Effects of Powder Additive on High-Volume Fly Ash Mixtures


Mitigation of problems in high-volume fly ash (HVFA) paste mixtures was explored using powder additives. Class C fly ash substitution levels of 25, 50, and 70% were examined at two levels of water reducer, gypsum, lime, and rapid-set cement (RSC) each. Compressive strength at 1, 3, 7, 28, and 56 days; semi-adiabatic calorimetry; Vicat setting time; and miniature slump were used for evaluation. Lime, RSC, or gypsum by themselves were not helpful in significantly improving early strengths. However, gypsum-lime was in some cases effective, but lowered later strength. Gypsum-RSC improved strengths at all ages. Gypsum by itself helped restore (retard) the fly ash-accelerated HVFA calorimeter curve positions, as did gypsum-RSC and gypsum-lime. Early stiffening tendencies were alleviated by gypsum and gypsum-lime, but made worse by gypsum-RSC. Diagnostic plots of semi-adiabatic peak heights, curve positions, and early stiffening were developed to aid in prediction of mixture combination behavior.


Civil, Architectural and Environmental Engineering

Keywords and Phrases

Additives; C (programming language); Calorimeters; Calorimetry; Compressive strength; Concrete beams and girders; Fly ash; Lime; Mixtures; Adiabatic calorimetry; Class C fly ashes; Early strength; High volume fly ash; Peak height; Rapid set; Setting time; Water reducers; Gypsum; High-volume fly ash; Mixture incompatibilities; Semi-adiabatic calorimetry

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Article - Journal

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© 2015 American Concrete Institute (ACI), All rights reserved.

Publication Date

01 Jul 2015