Geosynthetic Clay Liners Containing Bentonite Polymer Nanocomposite

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Abstract
Bentonite was modified at the nanoscale so that low hydraulic conductivity would be maintained under adverse conditions. Nanoscale modification consisted of polymerizing acrylic acid within a bentonite slurry to form a stable interconnected structure. This modified material is referred to as a bentonite-polymer nanocomposite (BPN). The BPN was then air dried and ground to simulate the granule-size distribution of granular bentonite in geosynthetic clay liners (GCLs). Index property tests indicate that BPN has different behavior than natural sodium bentonite (Na-bentonite). For example, free swell tests with natural Na-bentonite swelled to approximately 30 mL in deionized water, whereas BPN swelled to more than 70 mL in the same solution. GCLs were assembled and directly permeated with a range of calcium chloride (CaCl2) solutions known to cause large increases in the hydraulic conductivity (k) of natural Na-bentonite. Low hydraulic conductivities (k < 3 x 10–10 cm/s) were maintained by BPN for all solutions tested. In contrast, natural Na-bentonite tested under the same conditions had k more than 4 orders of magnitude higher (k > 2 x 10–5 cm/s). Additional study of the properties and the underlying mechanisms of BPN are ongoing.

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