The paste aggregates showed no
evidence of deterioration and the bond was still strong. There was no evidence of
leaching of cement components and the permeability was still very low. Hydrated DSP
cement pastes containing < 64 weight % silica fumes that reacted at < 120 o
C were
studied using X-ray diffraction, Si-29 solid state nmr spectroscopy and TGA [Suu et al.,
1991]. The amounts of Ca(OH)2, unreacted silica fume and residual cement were
determined. The silica fume appeared to participate in an incipient pozzolanic reaction
without reducing the content of Ca(OH)2. The combined effect of polymer and super
plasticizer, using acrylic based polymers and naphthalene formaldehyde condensates
(superplasticizer) on cement mortar-containing silica fumes were studied [Xu et al.,
1990]. Condensed silica fume works as an antifoaming agent in the case of polymers
having air-entraining properties. Properties like setting time, water absorption, freezing
thaw resistance and dynamic Young modules were measured. Experimental and
simulation studies of the interfacial zone in concrete were carried out by making direct
comparison between results obtained using a 3 dimensional microstructural model and
those obtained experimentally on a similar set of mixes containing various amounts of
silica fumes [Bentz et al., 1992]. Based on this model and experimental results it is
suggested that the presence of silica fumes produces a more homogeneous
microstructure by balancing the Ca/Si molar ratio in the interfacial zone relative to that
in the bulk paste. Unlike in the ordinary Portland cement concrete, where this ratio
increases dramatically as the aggregate surface is approached. A comparative study of
various silica fumes as additives has been carried out by testing twenty silica fumes in
presence of two cement superplasticizers [DeLarrad et al., 1992]. It was possible to