There is a recognized need worldwide for improved methods for the detection of corrosion of the tendons in post-tensioned concrete bridges [1,2]. Post-tensioning is used to construct light, strong bridges with the possibility of long spans. The technique involves constructing the concrete spans, leaving hollow tubes, called ducts, in place in theformwork while the concrete cures. Steel bars or strands, collectively called tendons, are then fed through the ducts and tensioned to force the concrete into compression. Finally the ducts are filled with grout to provide corrosion protection for the steel tendons. However voids which can form during the grouting process can allow water to collect in contact with the tendons, promoting corrosion. The detection of the corrosion of the tendons is very difficult because they are embedded deep within the bridge structure and are shielded by the ducts. Current inspection is primarily visual, involving drilling through to the ducts from the exterior of the bridge [1].