Conclusions, Recommendations and Design Guidelines for Corrosion Protection of Post-Tensioned Bridges

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 several reported examples of significant tendon corrosion damage. While experience in the USA has been generally good, some foreign experience has been less than satisfactory.

This report is the last technical report from a comprehensive research program started in 1993 under TxDOT Project 0-1405. The objectives were 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.

Four experimental programs were developed: improved and high-performance grout studies, to develop grout with desirable fresh properties to provide good corrosion protection to the prestressing strands; 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.

This report includes the final results after completion of exposure testing, performing comprehensive autopsies and updating the durability design guidelines to reduce the corrosion risk of the post-tensioning system.

After autopsies were performed, overall findings indicate negative durability effects due to the use of mixed reinforcement, small concrete covers, 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. Relying on epoxy and galvanized bar coatings was also found inappropriate because of local attack. On the other hand, very positive effects were found with the use of high performance concrete, high-performance grouts, high post-tensioning levels, plastic ducts, and sound epoxy filling at the joints.