Corrosion behavior of steel reinforcement in concrete exposed to composite chloride-sulfate environment

The corrosion of steel reinforcement in concrete is the most significant durability problem encountered in reinforced concrete structures. The concomitant presence of sulfate ions may affect chloride induced corrosion of steel reinforcement in concrete. In this paper the outcome of a comprehensive experimental investigation is presented wherein corrosion performance of steel reinforcement in concrete exposed to composite solutions of chloride and sulfate ions has been evaluated. In this investigation, concrete specimens with a centrally embedded steel bar have been prepared from two types of cement namely ordinary Portland cement (OPC) and Portland pozzolana cement (PPC), four w/c ratios and one type of steel reinforcement. The reinforced concrete specimens have been exposed to composite solutions of chloride and sulfate ions of different concentrations. Further in order to evaluate the effect of cation type associated with sulfate ions on corrosion parameters, sodium sulfate and magnesium sulfate were used individually with sodium chloride in the preparation of composite solutions. After exposure, the different corrosion parameters namely half-cell potential, relative resistivity and corrosion current density have been measured. From the results, it was observed that the specimens made with PPC exhibited higher values of relative resistivity and lower values of corrosion density as compared to those made with OPC in all the composite solutions. Further opposite behavior was observed between composite solutions of sodium chloride with magnesium sulfate and sodium chloride with sodium sulfate in terms of variations in relative resistivity and corrosion current density for both OPC and PPC. In addition on the basis of results of analysis of variance, the effect of different parameters on relative resistivity and corrosion current density in composite solutions of sodium chloride and magnesium sulfate and that in composite solutions of sodium chloride and sodium sulfate has also been evaluated.