Geosynthetic Clay Liners Containing Bentonite Polymer Nanocomposite

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.