Mössbauer, DTA and XRD study of Portland cement blended with fly ash and silica fume

Two octahedral Fe3+ positions with close isomeric displacements and quadrupole splittings were proved for plain cement using Mössbauer spectroscopy. In cements with silica fume iron is registered as two Fe3+ and one Fe2+ doublets. Hydrating cement pastes display a third doublet of tetrahedral iron indicating ettringite–monosulfate transformation. With silica fume and fly ashes addition the tetrahedral iron doublet forms earlier. With hydration the tetrahedral iron increases at the expense of octahedral iron. During hydration of plain cement portlandite and hydration products form below 450 °С. Silica fume and fly ashes react with portlandite and form products decomposing above 620–640 °С.

▸ Hydration of cement with silica fume and fly ash additions is studied with Mössbauer, DTA and XRD methods. ▸ Two octahedral Fe3+ positions with close isomeric displacements and quadrupole splittings were proved for plain cement. ▸ In cements with silica fume iron is registered by Mössbauer spectroscopy as two Fe3+ doublets and one Fe2+ doublet. ▸ Hydrating cement pastes display a third doublet revealing tetrahedral iron indicating ettringite–monosulfate transformation. ▸ Silica fume displays highest pozzolanic activity.