The hydration of two calcium hydroxide - silica fume mixtures was stud
ied at 25-degrees-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 che
mically combined water contents were determined at various time of hyd
ration from which the molar CaO/SiO2 ratioS Of the formed calcium sili
cate hydrate, C-S-H, were calculated. The results indicated that hydra
tion takes place in six steps where C-S-H (I) is formed at early stage
s 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 differenti
al thermal analysis.