Inspection and Monitoring of post‐tensioned bridges – advantages of electrically isolated tendons (EIT)

Problems in existing post-tensioning structures with metallic ducts occur mainly related to corrosion of the tendons due to chloride ingress at “weak points” in the structure. Despite this PT technology overall can be considered as proven and successful, sometimes severe damages and collapses without warning are reported. As none of the existing inspection and monitoring methods allows a complete and meaningful evaluation of post-tensioning tendons in existing structures, owners and engineers face uncertainty regarding safety and durability of existing post-tensioned structures with metallic ducts. The situation changed with the introduction of corrugated polymer ducts and electrically isolated anchorages (EIT) in civil engineering practice about 25 years ago. Polymer ducts prevent the ingress of aggressive substances into the tendons and the electrical isolation allows monitoring of the tendons with simple, hand-held instrumentation over the whole service life. Based on many results from laboratory and field It is concluded that EIT tendons can be considered a smart structure not necessitating additional sensors. For the first time the most important structural elements, the tendons, can be easily monitored over time and initiation of damage can be detected early.