THz spectral imaging to assess metal components in concrete structures

Long-term corrosion of steel in concrete structures is a particular concern for nuclear power plants as there is a compelling public interest in the safe operation of these plants for the many decades that they are in operation and the additional decades it takes for them to be decommissioned. Inspection techniques that are both non-destructive and which can detect long-term corrosion at its earliest stages are needed to identify when remedial steps need to be taken to insure the integrity of concrete structures at nuclear power plants. The overall objective of this research program is to establish terahertz imaging and spectroscopy as the pre-eminent non-destructive examination technique for locating and identifying corrosion in steel- reinforced concrete structures. We will accomplish this by pushing the limits of high-power terahertz systems to increase imaging depth and by enhancing the detection sensitivity of terahertz spectroscopic methods to directly detect corrosion by-products in concrete. In our Phase I effort, we will identify which corrosion by-product or promoting agent is most strongly detected with terahertz imaging and spectroscopy. We will establish this via a combination of theoretical and numerical modeling and experimental benchmarking at terahertz frequencies. We will also image steel in concrete to evaluate the imaging depth and quality. Our proposed technique will enable rapid inspection of nuclear plant structures and detect detection of corrosion in concrete. Similar corrosion issues afflict our nations aging infrastructure including highways, bridges, tunnels, buildings, and dams. Earlier identification of corrosion in these structures will significantly enhance public safety as well as reducing the cost of corrosion, estimated to be in the hundreds of billions of dollars annually.