The Kentucky Transportation Research Program has completed a laboratory study involving the use of flue gas desulfurization sludge (scrubber sludge) for potential application as a highway subbase and/or embankment material. Scrubber sludge is a waste produet formed when fly ash (and other residue) is combined with a lime dust slurry filter cake and stabilized with quicklime (calcium oxide). Samples of stockpiled (field) sludge and dry sludge components were obtained from the Robert Reid Station (Big Rivers Electric Corporation) in Sebree, Kentuclty. Dry sludge components (fly ash, filter cake, and quicklime) were uaed to prepare sludge samples in the laboratory, allowing a higher degree of quality control for compariaon purposes. Mixtures for testing included scrubber sludge, scrubber sludge with pond ash (bottom ash), and scrubber sludge with dense graded limestone aggregate (DGA). One objective of laboratory analyses was the determination of optimum mixture proportions. A mixture of 20-percent scrubber sludge and 80-percent pond ash was determined to be the optimum design mix. That mixture showed significant strength gain with curing and had a static-chord modulus of elasticity approximately 118 times the compressive strength. Strength and modulus tests indicated that mixtures of scrubber sludge and pond ash were superior to mixtures of scrubber sludge and DGA. The scope of the study, however, did not permit complete explanation of these observations. An economic study showed that scrubber sludge with pond ash can be used economically as a highway subbase material, especially on low-fatigue roads, by partially replacing more expensive pavement layers. Triaxial tests and computer simulations indicated that scrubber sludge could be used as an embankment material in some applications. However, this would be economical only if suitable fill material was not available at or near the fill site.

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The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Kentucky Transportation Cabinet nor of the University of Kentucky. This report does not constitute a standard, specification, or regulation.