The alkali stimulus provided by the Ca(OH)2 contained in desulfurization slag (DS), a byproduct generated in the preliminary treatment of molten iron and composed of Ca(OH)2, CaCO3, and 2CaO·SiO2, is used to cause a cement-free binder to harden by serving as an alkali activator for ground, granulated blast-furnace slag (BFS). The 28-day compressive strength of the BFSDS binder was found to be about 30% that of ordinary Portland cement (OPC), but the 28-day strength of a binder made from BFS, DS, and anhydrous gypsum (G) was found to be similar to that of OPC. It is confirmed that BFS-DS-G binders have very low hydration heat, which is of use in reducing the heat generated during the curing of mass concrete. The main hydration product of the BFS-DS-G binder is found to be ettringite. Scanning electron microscope images reveal that the needle-shaped ettringite formed in the BFS-DS-G binder is much thicker than that formed in OPC. This thick, needle-shaped ettringite forms a skeletal structure, providing structural stability, and fills the gaps between hydration products such as calcium silicate hydrates and calcium aluminum hydrates, making it highly effective in forming a dense structure. The widespread use of BFS-DS-G binders would result in the value-added utilization of byproducts from the iron & steel making process, and provide an environmentally friendly and more economical construction material, and contribute to a reduction in CO2 emissions generated by the cement industry.

Keywords: Slag cement, Cementless binder, Desulfurization slag, Ettringite.