Hydraulic Conductivity of Foundry Sands and Their Use as Hydraulic Barriers

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Even though many states have developed beneficial reuse regulations for industrial by-products, large quantities of foundry sands are being landfilled throughout the U.S. Since the major components of foundry sands are sand and bentonite, they are expected to be suitable hydraulic barrier materials. This project identified the key properties that foundry sands should have to be used as barrier layers, and investigated construction methods and durability of foundry sands. Factors affecting hydraulic conductivity of foundry sands were also investigated. The projected consisted of a laboratory study, a field study, and a modeling study. Sixteen foundry sands from four Midwestern states and one foundry sand from Georgia were testing during the laboratory study. Three test pads were constructed and instrumented during the field study. The field and laboratory studies showed that foundry sands having liquid limit (LL)>20 and/or a bentonite content >6% can be compacted in the field to achieve hydraulic conductivity < 10 (to the -7) cm/sec. tests were also indicated that foundry sands were resistant to freeze-thaw and wet-dry cycling. A network formulation was used to model the hydraulic conductivity of foundry sands as a function of benetonite content. The sand particles were assumed to be spheres. Pores between the spheres were approximated as a network of straight capillary tubes. Bentonite was modeled as a coating of sand particles. The relationship between hydraulic conductivity and bentonite content obtained from the network model was similar to that measured on foundry sands.