Failures of external Tendons in Prestressed Concrete Bridges: Causes, Investigations, Remediation and Prevention.

In the the early 1980’s, an evolution in the grouting operations took place with the use of increasingly fluid grouts to facilitate the injection of the prestress ducts. During a gammagraphy campaign carried out on a box girder bridge under construction in 1994, anomalies were detected at the upper point of the ducts of the external prestressing tendons. Observations carried out after opening of some ducts highlighted a lack of filling and the presence of a product having the consistency of a wet and soft white paste. After presenting several cases of external tendon failures that occurred in the past years in France, the article describes the mechanism leading to severe grouting defects resulting in failures of tendons by a rather rapid corrosion. Then it presents the development of an investigation device based on dielectric capacity measurement that was applied during the campaign of investigations launched on all box girder bridges of the French national road network.