The formation process of aluminum hydroxide in calcium sulfoaluminate pastes

Aluminum hydroxide phase (AH₃) is one of the hydration products for calcium sulfoaluminate. In this paper, the microstructure and formation process of AH₃ at different temperatures and water/solid ratios were investigated via scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results suggest that not only a high water/solid ratio but also a high temperature promoted the formation of AH₃, and changed the microstructure of AH₃. The AH₃ with various morphologies, formed together with ettringite and monosulfate, were found and confirmed in the pastes. The filamentous and lamellar AH₃ were observed in the early stages. Then, the AH₃ often gathered and grew forming smooth or lamellar spherical AH₃. At last, the spherical AH₃ usually continued to aggregate, forming dense or lamellar agglomerated AH₃ in the later stages.