Compaction characteristics and corrosivity of Indiana class-F fly and bottom ash mixtures

Abstract

Fly ash and bottom ash are the residual by-products of coal burning to produce electricity. They are typically treated as a waste, disposed together in ponds. Reutilization of these waste materials in civil engineering applications that require large volumes of fill or back-fill materials, such as embankments and retaining structures, is beneficial. The literature contains only limited information on the use of mixtures of fly and bottom ash in these types of applications. One advantage of using ash mixtures in the proportions in which they exist in the disposal ponds is that there are no costs associated with mixing the ashes in situ at the time of construction. In addition, use of ash preserves traditional materials and allows savings on both land acquisition and disposal operations. This study presents a laboratory investigation on the compaction characteristics and corrosivity of class-F fly and bottom ash mixtures. Standard compaction, maximum and minimum density, electrical resistivity, and pH tests were conducted on ash mixtures with different mixture ratios: 50%, 75%, and 100% fly ash content by weight. The compaction test results showed that, with increasing fly ash content, the maximum compacted dry densities decreased and the corresponding water contents increased. Comparisons with the maximum density test results revealed that relative compaction is a more appropriate quantity to control the density of ash mixtures than relative density. The electrical resistivity values of the ash mixtures also varied with fly ash content, and were found to be mainly a function of water content. Two corrosivity indicators (electrical resistivity and pH) suggested that ash mixtures may be potentially corrosive. The results presented in this paper show that ash mixtures have properties that allow their use in place of traditional materials in the construction of fills or backfills.