TY - CONF A1 - Retzlaff, J. A1 - Bronstein, Z. A1 - Müller-Rochholz, J. A1 - Böhning, Martin A1 - Robertson, Daniela A1 - Schröder, Hartmut T1 - Oxidative resistance of geosynthetics: practical aspects and developments of testing at elevated temperature and oxygen pressure N2 - Service life of geosynthetics made of polyolefin materials is mainly limited by oxidative degradation. Durability of polyolefin products depend on formulation, morphology resulting from manufacturing, design and particularly on the antioxidants used. Although the fundamental oxidative reactions are known, the complex effect of geosynthetic characteristics and external influences mean that durability assessments require practical tests. The assessment of oxidative durability involves exposure to accelerating conditions as well as the material characterisation with respect to the state of stabilisation and/or degradation (e.g. by tensile testing and/or oxidation induction time). The autoclave test developed by BAM for durability assessments of polyolefin geosynthetics is based on the simultaneous application of moderately elevated temperatures (up to 80 degrees Celsius) and elevated oxygen pressures (up to 5.0 MPa) in combination with a surrounding aqueous medium. Thus this test method provides several advantages in comparison to conventional oven testing, especially with respect to test duration, impact of surrounding environment and the potential to differentiate and rank oxidative resistance between products of very different dimensions (surface/volume) and stabilisation. In view of the increasing demand for durability assessments of geosynthetic products with lifetimes significantly exceeding 25 years, the contribution is focused on practical aspects concerning implementation and optimisation of test procedures, conditions and evaluation of results. Furthermore, advanced approaches based on multiple exposure conditions will also be included and corresponding calculations of expected service life in typical applications will be evaluated with respect to significance and repeatability. Thereby involved standards and recommendations - such as EN ISO 13438, Part C or EAG-EDT - are considered. T2 - EuroGeo4, 4th European Geosynthetics Conference CY - Edinburgh, UK DA - 2008-09-07 KW - Ageing KW - Degradation KW - HDPE KW - Laboratory test KW - Oxidation KW - Polypropylene PY - 2008 IS - Paper 178 SP - 1 EP - 4 AN - OPUS4-18423 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Böhning, Martin A1 - Robertson, Daniela A1 - Schröder, Hartmut T1 - Autoclave testing: a new approach for the evaluation of oxidative long-term resistance of geosynthetics N2 - Oxidative long time resistance is essential for many polyolefin based products, especially if repair or exchange is not possible as encountered in many building and geotechnical applications. Current regulations and recommendations for geosynthetics cover mainly the needs of a maximum lifetime of 25 years, though many applications require longer lifetimes up to 100 years and more. Reliable testing of the long time oxidation resistance is complicated by the complex interplay of physicochemical processes and reactions in combination with the need of relatively short testing durations, usually not exceeding 12 months. Thus for conventional atmospheric oven testing, the use of temperatures higher than 100 °C is inevitable, making conclusive Arrhenius extrapolations often questionable. Practical assessments of oxidative durability consist of exposures under accelerated ageing conditions with subsequent characterization of exposed material samples with respect to their residual stabilization and/or their mechanical properties. The autoclave test combines exposures at elevated temperatures with higher oxygen pressures and is performed with material samples immersed in a well defined aqueous medium representing critical environments in geosynthetic applications and including extraction of additives. Under these conditions meaningful results can be obtained within reasonable testing durations at only moderately elevated temperatures up to 80 °C. Application of different physicochemical methods, such as tensile testing, OIT /HP-OIT and analysis of residual antioxidant content (ICOT), in order to determine the time dependent degradation behaviour, reveal valuable information about mechanisms and effectiveness of the used antioxidants. Corresponding results for exposures at different temperatures and oxygen pressures are the basis for a 3D-extrapolation in order to estimate the expected service life. Different empirical models are presented and discussed with respect to their practical impact. T2 - EuroGeo4, 4th European Geosynthetics Conference CY - Edinburgh, UK DA - 2008-09-07 KW - Ageing KW - Degradation KW - Geotextiles KW - Polyolefin KW - Polypropylene KW - Oxidative resistance KW - Lifetime prediction PY - 2008 IS - Paper 143 SP - 1 EP - 8 AN - OPUS4-18424 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -