Geoenvironmental impacts of using high carbon fly ash in structural fill applications.

Details

• Creators:
  Aydilek, Ahmet ; Cetin, Bora
• Corporate Creators:
  University of Maryland (College Park, Md.). Department of Civil and Environmental Engineering
• Subject/TRT Terms:
  • Fly ash
  • Admixtures
  • Concrete
  • Environmental impacts
  • Leaching
  • Embankments
  • Laboratory tests
  • Toxicity
  • Metals Fly ash--Leaching
  • Embankments
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• Publication/ Report Number:
  MD-13-SP909B4P
• Resource Type:
  Tech Report
• Geographical Coverage:
  Maryland
• Edition:
  Final report.
• Corporate Publisher:
  Maryland. State Highway Administration
• Abstract:
  Fly ash produced by 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 metals in the ; fly ash. This study evaluated the leaching potential of metals from highway base layers stabilized with HCFA and highway ; embankment structures amended with HCFA. Three different laboratory tests were conducted: (1) batch water leach tests, (2) ; toxicity characteristics leaching procedure tests, (3) column leach test. 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. Laboratory test results indicated ; that an increase in fly ash content in the soil-fly ash mixtures yielded an increase in leached metal concentrations with the ; exception of zinc (Zn). The pHs had significant and different effects on the leaching of metals. The leaching of chromium (Cr), ; zinc, (Zn), aluminum (Al), arsenic (As) and selenium (Se) increased with increased pH levels, while leaching of barium (Ba), ; boron (B), cooper (Cu), iron (Fe), magnesium (Mn), silver (Sb), vanadium (V) decreased with increased pH levels.. Numerical ; model WiscLEACH was used to simulate the leaching behavior of leached metals from HCFA-stabilized highway base layers ; and HCFA-amended highway embankment structures. WiscLEACH predicted field metal concentrations were significantly ; lower than the metal concentrations obtained in laboratory leaching tests, and field concentrations decreased with time and ; distance due to dispersion in soil vadose zone. Numerical model MINTEQA2 predicted that leaching of metals were solubility ; controlled except As, Se and Sb. Speciation analyses indicated that leached metals were present at their less or non-toxic forms.
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• Format:
  PDF
• Funding:
  SP909B4P
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/25788/dot_25788_DS1.pdf
• File Type:
  [PDF - 2.01 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha-512:5db8431318eda601c708b20b40902ce2df2f6622def64cfcdab1ed19e7eeddc3e9e4c62cc392f32e1287032fe1f82d7ab24c668091f5a5beeec57c3aebe7e4f0