Performance of Geomembranes to Contain PCBS, Brine and Reverse-Osmosis Water
Accelerated ageing tests are used to examine the performance of geomembranes in three applications. The thesis examines a broad range of geomembranes produced over a time span of 30 years and highlights the progress made in the antioxidant/stabilizer packages as well as the resins. First, two high-density polyethylene (HDPE) geomembranes exhumed from a polychlorinated biphenyl (PCB) contaminated waste storage site constructed in the mid-1980’s are examined. The two geomembranes exhibited different antioxidant depletion mechanisms and mechanical performances. Both geomembranes were still performing their design function when exhumed after 22-23 years and a long period of effective performance is projected based on accelerated aging tests. Second, five high-performance geomembranes manufactured in 2014 and boosted with antioxidants and stabilizers are immersed in brine solution (the concentrate from the reverse osmosis process used to clean up hydraulic fracturing flowback waters from coal/shale gas recovery so that most of the water can be released as surface water for agricultural use). The thesis shows a difference in the performance between the five products in terms of antioxidants depletion, the estimated time to depletion (Stage I), morphological changes at the six test temperatures (95 to 40ºC) and the considerable decrease in stress crack resistance of 2-mm HDPE geomembrane with time prior to any oxidative degradation. The brine concentration greatly affects the antioxidant’s depletion rate. Third, the performance of the same five high-performance geomembranes is examined for immersion in reverse osmosis water (the clean side output from the reverse osmosis process used to clean up hydraulic fracturing flowback waters) at three temperatures. The products were also immersed in synthetic leachate at a high temperature for comparison. The geomembranes immersed in water behaved differently than in leachate and brine even at the lowest concentration. When compared to geomembranes produced in the 2000’s, the boost in the antioxidants/stabilizers concentrations of the high-performance geomembranes was not highly efficient in increasing the time to depletion. Nevertheless, the mechanical properties of the high-performance geomembranes did not decrease for the testing period unlike those produced in the 2000’s that exhibited a relatively an early degradation in mechanical properties.
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