Impacts of Dry Activators on One-Part Alkali-Activated GGBFS Pastes: Setting Time and Compressive Strength

Abstract

The use of one-part (just-add-water) alkali-activated binders is a simplified method to combine the distinct mechanical properties of alkali-activated pastes (AAPs) with their ease in practical applications. This study focused on evaluating the effects of various parameters on the properties of AAPs. The parameters included dry activator, partial replacement of ground granulated blast furnace slag (GGBFS) with cement and silica fume, activator/binder ratio, sodium hydroxide ratio, and activator anion. The investigated properties of the AAPs included workability, setting time, and compressive strength at different age intervals (7, 28, and 56 days). Microstructural properties were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) to understand the impact of the different activation methods. The study found that one-part mixing, which involves just adding water to the binder and dry activator, offered better fluidity and a slower rate of hardening compared with ready-mixed alkaline for all AAP mixes. However, it exhibited lower compressive strength. By replacing some GGBFS with cement, flow, and setting time were reduced while compressive strength was increased. The use of silica fume as a replacement for GGBFS led to enhanced flow and setting time for all one-part AAP mixes. Furthermore, the type of activator anion used affected the AAP’s properties. Silicates as dry activators resulted in quicker setting time, lower flowability, and higher compressive strength compared with carbonate and phosphate activators. AdaBoost analysis revealed that activator ratio, mixing method, and anion type had the highest influence on AAP mechanical properties. These findings provide insights into optimizing the performance and application of AAPs in practical scenarios.