Influence of calcium and sodium nitrate on the strength and reaction products of the CaO-activated GGBFS system

Abstract

The influence of the added nitrate salts (Ca(NO 3 ) 2 and NaNO 3 ) on the CaO-activated ground granulated blast-furnace slag (GGBFS) system was investigated. Both salts significantly increased the early strength of the binder, and the Ca(NO 3 ) 2 maintained this tendency until 28 days of curing, whereas NaNO 3 did not. At early days, the NaNO 3 likely increased pH of samples, resulting in more dissolving GGBFS and formation of C-S-H, while the Ca(NO 3 ) 2 slightly decreased pH due to the common ion effect, but because the Ca(NO 3 ) 2 supplied additional Ca ions, it also increased the strength. At 28 days, the NaNO 3 clearly induced the reduction in C-S-H, which was not the case for the Ca(NO 3 ) 2 samples. In addition, the pore size distribution was also significantly dependent on the cation type of nitrate salts.