Development of chloride binding capacity in cement pastes and influence of the pH of hydration products

Abstract

This study deals with the chloride binding capacity of cementitious materials. The binding capacities of ordinary Portland cement (OPC), 30% pulverized fuel ash (PFA), 60% ground granulated blast furnace slag (GGBS), and 10% silica fume (SF) pastes were monitored for 150 d using the water extraction method and the pH of the suspension (ground sample in distilled water) was simultaneously measured at 150 d. Results show that the binding capacity always increased with time, irrespective of binder, and the order of binding capacity with binders was 60% GGBS > 30% PFA > OPC > 10% SF. The pH of suspensions increased with time up to about 10 d, presumably due to a leaching out of alkalis, and then kept a certain value that was dependent on binder type. It was also found that an increase in the concentration of hydroxyl ions, derived from the pH of the suspension, resulted in a decrease in the mole ratio of free chloride to hydroxyl ions, reflecting the lower risk of steel corrosion.