Concrete structures throughout the world face the danger of sudden collapse if the condition of their steel reinforcement is not monitored regularly. Bridges are the most vulnerable to catastrophic failure as they continuously carry dynamic loads. In the United Kingdom, there are more than 150,000 concrete bridges and the annual repair bill is estimated at £500 million. In the United States of America, the situation is even more serious. It was reported in 1977 that more than one in six bridges were unsafe and that it would take more than two centuries to replace the 40,000 deficient structures, given the rate at which funds were currently available [1]. The repair costs for the rest of the world can only be guessed at.
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