Effect of Si/Al ratio on engineering properties of alkali-activated GGBS pastes

The effect of synthesis parameter, silicon/aluminum molar ratio, on the engineering properties of alkali-activated blast-furnace paste has been investigated. The article presents the study of the compressive strength and microstructure of alkali-activated blast-furnace slag paste specimens prepared using sodium silicate and potassium hydroxide solution as activators. The experimental results have indicated that the compressive strength, bulk density, apparent porosity, water absorption and microstructure of the specimens are significantly affected by the silicon/aluminum molar ratio of alkali-activated ground granulated blast-furnace slag (AAS) paste. The compressive strength at 28 d of 44·90–46·30 MPa was obtained for silicon/aluminum ratios of 2·03–2·26. Increasing silicon/aluminum ratio beyond 2·26 resulted in a decrease in compressive strength of AAS paste due to delayed precipitation of calcium silicate hydrate products. The microstructural changes of hardened AAS paste were studied using scanning electron microscopy/energy-dispersive X-ray spectroscopy, and mineralogical characterization was studied with X-ray diffraction and Fourier transform infrared spectroscopy.