Building Highway Embankments of Fly/Bottom Ash Mixtures

摘要

This research investigates the engineering properties of mixtures of bottom ashand Class F fly ash relevant to their utilization in highway embankment construction. The research included ash samples from two major power plants in Indiana that disposed of their ash differently. The first power plant disposes of the bottom ash and fly ash separately and hence explicit mixtures were synthetically formed and tested. The second power plant disposes of the bottom and fly ash together in a common location and hence they become mixed, forming implicit mixtures. The implicit mixtures were processed using a wet method, the Shallow Slurry Deposition Method, to produce homogeneous samples for the research. Characterization of the ash included grain size analysis, specific gravity, maximum and minimum density, in addition to microscopic investigation. The investigation of compaction behavior of a range of explicit and implicit mixtures was conducted at the standard energy effort. The effects of changing in the mixture composition on the maximum dry unit weight and optimum moisture content were established. In order to study the effect of changing the moisture content on penetration resistance, surface penetration tests were performed on the compacted samples. Beyond the optimum moisture content on penetration resistance of the samples drops significantly, which suggests that the compaction can better be conducted dry of optimum. To control the compaction appropriately, the degree of compaction of a sample must be determined using a compaction curve for a mixture of similar gradation. Consolidated drained triaxial tests were performed on a range of explicit and implicit mixtures as three levels of confining pressures. For each mixture tested, two groups of samples were prepared, one at a relative compaction (R%) of 90% and the other at 95%. The results indicate that the drained shear strength depends on the mixture composition, the degree of compaction, and the confining pressure. Adequate shear strength and volumetric behavior was observed for the samples compacted at 95%. It was concluded that the shear strength of the ash mixtures is comparable to the shear strength of sandy soils. Discussion and recommendations regarding the stability of slopes of ash mixtures is included. Using the critical state angles is more feasible in the slope stability analysis in the case of embankments of implicit mixtures due to mixture variability.