United States Department of Transportation
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Alternative Title:Fly ash in concrete.
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Abstract:This study was initiated to develop information regarding the use of fly ash in portland cement concrete for state construction projects.
Concrete mixes containing 10%, 20%, 30%, 40% and 60% fly ash were evaluated in the laboratory in combination with various cement contents. Type C fly ash was selected from three local sources which had been approved by the department for concrete mixes. Also, specifications were developed for using fly ash in a paving project.
In general, fly ash when used at replacement below 40% by weight of cement was found to be satisfactory in concrete. In areas that the maximum possible strength loss cannot exceed 10% of control, replacement rate of less than 25% is recommended. Increasing amounts of fly ash caused a reduction in compressive strength, especially when air-entraining agents were used or when the concrete was less than 28 days old. Retardation in the set times was also noticed with increasing amounts of fly ash. However, strength gains of up to 10% were noticed in some mixes after extended curing periods. There were no adverse effects observed on the plastic properties, freeze and thaw durability, modulus of elasticity, length change, abrasion resistance, or absorption characteristics of fly ash concrete at the replacement rates evaluated.
Based on the overall results of this study, no changes are recommended to the current fly ash concrete specifications developed earlier in this project.
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