University of Oklahoma, School of Civil Engineering and Environmental Science
ABSTRACT
Over 50 million cubic yards of raw chat, a waste material of lead (Pb) and zinc (Zn) mining,
are presently stockpiled in large piles on the surface of the Tar Creek Superfund Site. Raw
chat previously has been used in hot mix asphalt (HMA) for pavement applications by state
transportation departments in the region. Currently, the Oklahoma Department of
Transportation (ODOT) specifies the use of only 20% washed chat in HMA. This study was
aimed at maximizing the use of raw (pile run) chat in HMA in an environmentally sound
manner. Mix designs were performed following the Superpave mix design methodology.
Different percentages of raw chat were combined with locally available non-chat
aggregates in order to achieve the maximum percentage of raw chat in HMA meeting
mechanical specifications. For surface applications, three mix designs, SM40, SM60 and
SM80, containing 40%, 60% and 80% raw chat, respectively, were prepared. In the case of
base applications, 40%, 50% and 70% chat were used in BM40, BM50 and BM70,
respectively. Bench scale laboratory tests concerning consensus and source aggregate
properties were conducted on the aggregates. The volumetric properties were determined and
three types of performance tests (moisture sensitivity, rutting, and permeability) were
performed.
All three surface mixes met ODOT requirements for aggregate and volumetric
properties. They also passed the performance tests. Out of the three base mixes, BM40 and
BM50 met all the requirements, whereas, BM70 did not meet the dust proportion and rut
criteria. Therefore, BM70 was not considered for any other performance tests.
To obtain environmental data, TCLP and SPLP and total metals analyses were
performed on raw chat, size-fractionated raw chat, chat HMA, non-chat HMA and chat HMA
A Laboratory Study to Optimize the Use of Raw Chat in Hot Mix Asphalt for Pavement Application: Final Report
University of Oklahoma, School of Civil Engineering and Environmental Science
subjected to simulated millings. In addition, total metal analyses were performed on chat
HMA subjected to dry and wet rutting. It was found that none of the dry rutted and wet rutted
samples exceeded the EPA action limit for Pb. Even though the HMA samples were
weathered (by milling), none of the milled HMA has Pb concentrations exceeding the EPA
action limit of 400 mg/Kg.
Additionally, none of the milled HMA samples have
concentrations of Pb and Cd above the TCLP regulatory limits.
SM80 which contains the highest amount of raw chat among the designs that meet the
ODOT requirements, is safe as far as environmental recommended and regulatory limits are
concerned. In case of base mixes, BM50 has the highest amount of raw chat among the
designs that meet the ODOT requirements, and is safe according to the EPA requirements.
A Laboratory Study to Optimize the Use of Raw Chat in Hot Mix Asphalt for Pavement Application: Final Report
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