Effectiveness of Various Silica Fumes in Preventing Alkali-Silica Expansion


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Title: Effectiveness of Various Silica Fumes in Preventing Alkali-Silica Expansion

Author(s): Mitsunori Kawamura, Kunio Takemoto, and Shigemasa Hasaba

Publication: Special Publication

Volume: 100


Appears on pages(s): 1809-1820

Keywords: alkali-aggregate reactions; calcium hydroxide; chemical analysis; expansion; mortars (material); pozzolans; silica; tests; Materials Research

Date: 4/1/1987

To use silica fume as a pozzolanic material for inhibiting alkali-silica expansion, the effects of various silica fumes on expansion of mortars containing Beltane opal were investigated. Different silica fumes were found to vary widely in their effect on the expansion of mortars. The properties of silica fume affecting alkali-silica expansion were explored. Pozzolanic activity of silica fumes was evaluated by measuring the amounts of calcium hydroxide consumed by pozzolanic reaction in silica fume-bearing cement pastes. The amounts of calcium hydroxide in portland cement-silica fume mixtures were determined by DSC-TG analysis. Pore solutions obtained from mortars containing three different silica fumes were also analyzed. The silica fume with the highest pozzolanic activity was the most effective in reducing alkali-silica expansion of mortars. However, it was found that reduction in expansion by the addition of silica fume was not necessarily in line with the amount of calcium hydroxide consumed as a whole. Although the concentrations of alkalis and OH- ions in the pore solutions in mortars were reduced to the same level by the addition of three different silica fumes, the reductions in expansions of the three silica fume-bearing mortars were greatly different from one another.