In Situ Characterization of Mixture of Fly Ash and Fluidized Gas Desulfurization By-Product at Tennessee Valley Authority’s Gallatin Ash Stacking Facility†

This article presents the results of field and laboratory testing performed on a new coal combustion product (CCP) derived from a mixture of fly ash and dry fluidized gas desulfurization by-product at the Tennessee Valley Authority’s Gallatin Fossil Plant in Gallatin, TN. Field testing included geospatial mapping using a vibratory smooth drum roller instrumented with a validated intelligent compaction (VIC) system and by field testing to characterize elastic modulus, shallow shear wave velocity, moisture content, dry density, and shear strength properties. Field testing was performed in areas where the CCP had been placed several days before testing and in areas with freshly placed material. In situ tests were conducted to capture a wide range of material and support conditions to calibrate the VIC measurements. Overall, in situ testing revealed high strength and stiffness values, but with a high degree of spatial variability. In some areas, the in situ dry density measurements showed low relative compaction values relative to standard Proctor compaction maximum dry unit weight. Laboratory compaction tests conducted by preparing 2-in.-diameter by 2-in.-high specimens showed that the moisture content, compaction effort, and compaction delay time affect the achieved dry density. Laboratory unconfined compressive strength increased from about 450 psi after 8 days to about 2500+ psi after 6 months. Microanalysis tests were used to identify mineral phases in the CCP. Recommendations based on the laboratory and field test results for future process control operations are provided in this article.