Geoenvironmental Impacts of Using High Carbon Fly Ash in Structural Fill Applications.

摘要

Fly ash produced by some of the power plants in the United States occasionally contains significant amounts of unburned carbon due to the use of the increased prevalence of low nitrogen-oxide and sulphur-oxide burners in recent years. This ash cannot be reused in concrete production due to its reactivity with air entrainment admixtures, so it is largely placed in landfills. Highway structures have high potential for large volume use of high carbon fly ashes (HCFAs). However, in such applications, even though mechanical properties of the fly ash-amended highway base layers and embankments are deemed satisfactory, a key issue that precludes such highway embankments built with fly ash is the potential for negative groundwater effects caused by the leaching of metals in the material. This study evaluated the leaching potential of metals from HCFA used as a stabilizing agent and soil amendment in highway base layers and highway embankment structures, respectively. Three different laboratory tests were conducted: (1) batch water leach tests, (2) toxicity characteristics leaching procedure (TCLP) tests, and (3) column leach tests. Additionally, two numerical modeling analyses were conducted: (1) WiscLEACH and (2) MINTEQA2. Analyses were conducted on eight fly ashes and two locally available sandy soil materials that are mainly used in highway base layer and highway embankment structures.