stress waves and the other distributive PZT patches bonded on the outer surface of the tendon duct are applied as sensors to detect the propagated stress waves. The grout in tendon duct forms conduits between PZT ring actuator and PZT patch sensors. To quantitatively represent the grout's presence, the time-reversal method is used. The received signals from the sensors are reversed by the time-reversal operation and re-emitted. The grouting quality is evaluated by analyzing the peak value changes of the time-reversal focused signal. Experiments with 0%, 50%, 75%, and 100% grouting levels are conducted by the proposed method. The experimental results show that the grouting quality in the tendon duct can be estimated by monitoring the peak value changes of the time-reversal focused signal. (C) 2017 Elsevier Ltd. All rights reserved.