Calcium aluminates hydration in presence of amorphous SiO2 at temperatures below 90 °C

The hydration behaviour of Ca3Al2O6, Ca12Al14O33 and CaAl2O4 with added amorphous silica at 40, 65 and 90 °C has been studied for periods ranging from 1 to 31 days. In hydrated samples crystalline phases like katoite (Ca3Al2(SiO4)3−x(OH)4x) and gibbsite, Al(OH)3, were identified, likewise amorphous phases like Al(OH)x, calcium silicate hydrates, C–S–H, and calcium aluminosilicate hydrates, C–S–A–H, were identified. The stoichiometry of Ca3Al2(SiO4)3−x(OH)4x (0⩽3−x⩽0.334), which was the main crystalline product, was established by Rietveld refinement of X-ray and neutron diffraction data and by transmission electron microscopy.