Post tensioned concrete is used in many Florida transportation structures, many of which are exposed to fresh or salt water. The steel strands that supply the tension are encased in a plastic duct which is later filled with grout, so the strands are generally well protected from the elements. However, during construction, strands may reside in the pipe for a while before tensioning or grouting. During this time, the strands are vulnerable to corrosion. Florida Department of Transportation (FDOT) guidelines specify sealing the duct to exclude moisture or other harmful agents from reaching the steel strand. However, if moisture is sealed in the duct or the duct is inadequately sealed, corrosion can result. Ideally, ducts are grouted within hours of stressing, but there are circumstances that can delay grouting for days or, rarely, weeks. If damaged, strand failure can be immediate, or it can mature over time to produce delayed failure. Previously, University of South Florida researchers examined the impact of corrosion on unstressed steel strands (FDOT project BDK84-977-04). In that work, they found resistance to moderate amounts of corrosion. In this project, the same researchers applied their methods to stressed steel, which might be more susceptible.
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