Electrochemical investigation on the influence of sulfates on chloride-induced corrosion of steel bar in cement-based materials

The combined action of chloride and sulfate attacks is an important durability problem for RC structures long-termly dwelled in marine environment. This paper experimentally investigates the influence of sulfates on chloride-induced corrosion of steel bar in cement-based materials by accelerated corrosion experiment, in which some steel bar-mortar (SM) specimens were immersed in chloride-only (15% NaCl) and combined chloride-sulfate solutions (15% NaCl + 5% Na2SO4, 15% NaCl + 10% Na2SO4). Electrochemical measurements, like OCP, TP and EIS, were used to analyze the corrosion behavior of SM specimens immersed in the solutions. Results showed that sulfates play a significant role in accelerating the time at which the initial corrosion of steel bar in concrete begins. In 15% NaCl solutions containing 0%, 5% and 10% Na2SO4, the initial corrosion of steel bar occurred after 360, 240 and 160 days of immersion, respectively. Electrochemical results from OPC, TP and EIS were in good agreement regarding the corrosion behavior of steel bar, and either of them can be used in determining the onset of corrosion of steel bar in concrete.