Stabilization of Subgrade Soils Using Fly Ash

摘要

The subgrade soils in the Bryan District of TxDOT are currently stabilized with quick lime. With the availability of large quantities of fly ash close to the district, the focus of this study was to evaluate the use of fly ash as an alternative stabilizer. Two frequently encountered subgrade soils: a poorly graded sand (AASHTO A-3/USCS SP) and a plastic clay (PI 28 %, AASHTO A-7-6/USCS CL), and two fly ash types : ASTM Class C and Class F were included in the study. The soils were stabilized with varying percentages of fly ash and lime-fly ash admixtures and lime stabilized and unstabilized samples were included for comparison. Laboratory tests indicated.that the addition of fly ash and lime-fly ash admixtures, to the poorly graded sand resulted in : an increase in the maximum dry density (MDD), a decrease in the optimum moisture content (OMC), and an increase in the unconfined compressive strength (UCS). The addition of fly ash and lime-fly ash admixtures to the plastic clay resulted in : a decrease in the plasticity index (PI) and hence an increase in the workability, a decrease in the MDD, an increase in the OMC, an increase in the UCS, and a decrease in the % swell. The results of the laboratory tests will be used in an experimental full-scale pavement section to be constructed entirely with coal combustion by-products.