Microstructure of amorphous aluminum hydroxide in belite-calcium sulfoaluminate cement

Belite-calcium sulfoaluminate (BCSA) cement is a promising low-CO2 alternative to ordinary Portland cement. Herein, aluminum hydroxide (AH3), the main amorphous hydration product of BCSA cement, was investigated in detail. The microstructure of AH3 with various quantities of gypsum was investigated via scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The AH3 with various morphologies were observed and confirmed in the resulting pastes. Particular attention was paid to the fact that AH3 always contained a small amount of Ca according to the results of EDS analysis. The AH3 was then characterized via high resolution transmission electron microscopy (HRTEM). The results of HRTEM indicated that Ca arose from nanosized tricalcium aluminate hexahydrate which existed in the AH3.