Assessing the Effects of Texturing, Fusion, and Extrusion Welds on Stress Crack Resistance and the Relation Between Stress Crack Resistance and Work Hardening

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Authors
Ibrahim, Mahmoud Mouhamed Ali
Keyword
Geosynthetics , Textured geomembrane , Extrusion weld , Fusion weld , Textured , Strain hardening , Stress crack resistance , Smooth geomembrane
Abstract
The properties of high-density polyethylene (HDPE) geomembrane (GMB) sheet material and the geometry of the geomembrane surface (i.e., texturing the sheet surface and high irregularity of the weld) play a crucial role in assessing the expected lifespan of a constructed barrier system. In particular, the resistance to stress cracking and the preservation of antioxidants within the GMB are critical factors to both short-term and long-term performance. While the single point notch constant tensile load stress crack resistant (SP-NCTL SCR) test is a conventional method for assessing the stress cracking resistance of the HDPE GMB, the surfactant used to accelerate the test has shown negative effects on human health and the environment, leading to its prohibition in some countries, such as those in the European Union. Therefore, alternative test methods are investigated using the strain hardening modulus of smooth HDPE geomembranes. The proposed methods provide a quick assessment of the SP-NCTL SCR for the resins and conditions examined. The SCR of HDPE GMB extrusion weld for a 1.5 mm HDPE geomembrane is examined. It is shown that the average SCR for a good extrusion weld is 23% of that of the unnotched sheet SCR. The presence of welding-induced geometric irregularities (WIGI) and excessive grinding of the surface adjacent to the weld, caused by the operator, greatly affects the SCR of extrusion welds. High welding geometry irregularity (WIGI) overheated fusion welds and extrusion welds have been found to exhibit SCR failure times that are equivalent to those of notched sheets during 40 months of immersion in a synthetic leachate solution. This study also investigates the impact of texturing on the longevity of a GMB when exposed to MSW leachate over a period of ~8 years. The comparison of the textured/smooth edge portions of the HDPE GMB shows that the antioxidant depletion of the textured part is much faster than that of the smooth edge. However, the time to nominal failure (tNF) assessed based on SCR was similar at 85 and 75C. The degradation in the tensile break properties at 85C is faster for the textured part than for the smooth edge portion and smooth equivalent.
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