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Long-Term Post-Tensioned Beam Exposure Test Specimens: Final Evaluation

R. M. Salas, A. L. Kotys, J. S. West, A. J. Schokker, J. E. Breen, and M. E. Kreger

2003

In the last few years, the effectiveness of cement grout in galvanized or polyethylene ducts, the most widely used corrosion protection system for multistrand bonded post-tensioned concrete tendons, has been under debate, due to significant tendon corrosion damage, several reported failures of individual tendons as well as a few collapses of non-typical structures. While experience in the USA has been generally good, some foreign experience has been less than satisfactory.

This report is part of a comprehensive research program started in 1993, which has the objectives to examine the use of post-tensioning in bridge substructures, identify durability concerns and existing technology, develop and carry out an experimental testing program, and conclude with durability design guidelines.

Three experimental programs were developed: A long term macrocell corrosion test series, to investigate corrosion protection for internal tendons in precast segmental construction; a long term beam corrosion test series, to examine the effects of post-tensioning on corrosion protection as affected by crack width; and, a long term column corrosion test series, to examine corrosion protection in vertical elements.

Preliminary design guidelines were developed previously in the overall study by the initial researchers, after an extensive literature review.

This report documents the final evaluation of the long-term post-tensioned beam exposure test specimens, after comprehensive autopsies of selected beams and updating the durability design guidelines based on the exposure testing and autopsy results.

After autopsies were performed, overall findings indicate negative durability effects due to the use of mixed reinforcement, galvanized steel ducts, and industry standard or heat-shrink galvanized duct splices. The width of cracks was shown to have a direct negative effect on specimen performance. Grout voids were found to be detrimental to the durability of both galvanized ducts and strand. On the other hand, very positive effects were found with the use of high performance concrete, high post-tensioning levels, and plastic ducts.

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