Keywords and Phrases
Concrete; Durability; Fly Ash; Hardened Properties; Plastic Properties
This study was performed to examine the effects of high volumes of Class C fly ash modified by powder activators upon the plastic and hardened properties of concrete. In a companion study, five Missouri area cements and five Class C fly ashes were examined for incompatibilities, with the most and least reactive combinations being scaled up to full scale concrete testing. Two baseline concrete mixtures were examined, the only difference in mixtures being the sources of portland cement and fly ash. Fly ash replacement was examined at 50% and 70% replacement (by total cementitious mass). Three powder activators were used in combination with the cement and fly ash mixtures: 4% gypsum, 10% hydrated lime, and 20% rapid set cement (by mass of fly ash). Gypsum was present in all concrete mixes, with either hydrated lime or rapid set cement acting as an activator in combination with it. Both plastic concrete and hardened concrete properties were examined. The use of powdered activators in combination with fly ash resulted in the concrete exhibiting adequate 28 day strength, stiffer moduli, less drying shrinkage, lower chloride permeability, and improved resistance to freezing and thawing at 50% fly ash replacement when compared to a baseline mix, although the mixture suffered in abrasion resistance and salt scaling resistance. At 70% fly ash replacement, the mixtures performed poorly compared to their baseline counterparts, even with the addition of rapid set cement. The choice of activator primarily affected the early age strength and setting time, with rapid set cement mixtures exhibiting a quicker set and a higher earlier strength than the hydrated lime mixtures, though this did not correspond to improved characteristics in the long term. In applications where early properties are not important, the use of less expensive calcium hydroxide is recommended. In any applications, however, the specific cement and fly ash sources should be examined for possible incompatibilities.
Richardson, David Newton
Volz, Jeffery S.
Civil, Architectural and Environmental Engineering
M.S. in Civil Engineering
Missouri University of Science and Technology
xiv, 146 pages
© 2012 Drew Alexander Davis, All rights reserved.
Thesis - Open Access
Concrete -- Additives
Reinforced concrete -- Testing
Electronic OCLC #
Davis, Drew Alexander, "Effects of high volume fly ash and powder activators on plastic and hardened concrete properties" (2012). Masters Theses. 5330.