ENVIRONMENTAL ANALYSES OF HOT MIX ASPHALT MADE WITH MINING WASTE MATERIALS

摘要

Beneficial reuse of mining residuals may represent a cost-effective and environmental responsible option in land reclamation. At the Tar Creek Superfund Site of northeastern Oklahoma, approximately 75 million tons of un-vegetated mining waste materials (known as chat) litter the surface in large piles. Chat is primarily composed of chert, dolomite and calcite, and contains elevated concentrations of metals, particularly lead (Pb), zinc (Zn), and cadmium (Cd). Metals concentrations are particularly elevated in the finer (<0.425 mm) size fractions. At the present time, many county roads in the mining district are graded with raw or pile run chat gravel, raising substantial air and water quality concerns. However, chat also possesses certain properties indicative of high quality aggregates, e.g., hardness and angularity. Therefore, this laboratory study was designed to examine the mechanical and environmental properties of asphalt products which maximize the amount of raw (not size-fractionated) chat. Mix designs containing 80 percent and 50 percent raw chat, for surface and base mix designs, respectively, were found to meet mechanical criteria of the Oklahoma Department of Transportation. Detailed results are presented in a companion poster. In addition, raw chat, size-fractionated chat, asphalt products and residues created by simulated asphalt weathering were subjected to Toxicity Characteristic Leaching Procedure (EPA method 1311) and total metals analyses (EPA method 6010). Pb wipe tests (HUD method) were conducted as well. The results of these environmental analyses indicate that incorporation of raw chat into hot mix asphalt presents a beneficial reuse of this contaminated material. Concentrations in both weathered surface and base mix designs were below EPA action levels for Pb in soil and water. TCLP regulatory limits for Pb (5.0 mg/L) were not exceeded by either design. Longer-term, field-scale examinations of similar mix designs are planned through construction and monitoring of a pavement test section.