Effect of Chemical and Physical Ageing on the Longevity of Smooth and Textured Geomembranes in Geoenvironmental Applications
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Degradation of physical and mechanical properties of geomembrane (GMB) base liners in various geoenvironmental applications is investigated. This involved conducting immersion tests to simulate the ageing of GMBs on exposure to chemical solutions simulating field applications. The reduction in stress crack-resistance (SCR) due to physical ageing is examined. It is shown that a reduction in SCR was observed for a 1.5 mm smooth high density polyethylene (HDPE) GMB incubated in municipal solid waste (MSW) leachate and deionized water shortly after immersion to a value designated as SCRm and then stabilized until the end of the ~10-year study. The same GMB is incubated in air, high pH pregnant leach solution, and brine, and a similar reduction is observed in SCR to SCRm estimated by 50% of the initial SCR (SCRo). This early-time reduction in SCR is observed for other ten smooth HDPE GMBs and the mean magnitude of SCRm/SCRo is 0.37. A new definition for time to nominal failure (tNF) is introduced and assessed based on the time at which SCR=0.5·SCRm.This study investigates also the effect of texturing on the longevity of a GMB when immersed in a MSW leachate over a period ~3 years. The comparison of the textured/smooth portions of the HDPE GMB shows that texturing accelerated the OIT depletion by 40% (Std-OIT), but it does not affect the tNF assessed based on SCR. Finally, this study investigates the performance of 13 smooth GMBs when immersed in chlorinated water with concentration simulant to that in potable water reservoirs. A new degradation trend for GMBs stabilized with hindered amine light stabilizers (HALS) and immersed in chlorinated water is introduced. In this new trend, the degradation occurs in two stages. In the first stage, degradation of mechanical properties occurs before the depletion of antioxidants, then the mechanical properties stabilize for a lag time followed by a second stage of degradation until brittleness is reached. The comparison between the longevity of the 13 GMBs shows that the resin type and HALS contribute to a better resistance to degradation.