Chloride Corrosion Threshold of Reinforcing Steel in Alkaline Solutions—Effect of Specimen Size Available to Purchase

The effect of specimen surface area (S), varied by 3 orders of magnitude, on the pitting and repassivation potentials of concrete reinforcing steel specimens in alkaline solutions was determined using the conventional cyclic polarization technique. For most of the conditions examined, the pitting potential (E_p) was found to decrease significantly with increasing S; a slope as high as ~0.3 V per area decade was observed for steel with a 600-grit surface finish in saturated calcium hydroxide (Ca[OH]₂) solution with 0.1 M and 1.0 M sodium chloride (NaCl). The repassivation potential and the variability of E_p, however, were independent of specimen surface area. The experimental observation was reasonably explained with a simple probability model. The steel surface finish was an independent factor that also strongly affected E_p. The findings indicate that chloride corrosion threshold values inferred from tests with typically small laboratory specimens may be not conservative enough when applied to full-sized structures. Alternative treatments using a distribution of threshold values merit consideration.