Mِssbauer, 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.