United States Department of Transportation
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Effect of voids in grouted, post-tensioned concrete bridge construction : volume 2--inspection, repair, materials, and risks.
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2009-09-01
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By Trejo, David
[PDF-34.02 MB]
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Edition:Technical report; Sept. 2003-Aug. 2008.
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Abstract:Post-tensioned (PT) bridges are major structures that carry significant traffic. These bridges are designed and
constructed because they are economical for spanning long distances. In Texas, there are several signature PT
bridges. In the late 1990s and early 2000s, several state highway agencies identified challenges with the PT
structures: mainly corrosion of the PT strands. The Texas Department of Transportation (TxDOT) performed some
comprehensive inspections of their PT bridges. A consultant’s report recommended that all ducts be re-grouted.
However, the environment in Texas is very different than the environments in which the corrosion of the PT strands
were observed. The objective of this research was to evaluate the corrosion activity of strands for PT structures and to
correlate this corrosion activity with general environmental and void conditions. To achieve this objective, timevariant
probabilistic models were developed to predict the tension capacity of PT strands subjected to different
environmental and void conditions. Using these probabilistic models, time-variant structural reliability models were
developed. The probability of failure of a simplified PT structure subjected to HS20 and HL93 loading conditions
was assessed. Both flexural failure and serviceability were assessed. Results indicate that the presence of water and
chlorides can lead to significant corrosion rates and failure is dependent on this corrosion activity and the number of
strands exposed to these conditions. These results are presented in Volume 1 of this report. To assist TxDOT with
developing a plan to mitigate this corrosion, studies were performed to assess repair grout materials, inspection
methods, and repair methods. In addition, a general methodology is presented on optimizing repairs. These topics are
presented in Volume 2 of this report. An Inspection and Repair Manual was also developed from this research and is
presented in a separate report. Results indicate that TxDOT should prevent water and chlorides from infiltrating the
tendons — this can be achieved in part by repairing drain lines, ducts, and protecting anchor heads as these conditions
can lead to early failure of PT bridges. Recommendations on inspections, repairs, and materials are provided,
however, further research on the potential formation of galvanic coupling of strands embedded in both existing and
new repair grouts need to be assessed.
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