The current practice of landfilling thermally treated and untreated coal tar-contaminated soil is expensive, and it is a waste of a potentially useful material and landfill space. A less expensive and possibly more practical alternative is to use coal tar-contaminated soil as an aggregate in concrete. Because little work has been done in this area, the present study was undertaken to evaluate the effects of coal tar-contamination and thermal treatment on the physical properties of soil and the strength of concrete containing contaminated soil as an aggregate. Also assessed was the leachability of coal tar constituents (specifically, polycyclic aromatic hydrocarbons (PAHs)) from contaminated soil, concrete containing contaminated soil, and concrete containing thermally-treated contaminated soil. Mechanical sieve analyses and direct shear tests showed no significant change in grain size distribution or internal friction angle for contaminated and uncontaminated soil treated at 250 and 550 Compressive and splitting tensile strength tests performed on concrete specimens showed a slight decrease in strength with the degree of incorporation of contaminated aggregate. Concrete compressive strength, elastic modulus, and tensile strength also decreased as the aggregate treatment temperature increased, especially at temperatures in excess of 450 However, the strength decreases were small (less than 15%), and the concrete strength was still within typical values for structural concrete. The leachability tests showed that as treatment temperature was increased, levels of PAHs in the soil significantly decreased. From the leachability tests performed on samples of crushed concrete that contained contaminated soil, it appears that only low molecular weight PAHs (i.e., less than or equal tol66 g/mol) were stabilized by the concrete. The poor stabilization of higher molecular weight PAHs may be an artifact of the sample preparation method which required that the concrete be crushed prior to leaching.


Civil and Environmental Engineering



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