High Volume Fly Ash Concrete for Highway Pavements

Abstract

This paper encompasses the evaluation and research of high-volume fly ash (HVFA) concrete. The primary objective of this study was to examine increased levels of cement replacement with Class F fly ash for concrete used in Colorado highways. Fly ash is a byproduct of the combustion of pulverized coal in electric power generating plants. The benefits of using fly ash in concrete include increased compressive strength and durability, and reduced sulfate attack, shrinkage, and cost. Four HVFA concrete mixtures with 50%, 60%, 70%, and 80% Class F fly ash were designed and tested for compressive and tensile strength and permeability. Compressive strength tests were conducted at 3, 7, 28, and 56 days of age. The permeability and tensile strength of the mixtures were measured at 28 and 56 days of age. The Colorado Department of Transportation (CDOT) Class P mixture was used as the base mixture for this study. This class of concrete is specific for concrete pavements used for Colorado streets and highways. Required field compressive strength of Class P concrete is 29 MPa (4200 psi) at 28 days; a minimum cementitious content of 392kg/m3 (660 lbs/cy); air content ranges between 4-8% and a maximum water/cementitious material ratio of 0.44 is specified by the CDOT. The results of this study provide sufficient evidence that increased amounts of fly ash (above typical limits) can be incorporated into concrete mixtures for streets and highways.