Search

External prestressing tendons are a major structural element for the durability of concrete bridges. In France several cases of sudden breaks in external pre‐stressing tendon made of HDPE duct injected by cement grout directly in contact with strands have been recorded in the past decade [2]. In order to prevent this sudden breaks Cerema has experimented the magnetic rope testing technology from ropeways to develop a non‐destructive inspection technic of the free length and junction of prestressing. The method is based on magnetic leakage field detection and allows to detect defaults of the strands inside the tendon such as corrosion and wire breaks. The article first focuses on the magnetic rope testing technic. Then tests previously performed on laboratory tendons with reference wire breaks will be analyzed for defaults characterization. Finally, the particular methodology adapted to the nondestructive magnetic inspection of prestressing tendons on site will be detailed. A general feedback including handling issues and analysis of non‐destructive magnetic controls completed with visual controls by removing the high‐density polyethylene (HDPE) sheath will be given. [ABSTRACT FROM AUTHOR]

The article describes recent cases of tendon ruptures by corrosion and investigations carried out on some bridges in France. Several causes related to HDPE ducts have been identified such as damages during handling, threading and tensioning of strands, defective connection of the duct to the anchorage, damage during construction or operation, low quality of HDPE material, etc. These cases of tendon rupture exclusively concern ducts injected with cement grout. To our knowledge, no structure built after the application of the 2001 circular [1] (prohibiting cement grout for the injection of external prestressing) is currently exhibiting major disorders. A warning note on existing structures with external prestressing has been updated by Cerema in November 2018 [2]. It describes the diagnosis methodology based on analysis of documentation, thorough visual inspection, destructive and nondestructive investigations. New non‐destructive techniques such as guided‐wave ultrasonic technique and magnetic leakage field test using permanent magnets and induction coils are presented. Innovative methods of local repair of the ducts are also described. Finally, different protective devices are analysed in terms of worker safety in the event of a sudden failure of tendon. [ABSTRACT FROM AUTHOR]

In the context of the high‐level radioactive waste disposal CIGEO, the corrosion rate due to microbially influenced corrosion (MIC) has to be evaluated. In France, it is envisaged to dispose of high‐ and intermediate‐level long‐lived radioactive waste at a depth of 500 m in a deep geological disposal, drilled in the Callovo‐Oxfordian claystone (Cox) formation. To do so, a carbon steel casing will be inserted inside disposal cells, which are horizontal tunnels drilled in the Cox. A specific cement grout will be injected between the carbon steel casing and the claystone. A study was conducted to evaluate the possibility of MIC on carbon steel in the foreseeable high radioactive waste disposal. The corrosiveness of various environments was investigated at 50°C and 80°C with or without microorganisms enriched from samples of Andra's underground research laboratory. The monitoring of corrosion during the experiments was ensured using gravimetric method and real‐time corrosion monitoring using sensors based on the measurements of the electrical resistance. The corrosion data were completed with microbiological analyses including cultural and molecular characterizations. [ABSTRACT FROM AUTHOR]