The nation's civil transportation infrastructure of structural concrete bridges is aging and deteriorating - principally as a result of the corrosion of the steel reinforcement that gives these structures their tensile strength. State Departments of Transportation officials are faced with the challenge of determining which structures need to be rehabilitated or replaced and when to do so. Assessing the condition of the steel reinforcement is not simple, since the steel is typically buried beneath 1 to 2 inches or more of concrete. Currently, these assessments are based primarily on qualitative visual inspections and anticipated design lives. This subjective and empirical information has proven insufficient for developing cost-effective asset management and operating strategies. In the hands of decision-makers, .advanced, accurate information about the internal condition of steel reinforcement and the effectiveness of new materials and rehabilitation methods could save the nation billions of dollars annually.