Blast furnace slag (BFS) can be characterized by latent hydraulic reactivity, with low early strength caused by a hydration delay. When BFS mixes with water, aluminosilicate glass is formed on the surface of the BFS. The aluminosilicate glass disturbs the ordinary hydration of BFS. Therefore, to activate the hydration of BFS, activator materials are usually added to the BFS. To break up the aluminosilicate glass layer and activate hydration, ettringite can be formed on the surface of the slag - the formation of ettringite was the focus of this study. The heat of hydration of the hardened blast furnace slag is less than half of that of Ordinary Portland Cement (OPC); however, the formed ettringite contributes greatly to initiating BFS hydration, and hardened BFS formed by this method exhibited compressive strengths of 83%, 58% and 54% of that of OPC, after 28 days. Properties of the hardened blast furnace slag were characterized by the heat of hydration and X-ray diffraction analysis of the hydrates.

Keywords: Alkali activator, BFS, Cement hydrate, Calcium sulfoaluminate