Steel corrosion rate in soils by a.c. and d.c. electrochemical methods

Measurements of soil specific corrosivity were performed on bare steel in clay and sand at 15% moisture content (m.c). Polarization resistance (Rp) was measured by either the potentiodynamic linear polarization method or a.c. impedance techniques. The values obtained by the former method were corrected from IR ohmic drop contribution of the electrolyte resistance (Rs) deduced from a.c.impedance measurements, whereas, to avoid the effect of electrode processes with large relaxation time, proper sweep rates were chosen. A method to evaluate Rp by a.c. impedance technique is proposed which generally gives results close to d.c. Rp measurements. Impedance data allow also some interpretation of corrosion rate determining process. © 1990.