TY - JOUR A1 - Müller, Werner A1 - Büttgenbach, Beate A1 - Jakob, Ines A1 - Mann, Heidemarie T1 - Comparison of the oxidative resistance of various polyolefin geotextiles JF - Geotextiles and Geomembranes N2 - Data are reported from oven aging in circulating air and water immersion tests at 80°C on various polyolefin (polyethylene (PE) and polypropylene (PP)) needle-punched nonwoven geotextiles (GTnws) and the results of these long-term tests are compared with the oxidative resistance of high-density PE geomembranes (HDPE GMs) described in a preceding paper (Polym. Degr. Stability 79(1) (2003) 161). Polyolefin fibers used in geotextiles are typically less stabilized, have a very high surface-to-volume ratio and an oriented morphology compared with HDPE GMs. Therefore, significant differences in the oxidation behavior of these products are expected which may affect their durability. Two general results can be obtained from our measurements: Firstly, while the lifetime of the HDPE GM is essentially determined by the slow loss of stabilizers, for all GTnws a rapid reduction in the oxidative induction time (OIT) and, as we conclude, in the amount of stabilizer was observed during water immersion and air aging. Secondly, the mechanical property degradation of the GTnws depended strongly on the oxidation conditions: the induction period prior to the degradation was much longer for immersion in water than for oven aging in circulating air. After antioxidant depletion, an induction time of the oxidation reaction, which depends on the draw ratio of the stretched fibers and the oxygen supply, might substantially contribute to the induction period of the mechanical property degradation of GTnws. For one PP GTnw product, a sudden reduction in the mechanical strength occurred after onset of degradation which continued rapidly until complete deterioration. For other PP samples as well as for all PE GTnws the reduction in mechanical strength proceeded slowly. Best fits were obtained by modeling the degradation process of the PE GTnws by a second-order kinetic. Using an activation energy of 60 kJ/mol (Geotextiles, Geomembranes and Related Products, Balkema, Rotterdam, 1990; Conference Proceedings of the Sixth International Conference on Geosynthetics, Industrial Fabrics Association International (IFAI), Atlanta, USA, 1998, pp. 683–690; Clay Geosynthetic Barriers, Balkema, Lisse, The Netherlands, 2002, pp. 87–96), lower limits of the half-live of the degradation at worst case field conditions were obtained in the range 30–83 years. Some decades have to be added for the overall induction time. However, under field conditions with limited oxygen supply, the expected service lifetime might be at least half an order of magnitude longer. KW - Durability KW - Geotextile KW - Oxidative resistance KW - Test methods KW - Long-term testing PY - 2003 DO - https://doi.org/10.1016/S0266-1144(03)00032-3 SN - 0266-1144 VL - 21 SP - 289 EP - 315 PB - Elsevier CY - Amsterdam AN - OPUS4-2632 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Müller, Werner A1 - Jakob, Ines A1 - Li, Chunshan A1 - Tatzky-Gerth, Renate T1 - Antioxidant depletion and OIT values of high impact PP strands JF - Chinese journal of polymer science KW - Polypropylene KW - Stabilizers KW - Oxidative resistance KW - Antioxidant depletion KW - Oxidative induction time PY - 2009 DO - https://doi.org/10.1142/S0256767909004102 SN - 0256-7679 VL - 27 IS - 3 SP - 435 EP - 445 PB - World Scientific CY - Singapore AN - OPUS4-19458 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Müller, Werner A1 - Jakob, Ines A1 - Seeger, Stefan A1 - Tatzky-Gerth, Renate T1 - Long-term shear strength of geosynthetic clay liners JF - Geotextiles and Geomembranes N2 - Geosynthetic clay liners (GCLs) often have a sandwich-like multilayer structure, e.g. bentonite encased between two geotextile layers connected by fibers or yarns, either by needle-punching or stitch-bonding. Therefore, the internal shear strength of the GCL depends on the strength of reinforcing fiber bundles or yarns and their anchoring strength in the cover and carrier geotextiles. When used on long and steep slopes and covered with thick soil layers, the GCL is permanently exposed to a combined action of compressive and shear stress. Such load conditions are characteristic for landfill covers and the slope stability of the overall cover system in the long run strongly depends on the long-term internal shear strength of the GCL. A new test method was developed to study this long-term shear behavior. The focus was not only on creep, as it is normally done, but on aging effects. The shear test devices allow the measurement of creep curves and times-to-failure at elevated temperatures in different media (tap water and de-ionized water). In this publication, the main findings of the experiments on needle-punched GCLs with and without thermal treatment are summarized. Tap water as a test medium was essential to ensure sodium to calcium ion exchange in the bentonite layer. Under this condition extremely long test durations without failure were achieved. Sliding failure occurred when de-ionized water was used. Two failure modes were observed: brittle failure of the GCLs with thermal treatment and slow disentanglement of fiber bundles for untreated GCLs. Short-term shear strength (e.g. peel strength) is unrelated to the actual long-term shear strength, i.e. to the times-to-failure achieved in long-term shear strength test. Hence, short-term shear strength alone will not provide reliable dimensioning data for product design and choice of resins. Therefore, the often suggested approach, namely, restriction to short-term tests only and application of factors of safety, is challenged by these results. KW - Geosynthetic clay liner KW - Shear strength KW - Oxidative resistance KW - Test methods KW - Long-term testing PY - 2008 DO - https://doi.org/10.1016/j.geotexmem.2007.08.001 SN - 0266-1144 VL - 26 IS - 2 SP - 130 EP - 144 PB - Elsevier CY - Amsterdam AN - OPUS4-16710 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -