Laboratory Study for Comparison of Class C Versus Class F Fly Ash for Concrete Pavement


PI: Lawrence Sutter

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The two objectives of this research were to a) evaluate Class F and Class C fly ash sources for use in paving concrete and b) determine acceptable proportions of each ash type to use in paving mixtures. A combined study was performed involving characterization with respect to AEA adsorption using the foam index test, direct measurement of adsorption, and the iodine number test and a partial factorial experiment was conducted to evaluate concrete mixtures prepared using different fly ash, cement, and aggregate sources. The adsorption testing highlighted known inconsistencies of loss on ignition measurements. Freeze-thaw testing in 4% CaCl2 solutions indicated no statistical difference in performance with or without fly ash but fly ash type was a significant factor in mixtures that failed freeze-thaw testing. Compressive and flexural strength followed the classical behavior expected of fly ash mixtures. Maturity showed the largest impact of fly ash addition. Overall the Class F and Class C ash sources performed well and using either at substitution levels up to 30% is recommended. Additional scrutiny of some Class F sources, with respect to freeze-thaw performance, is warranted. Use at higher levels should be done only after performance testing of the specific combination of materials to be used at the job-mix proportions.

A copy of this report can be found on the Wisconsin Department of Transportation website.

Lawrence Sutter
Lawrence Sutter