| The effects of exposure to acidic mine drainage (AMD) on three geosynthetics were evaluated by a laboratory immersion program. The main objective was to assess how the mechanical, hydraulic, and polymer properties are affected by AMD. A second objective was to predict the lifetime of geosynthetics by extrapolating the experimental behavior to site-specific conditions. Three geosynthetics (a geomembrane, a geotextile, and a drainage geocomposite) were immersed in tanks containing synthetic AMD, acidic water, or deionized water at 20, 40, or 60°C. Specimens were periodically removed from the tanks and tested to determine their mechanical (tensile strength, puncture strength, and trapezoidal tear strength), hydraulic (transmissivity and permittivity), and polymer properties [melt flow index (MFI), molecular structure using fourier transform infrared spectroscopy (FTIR), oxidation induction time (OIT)]. Results of the tests were evaluated by comparison with the properties of unexposed geosynthetic materials. Analysis of variance (ANOVA) and linear regression were also used to determine if statistically significant changes in mechanical and hydraulic properties occurred. Each of these analyses showed that there were no visual or statistically significant changes in the mechanical and hydraulic properties of the geosynthetics due to immersion in AMD, acidic water, and DI water. These findings suggest that the three geosynthetic materials tested in this study are resistant to acidic mine drainage. Polymer tests were performed only on the geomembrane. Higher MFls were detected for the geomembrane exposed to AMD relative to exposure to DI water, and MFls for the geomembrane exposed to the AMD increased with increasing temperature. Only subtle changes were observed in the FTIR spectra, suggesting that exposure to AMD did not significantly change the polymer structure over the period of exposure. OIT decreased with exposure time for all exposure conditions, and approximately followed a first-order depletion rate. The depletion rates also increased as the temperature increased. Antioxidant depletion lifetimes, obtained using Arrhenius modeling, ranged from 46 to 426 yr depending on the field temperature, the initial OIT, and exposure condition (i.e., one-sided or immersion). |
