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

Post-tensioned concrete piers or columns may be exposed to very severe environments affecting their long-term durability. Two main exposure conditions are of special interest: partially submerged structures in sea water and structures exposed to deicing salts. The durability study of post-tensioned columns or vertical concrete elements under these conditions has unique characteristics. In order to provide detailed observations to improve the durability design of columns under these exposure conditions, a research study was started with the dual intent to evaluate how to use post-tensioning to improve corrosion protection and how to protect the posttensioning systems from corrosion damage.

This report is part of a comprehensive research program started in 1993, which has the objectives to examine the use of posttensioning 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.

This report documents the final evaluation, conclusions, recommendations and implementation measures from the long-term column exposure test specimens. A total of ten large-scale column specimens were designed, constructed and placed under exposure testing in July 1996. Comprehensive autopsies were performed in January 2003, after six and a half years of accelerated exposure.

After forensic examination, overall findings indicate negative durability effects due to the use of small concrete covers, galvanized steel ducts and rubber gaskets at the duct ends. Relying on epoxy and galvanized bar coating was also found inappropriate because of local attack. On the other hand, very positive effects were found with the use of fly ash concrete, post-tensioning through the columnfoundation interface, sound epoxy filling at the joints and plastic ducts.