The use of bottom ash in highway embankment and pavement construction

Interest in coal ash produced from power generating plants as a substitute for conventional construction material has increased considerably in recent years. The utilization of coal ash not only solves a waste disposal problem but also provides an economic construction material. In the past, studies on power plant ash have been concentrated on properties of fly ash. Very little has been developed on the productive use of bottom ash, primarily because of the lack of information on properties on this material. This study assesses those properties of bottom ash likely to affect its use in highway fill and pavement construction. Laboratory investigations were conducted on eleven bottom ashes collected from all parts of Indiana. Tests included complete chemical and mineralogical analysis. Physical properties such as appearance, grain size distribution, and specific gravity of bottom ash were also studied. The assessment of performance involved a series of tests consisting of sulfate soundness, Los Angeles abrasion, permeability, shear strength, compact ion characteristics, compressibility, and California bearing ratio. In addition, bottom ash was subjected to mechanical and chemical stabilization to evaluate its potential as a pavement material. To evaluate potential highway construction uses, the test results were compared with those of representative granular materials and appropriate existing specifications. Based on this laboratory investigation, it is concluded that the properties of most bottom ashes compare favorably with conventional granular materials. The potential environmental effects of bottom ash utilization center around possible leaching of heavy metals and soluable salts from ash-constructed embankments. Leaching tests were performed using the extraction procedure outlined in the EP toxicity test and an Indiana leaching method. Chemical analysis of the leachates generated from these tests showed that bottom ash is nonhazardous, and its effects on the quality of ground water are minimal. The economic potential was assessed for Indiana bottom ashes based on the quantities available and their location with respect to potential market areas. A study of the factors determining the cost of bottom ash in place was also included.