“Standard criteria for identifying high quality HDPE Geomembranes for successful projects ”

by

 Shivendra Singh, B.Tech. Civil Eng. Business Development Manager Technical – International Megaplast India Pvt. Ltd.

shivendra.singh@megaplast.in

 

Abstract:

Geomembranes are flexible polymeric sheets mainly used as liquid and/or vapour barriers. Polymeric geomembranes are designed as relatively impermeable liners for use in a variety of containment situations (e.g. to contain water, process fluids, leachates, mine liquors and contaminated industrial liquid effluents), in applications where natural clay or other containment options are not possible or viable.

Geomembranes are used extensively in a broad array of industries such as water conservation, mining, construction, waste management, agriculture, aquaculture, and wine making. Their diverse applications include water protection; conveyance and storage; basins and ponds; municipal solid waste (MSW) and hazardous waste (HSW) landfills; process water ponds and leachate collection ponds; storm water collection ponds; evaporation aprons; private and commercial water features; floating covers and other containment facilities. In all these applications geomembranes intercept the flow path of liquid through soil, performing fluid barrier functions in the containment system.

Geosynthetic engineers, specifiers, designers, facility owners and operators are presented with a diverse range of geomembrane materials which all appear to provide similar benefits based on basic mechanical properties. This paper helps to identify the key factor to consider when assessing the suitability of a given geomembrane product about its performance when it comes to warranty, installation, welding, chemical resistance and environmental durability.

Introduction to Megaplast – Quality HDPE /LLDPE geomembrane Manufacturer:

Megaplast is a leading manufacturer of Geomembranes (HDPE/LLDPE).

A dependable PE products manufacturer, Megaplast has gained a reputation for reliability, for providing product innovation, quality consistency, price stability and trustworthiness.

Manufactured in India, its products are sold in different countries around the world also in high quality oriented markets like Australia, Qatar, United States of America (USA), Africa, South America (PERU), Canada, Europe (ITALY, SWEDEN AND SPAIN), Israel, Egypt, Malaysia, New

Zealand , Africa ( Nigeria, UGANDA, Tanzania, Kenya etc.). Megaplast Geomembranes are used by the biggest names in the mining, petroleum, waste management, water, and civil engineering sectors. With a manufacturing plant equipped with the latest technology and run by a skilled workforce, we maintain an output capacity of 12,000 Metric Tonne per year. Geomembrane manufacturing facility is spread over 40,000 Sq. Mt. floor area, equipped with highly precise automated machinery, where we produce Liners for a variety of end-use applications. Our manufacturing units are in Daman, the hub of plastic industry in India and also close to the Nhava Sheva port. We maintain global quality and manufacturing standards, to give our best to the customers.

An ISO 9001:2015 certified company & equipped with the latest tech in the plastics industry, we are here to achieve higher quality output. Our laboratory, run by dedicated staff, ensures uncompromising on-line and off-line quality testing results, to make the best quality product, which consistently exceeds customer expectations. This combination of outstanding resources, dedicated employees and latest technologies that are professionally managed, makes Megaplast a leader in PE products and become a single source solution.

Made in India used across the World, Applying the best of People, process and technology.

Megaplast Geomembranes are manufactured to international and various national standards such as GRI GM 13 and 17, CE etc.

Megaplast has the following credentials to credit:

 

  1. ISO 9001:2015 certified company
  2. Geomembrane rolls with width of 8 meters.
  3. Three-layer co-extruded geomembranes adhering to GRI GM13
  4. GAI-LAP certified laboratory
  5. CE marking for European markets
  6. HDPE/LLDPE – smooth / textured liners
  7. High UV/ chemical / Thermal resistance
  8. Environmental stress & crack resistance
  9. Supply to reputed projects in India and international market
  10. Third party product certifications
  11. Black coloured geomembranes (other colours like white, blue, green, grey, etc. available on request)

STANDARD CRITERIA FOR IDENTIFYING HIGH QUALITY HDPE GEOMEMBRANE LINERS FOR SUCCESSFUL PROJECTS

It is highly recommended to use the minimum specifications for a quality HDPE geomembrane product which are contained in The Geosynthetic Research Institute (GRI) test method GM13 “Test Properties, Testing Frequency and Recommended Warrant for High Density Polyethylene

HDPE) Geomembranes” sets forth a set of minimum properties that must be met, or exceeded, by both smooth and textured high density polyethylene (HDPE) geomembranes upon being manufactured. In some of the properties, a range is specified. In the context of quality systems and management, this specification is targeted toward manufacturing quality control (MQC). This standard specification is intended to ensure good quality and performance of HDPE geomembranes in general applications. If the HDPE geomembrane product meets the requirements of the GRI GM-13 specifications, then it is regarded as a best practice product.

The highly recommended standard performance criteria for HDPE geomembrane can be summarized as follows:

Physical Properties

This category includes thickness, asperity height, density, and melt index.

Thickness – For all geomembranes, the nominal thickness of the geomembrane is the obvious target value. For smooth sheet, the average thickness must be the nominal value; however, the lowest individual of 10 values can be -10% due to variation of the material and testing. For textured geomembranes, the average core thickness can be 5% less than the nominal thickness of the sheet. ASTM D 5994, was adopted to measure the core thickness of textured HDPE geomembranes. For textured geomembranes, the average core thickness can be 5% less than the nominal thickness of the sheet.

  • Asperity Height – An index test, ASTM D 7466, was developed to measure the height of textured profile using a depth gauge. This is an index property and is only applicable to textured geomembranes. The property has no known correlation to the interfacial shear strength behaviour of the geomembrane, e.g., as determined using ASTM D 5321 direct shear testing. The minimum average value should be 0.40 mm.
  • Density – A minimum value of 0.940 g/ml is required for the as-formulated manufactured geomembrane, as per ASTM D 883 and ASTM D 1505/D 792 .It should be recognized that the virgin resin has a lower density value than the formulated material.
  • Melt Index – ASTM D 1238 is the standard for this property .The difference between melt flow index values per ASTM D 1238 for HDPE geomembrane made from blown film versus flat extrusion methods is significant. Since both manufacturing methods are appropriate, a range was considered, but it is so broad as not to be meaningful.

 

Mechanical Properties

This category includes tensile properties, tear resistance, and puncture resistance.

  • Tensile properties – ASTM D 6693 is consider to be standard for tensile properties .The test is performed according to ASTM D 638 Type IV using dumbbell shaped specimens. Four test parameters are required: yield stress, break stress, yield elongation, and break elongation. The minimum average value of these four parameters refers to both machine and cross machine directions with 5 test specimens being required in each direction. The minimum yield stress for both smooth and textured geomembranes is 15,000 kN/m2 and the break stress is 27,000 kN/m2. In the specification, these values are presented in units of “N/m” by multiplying the stress by the nominal thickness of the geomembrane. Regarding the elongation, the minimum yield elongation for smooth and textured sheets is 12% using a gage length of 33 mm. The break elongation for smooth and textured geomembranes is 700% and 100%, respectively. The gage length used to determine the break elongation is 50 mm. The relatively low break elongation for textured geomembranes is for textured sheet manufactured by the blown film co-extruded texturing process. The test frequency for these tensile properties is every 9,000 kg.
  • Tear resistance – As per ASTM D 1004 the minimum average tear resistance is 125 kN/m (125 N) for both smooth and textured geomembranes. Data in the tables are presented in units of “N” by multiplying the above value by the nominal thickness of the geomembrane. The test frequency is every 20,000 kg.
  • Puncture resistance – This value is evaluated according to ASTM D 4833. The minimum average puncture resistance is 320 kN/m (320 N). Data in the table are presented in units of “N” by multiplying the above value by the nominal thickness of the geomembrane. The test frequency is every 20,000 kg. It should be noted that the required value for the above three mechanical properties varies linearly with thickness. It is assumed that the thickness of the geomembrane has no influence on the fundamental stress, or strength, of the geomembrane. Generally, the strength of the bulk material increases slightly with thickness due to the increase in crystallinity in bulkier products. However, the actual correlation is not well defined, and is strongly dependent on the processing method. As a conservative approach, strength values obtained from thinner geomembranes are used in the calculation for greater geomembrane thicknesses

Endurance Properties.

Though all the physical, mechanical and endurance properties are important but the author is of the opinion that endurance properties becomes key in successful projects in the long run.

The key for getting good endurance properties is that the geomembrane must be made of high density polyethylene (HDPE) and not contain any recycled polymer.

This category includes stress cracking resistance, carbon black content and dispersion, OIT, oven aging, and UV resistance. They are essential in assuring the long-term performance of the geomembrane.

  • Oxidative induction time – Both the standard (Std-OIT, ASTM D 3895) and high pressure (HP- OIT, ASTM D 5885) tests are used in the specification. Either the Std-OIT test or the HP-OIT test can be used to evaluate this property. The oxidative induction time of the geomembrane must exceed (a) 100 min, as determined by ASTM D-3895(Test Method for Oxidative-Induction Time of Polyolefins by Differential Scanning Calorimetry) or (b)400 min, as determined by ASTM D-5885 (Test Method for Oxidative-Induction Time of Polyolefin Geosynthetics by High-Pressure Differential Scanning Calorimetry).

The oxidative induction time of the geomembrane after oven ageing at 85 ◦C for 90 days, as described in ASTM D-5721 (Standard Practice for Air-Oven Ageing of Polyolefin Geomembranes), must exceed (a) 55% of the value for the original geomembrane, as determined by ASTM D-3895-95 (Standard Test Method for Oxidative-Induction Time of Polyolefins by Differential Scanning Calorimetry), or (b) 80% of the value for the original geomembrane, as determined by ASTM D-5885 (Standard Test Method for Oxidative-Induction Time of Polyolefin Geosynthetics by High-Pressure Differential Scanning Calorimetry)

  • Carbon black content – The test is performed according to The test is performed according to ASTM D 1603 /D 4218, , with a specified range from 2 to 3 %. The 3% carbon black value is the maximum capacity level above which no significant improvement in ultraviolet resistance occurs.
  • Carbon black dispersion – The standard test is ASTM D 5596 for this property .The specification for this property is based on viewing ten microtome slides, which are taken from various locations along of the width geomembrane. The image that is observed under 100x of a transmission light microscope is compared with patterns that are shown on the reference chart. Nine of ten views should be in Category 1or 2 and one can be Category 3 to assure the uniformity of the carbon black in both dispersion and distribution.
  • Ultraviolet (UV) resistance – For HDPE geomembranes that are exposed to sunlight during their service life, UV resistance is a major property that must be evaluated. The exposure procedure used to assess UV resistance is conducted according to ASTM D 7238 using an UV-fluorescent weatherometer. The exposure time is for 1600 hours, with alternating 20 hour of UV at 75°C followed by 4 hour condensation at 60 °C. For exposed geomembranes, the material’s UV resistance is obviously a critical property. only the HP-OIT is recommended to be used in the UV resistance test. The average HP-OIT retained value was initially set at 50% .
  • Oven aging – The purpose of oven aging is to challenge the long-term thermal oxidation behavior of the HDPE geomembrane. The incubation procedure is conducted according to ASTM D 5721 in forced air ovens at 85°C for 90 days. The OIT is designed as an index test to verify the existence of antioxidant after high temperature exposure. The percent- retained value cannot be less than 55% for Std-OIT or 80% for HP-OIT testing
  • Stress cracking resistance – This property is evaluated using the SP-NCTL test as 500 hours failure time as per ASTM D 5397

 

HDPE GEOMEMBRANES SELECTION IN AGGRESSIVE ENVIRONMENTS

Geomembranes have become critical components in the design and environmental performance of mining applications. The mining industries extensively utilize geomembranes in heap leach pads, solution ponds and evaporation ponds. Due to the enormous size of many of these mining applications, mines have come to represent a significant percentage of geomembrane consumption. Mining companies stretch the capabilities of geomembranes to their limits and sometimes to the point of failure. For example, leach pads are heaps of rocks/ore up to 120–180 m high piled on a geomembrane pad. In addition, there is traffic on the liner leach pad in the form of truck hauls or dozer pushes. Furthermore, the liquors used are highly acidic with pH values of around 1. Thus, leach pads present one of the most aggressive service environments for geomembranes.

Due to their functionality geosynthetic liners and membranes are utilized in some of the most demanding applications that synthetic materials have been called upon to perform in. Service environments often combine extreme heat and UV exposure together with high mechanical loading and exposure to aggressive solutions and slurries. In addition, geosynthetic liners are expected to exhibit long-term durability with service lives being measured in decades rather than years. Expected service lives generally range from 20 to >100 years.

Geosynthetic liners are used extensively in critical applications such as protecting the water table from toxic landfill leachates or preventing corrosive mine process solutions from contaminating soil and aquifers. The failure of such geosynthetic barriers can have devastating environmental consequences. Given that they must withstand the extremes of weather and be laid over coarse and soft subgrades it is important that a generous safety factor is employed in their installation designs.

Geosynthetic liners such as landfill caps need to have excellent longevity since they are intended to become permanent features of the landscape. In landfill design, geomembranes are typically used as base liners (or basal liners) which are placed below waste to minimise seepage of leachate into the underlying soil and into the water table. Geomembrane covers are placed over the final waste to keep surface water and rainwater from infiltrating the waste and adding to the volume of leachate solution. The geomembrane cover also serves to capture the landfill gas preventing release of methane which is a potent greenhouse gas. Base liners are typically HDPE because of its inherently good chemical resistance and strength, whereas the covers are generally LLDPE since they are more flexible than HDPE.

SUMMARY AND CONCLUSIONS

Although modifications, upgrading and enhancement of properties of HDPE geomembranes is a continuous process. Megaplast can produce HDPE geomembranes in accordance with latest acceptable specification continuously innovate the products. In order for the identification of quality HDPE geomembranes to be fully effective, however, the owner/specifier/regulatory communities must adopt and require it use if the relevant test methods, achievable property values, and appropriate long-term performance is the goal of a HDPE geomembrane user, Manufactures like Megaplast should be seriously considered for adoption and use for successful projects.

Future is a way too exciting for the geomembranes. We may find Single-unit composite liners, Seven and Eight layer geomembranes with self-healing capabilities, infrared thermography for the non-destructive measurement of seam bond strength over 100% of the width and length of a weld and feedback for welding machine control, increased use of electrical (and other) surveys for leak location, spray applied seamless liners on GCLs and geocomposites, and exposed geomembranes with nano-photovoltaic surface layers for the generation of electricity. Lining technology is only just beginning to take its shape now and Megaplast is committed to research and development for successful projects across the world.

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