Investigation into a field site where cementitious fly ashes (Class C and off-specification) were used to stabilize road-surface gravel (RSG) to form a base during construction of a flexible pavement in Chisago County, MN. The project involved conversion of a gravel road to a paved road. It consisted of mixing fly ash (10% by dry weight) and water into the gravel surface to a depth of 254 mm and compacting the mixture to form a firm base, and placement of an HMA surface. California bearing ratio (CBR), resilient modulus (Mr), and unconfined compression (qu) tests were conducted on a composite sample of the RSG alone and the fly-ash stabilized RSG (S-RSG) samples prepared in the field and laboratory to evaluate how addition of fly ash improved the strength and stiffness. In situ testing was also conducted on the subgrade and S-RSG with a soil stiffness gauge (SSG), dynamic cone penetrometer (DCP), and falling weight deflectometer (FWD). A pan lysimeter was installed beneath the roadway to monitor the quantity of water percolating from the pavement and the concentration of trace elements in the leachate. Column leach tests were conducted in the laboratory for comparison.
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