Non-Destructive Evaluation Method for Determination of Internal Grout Conditions Inside Bridge Post-Tensioning Ducts Using Rolling Stress Waves for Continuous Scanning:Final rept. (Jun 03-Dec 06)

摘要

This project developed a nondestructive method based on impact-echo and ultrasonic reflection techniques with continuous scanning features for determining the grout condition inside post-tensioned bridge ducts. Initial efforts were focused on evaluating and establishing the accuracy/reliability of the impact echo scanning test. The impact echo scanner hardware was modified by incorporating a rolling transducer into the prototype to overcome the problem of variable thickness. The scanner software was also improved to provide three-dimensional display of impact echo results. Data on a mock-up slab fabricated with defects of different types and sizes and collected using the modified instrument was analyzed. Visualization from three-dimensional surface plots helped interpret the data. The presence of a tendon duct and grouting discontinuities appeared to cause an increase in the apparent slab thickness. Two U-shaped precast bridge girders with four ducts on each wall were procured from Colorado DOT for full-scale tests. Impact echo tests using a rolling scanner at different times after the grouting processes were performed on the walls of the girders. The results showed good agreement with the actual defect design. The clearest indication of the presence of grouting defect was given by the apparent increase in slab thickness due to a reduction in the impact echo resonant frequency (caused by a decrease in stiffness associated with a defect). The equipment is now ready for field implementation and is commercially available.