Comparison of alkali and silica sources in one-part alkali-activated blast furnace slag mortar

Alkali-activated materials (AAMs) are one of the alternative low-CO₂ binders. One-part AAMs, (that is, mixing a solid precursor with a solid alkali activator and adding water) have recently attracted increasing interest. The purpose of this study is to examine if fast-dissolving solid synthetic sodium metasilicate could be replaced by a combination of sodium hydroxide and slow-dissolving silica derived from rice husk ash or microsilica in the preparation of one-part alkali-activated blast furnace slag mortar. The replacement would improve the carbon footprint and the cost efficiency of the binder. The results demonstrate that silica availability significantly affects compressive strength development as a function of time or mixture composition. The highest compressive strength (107 MPa, 28 d) was obtained with fast-dissolving silica. Furthermore, setting times could be adjusted based on the mix composition, and the durability of mortar remained good after 120 freezeethaw cycles. The results highlight the overall effect of silica availability on the fresh and hardened properties of one-part AAMs.