Strength development and microstructural characteristics of barium hydroxide-activated ground granulated blast furnace slag

In this study, barium hydroxide was proposed as a main activator for ground granulated blast-furnace slag (GGBFS) to produce a strong binder, and it was compared to calcium hydroxide in terms of strength development, reaction products, and microstructure. The Ba(OH)2-activated GGBFS (BHAS) achieved a significantly higher compressive strength than Ca(OH)2-activated GGBFS (CHAS), except at 3 days, mainly due to (1) the more formation of hydration products, leading to a notable reduction in pore sizes and volume, and (2) the higher solubility of Ba(OH)2, resulting in a higher dissolution of GGBFS than that of Ca(OH)2. Although calcium silicate hydrate (C-S-H) was a major reaction product in both mixtures, the Ca/Si ratios were much different. In the BHAS, the presence of barium ions prohibited the synthesis of ettringite and monocarboaluminate, which formed in the CHAS mixtures, but it induced Ba-bearing products, strätlingite, and the hydrotalcite-like phase. The removal of ettringite was the cause of the lower strength of the BHAS at 3 days compared to that of the CHAS.