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Publication Number: FHWA-HRT-14-039
Date: May 2014
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Elevated levels of chloride were recently discovered in a commercially available pre-bagged grout product made for post-tensioned (PT) tendons. These chloride values exceed the current limits set by all of the domestic and international regulatory committees. However, there is limited information reported in the literature pertaining to actual chloride threshold of seven-wire PT strands. For this reason, the Federal Highway Administration sponsored a 6-month accelerated corrosion testing program to determine chloride threshold(s) of PT strands exposed to chloride-contaminated grout. The findings of this study should be useful to bridge owners who may be responsible for similarly affected PT bridges.
This report presents two chloride threshold values determined for the PT strands that are fully encased in the commercially available grout described above. The first threshold is 0.4 percent chloride concentration by weight of cement, which is the lowest amount to initiate corrosion of strands. At this threshold, the testing program demonstrated that rust spots can form, and a small number of pits start to form beneath some of the rust spots. The second chloride threshold is 0.8 percent chloride by weight of cement in association with corrosion propagation. At this threshold, the testing program demonstrated that corrosion starts to intensify in terms of number of pits and pit depth; therefore, this threshold is considered to be critical. Once chloride concentration exceeds the critical threshold, significant corrosion damage can be anticipated, and the long-term structural integrity of the PT bridges may be compromised. If PT tendons contain carbonated grout, segregated grout, duct cracks, grout voids filled with water with or without chloride ions, or free sulfate ions in contact with the strands, corrosion might start below the proposed threshold values.
Jorge E. Pagán-Ortiz
Director, Office of Infrastructure
Research and Development
This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification or regulation.
The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.
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Topics: research, infrastructure, structures
Keywords: research, structures, Chloride threshold, Chloride, Corrosion initiation, Corrosion propagation, Seven-wire strand, Post-tensioning, Grout, Autopsy, Accelerated corrosion testing, Sulfate ions, Void
TRT Terms: research, infrastructure, Facilities, Structures