Hydration of alkali-activated slag: comparison with ordinary Portland cement

A multi-method approach was used for the investigation and comparison of alkali-activated slag binders (AAS), pure slag and ordinary Portland cement (OPC). X-ray fluorescence, X-ray powder diffraction, granulometry, calorimetry, thermo-gravimetric analysis and environmental scanning electron microscope investigations of the microstructure with energy dispersive X-ray analyses were used to characterise the cements and their hydrate phases. In addition, the chemical composition of the pore solution, including the different sulphur-containing ions, was analysed. The precipitation mechanisms during binder hydration in the AAS and OPC systems exhibit significant differences: in AAS the formation of the ‘outer product’ C-S-H is much faster than in OPC. The high Si concentrations in the pore solution during the early hydration of AAS are related to the fast dissolution of Na-metasilicate. The fast reaction of Na is an important factor for the voluminous precipitation of C-S-H within the interstitial space alread...