The Corrosion Propagation Stage of Stainless-Steel Reinforced Concrete: A Review

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. 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.