Evaluation Of An In Service Post-Tensioned Bridge: Condition Assessment Of Decommissioned Post-Tensioned Tendons

Abstract

Post-Tensioning (PT) systems can be an effective design method for bridge construction by providing structural benefits and accelerated construction processes. The PT system can provide the bridge with crack control and corrosion protection via the precompression induced into the bridge, and the multi-layered PT system, respectively. However, proper design, detailing, construction, and inspection procedures are critical in the overall integrity, durability, and service life of the bridge. Deficiencies related to the aforementioned procedures for the PT system can lead to serviceability issues for the bridge and can provide an environment that is susceptible to chloride ingress. Post-tensioned bridge tendon failures are typically the result of deficient grout along with an environment that leads to corrosion of the prestressing strand. Advancements in the quality control of grout and the materials used in PT systems have mitigated these issues; however, it is imperative that the industry continues to iterate upon these specifications and PT technologies to improve the durability of PT systems used in bridge construction. History has provided instances of PT bridge failures due to poor quality grout leading to corrosion of the PT system, however, there have been few case studies documented in the literature which demonstrate the efficacy of PT systems. The objective of this research is to perform a condition assessment of 44 PT tendon samples removed from the High Bridge in St. Paul, MN during a reconstruction project. The results of the condition assessment are cataloged to provide a successful case study of decommissioned external PT tendons which have been in-service for approximately 30-years. Lessons learned from this project reinforce the use of materials and practices that have developed in the past two decades.