Use of Fly Ash in Concrete by State Transportation and Highway Departments

About the report:

This report provides a summary of replies to a questionnaire on the use of fly ash and blended cement (Type IP) in concrete. The questionnaire was directed to members of the Subcommittee on Materials of the American Association of State Highway Officials. The states' representatives on this subcommittee are usually the state materials engineers. The subcommittee also includes associate members from some of the provinces of Canada and some federal agencies involved in roadway or airport construction. Fifty-nine agencies responded to the questionnaire. These included all of the state highway and transportation departments, the District of Columbia, three provinces of Canada, and five federal agencies. Twenty-four agencies reported that they made no use of either fly ash added to the concrete as an admixture (FAC) or of concrete made with Type IP blended cement (IPC). The remaining 35 agencies permitted the use of either IPC or FAC, or both, usually at the option of the contractor. However, only 4 states had placed more than 100 lane-miles of FAC, and only two states had placed more than 100 lane-miles of IPC. This lack of large usage of FAC or IPC is believed to reflect a lack of significant economic incentives for use by a state or contractor under present circumstances. The initial capital investment for the required separate silos or storage bins for fly ash deters a small contractor from using FAC, as does the increased quality control testing. IPC is not attractive since the blended cement (Type IP) usually costs the same as regular portland cement. Accordingly, the more familiar product (regular portland cement) is selected for use when both types are available. The states making substantial use of either of FAC of IPC all report satisfactory performance. The primary control problem reported is that of assuring the proper amount of entrained air. When fly ash is used, more air-entraining agent is required to entrain the desired amount of air than is required for similar concrete without fly ash. Prior approval of the source of the fly ash is required by almost all agencies. The specification most often cited by all agencies is ASTM Specification C618 Class F (fly ash). However, in all cases the loss on ignition is limited to a maximum of 6.0% in lieu of the 12.0% limit given in C618. Some state specifications also differ from C618 in the limitations on chemical composition but it is likely that all materials being used would meet C618 requirements, except where fly ash high in calcium oxide is encountered.

Authors