Nanostructural evolution of Al(OH)3 gel formed by the cubic and orthorhombic ye'elimite clinkers of calcium sulfoaluminate cements in an ultra-wide hydration temperature range

Abstract This paper investigated the influence of hydration temperature on the nanostructure of the AH3 phase formed in calcium sulfoaluminate cements. Orthorhombic ye'elimite (st-ye'elimite) and cubic ye'elimite (ss-ye'elimite) were hydrated in an ultra-wide temperature range (5–220 °C). Results showed that the AH3 phase formed by ss-ye'elimite was always microcrystalline in nature at various curing temperatures (5–130 °C), and transformed into the AlOOH phase at 150 °C and above. However, the AH3 phase formed by st-ye'elimite grew from a microcrystal to a favorable crystal as the temperature increased, and transformed into the AlOOH phase at 170 °C and above. The nanostructure of hydration products was further investigated using TEM/SAED analysis together with FE-SEM images, directly evidencing that the formed AFm-12 phase was single-crystal in nature, and the formed AH3 phase was microcrystalline at low temperatures and grew into single-crystal hexagonal prisms with the preferred growth direction along [001] direction at high temperatures.