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Würzburg, Germany

Koo H.-J.,FITI Testing and Research Institute | Cho H.-W.,FITI Testing and Research Institute | Oh J.-T.,FITI Testing and Research Institute | Zanzinger H.,SKZ
10th International Conference on Geosynthetics, ICG 2014 | Year: 2014

Geosynthetics for all applications have to be tested for resistance to weathering because polymers are generally degraded under the exposure to UV spectral region. EN 12224 and ASTM D4355 describe accelerated weathering tests with different light sources. EN 12224 is based on the 50 MJ/m2 radiant exposure which is equivalent to one month exposure in southern Europe during summer. There are various approaches to reach the same radiant exposure given in EN 12224. The duration required was 320 h for devices with a combination of fluorescent UV lamps, 350 h for devices with UV-A lamps if the lamps are left on during the water spray and 430 h for devices with UV-A lamps if the lamps are turned off during the water spray. ASTM D4355 uses a Xenon arc light source having a spectrum that simulates natural daylight, including the UV region. In this study, we have performed the accelerated weathering tests according to EN 12224 using combination of fluorescent UV and UV-A lamps, and ASTM D 4355 using conventional weatherometers and investigated the effects of different light sources on degradation properties of non-woven geotextiles. It was found that the two light sources used in EN 12224 show different degradation behaviors due to the larger portion of UV region in UV-A lamp while the combination UV and Xenon arc lamp used in ASTM D4355 show the similar degradation rate on non-woven geotex-tiles. In addition, lamp left on during water spray accelerates the degradation of non-woven geotextiles. The results suggest the necessity for the weathering test method which can simulate the actual degradation behavior in the field.

Zanzinger H.,SKZ | Saathoff F.,University of Rostock
Geotextiles and Geomembranes | Year: 2012

Clay geosynthetic barriers (GBR-C) - a synonym for geosynthetic clay liners (GCL) - used on steep slopes, e.g. landfill capping systems, have to withstand permanent shear forces over the long-term. Thermoplastic materials deform under static load. Creep and chemical ageing processes (e.g. oxidation) also influence the strength of the synthetic fibres over the long-term. The lifetime of these geosynthetics (GSY) is a very important issue as GBR-Cs have to demonstrate their long-term durability for more than 100 years in cases such as e.g. landfill capping systems in Germany.The long-term shear strength will be modelled by applying shear stress for long durations at elevated temperature (i.e. to accelerate ageing). In laboratory tests running up to 2 years on a stitch-bonded GBR-C in deionised (DI) water, specimens experienced internal rupture (i.e. rupture of fibres) at higher shear stress. Results showed the times to shear failure directly depend on the applied shear stress. Using the extrapolation of the regression line of times to shear creep rupture together with a lifetime prediction the applicable shear stress was found to 28 kPa for a minimum of 100 years under a normal stress of 50 kPa at a field temperature of 30 °C. Short-term tests cannot give the answer for any long-term behaviour of GBR-Cs. There is always the need for shear creep rupture tests. This new method determines the long-term shear strength of GBR-Cs for any lifetime. © 2012 Elsevier Ltd.

Wrigley N.E.,Newgrids Ltd | Zheng H.,BOSTD Geosynthetics Qingdao Ltd | Liu X.J.,BOSTD Geosynthetics Qingdao Ltd | Sama S.R.,SKZ
9th International Conference on Geosynthetics - Geosynthetics: Advanced Solutions for a Challenging World, ICG 2010 | Year: 2010

It is now well accepted that the primary fill stabilisation mechanism of geogrids is confinement of the fill by the geogrid. To gauge the potential for this and to compare products, index properties such as the load at 2% strain in each of the two primary directions have been used in the past. This approach has had some merit whilst all geogrids available were square or rectangular structures. Now, however, the introduction of innovative products to the market has rendered this comparison ineffective. To overcome this, the option of doing tensile tests in more directions than just along the two primary axes has been proposed and used. However, this also is ineffective as it still fails to model the omni-directional confinement required to stabilise fill under a wheel load. In a paper presented at the EuroGeo4 Conference in 2008 it was shown that from index tests on the elements of a geogrid and a simple calculation, the confinement potential of different products can be readily determined and compared. The paper also showed that simply using tensile testing in different directions is inappropriate for this purpose. This concept of confinement potential can be defined as: Confinement Load: The load that a circle of geogrid can provide at a specified strain to confine a layer of soil placed upon it.The present paper takes this concept forward by describing the measurement of the properties of a number of geogrids, both rectangular and non-rectangular. From this the Confinement Load available from each geogrid is calculated. Also described is work towards developing an index test that could measure this property directly.

Zanzinger H.,SKZ | Sama S.R.,SKZ | Dobrat A.,Colbond B.V.
9th International Conference on Geosynthetics - Geosynthetics: Advanced Solutions for a Challenging World, ICG 2010 | Year: 2010

For the design of drainage geocomposites (GCDs) the relevant property is the long-term water flow capacity. Different methods have been used to calculate or to simulate this property. First design recommendations were made to calculate the "long-term water flow capacity" by using reduction factors for local deformations and for compressive creep behaviour. Others simulated the "long-term water flow capacity" by short-term water flow capacity tests under soft bedding but under elevated compressive stress - representative for the "long-term thickness" of the core under the identical normal stress. The variety of combinations of different core types and geotextile filters in GCDs are high. And not all effects like compressive creep of the core and the initial deformation together with the time dependent deformation of the filter at various normal stresses will be taken into account by following the above mentioned methods. A new method by using direct measurements of the "long-term water flow capacity" of GCDs after long-term compressive loading with soft bedding shows that real decrease in water flow capacity can be much higher than taken into account by short-term generated reduction factors. With typical commercially used GCDs, long-term compressive creep tests with soft bedding and different loads have been carried out in two laboratories. These "measured long-term water flow capacities" will be compared with "calculated" and with "simulated long-term water flow capacities".

Kloke P.,University of Paderborn | Rudloff J.,SKZ Das Kunststoff Zentrum | Schoppner V.,University of Paderborn | Potente H.,KTP | And 3 more authors.
Kunststoffe International | Year: 2011

The properties of glass fiber-reinforced polymers are principally determined by glass fiber content, fiber diameter, glass fiber length distribution, the orientation of the fibers within the component part and the adhesion between the matrix material and the fibers. The operating points varied in screw speed and torque with at first constant glass fiber content and matrix polymer system. These trials were conducted using the so-called dead stop technique where the machine is abruptly stopped before pulling the screws. The variations of the process parameters covered screw speed, overall throughput, barrel temperatures and pressure at the screw tips which could be controlled by a choke arrangement. The average fiber length falls with increasing screw speed and back pressure. Equally longer fibers were seen with the low viscosity material than for the higher viscosity. An increase in the overall throughput had a positive effect on the average fiber length.

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