Abstract
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.
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