Fresh and hardened state properties, reaction kinetics and microstructure of sodium sulfate/sodium hydroxide

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

Dai, Xiaodi / Aydin, Serdar / Yucel Yardimci, Mert / De Schutter, Geert

Abstract

Highlights • Fresh state and hardened properties of AAC activated by NaOH and Na2SO4 were investigated. • The Na2SO4-activated slag mixture with desirable engineering properties can be achieved by optimized addition of NaOH. • The rapid increase in early storage modulus could be related to the C-A-S-H and ettringite precipitation. • The addition of NaOH to the Na2SO4 activator resulted in a more densely packed microstructure.

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.