Recap of ASTM/GRI-23.
By Bob Koerner
A workshop on field and laboratory experiences of geosynthetic materials durability was held in conjunction with ASTM’s Committee D35 meeting in San Antonio, Texas on Jan. 29, 2010.
This one-day event was organized by Sam Allen of TRI Environmental and George Koerner of the Geosynthetic Institute. There were 19 presentations and to say that the topics, presentations, and audience participation were all excellent is a decided understatement. Rave reviews and numerous compliments were expressed at the workshop’s conclusion and in the days following. A glimpse of the material presented by each speaker follows.
The morning session focused on geomembrane durability. Bob Koerner of GRI presented a review of laboratory-exposed geomembrane durability via 5 years of incubation in ultraviolet fluorescent weathering devices. HDPE, LLDPE, fPP, and EPDM were included in the evaluations and, properly formulated, all should function for at least 30 years in a hot climate. Rick Thomas of TRI followed, describing how an investigator assesses the remaining life of exposed geomembranes that have already been in service. The issue, of course, is how much longer is the material viable. Rick gave several interesting illustrations of his technique. Ian Peggs of I-Corp followed with his approach toward predicting end-of-life for exposed HDPE geomembranes. For HDPE he looks at surface oxidation, embrittlement, and initiation of stress cracking. These three opening presentations dovetailed in a very instructive manner.
George Koerner of GSI then presented two case histories of exposed HDPE geomembranes (16 and 20 years), with comparison of various property values as-manufactured vs. their current condition. Oxidative induction time was seen as the key parameter to monitor in this regard. Mark Wolschon of EPI International illustrated how a PVC geomembrane retained its functionality after 30 years of exposed service. Bob Koerner of GSI then illustrated the basic failure modes of fPP geomembranes: cracking, powdering, and flaking. This latter mode has never been reported before. Craig Benson of the University of Wisconsin gave his results of the behavior of various exhumed geosynthetics in landfill covers after service lifetimes of 5-9 years at 9 different landfills. Most significant in this regard was the reported loss of interface strength of thermally bonded geotextile-to-geonet drainage composites.
In a change-of-pace presentation, Chris Athanassopoulos of CETCO (for Archie Filshill) described how polymer additives inserted into the structure of bentonite enhances physical and mechanical properties of geosynthetics using data from HDPE testing. Indeed, nanotechnology has come to geosynthetics!
Jimmy Youngblood of GSE illustrated the 9-year and 20-year performance of two HDPE lined surface impoundments. As illustrated by physical and mechanical testing, there was no apparent degradation. John Cowland of GeoSystems Ltd. gave a presentation that compared steel tank containment of hazardous liquids against a floating geomembrane cover system. The latter is significantly more economical. Five years of performance data for such an application was also presented. This particular presentation engendered much participant discussion with respect to geomembrane additives, and whether the specific anti-oxidant formulations should be made public (at least to the owner/designer/purchaser). It was a lively discussion to say the least!
The afternoon session focused on durability of geosynthetics other than geomembranes. Willie Lieu of Tensar began by presenting data on exposed PP geogrids in laboratory incubation for 80°C, 70°C and (anticipated) 60°C with a resulting halflife of 114 years. Ben Doerge of the USDS-NRCS federal agency presented geotextile information after exhuming samples that had been in place for 20 years. There were no changes in any of the mechanical properties. This type of “no change” is a powerful inducement for agencies to use geosynthetics for long-term applications. Robert Lozano of Linear Composites presented data on three MSE walls that had been in-place for 20-30 years. The PET reinforcement geogrids showed no signs of hydrolytic degradation. J. P. Kline of Geotechnics presented results of an overlap test to evaluate possible leakage between adjacent GCL panels. The resulting permeability through the seam overlap indicates a maximum permeability of 5 x 10-9 cm/s, which meets the GRI-GCL3 specification. Eric Blond of SAGEOS and Pascal Saunier of Afitex-Texel presented their laboratory evaluations of a new drainage geocomposite insofar as mechanical and hydraulic properties are concerned. Joel Sprague of TRI Environmental illustrated a potential in-situ test method to evaluate the tensile strength (aka, possible degradation) of rolled erosion control products.
H.-Y. Jeon of INHA University used accelerated immersion testing with different liquids at different pH values to evaluate possible degradation of geotextiles. Guidance on the conditions and criteria for acceptable long-term performance were also presented. Kent von Maubeuge of NAUE gave two sets of exposed durability data on black vs. white geotextiles. In the laboratory weathering device, the black geotextile outperformed the white geotextile, while in the field the exact opposite was observed. The discussion as to why and how this occurred was fascinating. Dhani Narejo of Caro Engineering offered historical insight into two geocell walls, one nonvegetated, the other vegetated. No noticeable degradation to the HDPE material was noticeable in either wall after 25 years of service.
Sam Allen was the excellent moderator of the workshop and George Koerner closed the event by summarizing each paper in an accurate and succinct manner. A booklet of the 19 abstracts is available from GSI. That said, if specifics of any presentation is desired the presenter should be contacted directly. Also to be mentioned is that many of the abstracts are coauthored. To those coauthors, appreciation is also extended. Lastly, Sam and George thanked the audience for their active and lively questions that followed each of the 19 presentations.