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Chapter 1 - Understanding Silica Fume
Silica Fume Reactions

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Slide
Socket where a sand grain has been pulled away from cement paste in 28-day old mortar containing silica fume. The sand grain was originally at the top of the picture. Note the dense structure without the gaps and crystals seen in the previous photo. "When 15% CSF by weight of cement is added to the mortar, the microstructure of the interfacial zone is significantly changed. Its structure is homogeneous and dense without the presence of a massive CH rim or gaps. These changes can be the result of the suppression of bleeding in the fresh mortar and the ability of the CSF particles to fill the space in the vicinity of the sand grain surface much more efficiently than the bigger cement particles." "The effect of CSF on densifying and homogenizing the microstructure of the interfacial zone may have a considerable influence on the performance of mortars and concretes. Therefore, when the effect of CSF on mortars and concretes is being considered, the interfacial effects should be taken into account in addition to the influence of the CSF on the bulk paste matrix." Arnon Bentur and M. D. Cohen, "Effect of Condensed Silica Fume on the Microstructure of the Interfacial Zone in Portland Cement Mortars," Journal of the American Ceramic Society, Vol. 70, No. 10, pp. 738-743, 1987.