Class F Fly-Ash-Amended Soils as Highway Base Materials

Abstract

Class F fly ash cannot be used alone in soil stabilization applications as it is not self-cementing. An activator such as Portland cement or lime must be added to produce cementitious products often called pozzolan stabilized mixtures. The developed mixture must possess adequate strength and durability, should be easily compacted, and should be environmentally friendly. Roadways have a high potential for large volume use of the fly ash stabilized soils. The main objective of this study is to investigate the use of Class F fly ash amended soil–cement or soil–lime as base layers in highways. A battery of tests were performed on soil–fly ash mixtures prepared with cement and lime as activators. Unconfined compression, California bearing ratio, and resilient modulus tests were conducted. Finally, required base thicknesses were calculated using the laboratory-based strength parameters. Results of the study show that the strength of a mixture is highly dependent on the curing period, compactive energy, cement content, and water content at compaction. Lime treatment does not provide sufficient strength for designing the mixtures as highway bases. Freeze–thaw cycles do not have any detrimental effect on cement-treated mixtures. A power function in terms of bulk stress used for granular soils can accurately model the resilient moduli. Most of the factors considered have an impact on the thickness of the base layer.