Hydraulic properties of foundry sands and their use as hydraulic barriers

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 have hydraulic properties similar to those of sand-bentonite mixtures. Sand-bentonite mixtures are being used as barrier layers throughout the U.S. This project addressed the following issues regarding the reuse of foundry waste sands as barrier layers: identify the key properties that foundry sands should have to be used as barrier layers, investigate construction methods, and investigate the durability of foundry sands when exposed to weathering distress or chemical permeation. The project consisted of a laboratory study, a field study, and a modeling study to predict the hydraulic conductivity of soil-bentonite mixtures such as foundry sands.; Sixteen foundry sands from 4 Midwestern states were tested in the laboratory. Nine of these foundry sands yielded hydraulic conductivities lower than 1 x 10-7 cm/sec. All, but one foundry sand showed resistance to freeze/thaw and desiccation actions. Foundry sands were also found to be resistant to permeation with MSW leachate and brine solutions. This study has also shown that foundry sands having liquid limit (LL) > 20 and/or a bentonite content > 6% are suitable for the construction of barrier layers.; The laboratory study is followed by a field study to investigate if the field behavior of foundry sands is similar to that observed in the laboratory. Three test pads were constructed and instrumented during this field study. The field study 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--7 cm/sec. The field hydraulic conductivity also seems not to be affected by freeze-thaw deterioration associated with clay soils.; The final step in this project was to understand the hydraulic behavior of sand bentonite mixtures such as foundry sands and to develop a computer model to predict the hydraulic behavior. The model consisted of extracting a pipe network from packings of spheres and then introducing bentonite into the network in different schemes. The hydraulic conductivity of the network was then evaluated as the bentonite content increased. The introduction of the bentonite schemes were based on the study of the microstructure of real sand bentonite mixtures. The change in hydraulic conductivity with bentonite content predicted by the model is similar to that observed on real sand bentonite mixtures and of foundry sands.