Development of a capacitive sensor for concrete structure health monitoring

A novel low-cost capacitive transducer (CT) using capacitance signals, which has the potential to provide accurate health assessment and damage prediction for reinforcement concrete structures, is developed in this study. Two designs of capacitive transducers are discussed for condition assessment of rebar and concrete, respectively. Both of them consist of a supporting structure and a pair of corresponding parallel electrode plates. In order to verify the effectiveness of the designed capacitive sensor, a series of preliminary experiments are conducted. The results show that the detected CT signals rise with the increasing rebar size. Pure cement paste and fiber-reinforced concrete have demonstrated a stable dielectric constant under the same fabrication conditions. To simulate the real reinforced concrete case, various sizes of rebars were placed in fiber reinforced concrete. It is found that monitoring the CT signals is an effective way to assess the rebar diameters inside concrete. Experiments results also showed that CT signals could be applied to predict rebar positions inside the concrete. Finally, FEM simulations were implemented for the last experiment, and comparison results have well verified the effectiveness of the developed capacitive sensor. The whole work has demonstrated a promising application of the capacitive sensor in NDT of reinforced concrete in the future.