The concept of floating electrode for contact-less electrochemical measurements: Application to reinforcing steel-bar corrosion in concrete

The concept of floating electrode is introduced for defining the common electrochemical behaviour of any non-connected, electronically conducting, body immersed in an electrolytic medium. The emphasis is put on both its own polarisation features and its influence on the d.c. and a.c. current and potential across the cell, hence the feasibility, among others, of contact-less electrochemical measurements on floating electrodes. Application to reinforcing steel bars in concrete is investigated by numerical computation of the a.c. current and potential fields in a broad range of concrete resistivity, interfacial resistance and capacitance. Impedance defined in a 4-electrode configuration, when rationalised against the concrete resistivity, is shown to provide, within a realistic range of parameters, a practical mean to access the properties of the bar–concrete interface.