Alkali-activated concrete (AAC) is a potential sustainable alternative to traditional portland cement concrete.However, many AAC formulations exhibit poor workability, and slow strength development unless cured at elevated temperatures, which tends to limit the applicability of activated concrete.Nanoparticles, including nanosilica and nanoalumina have been used to modify setting times, rheology, and mechanical strength of portland cement-based binder systems.The present study evaluates the role of nanosilica and kaolinite clay on the setting time, workability, and mechanical strength of AAC, and to identify the mechanisms of enhancement or degradation.Activated fly ash (FAC) and ground granulated blast-furnace slag (slag) mortar with 1-2% dosages of nanosilica (NS) and kaolinite clay (KC) were evaluated here.The effect of activator concentration is also discussed in this paper.Significant improvement in compressive strength of alkali-activated slag mortar was observed when modified by either nanosilica or kaolinite.The use of kaolinite is preferred since it is a natural material with lower environmental impact than commercially-processed nanosilica.A slight improvement in mechanical strength of activated class-C fly ash was observed when modified with nanosilica, while a reduction in strength accompanied modification with kaolinite.