In this work, a rotating disk electrode was used to measure the cathodic kinetics on stainless steel as a function of diffusion layer thickness (6 to 60 μm) and chloride concentration (0.6 to 5.3 M NaCl). It was found that, while the cathodic kinetics followed the Levich equation for large diffusion layer thicknesses, the Levich equation overpredicts the mass-transfer limited current density for diffusion layer thicknesses less than 20 μm. Also, an unusual transitory response between the activation and mass-transfer controlled regions was observed for small diffusion layer thicknesses that was more apparent in lower concentration solutions. The presence and reduction of an oxide film and a transition in the oxygen reduction mechanism were identified as possible reasons for this response. The implications of these results on atmospheric corrosion kinetics under thin electrolyte layers is discussed.

Stainless steel (SS) reinforcement is increasingly used to control corrosion of reinforced concrete in aggressive marine and deicing salt service. It is well established that the chloride threshold of SS is greater than that of plain steel (PS) rebar, yielding substantially increased duration of the corrosion initiation stage (ti). Much less known, however, is if there is a similar benefit to the duration of the corrosion propagation stage (tP). Thus, credit for increased tP in durability forecasts for SS use tends to be conservatively limited. To reduce that uncertainty, the literature was gleaned for the few instances where SS reinforcement had reached, and preferably completed, the corrosion propagation stage. Particular attention was given to actual structural service experience, outdoor tests, and realistic laboratory conditions. Only a single case of actual service in a structure was found for which tP could be estimated, albeit indirectly. The result suggests a tP of several decades for the case of austenitic Cr-Ni rebar in marine service. Outdoor tests without unnatural acceleration showed a few cases where tP was reached, but only for straight Cr ferritic alloys, which showed some limited improvement over tP for PS. With the additional insight from laboratory tests, it was concluded that SS rebar made with high pitting-resistant grades, and thoroughly descaled, had a positive outlook for propagation stage durations that substantially exceed those of PS rebar. Quantification of that improvement is much in need of further field and laboratory assessment.

Bipolar electrochemistry provides a wireless approach for driving redox reactions and has been applied in corrosion, electrodeposition, sensing, and electrocoagulation. Despite the extensive study of the method, the significance of geometric aspects of the experimental setup still remain ill-explored, and a justification for geometries used in previous works is missing. The aim of this study is to provide information about how current/potential distributions of a split bipolar electrode in an open configuration are affected by geometric components. Through PDE-constrained optimizations, the most influential parameters are identified to be the bipolar electrode size, electrolyte height, and applied current. It is shown that a general Wagner number may be used to inform the form of the current distribution for bipolar electrochemistry but with limitations. The results also show that the current through the bipolar electrode is directly associated with cell components and higher bipolar current efficiencies will promote the primary current distribution.

Most damage prediction models for reinforcing steel in concrete treat the corrosion initiation stage as being nearly independent of the propagation stage elsewhere in the system. A next-generation chloride-induced corrosion interdependent model addresses those interactions by incorporating the corrosion prevention effect of the local potential drop caused by prior active-to-passive transitions in nearby steel portions. The effect of this potential-dependent threshold (PDT) approach was examined in a 3D realization, confirming and expanding conclusions from previous 1D and 2D models. Exploratory analysis was conducted for model result sensitivity to time step duration and activation zone size. It was found that the main outcome—a strongly lowered long-term damage projection when PDT is taken into consideration was reasonably robust to changes in those variables. The precise damage amount forecast was however sensitive to an extent that needs more detailed analysis. Sensitivity to time step choice appears to be resolvable in the limit, but the selection of appropriate activation zone size needs addressing in future work.