Effect of the activator on the performance of alkali-activated slag mortars with pottery sand as fine aggregate

Abstract

Recently, alkali-activated slag mortars have attracted considerable attention as environmentally friendly materials. The objective of this paper was to explore the influence of an alkaline activator (NaOH or NaOH/Na2CO3 solutions) on the performance of alkali-activated slag (AAS) mortars with pottery sand as fine aggregate. Five Na2CO3-to-NaOH ratios of 0/100, 20/80, 40/60, 60/40, and 80/20, and three Na2O contents of 4%, 6%, and 8%, were used to prepare AAS mortars. The water-to-slag ratio and slag-to-aggregate ratio were kept constant, at 0.38 and 0.8, respectively. The setting time, fluidity, compressive strength, and drying shrinkage were measured. The reaction hydrates were analyzed using microscopy and elemental analysis, while the pore structures were characterized using mercury intrusion porosimetry. The experimental results showed that both the Na2CO3-to-NaOH ratio and Na2O content had a significant effect on the fresh and hardened properties of AAS mortars. A high Na2CO3-to-NaOH ratio and low Na2O content resulted in AAS mortars with longer initial and final setting times. The higher Na2CO3-to-NaOH ratios led to a higher late compressive strength of AAS mortars, where the 6% Na2O samples showed the best performance with Na2O contents of 4–8%. In addition, the drying shrinkage behavior of AAS mortars as a function of Na2CO3-to-NaOH ratio was dependent on the Na2O content. Moreover, the compressive strength and drying shrinkage have a direct relationship with the microstructure of AAS mortars.