Evaluation of corrosion resistance of new and upcoming post-tensioning materials after long-term exposure testing
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This thesis focuses on the forensic analysis of ten full-scale post-tensioned beam specimens after four years of aggressive exposure testing. The research was funded by FHWA and TxDOT. Post-tensioned structures have been under scrutiny due to their vulnerability to corrosion damage. Recent corrosion failures have been traced to inadequate materials and construction procedures. The purpose of this research project is to evaluate the corrosion performance of new and upcoming post-tensioning materials and systems and to determine their suitability for preventing durability issues which were found in older structures. The following variables were tested in the full-scale beam specimens: strand type, duct type, duct coupler type, anchorage type, tendon encapsulation. Non-destructive and destructive testing methods for evaluating corrosion damage were examined. Cost analysis of each material was conducted using tendon quantities from a typical post-tensioned bridge for comparison. Galvanized steel ducts performed poorly, showing substantial pitting and area loss. Plastic ducts were intact, but elevated grout chloride levels indicate that moisture was able to enter the ducts at the locations of couplers and grout vents. Strand corrosion was minor and uniform for all the types which were examined, suggesting that chloride traveled the length of the tendons through strand interstices. Stainless steel strands were nearly corrosion-free. Pourback quality was found to protect anchorages more than galvanization of bearing plates. The electrically isolated tendon did not completely prevent strand corrosion, but the system resulted in much lower chloride concentrations along the tendon than the conventional systems.