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

Abstract

Synopsis 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.