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

• Published in: Construction & building materials 2018-04, Vol.167, p.587-596
• Main Authors: Zhang, Yangyang, Chang, Jun, Ji, Juan
• Format: Article
• Language: English
• Subjects: AH3 phase; Calcium sulfoaluminate cement; Crystallite size; Hydration; Rietveld methodology
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2018.02.052

•Microstructure of AH3 phase in both of the AFm-AH3 and AFt-AH3 systems was thoroughly characterized.•AH3-H phase in both of the AFm-AH3 and AFt-AH3 systems has a microcrystalline or nanocrystalline structure.•Average crystal size of the AH3-H phase in AFt-AH3 system is close to 20 nm.•Ion activity product of the AH3-H phase in the AFm-AH3 system is smaller than that in AFt-AH3 system. 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.