Hydrothermal synthesis of tobermorite from fly ashes

Abstract

The hydrothermal behaviour of oxide mixtures whose compositions simulate those of fly ashes is discussed. These model systems were synthesized using phase-pure starting materials, so that the exact compositions of the mixtures could be specified. Fly ashes were then used as starting materials to compare their behaviour under hydrothermal conditions. The compositions of class F and C fly ashes were adjusted to those of the systems made with the pure oxide starting materials. It was demonstrated that tobermorite can be synthesized from fly ash based materials under hydrothermal conditions, and the process was accelerated at high sodium hydroxide concentrations. The pore size distributions of tobermorites prepared from fly ashes showed an increase in pore volume over the size range from 19 Å to almost 0·1 μ;m.