Use of CaO as an activator for producing a price-competitive non-cement structural binder using ground granulated blast furnace slag

The use of calcium oxide (CaO) demonstrates a superior potential for the activation of ground granulated blast furnace slag (GGBFS), and it produces a higher mechanical strength than calcium hydroxide [Ca(OH)₂]. The mechanical strength differences between CaO- and Ca(OH)₂-activated GGBFS binders are explored using isothermal calorimetry, powder X-ray diffraction, thermogravimetric and differential thermal analysis (TGA and DTA) as well as compressive strength testing. Calcium silicate hydrate (C-S-H), Ca(OH)₂ and a hydrotalcite-like phase are found as reaction products in all samples. The TGA and DTA results indicate that the use of CaO produces more C-S-H, although this is not likely to be the primary cause of higher strength development in the CaO-activated GGBFS. Rather, other factors such as porosity may govern the strength at a higher order of magnitude. Significant reduction of Ca(OH)₂ occurs only with the use of Ca(OH)₂, followed by the formation of carbonate (CaCO₃), indicating carbonation.