Suitability of Assessment Methods for Identifying Active and Passive Zones in Reinforced Concrete

Abstract

The ability of various electrochemical techniques to differentiate between areas of reinforcing steel (rebar) with high and low corrosion activity and to define the boundary between such areas was studied. These techniques are based on determining the corrosion potential (E_corr), the galvanic current between an external stainless steel (SS) sensor and the bar (I_g), the apparent polarization resistance (R_p^ap), or the polarization resistance (R_p) under electric confinement conditions. Values of E_corr and I_g (the current flowing between a SS counter electrode [CE] and the rebars) were shown to distinguish active areas from passive ones very well when the areas were isolated electrically, but with difficulty when the areas were in electric contact, which is usually the case. Values of R_p^ap or i_corr (both calculated using the Stern-Geary equation) were shown to define areas of high corrosion rates in a structure where passivity prevailed much better. However, excessive i_corr values were estimated because the polarized area of the rebar (especially with passive rebars) was much greater than the CE area. Finally, the confinement of signal distribution permitted definition of the exact boundary between active and passive areas, regardless of whether they were isolated or interconnected. In addition, i_corr values obtained with this technique were shown to provide a reliable quantitative index of the damage rate in reinforced concrete structures.