Thermal analysis and microstructure of Portland cement-fly ash-silica fume pastes

Thermal analysis (thermogravimetry and differential thermal analysis) was used with scanning electron microscopy technique to investigate the hydration mechanisms and the microstructure of Portland cement-Fly ash-silica fume mixes. Calcium silicate hydrate (C–S–H), ettringite, gehlenite hydrate (C2ASH8), calcium hydroxide (Ca(OH)2) and calcium carbonate (CaCO3) phases were detected in all mixes. In the mixes with the use of silica fume addition, there is a decrease in Ca(OH)2 with increasing silica fume content at 5 and 10% compared to that of the reference Portland-fly ash cement paste and a corresponding increase in calcium silicate hydrate (C–S–H).