The microstructure of tricalcium silicate/pulverized-fuel ash blended cement pastes

The microstructure and composition of the reaction products in a C₃S/pfa blended cement paste have been studied by analytical electron microscopy of thin sections. The presence of pfa does not significantly affect the morphology of the hydration products of C₃S but the C/S ratio of the C-S-H is reduced in all areas. The reaction products of the pfa after one year are partial shells of hydrogarnet formed within the reacted zones of the pfa particles, radially fibrillar C-S-H within reacted zones and shells of dense C-S-H, the first forming immediately outside the pfa particle surface and later shells forming within the reacted zone by rhythmic precipitation. These two forms of C-S-H have similar C/S ratios, averaging between 1·4 and 1·5. Silica and alumino-silicate glass particles have similar reactivities.