Electrochemical impedance and electrical resistance sensors for the evaluation of anticorrosive coating degradation

Anticorrosive coatings are commonly used to protect metal structures from corrosion and thus assure constancy of the metal profile area, and consequently the mechanical stability of the metal structure. Due to environmental factors, corrosion of metal structures is inevitable and is considered during the design process; however, it is very difficult to predict the corrosion rate a priori, and the designer usually relies on empirical data to make an assessment. In an attempt to address this issue, various types of sensors that monitor the state of metallic coatings have been developed. In this study, the abilities of two systems, one based on electrochemical impedance and one using electrical resistance, developed by the authors to allow remote real-time monitoring of bridges are described. A laboratory study is presented in which three different sensor coating configurations were evaluated in three simulated environments: a salt spray chamber, a humid chamber, and an industrial chamber. The corrosion rates were monitored over a 9-month study period. Periodic measurements were made of the sensor output signals, and visual inspections (close-up photographs) were made to compare the visual and monitored response of the sensors. The sensitivity of the sensors is described, and the advantages and disadvantages concerning their deployment for field operations are discussed.