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Celebrating a decade of GSI/GRI polyolefin specs

June 1st, 2008 / By: / Specifications, Updates

From the very beginning of the GSI/ GRI consortium in 1986, it was recognized that specific focus groups were the way to initiate individual programs and documents. After a draft document is eventually established within a group, the entire membership is then brought into the activity for modification and eventual agreement. This approach has worked well over the years. At a Sept. 16, 1993, meeting in Philadelphia, the issue of crafting GRI specifications was seriously discussed among a combined group of resin producers and geomembrane manufacturers. The status of geomembrane specifications at that time were:

  • The only generic geomembrane specifications were from the National Sanitation Foundation (NSF).
  • The values were minimal, particularly those related to geomembrane durability.
  • Many withdrawn and unavailable geomembranes were included.
  • Many new geomembrane types were available but not included.
  • Regulators were apprehensive with the continued use of these specifications.
  • Consultants and specifiers would support a credible alternative effort.

At a Dec. 23, 1993, meeting in San Diego, a high-density polyethylene (HDPE) specification was targeted, beginning with the development of the required durability methods and criteria. This was followed by 2 years of research primarily on stress cracking and oxidative induction time (OIT) testing after oven aging and ultraviolet exposure. The work was supported by the U. S. EPA and by membership fees, and was primarily done by Grace Hsuan at GRI’s lab at Drexel University.

At a Dec. 13, 1995, meeting in Philadelphia, work began in earnest on template specification development for HDPE, followed a few years later by very flexible polyethylene (VFPE), and then still later by flexible polypropylene (fPP) geomembranes. This decision brought in all of the resin producers and geomembrane manufacturers to help craft the necessary physical, mechanical, and durability property values for the new specifications. Those involved at the time were:

Resin producers: Phillips–Rex Bobsein, Novacor–Nolan Edmonds, Solvay–Phil Dunaway, Mobil–Frank Nagy, Quantum– Adel Haddad, Chevron–Pam Maeger

Geomembrane manufacturers: GSE– Fred Struve/Bill Walling, NSC–Gary Kolbasuk/George Zagorski, PolyFlex– Jim Nobert/George Yazdani, Serrot–Bob Otto, S. D. Ent.–Dave Eakin

Following this meeting, intense HDPE testing was performed by all of these organizations in assessing the stress cracking performance of their materials via the new ASTM D5397 notched constant tensile load (NCTL) test developed and pushed through ASTM by Grace Hsuan. (The test method subsequently won a Heritage Award by ASTM.)

In addition, the standard and highpressure OIT initial values and subsequently after oven aging and ultraviolet fluorescent exposure were major durability items worked on by all. Note that both stress cracking and OIT performance are largely resin and additive related, thus the large group of resin producers was extremely active, and to a slightly lesser extent, the geomembrane manufacturers also. Simultaneous with the durability criteria development was the physical and mechanical property development. Here the geomembrane manufacturers played the major role, as did George Koerner, in evaluating and homogenizing the data into a single set of acceptable values.

After 3 meetings and countless telephone calls among the parties involved, the HDPE specification tables were completed. Text was then added and agreed upon by the 2 focus groups. The complete draft specification was sent to the general membership for comments, and there were many. The focus groups then assessed these comments and agreed to the final specification. It was launched June 17, 1997, under the title:

GRI-GM13: Standard Specification for “Test Methods, Test Properties, Testing Frequency for High Density Polyethylene (HDPE) Smooth and Textured Geomembranes.” Subsequently, this specification had 8 minor revisions.

Lagging by a few years, but under a similar development methodology, the LLDPE specification was adopted on Apr. 3, 2000, under the title:

GRI-GM17: Standard Specification for “Test Methods, Test Properties, Testing Frequency for Linear Low Density Polyethylene (LLDPE) Smooth and Textured Geomembranes.” Subsequently, this specification had 5 minor revisions.

The most recent versions of #13 and #17 are available free at GSI’s Web site: www.geosynthetic-institute.org.

Continuing with all of the available polyolefin resin types, the fPP specification was adopted on Feb. 18, 2002, under the title:

GRI-GM18: Standard Specification for “Test Methods, Test Properties, and Testing Frequencies for Flexible Polypropylene (fPP and fPP-R) Nonreinforced and Reinforced Geomembranes.”

Subsequently, this specification was temporary suspended on May 3, 2004, and then withdrawn on Jan. 22, 2007, due to concerns about OIT being able to predict long-term durability. Apparently, the antioxidant depletion characterized by oxidative induction times in HDPE and LLDPE geomembranes is more complicated (and less reliable) for fPP geomembrane formulations.

The last in this sequence of GRI polyolefin specifications that the combined groups addressed was field seam performance. The previously discussed specifications are silent on the topic of seams, thus the necessity of a separate specification. This specification addresses HDPE, LLDPE, and fPP geomembrane seams in all sheet thicknesses and types (e.g., smooth, textured, and scrim reinforced). The seam specification was adopted Feb. 18, 2002, under the title:

GRI-GM19: Standard Specification for “Seam Strength and Related Properties of Thermally Bonded Polyolefin Geomembranes.”

This set of 4 specifications and, in particular, GRI-GM13 for HDPE geomembranes, has revolutionized all aspects of the respective polyolefin geomembrane materials technologies. The required tests, their properties, and minimum testing frequency affects resin producers, additive suppliers, manufacturers, designers, specifiers, installers, inspectors, regulators, and owners alike. The impact of the specifications was never felt stronger than within weeks after suspending GRI-GM18, when we heard first from European producers and designers followed shortly by organizations in Australia, Israel, and South Africa. The entire set of specifications is currently worldwide in acceptance, utilization, and compliance.

Obviously, we at GSI/GRI are proud of the role we played in the process of polyolefin specification development. However, we recognize that many people and their respective companies were involved. To all of them, we extend our heartfelt appreciation. In this regard, we promise that we will be good stewards of these specifications, updating them when needed and continuing to offer them free to everyone. This applies also to our other specification development with other geomembranes and the geotextile, geogrid, geonet, and geocomposites specifications. In citing any of them, please include the appropriate GRI number and the words “latest modification.” It is this latest version that is regularly updated on our Web site: www.geosynthetic-institute.org

Robert M. Koerner, Director of GSI.

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