The Influence of Silica Fume on the Strength of the Cement-Aggregate Bond

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Title: The Influence of Silica Fume on the Strength of the Cement-Aggregate Bond

Author(s): C. Perry and J. E. Gillott

Publication: Special Publication

Volume: 156

Issue:

Appears on pages(s): 191-212

Keywords: aggregates; alkali-aggregate reactions; bonding; silica fume; carbonate aggregates; cements; flexural strength; siliceous aggregates; strength; Materials Research

Date: 9/1/1995

Abstract:
Describes a small scale flexure test for the determination of cement- aggregate bond strength. Cylindrical test specimens were prepared by drilling cores in a perpendicular direction through slabs of rock against which mortar had been cast. A special casting procedure eliminated many sources of experimental variation and allowed the bond strengths of different mortars and rock types to be compared directly. Long term tests were conducted by coring the mortar/aggregate slabs at a number of curing times and coefficients of variation of 5 to 10 percent for bond and mortar strengths were obtained. The effect on cement-aggregate bond strength of partial cement replacement by silica fume was evaluated for a number of aggregate types. For siliceous aggregates (glass, obsidian, and quartzite), bond strength was increased significantly by the addition of silica fume; failure tended to occur away from the interface particularly in long term tests. For carbonate rocks (limestone and dolostone), similar bond strengths were obtained at seven days with and without the addition of silica fume. At later ages, silica fume interfered with strengthening of the cement-carbonate rock interface and lower bond strengths were obtained. For specimens not containing silica fume, bond strength increased more rapidly to glass and obsidian than to quartzite, which showed essentially "inert" behavior. This was tentatively attributed to strengthening of the transition zone by a pozzolanic mechanism involving reactive silica from the aggregate. A marked reduction in bond strength occurred with glass specimens containing boosted alkali content. This was attributed to alkali- silica reaction at the interface and was suppressed by the addition of 15 percent silica fume.