Effect of cement alkalinity on pore solution chemistry and chloride-induced reinforcement corrosion

This paper reports the results of a study conducted to evaluate the influence of cement alkalinity on the pore solution chemistry and chloride-induced reinforcement corrosion in ordinary and sulfate resisting Portland cement concretes. To evaluate the influence of cement alkalinity on the pore solution chemistry, cement paste specimens were prepared and admixed with fixed quantity of sodium chloride and various dosages of alkalinity (in the range of 0.4 to 1.4% Na2O equivalent). The pore solution was extracted and analyzed to determine the OH-, Cl- and SO4 -- concentrations. The influence of cement alkalinity on chloride-induced reinforcement corrosion was also assessed by measuring corrosion potentials and corrosion current density at regular intervals. The results indicated that the OH-, Cland SO4 -- concentrations of the pore solution increased with increasing alkali content of the cement. Further, the Cl-/OH- ratio decreased with increasing alkali content up to 0.8% Na2O and then increased with a further increase in the alkalinity. Furthermore, an improvement in the corrosion-resistance of the SRPC and OPC concrete specimens was noted with increasing alkali content of cement. However, the highest improvement was noted when the alkalinity was 0.8% Na2O equivalent.