Alkali-activated slag: hydration process and development of microstructure

This paper presents the results of an investigation into the hydration process and development of the microstructure of alkali-activated slag. Samples were examined by X-ray diffraction, scanning electron microscope, X-ray microanalysis of energy dispersive spectrum, and solid-state nuclear magnetic resonance. Hydration products have been identified as calcium-silica-hydrate (C–S–H) gel of low Ca/Si ratio, hydrotalcite, AFm phases and CH. It has been found that two types of AFm phase exist, depending on the exposure conditions. The initial AFm phase is formed through the transformation of CH and, upon exposure to air, it transforms into a carbonated form, hemicarbonate. It has been proposed that aluminium plays a key role in enhancing silicate polymerization. Slag compositional effects are discussed on the formation of hydration products and the development of microstructure.