Detection and monitoring of gap in concrete-based composite structures using microwave dual waveguide sensor

A recently developed microwave dual waveguide sensor is applied for the measurement of gap in concrete-based composites in this paper. The sensor includes two waveguide sections embedded in a metal plate and opened in the structure under test. A transceiver that generates, transmits, and receives microwave signals, and a measurement unit that measures reflection and transmission coefficients is the other components of the sensor measurement system. The sensor is designed, built, and tested with concrete-metal and concrete-dielectric layer-metal specimens. Then, the sensor with the specimens has been modelled using Computer Simulation Technology Microwave Studio. Extensive simulations are performed to determine the complex dielectric permittivity of concrete in the area of measurement from the measured data, and to carry out the parametric study of concrete-based composites. It is demonstrated that the measurement and simulation results are in good agreement. It is also shown that the proposed system can measure relatively small gaps (0.2–2 mm) in the concrete based composite structures at the X-band. Measurement and simulation results show that the proposed sensor can be used for detection and evaluation of gap in composite structures, such as concrete-filled steel tubes and concrete members covered by dielectric coatings.