Testing of geosynthetic barriers - Polymeric
Testing of Geosynthetic Barriers - Polymeric
The definition of a geomembrane, taken from EN ISO 10318, is: “Factory-made very low-permeable material made as a synthetic, polymeric or asphalt (bitumen) plate used for grading and building in order to prevent the flow of a liquid and/or vapour through the structure”.
Geotextiles (and geotextile-related products), in contrast to geosynthetic barriers, are basically fabrics which are permeable to fluids such as water and gas.
BTTG™ offer an unrivalled testing service of Geosynthetic Barriers, both polymeric (geomembranes) and clay (geosynthetic clay liners), to manufacturers, consulting engineers, contractors and landfill operators among others. We are able to perform a wide range of tests. The tests are co-ordinated and carried out by the High Performance Materials (HPM) department in custom designed premises in Trafford Park, Manchester. The laboratory building contains three separately conditioned laboratories and a large preparation area with a loading bay to handle samples directly from site and from manufacturers.
BTTG™ is the UK’s leading laboratory for testing geosynthetic materials and was the first UK laboratory to be UKAS accredited for any geosynthetic tests. BTTG™ hold UKAS accreditation to ISO 17025 for an extensive range of geosynthetic tests, including opinions and interpretations. View our schedule of UKAS accredited tests.
The principals of commonly performed tests
Where two or more standards have been grouped together under one heading, the test methods are not necessarily identical, nor would they produce the same results, but they follow similar principals of test.
BS EN ISO 9863-1; BS EN 1849-2; BS EN 964-1; ASTM D751; ASTM D5199
The nominal thickness is determined by measuring the distance that a movable plate is displaced from a parallel surface by the material while under a specified pressure. The results are usually expressed in mm (at a specified pressure).
Specimens of known size are cut and weighed. Using the weight, area and density (determined by ASTM D1505 or ASTM D792), thickness is calculated.
ASTM D7466; GRI GM12
The asperity height of a textured geomembrane is measured with a depth gauge, the setting block of which rests on top of the asperities while the contact point extends to the sheet’s core thickness.
Carbon black content
Specimens of known weight are heated to 600 ˚C in a nitrogen atmosphere; the polymer decomposes leaving carbon black. The residue is weighed and percentage carbon black determined.
Carbon black dispersion
ASTM D5596; ASTM D3015 (NSF Mod.)
Very thin slices of geomembrane are cut and examined microscopically (100x magnification) for quality of pigment dispersion. The appearance is compared to a dispersion reference chart.
BS EN ISO 12236; BS 6906: Part 4; DIN 54307; ASTM D6241; ASTM D4833; FTMS 101C/2065
Specimens for test are clamped between circular rings with a specified internal diameter and a puncture probe of known material and dimensions is pushed centrally against and normal to the fabric at a specified speed until failure of the specimen occurs. Push through force (N) and plunger displacement (mm) / elongation (%) (where appropriate) are measured.
This test measures the changes in linear dimensions of specimens of known size, when exposed to specific conditions of elevated temperature and time.
Specimens are immersed in a density gradient column and their height in the column compared with standards of known density.
A specimen is weighed in air. It is then immersed in liquid, its loss in weight upon immersion is determined and its density calculated.
Melt flow index
This test measures the rate of extrusion of molten polymer through a die of specified length and diameter at specified conditions of temperature, load, and piston position in the barrel as a timed measurement is made.
BS EN ISO 527-1; ISO 527-3; ASTM D6693; ASTM D638
Dumbell shaped specimens are extended to break at a constant speed and tensile strength and extension at both yield and break measured.
Determination of 2% Secant Modulus for polyethylene geomembranes
Dumbell shaped specimens are extended at a specified speed and the load at 2% strain measured.
This test method is designed to measure the force to initiate tearing at a low rate of loading. The specimen geometry of this test produces a stress concentration in a small area of the specimen. The maximum stress, usually found near the outset of tearing, is recorded as tear resistance.
Resistance to stress cracking using notched constant tensile load test
BS EN 14576; ASTM D5397
This test consists of subjecting a dumbbell shaped notched specimen to a constant tensile load in the presence of a surface-active agent at an elevated temperature. The time to failure of the test specimen is recorded.
This test measures the amount of water absorbed by the test specimen under defined conditions of time and temperature.
Oxidative Induction Time (OIT)
ASTM D3895; BS EN ISO 11357-6
Oxidative Induction Time (OIT) is determined by differential scanning calorimetry. The specimen for test and a reference material are heated at a constant rate in an inert gaseous environment. When the specified temperature has been reached, the atmosphere is changed to oxygen maintained at the same flow rate. The specimen is then held at constant temperature until the oxidative reaction is displayed on the thermal curve. The time interval from when the oxygen flow is first initiated to the oxidative reaction is referred to as the induction period. The end of the induction period is signalled by an abrupt increase in the specimen’s evolved heat and may be observed by a deferential scanning calorimeter (DSC). The OIT is determined from the data recorded during the isothermal test.
Low Temperature Brittleness
This test method covers the determination of the temperature at which plastics exhibit brittle failure under specified impact conditions.
Integrity of geomembrane seams
ASTM D6392; ASTM D4437 (NSF Mod.); ASTM D413 (NSF Mod.)
Ten specimens of known dimensions are taken from the seamed sample. Five specimens are subjected to the 90˚ T-Peel test and five to the shear test, all under specified conditions.