Use of Condensed Silica Fume as Filler in Blended Cements

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Title: Use of Condensed Silica Fume as Filler in Blended Cements

Author(s): M. Regourd, B. Mortureux, and H. Hornain

Publication: Special Publication

Volume: 79

Issue:

Appears on pages(s): 847-866

Keywords: blended cements; bond (paste to aggregate); compressive strength; C-S-H; electron microscopes; fly ash; microstructure; mortars (material); pozzolans; silica; slags.

Date: 5/1/1983

Abstract:
At early ages, blended cement mortars with 30 % hydraulic slags or active pozzolans have lower mechanical strengths than mortars incorporating 100 % Portland cement. The action of 5 % condensed silica fume replacement for slag or pozzolan or material considered as inert has been studied from 7 days to 3 months by measuring the mechanical strengths of mortars made according to IS0 test method and by observing the microstructure of fractured samples. This action of the condensed silica fume is a function of the nature of the additive. With hydraulic slags, there is a competition between slag and silica fume for the available lime. With slightly or slowly reactive pozzolans (volcanic rock, fly ash) mechanical strengths and microporosity of mortars show improve-ment at 28 days. With inert materials (crystalline slag or quartz), the improvement is more marked. This is due to the formation of dense C-S-H, strong cement paste-aggregate bond and 20 % increase in mechanical strengths.