Enhancing the workability retention of one-part alkali activated binders by adjusting the chemistry of the activators

Abstract

Alkali activated materials (AAMs), are gaining traction as sustainable alternatives to traditional Portland cement. However, their practical application is often limited by rapid setting times and poor workability. Although sodium carbonate and silica fume have been applied in synthesising AAMs, their effects on the reaction kinetics and structural development of one-part AAMs remain unknown. This research addresses this knowledge gap by investigating the impact of partially replacing sodium metasilicate with a blend of sodium carbonate and densified silica fume. Our study reveals that this substitution extends the setting time of one-part AAMs by eight times while maintaining comparable compressive strength after three days of curing. Detailed analyses using in-situ FTIR, activator dissolution, and isothermal calorimetry show that delayed dissolution of silica fume and carbonate ions significantly slows early-age reactions. This delayed reaction enhances the workability retention of one-part AAMs. Moreover, the modified AAM develops a more robust C-(N)-A-S-H gel structure, characterised by longer chain lengths and higher crosslinking. These findings provide a practical solution for improving the workability and structural integrity of one-part AAMs, paving the way for the development of advanced one-part AAMs with commercial viability and superior performance.