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Abstract-Health monitoring of infrastructure is very important in the transportation and infrastructure industries. Many nondestructive testing (NDT) techniques have been applied for structural health monitoring including microwave NDT, ultrasound, thermography, etc. Due to the complex materials (composites, concrete, etc.) commonly used, it may be difficult to thoroughly inspect a structure using one method alone. Thus, hybrid NDT methods have also been developed. Recently, the integration of microwave NDT and thermography, herein referred to as Active Microwave Thermography (AMT), has also been considered as a potential structural health monitoring tool. This hybrid method uses microwave energy to heat a structure of interest, and then the thermal surface profile is measured using a thermal camera. This paper investigates the potential of AMT to inspect rehabilitated cement-based structures. Preliminary simulations and measurements provided herein indicate that AMT has the potential to detect delaminations under carbon fiber patches bonded to concrete.

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Abstract. Infrastructure health monitoring is an important issue in the transportation industry. For the case of cementbased structures in particular, detection of corrosion on reinforcing steel bars (rebar) is an ongoing problem for aging infrastructure. There have been a number of techniques that have shown promise in this area including microwave nondestructive testing (NDT) and thermography. Thermography is quite advantageous as it is an established method, and can be utilized for large inspection areas with intuitive results. Typical heat sources include induction heating and flash lamps, but these are not without drawbacks. Microwave nondestructive testing has also been successful at detecting corroded rebar, but at the cost of lengthy scan times. This paper presents an investigation into the potential of utilizing aspects of microwave NDT and thermography to create a hybrid NDT method, herein referred to as Active Microwave Thermography (AMT). AMT takes advantage of the electromagnetically lossy nature of corrosion byproducts and uses microwave energy to induce heat in the corrosion. Subsequently, the resultant heat profile is captured using an infrared camera. This paper presents initial simulations and measurements that highlight the potential of AMT to detect corroded rebar.