Polymer Fouling and Hydraulic Conductivity of Mixtures of Sodium Bentonite and a Bentonite-Polymer Composite

The impact of entraining water-soluble polyacrylate eluted from a bentonite-polyacrylate composite (BPC) in sodium bentonite (Na-bentonite) was evaluated as a means to achieve low hydraulic conductivity to aggressive CaCl2 solutions that reduce interlayer swell in conventional Na-bentonite. Up to 73% of the polymer initially contained within BPC (28.5% polymer by mass) was soluble and elutable polyacrylate. This polymer fouled pores that would typically conduct the bulk of flow in Na-bentonite permeated with aggressive CaCl2 solutions (>= 50 mMCaCl(2)). Similar fouling was observed with kaolinite and low-plasticity clay combined with BPC, but not fine sand or nonplastic silt combined with BPC. Granular mixtures of Na-bentonite blended with BPC had hydraulic conductivity to 50 mM CaCl2 as much as 1,500 to 6,700 times lower than Na-bentonite alone. Blends of granular Na-bentonite and granular BPC with as little as 1% BPC had hydraulic conductivities lower than BPC alone when permeated with 50 mM CaCl2. However, mixtures of BPC and Na-bentonite did not exhibit low hydraulic conductivity to 500 mM CaCl2 unless the mixture contained at least 90% BPC. The findings suggest Na-bentonite-BPC mixtures have the potential to be tailored to contain specific leachate chemistries. Mixtures of BPC with other clay soils (viz kaolinite, low-plasticity clay) may also be effective in achieving very low hydraulic conductivity with aggressive solutions. (C) 2016 American Society of Civil Engineers.