Influence of chloride salt type on critical chloride content of reinforcement corrosion in concrete

Abstract

The objective of this study is to examine the influence of chloride salt type on the critical chloride content for the corrosion of steel reinforcement in concrete. The experiment was carried out in Portland cement concrete and concrete incorporating fly ash and ground granulated blast-furnace slag. Sodium chloride (NaCl), potassium chloride (KCl), calcium chloride (CaCl2) and magnesium chloride (MgCl2) were chosen to corrode the steel reinforcement. The initiation of pitting corrosion was detected by half-cell potential, linear polarisation and electrochemical impedance spectra methods. The critical chloride content was expressed as free chloride or total chloride by mass of binder, as well as [Cl−]/[OH−]. In addition, X-ray diffraction and differential scanning calorimetry–thermogravimetry analyses were employed to study the products in concrete. Test results show that the chloride salt type has a marked influence on the critical chloride content. The critical chloride contents expressed as free Cl− for the specimens contaminated by external magnesium chloride and calcium chloride are lower than those for the specimens contaminated by external sodium chloride and potassium chloride. Contrary to the trend for free Cl−, the critical chloride contents expressed as total Cl− and [Cl−]/[OH−] for the specimens contaminated by external magnesium chloride and calcium chloride are higher than those for the specimens contaminated by external sodium chloride and potassium chloride. The concrete specimens contaminated by external sodium chloride have the same critical chloride content as those contaminated by external potassium chloride, regardless of the water–binder ratio, mineral admixtures, or the form of critical chloride content.