Corrosion Propagation of Stainless Steel Reinforced Concrete

Structural durability is a growing concern in global infrastructure. The infrastructure report card released by the American Society of Civil Engineers (ASCE) indicates that approximately 9.1% of the total bridges in the United States were structurally deficient in 2016. In addition, it suggests that about 40% of the total bridges in the country are now 50 years or older. This issue becomes even more critical in structures exposed to aggressive environments such as marine structures. Thus, federal and regional efforts are now being directed towards infrastructural durability improvement to improve the long-term cost-efficiency of civil infrastructure. Corrosion prevention strategies may include increased concrete cover thickness, higher concrete quality, and corrosion-resistant alloys (CRAs) such as stainless steel (SS). Over the past couple of decades, SS reinforcement has garnered attention due to its increased service life. Several investigations have found that the life cycle cost of structures reinforced with SS may be considerably lower than that of plain carbon steel (CS). The service life of steel reinforcement may be divided into two stages: the corrosion initiation stage (CIS) and corrosion propagation stage (CPS). The durability of SS reinforcement has been commonly approached using the model proposed by Tuutti [6] where the service life of a structure, which is the time required for corrosion loss in the steel to reach a serviceability limit state, is determined by the added duration of the CIS and the CPS. The increased durability of SS reinforcement has been primarily attributed to a greater corrosion initiation threshold (CT) which could be up to one order of magnitude greater when compared to that of CS. Nevertheless, no significant benefit has yet been associated to extensions in the subsequent CPS. Hence, existing durability projections of concrete reinforced with SS are limited by the scarce information available regarding the CPS, leading to highly conservative approaches based on investigations performed on concrete reinforced with CS. This investigation compiles relevant information from the literature of the CPS focusing on the few cases where SS reinforcement had reached, and preferably finalized, the corrosion propagation stage. Where literature evidence of SS reinforcement was not available, findings from CS reinforcement were considered. The information garnered was compared to laboratory experimental and computational model simulation results obtained at the Infrastructural Corrosion Laboratory of the University of South Florida. This work focused on identifying influential parameters that may play a major role in estimating the duration of the CPS. The CPS of SS reinforcement was assessed in terms of four governing factors consisting of the corrosion morphology, corrosion products, corrosion rates, and the limit state. Different failure mechanisms were examined as a first approach to determine the expected limit state of concrete reinforced with SS. The effect of the concrete condition -i.e., sound and locally-deficient-, on the potential limit state of SS reinforced concrete was also considered. Experimental results and available evidence from previous investigations served as inputs to update estimates of duration of the CPS of concrete reinforced with SS in current civil engineering practice. The reliability of traditional corrosion detection and monitoring techniques -i.e., half-cell potential and electrochemical impedance spectroscopy- was examined for SS reinforcement. Current standards relating the probability of corrosion damage and experimental measurements are based on CS reinforcement. Findings from this research suggest that the existing relations may not be applicable to SS reinforcement and that further work is required to develop similar relations that consider the CPS parameters of SS reinforcement