The role of nano magnesia in accelerating the early hydration rate of sodium sulfate activated slag

Abstract

The present work aimed at accelerating the early hydration rate of sodium sulfate (Na2SO4) activated slag via nano magnesia (nM). Slag was activated by two Na2SO4 concentrations equivalent to 1 and 3 wt% Na2O (SS1 and SS3, respectively). The results demonstrated that the addition of nM accelerated the hydration rate and raised the pH of the medium, resulting in a marked enhancement of the early compressive strength of the hardened SS3 mixture. Specifically, the samples containing 0.5, 1.0, and 1.5 wt% nM recorded 3-day compressive strengths 12, 21, and 15 times higher than the control sample (SS3). As time progressed up to 90 days, the strength gap between SS3-nM and SS3 mixtures decreased, but samples containing 0.5 and 1.0 wt% nM still showed higher strengths. By contrast, the mixture containing 1.5 wt% nM recorded lower 90-day compressive strength. Nonetheless, higher nM content bolstered the formation of ettringite and calcium aluminum silicate hydrate phases while simultaneously decreasing both the pore volume and drying shrinkage of Na2SO4-activated slag. Utilizing nM successfully addressed the issue of poor initial performance of Na2SO4-activated slag, leading to improved commercial viability and increased mass production of such binder.