Surface and Colloidal Properties of Silica Fumes in Aqueous Medium

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Title: Surface and Colloidal Properties of Silica Fumes in Aqueous Medium

Author(s): Q. Chu, S. Bonnamy, and H. Van Damme

Publication: Special Publication

Volume: 153

Issue:

Appears on pages(s): 719-740

Keywords: bleeding (concrete); particle size distribution; silica fume; Materials Research

Date: 6/1/1995

Abstract:
To better understand the behavior of silica fumes (SF) in fresh mortar and concrete, four French silica fumes, with different chemical and textural properties, were characterized with respect to their surface properties and their behavior in aqueous dispersion. Zeta potential measurements were performed as a function of pH and ionic strength. Below about pH=4, all materials behave similarly, whereas at higher pH, the electrochemical potential was found to be related to the Ca content. In suspension, the decrease of the average particle size (bimodal distribution) is directly related to the power input (ultrasonic treatment) and to the intragranular compactness, mass-fractal dimension, and densification treatment. With Ca-rich SF, sedimentation volumes and velocities were found to increase as dispersion proceeds, which suggests that the elementary sub-micrometric silica spheres re- agglomerate after the dispersion treatment, probably due to bridging by calcium silicate hydrates.