Determination of Ash Mixture Properties and Construction of Test Embankment - Part A

Class F fly ash and bottom ash are solid residue byproducts produced by coal-burning plants. They are usually disposed off with a typical disposal rate of 80 % fly ash and 20 % bottom ash. To maximize the use of the coal ash, and thus significantly reduce the disposal problem that electric utility companies and our society in general face, the direct use of ponded or landfilled ash that is composed of high proportions of fly ash would be desirable. However, a general understanding of the behavior of high volume fly ash mixtures is needed. Although there have been investigations into the properties of separated single types of ash, the studies of the fly/bottom ash mixtures, especially with high fly ash contents, are very limited. Representative samples of class F fly ash and bottom ash were collected from two utility plants in Indiana and a series of extensive laboratory tests were conducted to obtain the mechanical properties of the mixture. Since the mechanical properties of ash mixtures are dependent on the mixture proportions, the investigations evaluate fly/bottom ash mixtures with different mixture ratios (with Fly ash contents of 50%, 75%, and 100%). The results obtained are merged with other considerations relevant to embankment design and construction and used to develop guidelines on coal ash utilization in highway embankments. In order to examine suitable fly/bottom ash mixture compositions and embankment geometries, slope stability analyses were performed on ash embankments with different geometries using the different properties of the ash mixtures with different mixture ratios. The limit equilibrium method was used for the stability analyses. Additionally, the corrosion potential to metal structures, which are commonly included in highway construction, is examined by performing corrosivity tests on the ash mixtures.