Post-tensioned tendons: problems, inspection, solutions = Cavi di precompressione post-tesi. Problemi, ispezione, soluzioni

Problems in existing post-tensioning structures constructed 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 corrosion of the strands cannot be detected by visual inspection, inspection of post-tensioning structures with non-destructive testing and evaluation (NDE) methods is required. Here selected NDE methods are briefly described and evaluated regarding capability of inspection of internal bonded post-tensioned tendons. Attention is given to time domain reflectometry (TDR), marketed and applied in the past as RIMT, where detailed results and evaluation so far were scarse. Despite some progress, none of the existing inspection and monitoring methods allows a complete and meaningful evaluation of post-tensioning tendons in existing structures. Thus owners of structures and engineers face uncertainty regarding safety and durability of existing structures. With the introduction of corrugated polymer ducts and electrically isolated anchorages (EIT) in civil engineering practice about 25 years ago the situation changed: polymer ducts prevent the ingress of aggressive substances into the tendons and the electrical isolation allows quality control and monitoring of the tightness of the duct. For the first time the most important structural elements, the tendons, can be easily monitored and initiation of damage can be detected early. EIT technology wasdeveloped and successfully applied in Europe and is now expanding in the US.