Comparison of the Extrusion Laminated Polyester Scrim Reinforced Geomembranes (30 Mil LLDPE-R) and Coated Woven Geotextile (30 Mil RPE)
This purpose of this article is to explain the difference between extrusion laminated polyester scrim reinforced “geomembranes” (Dura-Skrim® N30B or 30 Mil LLDPE-R) – as defined in GRI GM25 and Coated Woven “geotextiles” (30 Mil RPE) as defined in GRI GM30.
Coated woven geotextiles are produced using highly tinseled high-density polyethylene (HDPE) tapes that are woven together and coated with a thin layer of linear low-density polyethylene (LLDPE). The two polymers that go into the manufacturing of this product are dissimilar in nature. During the process, the hot melted LLDPE is applied to a cold sheet of HDPE woven tapes. For a 30 Mil RPE, the coating is only 2-3 Mils thick.
30 mil Woven Coasted Product
30 mil LLDPE R
Due to the way this product is manufactured, one inherent issue is the dis-bonding of polymers during any factory or field welding operations. This is because the two polymers that makeup a coated woven product heat-up at different rates. The heated LLDPE coating of the two sheets being welded together will bond (LLDPE to LLDPE) but tend to dis-bond from the high-density reinforcing inner tapes. This weakens the seams and compromises the structural integrity of welds.
Coated woven geotextiles should not be considered for long-term liquid containment applications due to the inherent risks of lightly coated materials. Another risk is pin-holding — the separation of woven tapes. Pin-holding is caused by downward pressure on the product from traffic running over the material during installation or end-use operation. It is too-lightly coated resulting in the critical loss of the products barrier properties.
Another issue with woven coated geotextiles is UV stability. Since there is typically only 2-3 Mils of LLDPE, the light-weight coating needed to protect the overall integrity of the product can be jeopardized, which in turn then loses its ability to perform as a barrier in liquid containment applications.
30 RPE woven coated geotextiles also have another curiosity to them. They claim to be 30 Mils in thickness, and yet typically weigh about the same as a 20 Mil geomembrane — mostly due to the weaving of the high-density tapes and the voids that are created. It allows for thickness, but the polymer usage is much less.
The Geosynthetics Research Institute (GRI) sets the standards for materials used across the industry for various applications. Reference the GRI standards here: http://www.geosynthetic-institute.org/specs.htm
GM25 was established to govern the use of scrim reinforced geomembranes (LLDPE-R) for geomembrane liner applications: Severe (45 Mil) Category 2; Moderate (36 Mil) Category 3; Standard (24 Mil).
GM30 was established to govern the use of coated woven geotextiles for cover applications: Category 1; Severe (40 Mil) Category 2; Moderate (30 Mil) Category 3; Light (24 Mil).
GRI does not recognize a coated woven (RPE) as a geomembrane, but rather a geotextile coated with a light thin layer of polyethylene, resulting in the loss of the barrier.
For Dura-Skrim N30B, the initial step in the manufacturing process is to extrude a first pass sheet geomembrane that is highly UV stabilized. Next, the product goes through an extrusion lamination process where the first pass geomembrane is bonded together with the reinforcing scrim and a hot sheet of the same LLDPE polymer to produce one homogenous sheet of material. The whole product is made of the same polymer and forms one continuous homogenous membrane — classified as a “geomembrane.”
Dura-Skrim N30B is highly UV Stabilized and carries a 20-year exposed warranty. Depending on duration and performance expectations, this may be something to consider.
All of Raven Engineered Films products, including Dura-Skrim, are produced and fabricated by Raven. All woven manufacturers rely on downstream conversion by fabricators who purchase the product, then convert it into larger panels. If something goes wrong in the process, it is difficult to track who is at fault. Raven is fully integrated manufacturing, fabrication, and installation abilities allow them to be alongside the customer throughout the entire project for a seamless customer experience.