Strength Development of Ternary Blended Cement with High-Calcium Fly Ash and Amorphous Silica

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Title: Strength Development of Ternary Blended Cement with High-Calcium Fly Ash and Amorphous Silica

Author(s): S. Antiohos, D. Giakoumelos, and S. Tsimas

Publication: Special Publication

Volume: 221

Issue:

Appears on pages(s): 153-168

Keywords: amorphous; blended cement; high-calcium fly ash; silica; ternary blend

Date: 5/1/2004

Abstract:
The work presented herein is a laboratory study on the mechanical properties of ternary blended cement built with various combinations of two different high calcium (ASTM Class C) fly ashes and an amorphous silica. A commercial amorphous silica agent of great specific surface was added in binary fly ash-cement (FC) systems in order to compensate for the certain shortfalls associated with the presence of high lime ashes in cementitious blends and furthermore to provide a benchmark for utilizing supplementary cementing materials rich in active silica (such as silica fume, metakaolin and rice husk ash) in resembling ternary systems. For the purpose of this study, both fly ashes were substituted by 5, 10 and 20% amorphous silica and the new blends replaced 20 and 30% of cement. The generated ternary blends were examined in terms of compressive strength development, efficiency factors (k-values) and strength gain. It was found that in the case of 20% cement replacement, up to 10% amorphous silica addition accelerated the strength development of all blends. For higher cement replacement (30%), 5% amorphous silica introduction was the optimum percentage for the blends incorporating high-calcium ashes. Amorphous silica acts immediately after inclusion in the mixture, improving the early strength of all binary systems, while in the later stages of the hardening process, the behavior of all mixtures is highly depended on the active silica content of the ashes they incorporate.