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Highlights • A mixture of Na 2 CO 3 and NaOH was used as alkaline activator for AAS mortars. • Properties and microstructural characteristics of AAS mortars were investigated. • Characteristics of AAS mortar depend on Na 2 CO 3 -to-NaOH ratios and Na 2 O contents. • Na 2 CO 3 can prolong the setting time and improve compressive strength of AAS mortar. • Both Na 2 CO 3 -to-NaOH ratio and Na 2 O content obviously affected drying shrinkage. 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/Na 2 CO 3 solutions) on the performance of alkali-activated slag (AAS) mortars with pottery sand as fine aggregate. Five Na 2 CO 3 -to-NaOH ratios of 0/100, 20/80, 40/60, 60/40, and 80/20, and three Na 2 O 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 Na 2 CO 3 -to-NaOH ratio and Na 2 O content had a significant effect on the fresh and hardened properties of AAS mortars. A high Na 2 CO 3 -to-NaOH ratio and low Na 2 O content resulted in AAS mortars with longer initial and final setting times. The higher Na 2 CO 3 -to-NaOH ratios led to a higher late compressive strength of AAS mortars, where the 6% Na 2 O samples showed the best performance with Na 2 O contents of 4–8%. In addition, the drying shrinkage behavior of AAS mortars as a function of Na 2 CO 3 -to-NaOH ratio was dependent on the Na 2 O content. Moreover, the compressive strength and drying shrinkage have a direct relationship with the microstructure of AAS mortars. [ABSTRACT FROM AUTHOR]