United States Department of Transportation
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Effect of voids in grouted, post-tensioned concrete bridge construction : volume 1--electrochemical testing and reliability assessment.
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2009-09-01
[PDF-6.66 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. PT bridges 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 its 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, time-variant 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. Volume 1 of this report presents these results. 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 and 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 needs to be assessed.
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