Fresh and hardened state properties, reaction kinetics and microstructure of sodium sulfate/sodium hydroxide – Activated slag mixtures

Abstract

This study investigated the impact of incorporating sodium hydroxide (NaOH) on the properties of ground granulated blast furnace slag (GGBFS) activated by sodium sulfate (Na2SO4). Specifically, the rheological properties, setting behavior, reaction kinetics, mechanical performance, and microstructure of the mixtures were examined. Results indicated that using only Na2SO4 as the activator resulted in mixtures with long setting times and no compressive strength at early ages. However, the addition of NaOH to the Na2SO4 activator significantly improved the reaction kinetics of the GGBFS. By optimizing ratio between NaOH and Na2SO4, mixtures with improved workability, faster structuration, reasonable setting times, and desirable mechanical properties were achieved. The superior mechanical properties were attributed to a well-packed microstructure consisting of C-(A)-S-H, ettringite, and hydrotalcite in the binary NaOH-Na2SO4 activator systems.