Ultra Fine Admixtures in High Strength Pastes and Mortars

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Title: Ultra Fine Admixtures in High Strength Pastes and Mortars

Author(s): A. Charles-Gibergues, J. P. Olliver, and B. Hanna

Publication: Special Publication

Volume: 114

Issue:

Appears on pages(s): 1101-1116

Keywords: admixtures; calorimeters; carbon; compressive strength; fineness; high-strength concretes; hydration; mortars (material); plasticizers; silica fume; specific surface; x-ray diffraction; Materials Research

Date: 5/1/1989

Abstract:
Purpose was to throw light on the behavior of ultra-fine admixtures introduced with superplasticizer in high-strength concretes as partial portland cement replacement. Paper describes results from different pastes and mortars prepared with normal portland cement including 10 percent silica fume or alumina powder as replacement for cement. Conclusions are as follow. 1) Water demand is modified only by CSF. When associated with superplasticizer, all admixtures lower the water demand. No relationship was found between fineness and water-reducing effect. 2) Superplasticizer acts as a set-retarder and the admixtures as accelerators, but they cannot compensate for the superplasticizer's retardation except for one of the silica fumes used. 3) Two silica fumes showed an important pozzolanic effect; another silica fume and the alumina powder were inert. 4) All admixtures in the presence of superplasticizer increase the compressive strength of mortars. This is due not to the pozzolanic reaction, but is explained by the lowering of w/c.