Examining the effect of hybrid activator on the strength and durability of slag-fine metakaolin based geopolymer cement

One of the challenges in synthesizing geopolymers is selecting the appropriate activator that facilitates handling, optimizes performance, and is environmentally compatible. This study investigates the effects of using a combination of sodium silicate (SS, Na2SiO3) and sodium carbonate (NC, Na2CO3) as alkaline activators on the mechanical properties and durability of a geopolymer (GP) made from blast furnace slag (BFS) and fine metakaolin (FMK). The findings indicate that using a blend of SS and NC as an alkaline activator prolongs the setting process compared to sole sodium silicate, but it is much faster if sodium carbonate is only used. The activator consists of (7% SS + 3% NC) resulting in 22.5% increase in the GP compressive strength after 28 days, while the blend (5% SS + 5% NC) demonstrated a 12% improvement in strength after the same period. Using a hybrid alkaline activator made from SS and NC reduces the porosity of the geopolymer matrix, enhances its bulk density, and decreases the moisture absorptivity compared to using either SS or NC alone. These improvements in the characteristics of the geopolymer help mitigate the harmful effects of sulfate ions (SO42-) for approximately six months of severe exposure. Additionally, the thermal resistance of the fabricated geopolymer is enhanced, allowing it to withstand temperatures of up to 800 degrees C. XRD and FTIR showed the GP mixes activated using a blend of SS and NC facilitate the formation of sodium aluminosilicate hydrates (NASH) with a more well-packed microstructure, as seen in SEM images.