Geotechnical and Leaching Properties of Municipal Solid Waste Incineration Fly Ash for Use as Embankment Fill Material

The beneficial use of municipal solid waste incineration (MSWI) fly ash promotes sustainability in highway construction. This study investigated the geotechnical and chemical leaching characteristics of fresh and aged MSWI fly ash samples for use of the material in highway construction applications. The results show that the geotechnical properties of MSWI fly ash resemble those of silty sands with poor drainage capacity. Compared with fresh ash (<10 days since placement), aged ash (3 to 6 months) has a higher California bearing ratio, higher unconfined compressive strength, and greater freeze-thaw durability. The concentrations of cadmium, chromium, selenium, silver, and sulfate from water leach tests are below the limits stipulated in Wisconsin NR 538. The concentrations of heavy metals in leachate from Synthetic Precipitation Leaching Procedure tests are below the U.S. Environmental Protection Agency's standard maximum contaminant level, with the exception of arsenic. Cumulative mass release from column leach tests indicates that fresh ash will release more heavy metals than aged ash during long-term leaching processes. According to the geotechnical and environmental test results in this investigation, aged MSWI fly ash is identified as a viable material for potential use in roadway construction.