Corrosion performance of steel in composite concrete system admixed with chloride and various alkaline nitrites

Composite concrete systems consist of both binary and ternary cements were designed. The corrosion performance of steel in composite concrete systems admixed with sodium chloride (3% NaCl) and different alkaline nitrites (0.5% NO2-), namely sodium nitrite (NaNO2), potassium nitrite (KNO2) and calcium nitrite [Ca(NO2)(2)] were studied by conducting various electrochemical and non-electrochemical techniques. Open circuit potential and weight loss measurements were carried out for 180 days of exposure. The permeability characteristics of the composite concrete systems were studied using impressed voltage technique and rapid chloride permeability test. Linear polarisation studies showed better corrosion resistance properties of steel in binary and ternary cement concrete even in the presence of 3% sodium chloride. Chloride diffusion studies revealed that the diffusion coefficient was found to be much less for (OPC + PSC) and ternary systems. Nitrites of sodium, potassium and calcium act as anodic inhibitors and they compete with chloride ions for the ferrous ions at the steel surface to form a film of ferric oxide. Ternary systems and (OPC + PSC) performed better even in the presence of a higher amount of aggressive chloride ions. The reduction in the corrosion rate of steel in composite concrete systems follows the order: (OPC + PPC + PSC)>(OPC + PSC)>(OPC + PPC)>(PPC + PSC).