Assessment of long-term corrosion resistance of recently developed post-tensioning components
Moyer, Kevin Lee
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The forensic analysis of fourteen post-tensioned beam specimens after six years of aggressive exposure testing is the focus of this thesis. Funding for this research came from TxDOT and FHWA. Current post-tensioning materials and construction practices have been deemed inadequate due to fairly recent corrosion failures. Recently developed post-tensioning components and systems were assessed to determine their suitability to prevent durability concerns that had been found in older structures. Testing was conducted on the following variables: Strand Type, Duct Type, Duct Coupler Type, Anchorage Type, Electrically Isolated Tendons. Non-destructive and destructive testing methods were used to study the specimens and were evaluated on their effectiveness in predicting corrosion. Service life analysis was done on a structure using the strands and ducts study in the project. Galvanized duct showed substantial pitting and area loss. The majority of the plastic ducts had no observed damage. However, tendon grout chloride concentrations in most cases were extremely elevated with both galvanized and plastic ducts. This indicated that moisture had entered the duct, through either the couplers and/or grout vents. Except for strands from one specimen, the strands had minor corrosion with occasional mild pitting. The exception had heavy mild pitting confined to a small portion of the strand due to a hole in the duct. Backfill quality was good but it did not bond well with the base concrete. Therefore, moisture and chlorides entered the anchorage region. The electrically isolated tendon did not perform as well as expected. The grout chloride concentrations and level of corrosion damage were comparable to the concentrations and corrosion damage from the more conventionally protected specimens.