Geomembrane Composition and Antioxidants

The HDPE geomembrane contains antioxidant packages to protect the liner from oxidation during the production of the membrane and during the field life of the membrane. HDPE formulation consists of weight percentages 96-97.5% polyethylene (PE) Resin, 2-3% carbon black and up to 0.5% antioxidants. Carbon black is added to the geomembrane to limit potential damage by UV radiation. The amount of carbon black added is generally less than 3%. Amounts greater than that required to reduce opacity are wasted. The specific antioxidant package used in the HDPE formulation is dependent on the manufacturer of the HDPE. Antioxidants that are most widely used are indicated in Figure 8 Antioxidant Types (Koerner, 1998). Antioxidants are divided into two types; Primary, which limits oxidation during the geomembrane manufacturing process, and Secondary, which provide long-term protection during the service life of the material.

The chemical ageing of a geomembrane follows three stages:

  1. A period where the antioxidant is depleted.
  2. An induction period where the polymer degrades following the depletion of the antioxidant.
  3. Time to reach 50% degradation of a particular property (Half-Life)

The depletion of antioxidants is the result of the intrusion of oxygen into the structure of the geomembrane.

The rate of depletion of antioxidants is a function of among other things; the service temperature of the geomembrane and the presence of oxidizing liquid on one or both surfaces of the geomembrane. The rate of extraction of the antioxidant is controlled by the dissolution of the antioxidants at the surface of the geomembrane and the rate of diffusion from the interior to the surface of the geomembrane. It has been found that the consumption of antioxidants is three times faster in water than air (Smith, 1992).

Testing has been developed to measure the level of remaining antioxidants in a sample of geomembrane and thus provide an indication of the remaining service life of the HDPE. Two tests are:

OIT (Oxidative Induction Time). Samples are heated up under a nitrogen atmosphere, typically to 200C. Oxygen is then introduced to the sample cell, and the length of time before the onset of degradation, as seen by the initiation of an exothermic process in the DSC trace is measured

HPOIT (High Pressure Oxidative Induction Time). Similar to OIT testing but is carried out at lower temperature, 150C and higher pressure. The procedure was developed because heating to 200C can cause the decay of some types of antioxidants (HALS or Hindered Amine Light Stabilisers)and provide a false (low) indication of the level of antioxidant remaining in the formulation.

What Kind of Dam Liners We Should Use for a Pond

We are often asked what kind of liner we should use for a pond. The answer is not simple. There are many variables:

  • What is being stored? What is the PH of the liquid being stored? This will determine the type of polymer that is to be used if indeed a polymer is suitable at all. Liner manufacturers produce chemical resistance charts – these should be consulted.
  • Once the chemical compatibility is determined then we can decide what thickness of the liner is to be used. The thickness will be determined by the condition of the subgrade (How many rocks and what size and shape) and what life is required from the liner. The thicker the liner the more resistance there is to subgrade conditions and the longer the life in the sun. Resistance to rocks in the subgrade can be increased by the use of geotextile under the liner. It has been shown that a geotextile will act compositely with an HDPE liner to give better performance. HDPE is provided with antioxidants and UV stabilisers in its composition. The antioxidants are provided to give protection against oxidation during the manufacturing process and long term. The UV stabiliser is usually carbon black.
  • What colour liner. White liners expand less in the sun than black liners and produce smaller ripples when heated up. If the pond is an evapouration pond and is to be empty some or most of the time then the use of a white liner should be considered.
  • The batter slope and length will also have an effect on the type of liner. Where the batter length is long then the use of a rough-textured liner should be considered to give added frictional restraint to the sub-grade.

Liner type and thickness and configuration is a science on its own and has been the subject of extensive research. When making the call on a liner type consult someone with a background in the subject.

GDT Lining Sysems

GDT Lining has a mission to improve the industrial landscape by containing any harmful waste. We accept that waste is a biproduct of our industrial society. We aim to mitigate the downside to a level which is acceptable, by limiting the spread and effect of waste materials on everyday life.

We are always eager to work with our mining partners in the extraction of products which benefit the quality of life.

GDT Lining Systems has been in operation for over 20 years. We run a crew of up to 15 technicians and undertake projects with a value of up to $(AUD)6.0mil. GDT is located in rural Queensland in the town of Innisfail, approximately 100km south of Cairns. We service customers throughout Australia and Papua New Guinea. We specialise in remote work.

We undertake:

  • Design and Construct work.
  • Supply and install of lining systems.

We work with HDPE, Polypropylene, GCL’s and other geosynthetic products. Our preferred supply partners are:

  • Solamax www.solmax.com suppliers of HDPE
  • Cooley Group www.cooleygroup.com suppliers of polypropylene lining systems

The use of geosynthetic liners in mining applications has been established science for 40 years. Specifically, HDPE has been used extensively as the lining medium for Heap Leach Pads and lining of Tailings Dams. Other geosynthetic applications have included Evaporation Ponds for the reduction of liquid waste. The complexity of the lining system for a particular application depends on the nature of the material being stored or treated. When it comes to the need for liner systems for your industrial waste management requirements, we have the experience to provide meaningful advice.

GDT have designed and constructed many floating covers over; water, molasses, Dunder (Vinasse) and wastewater. We have had extensive experience with gas collection covers.

GDT Lining Systems can design, and construct liner based civil projects in a practical, easy to construct manner. We employ professional engineers experienced in civil and structural design.

GDT has designed and constructed many in-ground molasses storages throughout Queensland in the last 25 years. The largest of which has the capacity to hold up to 37,000 tonnes of molasses. The excavation for this molasses storage is approximately 140m long, 140m wide and 11m deep. As a result of GDT’s experience with Molasses Storages construction, they have become specialised in the requirements to make such a project successful.

WE work from start to finish on your geosynthetic projects.

Get Assistance with Dam Liners from the Experts

GDT Lining Systems have recently completed the construction of a Molasses Bladder Molasses generates CO2 and H2S when stored. Molasses often enters the storage hot and cools of emitting gas as it loses heat. If the gas is not removed from under the cover it will interfere with the roof drainage which may cause the gas flow under the cover to be blocked and large bubbles in the cover system to form.

A large central float with a gas collection pipe system on either side provides positive extraction of the gas by way or an inline industrial fan. Application of a small negative pressure under the cover has a big effect, pulling the cover down against the stored molasses and allowing water that is collected on top of the cover, from precipitation, to find its way to the perimeter drainage sump. Provide perimeter rather than central weights to the system.

GDT has been installing molasses storages for 30 years and has learned about the problems of gas produced.

GDT Lining has a mission to improve the industrial landscape by containing any harmful waste. We accept that waste is a biproduct of our industrial society. We aim to mitigate the downside to a level that is acceptable, by limiting the spread and effect of waste materials on everyday life.

Our Products and Services:

  • Dam Liners
  • Low cost water storages
  • Landfill liners
  • Mining applications including tailings dams, leach pads and acid rock covers.
  • Sewerage Ponds

Contact Us

  • Phone: 07 40617770
  • Email: andrewmaddocks@geosynthetic.com.au
  • Web: www.gdtliningsystems.com.au