Correlating slag chemistry to setting and mechanical behaviors of alkali-activated slag

Abstract

Aiming at uncovering the critical chemical parameters that govern the performance of alkali-activated slag (AAS), this work investigates the phase assemblage, microstructure, and setting and mechanical properties of AAS prepared using five different slags and two activators (sodium hydroxide or sodium carbonate). The results suggest that the ratio of non-bridging oxygens to tetrahedral cations (NBO/T) of slag structure is an appropriate reactivity indicator, correlating reasonably well with the mechanical performance of AAS at late ages. However, the NBO/T value of slag structure is relatively incompetent in indicating the setting performance of AAS, particularly for the sodium carbonate-activated system. The variability of slag chemistry has considerable impacts on the setting behaviors of AAS, but relatively insignificant effects on compressive strength, suggesting that the strength of AAS is dominated by activator and mixture proportioning parameters. Regardless of activator chemistry, the AAS with a higher amount of hydrotalcite formation tends to have higher compressive strength, implying the beneficial roles of hydrotalcite in microstructure densification and strength achievement.