Case studies will be presented focusing on post-tensioned (PT) bridge evaluation projects involving varying structure types and bridges for multiple DOT’s. DOT’s recognize that beneath the surface of otherwise visibly sound PT bridges lies potentially significant corrosion and deterioration that, if left untreated, can lead to shortened service life and reduced load carrying capacity of bridges. Tendon corrosion is more common in bridges built prior to 2003 due to the grouting materials and construction procedures that were used at the time. If identified early, measures can be taken to arrest corrosion and protect tendons from further deterioration at relatively low costs.
The first project involves 10 PT bridges which first required extensive review of the construction documents of all the bridges. From this review, all 10 bridges received a field assessment, including arms-length visual surveys. A nondestructive testing (NDT) program was then developed for the PT tendons using a risk-based protocol. The NDT techniques consisted of in-situ testing procedures to assess the condition of the tendons taking care to not damage the strands. Assessment methods included visual inspection utilizing a borescope, corrosion rate testing of strands, as well as sampling and testing of the grout. Significant deficiencies were identified in four of the bridges and repair plans were prepared for these structures. Repairs included remedial grouting, removal and replacement of anchorage pourbacks, and installation of a corrosion-resistant impregnation system. Construction observation was also performed to assist DOT personnel during the final phase of repairs.
The second project involves two, three-span PT bridges. A Phase 1 risk-based protocol NDT program was developed to utilize borescope testing, corrosion rate testing of the steel strands, as well as sampling and testing of the grout. 120 tendon locations were borescope tested, and five locations were selected for corrosion rate testing and grout sampling. Of the 120 borescope tested locations, 21 locations had large voids with corrosion of the steel strands that varied from light to heavy deterioration. This project is at its initial stages of development and is currently ongoing.
Overviews of both projects will be presented along with descriptions of the specialized techniques utilized to thoroughly, yet cost effectively, assess the PT systems of the bridges. Important lessons learned will also be discussed.