The effect of pH and fly ash on the electrochemical performance of AISI 304L stainless steel concrete reinforcement in harsh environments

The investigation of the effect of pH and fly ash (FA) as a corrosion inhibitor on the electrochemical behavior of 316L and 304L concrete reinforcement in a simulating concrete pore solution exposed to aggressive environments, i.e. acid rain, is the main objective of the present study. The corrosion performance of 316L and 304L stainless steel is examined by means of cyclic (reverse) polarization in order to evaluate the susceptibility of the rebars to localized corrosion. Two types of electrolyte were used. The first electrolyte is a highly alkaline solution simulating fresh concrete exposed to acid rain (pH » 12), while the second electrolyte is a mildly alkaline solution simulating corroded concrete cover that exposed the reinforcement to direct acid rain attack (pH » 8). Both solutions contained saturated Ca(OH)₂, an acid rain simulating solution and FA (0 wt.% - 25 wt.% of the dry mixture) as corrosion inhibitor. In both electrolytes the beneficial effect of FA up to 20 wt.% content on the corrosion resistance of both 316L and 304L rebars was manifested. However, this trend was reversed at 25 wt.% content due to the localized presence of agglomerates of FA on the surface of the steel. The above finding was confirmed by SEM/EDX examination of cross-sections after cyclic polarization. An important conclusion of this study was the feasibility of replacing 316L stainless steel with 304L in critical applications, such as the restoration of ancient monuments, provided that FA is included in the concrete mixture, even at low contents (10 or 15 wt.%).