Candidate corrosion resistant reinforcement materials for concrete structures: corrosion propagation behavior

Previous work has focused on the corrosion initiation behavior of rebar embedded in concrete. However, a complete assessment of the potential benefit afforded by new candidate rebar alloys from a corrosion resistance standpoint must address the corrosion propagation behavior and other factors that might affect the risk of corrosion-induced concrete cracking. In this study various electrochemical techniques were employed to characterize the radial (depth) and lateral (length) corrosion propagation behavior of 316LN stainless steel (S31653), 2101 duplex stainless steel (21% Cr, 1.6% Ni 0.29% Mo, 4.8% Mn), and MMFX-2 (9.3% Cr, 0.089% Ni, 0.023% Mo, 0.46% Mn) compared to carbon steel in saturated Ca(OH) ₂ with NaCI additions. Radial corrosion was investigated by monitoring the anodic dissolution rate following propagation of local corrosion in a confined anode area. A pitting factor was also determined for each alloy, which describes the degree of corrosion localization. Lateral propagation was characterized using closed packed microelectrode arrays simulating a continuous electrode in order to monitor the spreading of active corrosion from initiated pit sites to adjacent surfaces. Radial pit growth was ohmically controlled but repassivated more readily at high potentials in the case of S31653 and 2101 stainless steels. Conversely, pit growth on carbon steel propagated at all applied anodic potentials and did not repassivate until deactivation by cathodic polarization. Stainless steel showed the highest resistance to lateral corrosion propagation from an active site during microelectrode array testing. In contrast, carbon steel was found to easily undergo widespread depassivation along the surface compared to stainless steel. 2101 and MMFX-2 duplex steels showed similar radial propagation behavior and corrosion morphology, which was intermediate between carbon steel and stainless steel.