The hydration of two calcium hydroxide— silica fume mixtures was studied at 25°C, these are Mix I and Mix II with molar lime/silica
ratios of 1 and 1.7, respectively. The free lime, free silica and chemically combined water contents were determined at various
time of hydration from which the molar CaO/SiO2 ratios of the formed calcium silicate hydrate, C−S−H, were calculated. The results indicated that hydration takes place in
six steps where C−S−H (I) is formed at early stages of hydration, for Mix I, While for Mix II formation of C−S−H (I) and C−S−H
(II) were detected by X-ray diffraction analysis and differential thermal analysis.