The Use of Condensed Silica Fume in Grouts


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Title: The Use of Condensed Silica Fume in Grouts

Author(s): Pierre-Claude Aitcin, G. Ballivy, and R. Parizeau

Publication: Special Publication

Volume: 83


Appears on pages(s): 1-18

Keywords: bleeding (concrete); compressive strength; grout; plasticizers; porosity; pozzolans; shrinkage; silica; thixotropy viscosity; water-cement ratio.

Date: 10/1/1984

Condensed silica fume is a by-product of the fabrication of silicon or ferrosilicon alloys. It is composed of very fine glassy spheres of quite pure silica having an average diameter of 0.1 pm. It is a very reactive pozzolan that has been found to increase drastically the compressive strength of concrete and to reduce significantly its permeability. The unique properties of condensed silica fume can also be used advantageously in grouts if condensed silica fume is used in combina-tion with a superplasticizer. The very fine silica particles give stability to the grout, there is no sedimentation of the cement particles and no bleeding. By adjusting the respective proportions of portland cement, of condensed silica fume,and of the superplasticizer a thixotropic grout can be made. The hardened grout is stronger and less porous when it contains condensed silica fume because the lime liberated during the hydration of portland cement reacts with the very fine silica particles to form a compact secondary CSH. By this way the possibility of leaching out of the lime is practically suppressed and the resistance of the grout to chemical attack should be improved.