Prediction of corrosion behaviour and calculation of novel pitting resistance equivalent number (PREN) for stainless steel reinforcing bar

Electrochemical assessment of corrosion resistant material, such as stainless steel (SS) reinforcing bars (rebar), is both destructive and time- and resource-intensive, limiting efficient material and structural design, development, and selection. A reliable non-destructive, cost- and time-effective assessment tool, such as pitting resistance equivalent number (PREN), is therefore essential for pre-determining the corrosion performance of SS rebar to be used in specific structures. Existing PREN was developed for SS alloys under high-temperature acidic or near-neutral exposure conditions and was derived based on critical pitting temperature by matching pitting potentials with boiling acid temperatures. These exposure conditions do not represent the highly alkaline and ambient-temperature environments experienced by rebar in concrete, while the performance criteria do not reflect the common laboratory and field corrosion-resistant properties used to assess SS rebar. The current study experimentally assessed five commercial SS alloys in different concrete pore solutions and chloride levels via potentiodynamic polarization. Obtained electrochemical properties, and others extracted from the literature, were then used develop models trained on major costly alloying compositions (chromium, nickel, molybdenum, manganese), concrete alkalinity, and chloride concentration that predicts electrochemical properties (e.g., corrosion potential, corrosion current, pitting potential, pitting current) and PREN index. Key variables governing SS rebar corrosion resistance were also identified to motivate a purpose-designed experimental program for reliable rebar/concrete-specific PREN derivation.