Utilization of Flue Gas Desulfurization (FGD) gypsum and coal ashes in road construction

Vita.In the past few decades, America's demand for energy has increased, and in equivalent proportions, so has the quantity of by-products from coal fired electric power plants. These by-products include calcium sulfate and sulfites, fly ash, and bottom ash. Calcium sulfate dehydrate (gypsum) is produced by a Flue Gas Desulfurization (FGD) scrubbing system that uses a limestone slurry to react with federally regulated sulfur gas emissions. Fly ash is the light airborne particles of coal ash while the bottom ash is the heavy remains of the burned coal in the boiler. Stockpiles are growing and landfills are being burdened by these materials while researchers look for large-volume uses in such industries as road and building construction. Projected disposal estimates of these stockpiles will reach 600 million tons in the next 40 years. This study evaluates the high volume use of these materials in road construction as an alternative to a landfill or stockpiling. Laboratory testing analyzed the by-products for engineering value and used American Standards of Testing Materials (ASTM) methods to provide an acceptable mix design that meets Texas Department of Transportation (TEXDOT) criteria. A field demonstration followed using the by-products in an experimental road base to establish their in-service road performance during a 32 month post construction period. Field tests involved visual inspections, Falling Weight Deflectometer (FAD) testing, Multi-Depth Deflectometer (MDD) testing, and on-site environmental impact study of leachates in surface and groundwater. This research provides conclusive evidence that these by-products, when stabilized with cement, can be incorporated into TEX DOT road systems as an alternative to conventional road aggregates. It is also shown that these materials, when property implemented, will equal and often exceed TEX DOT specifications and can be built with conventional construction equipment. Post construction evaluation results were statistically analyzed and reflect that, after 32 months in-service, the experimental road is still gaining strength with little or no signs of incipient failure. Environmental impact studies on and in the vicinity of this test section reveal that neither leachates nor ground water pose any environmental impact to drinking water or the environment