On The Determination of Polarization Diagrams of Reinforcing Steel in Concrete Available to Purchase

Polarization (E-log i) diagrams of steel in concrete are often drawn from measurements obtained while using a current interruption or “instant-off” technique, in an attempt to eliminate error from ohmic resistance effects. A finite-difference computer model of a reinforced concrete system was used to predict the shape of polarization curves that would result when corrosion macrocells, involving active and passive reinforcing steel regions, are present. The results show that apparent polarization (Tafel) slopes, several times greater than the actual values, could be observed as a result of nonuniform current distribution effects. The calculations also showed that considerable distortion of the E-log i diagram could result from the current distribution effects and from redistribution of the oxygen concentration within the concrete during the polarization test. Implications of the results on the validity of commonly used cathodic polarization criteria were examined.