Properties of coal ash mixtures and their use in highway embankments
Abstract
Class F fly ash and bottom ash are the solid residue by-products produced by coal-burning electric utilities. They are usually disposed of together as a waste in utility disposal sites with a typical disposal rate of 80% fly ash and 20% bottom ash. The fly and bottom ash accumulated daily in disposal areas have been a significant concern to utility companies, and is fast becoming a social problem. Direct use of these materials in construction projects consuming large volumes of materials, such as highway embankment construction, not only provides a promising solution to the disposal problem, but also an economic alternative to the use of conventional materials. The objective of this study was to evaluate the suitability of class F fly/bottom ash mixtures with high fly ash contents as construction materials for highway embankments. For this purpose, representative samples of class F fly and bottom ash were collected from three utility power plants in Indiana and extensively tested in the laboratory. The testing program included ash characterizations and evaluations of mechanical properties (compaction, permeability, strength, stiffness, compressibility, and collapsibility) and corrosivity of ash mixtures. For the ash samples from each power plant, three mixtures with different mixture ratios (i.e. 50%, 75%, and 100% fly ash content) were formed for testing. The mechanical evaluation focused on the effects of mixture ratio, compaction level, compaction water content, and inundation on the behavior of ash mixtures. The corrosivity of ash mixtures was evaluated by investigating two corrosion parameters: electrical resistivity and pH. The test results were compared with those of representative granular materials and appropriate existing specifications. Based on this laboratory investigation, it is concluded that ash mixtures with high fly ash contents are compared favorably to conventional granular materials, but potentially corrosive. Simple slope stability analyses were performed to investigate stability of ash embankments and determine stable embankment geometries by using the properties of ash mixtures found in laboratory. Three types of considerations (environmental, design, and construction) of interest for highway embankment applications of coal fly/bottom ash mixtures were addressed in the final chapter based on the results of the testing program and the slope stability analyses.
Degree
Ph.D.
Advisors
Salgado, Purdue University.
Subject Area
Civil engineering
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