United States Department of Transportation
i
Evaluation of fly ash as an admixture in Portland cement concrete.
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1984-07-01
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[PDF-2.11 MB]
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Abstract:The investigation of fly ash as an admixture in Portland cement concrete (PCC) was divided into two phases. Phase I consisted of an experimental program while phase II involved an evaluation of fly ash concrete based on research reported by other agencies.
Data obtained in the experimental program provide evidence that both Class F and Class C fly ash can be used to manufacture concrete of comparable strength as that produced from conventional materials. In some cases fly ash concrete showed higher compressive strengths at both high and low cement factors depending on the fly ash source and its replacement ratio. The variable properties and characteristics often associated with fly ash and fly ash sources on the compressive strength of concrete cylinders were verified. Fly ash showed little effect on promoting expansion due to the alkali aggregate reaction, when used with a high alkali cement. The alkali content of fly ash may be more significant when used with a low alkali cement.
Research conducted by a wide variety of agencies lead to the conclusion that the addition of fly ash to PCC may cause a reduction in the water requirements of the mix, increased workability, reduced heat of hydration, increased time of set, reduced permeability, and lower early strength. Although much is still unclear concerning the effect of fly ash on the air void system and freeze thaw durability of concrete, some research has indicated that fly ash may actually improve durability, depending on fly ash type and replacement ratio.
Recommendations have been developed in this report for specifications, mix deigns procedures, and testing of fly ash. Fly ash should conform to ASTM C618 except for the modifications as listed in this report.
It is recommended that fly ash not be allowed in bridge decks, PCC pavements, or in prestressed concrete at this time. Further study should be undertaken to determine the feasibility of using fly ash in this manner. Except for seals, fly ash for use in substructure work, walks, curbs, barriers, other noncritical structures, and cement treated base (CTB) should be considered as a substitute for Portland cement for a minimum of 10% to a maximum of 20% by weight of Portland cement.
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