Effect of the sodium acetate/hydroxide activator ratio on the phase assemblage of hybrid organic−inorganic blast furnace slag binders

Abstract

Sodium acetate can be used as an activator to produce blast furnace slag binders with reduced permeability; however, acetate-activated slag cements present delayed setting times compared with NaOH-activated slag cements. As a potential solution to accelerate the reaction kinetics of these promising binders, the effects of partially replacing sodium acetate with sodium hydroxide at different ratios (ranging from 0 % to 100 %) on the phase assemblage evolution, compressive strength and wettability of these cements were investigated. A higher content of sodium acetate resulted in a lower activating solution pH, slower reaction kinetics and generally lower cumulative heat up to 28 days. Aluminium substituted calcium silicate hydrate (C-(A)-S-H) type gel, along with Mg-Al layer double hydroxide phases, were identified as the main reaction products in all systems. Decreasing sodium hydroxide content in the activating solution induced only slight changes in composition of the C-(A)-S-H and the Mg-Al layer double hydroxide phase. The compressive strength increased at higher replacement of sodium acetate by sodium hydroxide, with a lower wettability observable in the 50/50 acetate/hydroxide activated binders. These findings demonstrate the potential to tailor reaction kinetics and hardened properties of alkali-activated slag cements by substituting sodium acetate with varying amounts of sodium hydroxide. Characteristics of the binders produced with the combined sodium hydroxide and sodium acetate activators demonstrate potential for applications as coating materials.