In Situ Characterization of Lime-Treated Fly Ash at TVA’s Gallatin Ash Stacking Facility

摘要

This paper presents results of field and laboratory testing performed on the ash stack at TVA’s Gallatin Fossil Plant in Gallatin,Tennessee.Field testing included geospatial mapping using a vibratory smooth drum roller instrumented with Validated Integrated Compaction Monitoring(VICM)system and conducting field testing to characterize elastic modulus,shallow shear wave velocity,moisture content,dry density,and shear strength properties.Field testing was performed in the areas where lime-treated fly ash material was being placed in the stacking area,which consisted of sub areas with material that was freshly placed to material placed several days prior to testing.The fly ash material consisted of a mixture of fly ash,gypsum,and hydrated lime.In situ tests were conducted to capture a wide range of material and support conditions to calibrate the VICM measurements.Results showed relatively high strengths and stiffness values,and high degree of variability.In situ dry density measurements showed relatively low relative compaction values.Laboratory compaction study conducted by preparing 2 in.diameter by 2 in.height specimens showed that the batching moisture content,compaction effort,and the compaction delay time can significantly affect the achieved dry density.Unconfined compressive(UC)strength tests were conducted on specimens cured for 8,28,90,and 204 days.Results showed that UC strength increased from about 450 psi after 8 days to about 2,500+ psi after 200 days.Micro analysis tests on the material showed formation of ettringite mineral up on wetting.Ettringite minerals can contribute to strength loss and volume expansion due to wetting.Recommendations based on the laboratory and field testing results for future process control operations using the lime-treated fly ash material are provided in this paper.