Long-Term Hydraulic Conductivity of a Bentonite-Polymer Composite Permeated with Aggressive Inorganic Solutions

• Published in: Journal of geotechnical and geoenvironmental engineering Vol. 140; no. 3
• Main Authors: Scalia, Joseph, Benson, Craig H, Bohnhoff, Gretchen L, Edil, Tuncer B, Shackelford, Charles D
• Format: Journal Article
• Language: English
• Published: American Society of Civil Engineers 01.03.2014
• Subjects: Bentonite; Fluid dynamics; Fluid flow; Hydraulics; Polymerization; Sodium; Superabsorbent polymers; Technical Papers
• ISSN: 1090-0241; 1943-5606
• DOI: 10.1061/(ASCE)GT.1943-5606.0001040

AbstractBentonite was modified to prevent alterations in hydraulic conductivity when permeated with aggressive inorganic solutions. Acrylic acid within bentonite slurry was polymerized to create a bentonite-polymer composite (BPC). Tests indicate that BPC generally swells more and retains low hydraulic conductivity compared with natural sodium bentonite (Na-bentonite) when contacted with aggressive inorganic solutions. BPC in deionized water swelled greater than 3.8 times the swell of the Na-bentonite used to create BPC (73 versus 19 mL/2 g). In 500 mM CaCl2, however, swell of BPC was similar to swell of calcium bentonite (<10 mL/2 g). Thin layers of BPC simulating geosynthetic clay liners were permeated directly with 5–500 mM calcium chloride (CaCl2) solutions and extreme pH solutions (1 M NaOH with pH 13.1, 1 M HNO3 with pH 0.3). BPC maintained low hydraulic conductivity (<8×10−11 m/s) for all solutions for the duration of testing (>2 years). In contrast, Na-bentonite and superabsorbent polymer (similar to the polymer in BPC) permeated with the same solutions had hydraulic conductivities at least three orders of magnitude higher (except for 5 mM CaCl2). Hydraulic conductivity of BPC does not follow the classical hydraulic conductivity-swell relationship typical of Na-bentonite. BPC eluted polymer during permeation but maintained low hydraulic conductivity. Polymer elution was lower in more concentrated CaCl2 solutions.