Effect of blended inorganic salts containing negative hydration ions on hydration and properties of alkali-activated slag cement

Abstract

Water glass (WG) is generally considered to be the most effective activator to prepare alkali-activated slag (AAS) cement in terms of strength and durability. However, the rapid setting and hardening of WG activated slag results in rapid loss of fluidity of AAS concrete mixture, which limits its engineering application. In the paper, the effect of blended inorganic salts containing negative hydration ions on the fluidity, setting time and mechanical strength of AAS cement was studied. The hydration process and hydration products were used to explore the action mechanism. Ba(NO3)2 greatly delayed the hydration of AAS cement. The four inorganic salts (KCl, KNO3, KBr and NaCl) blended with a small amount of Ba(NO3)2 can improve both the initial fluidity and fluidity retention, and a wide setting time range can be obtained to meet engineering requirements. The compressive strength decreased with the increase of inorganic salts. The incorporation of inorganic salt did not change the composition of the main hydration products. Considering the fluidity required by construction, mechanical properties and the durability of structure, it is recommended to add 4%–5% KBr or KNO3 blended with no more than 0.2% Ba(NO3)2 into AAS cement.