Field and Laboratory Experience with Electrochemical Methods for Assessing Corrosion of Steel Concrete

Abstract

The electrochemical techniques treated are: potential mapping with reference electrodes at the surface, corrosion potential monitoring with reference electrodes embedded in the concrete, potentiodynamic scans, potentiostatic polarization, galvanostatic pulse technique, AC-impedance spectroscopy and monitoring of electrochemical noise. Extensive laboratory experiments have been carried out in alkaline solutions, in mortar slabs with and without chloride additions and at a 840 m long, 16 years old bridge at the coast of Northern Norway. It is concluded that the standard electrochemical techniques for determination of the corrosion rate in aqueous solutions do not function well for steel in concrete, at least not for routine applications. This is caused by a very complex electrochemistry of iron in alkaline media and the very low volume of pore water in contact with the steel. Due to the low volume even very small impressed polarization currents alter the composition of the environment adjacent to the steel. This complicates the interpretation of the electrochemical tests, leading to a series of pitfalls.