AH3 phase in the hydration product system of AFt-AFm-AH3 in calcium sulfoaluminate cements: A microstructural study

In calcium sulfoaluminate cements, two hydration product systems, namely the monosulfate (AFm) - aluminum hydroxide (AH3) system and the ettringite (AFt) - AH3 system, were created based on the reactions of ye'elimite with and without gypsum. From chemically synthesized samples, the composition and microstructure of the AH3 phase in the hydration product system AFt-AFm-AH3 were characterized using X-ray diffraction, Rietveld method, thermogravimetric analysis, 27Al magic angle spinning nuclear magnetic resonance spectroscopy, field emission scanning electron microscopy, and inductively coupled plasma optical emission spectroscopy. It was seen that AH3 phase in both AFm-AH3 system and AFt-AH3 system had a gibbsite-like structure presented in a microcrystalline or nanocrystalline structure, while the AH3 phase in the AFt-AH3 system had an average crystallite size close to 20 nm.