Durability Evaluation of Post-Tensioned Concrete Beam Specimens After Long-Term Aggressive Exposure Testing

This thesis focuses on the forensic analysis and evaluation of large-scale post-tensioned beam specimens after nearly 8 years of aggressive exposure testing. The research was funded jointly by both FHWA and TxDOT. The durability of ost-tensioned bridge structures in aggressive environments has been of concern in recent years. Major concerns include the effectiveness of grouting materials, the splicing of ducts, and the soundness of anchorage zones. The relationship between durability performance and the following variables was evaluated in this study:

-Level of applied load & initial cracking

-Level of prestress

-Duct type

-Strand type

-Grout type

-Grouting method

-Use of encapsulated system for anchorage protection

-Galvanized duct splice type

In addition, the accuracy of non-destructive testing methods for evaluating corrosion was examined. These methods included half-cell potentials and chloride penetration tests.

Major findings include that mixed reinforcement (also known as partial prestressing), performed poorly from a durability standpoint. Only fully prestressed beams offered better durability performance than those which were not prestressed at all. Corrugated steel galvanized ducts were found to perform very poorly. Large holes were found in the ducts, and in some cases the ducts completely corroded away across several inches. Corrugated plastic ducts will offer better performance as long as they are “robust.”

Non-flowfilled epoxy coated strand and galvanized strand offered no significant improvement in long-term durability over conventional strand.

In addition, installing plastic caps over anchorheads rather than just filling the anchorage pocket with non-shrink grout increases the long-term durability of the anchorage.