Post-tensioning is a common form of construction for medium to long-span concrete bridges. After tensioning, the ducts are usually filled with a cementitious grout to provide a structural bond between the stressed tendons and the concrete, and to protect the tendons against corrosion. However there is a possibility that some parts of the duct will remain ungrouted and the subsequent ingress of water or chlorides from de-icing salts could initiate corrosion.

An investigation was carried out to provide information on corrosion rates for post tensioning tendons in post tensioning ducts with a range of void types. The main part of the experiment comprised a support beam with a stressed tendon running along each side. Along each tendon were sections of grouted duct with different types of void and exposed to different levels of chloride. The development of corrosion was monitored visually, by electrochemical testing, and destructive examination. There were also some smaller individual sections of ducting where the tendons were not stressed. The voids in these were the same as in the main part of the experiment.

Destructive examinations were carried out after two and three years exposure on both the stressed and unstressed samples and the condition of the tendons in the different void types was assessed.

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