Details:

Creators:
Aydilek, Ahmet ; Cetin, Bora
Aydilek, Ahmet ; Cetin, Bora Less -
Corporate Creators:
University of Maryland (College Park, Md.). Dept. of Civil and Environmental Engineering
Subject/TRT Terms:
[+]
Embankments
Fly Ash--Leaching
Metals--Environmental Aspects
Admixtures
Concrete
Environmental Impacts
Fly Ash
Laboratory Tests
Leaching
Metals
Toxicity

Publication/ Report Number:
MD-13-SP909B4P
Resource Type:
Tech Report
Geographical Coverage:
Maryland
Edition:
Final report.
Corporate Publisher:
Maryland. State Highway Administration
NTL Classification:
NTL-HIGHWAY/ROAD TRANSPORTATION-HIGHWAY/ROAD TRANSPORTATION ; NTL-ENERGY AND ENVIRONMENT-ENERGY AND ENVIRONMENT ;
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.


Format:
PDF
Funding:
SP909B4P
Collection(s):
US Transportation Collection
Main Document Checksum:
[+]
urn:sha256:6622a3cdff9f8c65aff353ed03998087b81fc975b28c2948aa6bc7fcd17f3524
File Type:

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