The Geosynthetic Institute (GSI) will sponsor a webinar, “Lifetime Predictions of Nonexposed and Exposed Geosynthetics,” on Sept. 8, from 11:30 a.m. to 1 p.m. EDT. Geosynthetic Materials Association (GMA) member companies and their employees receive discounted rates on all GSI webinar and short course registrations.

A most frequently asked question regarding all types of geosynthetics is, “How long will they last?” This webinar answers the question for exposed geotextiles and geomembranes assuming that they were properly designed and installed. Furthermore, it compares these new results to earlier lifetime prediction results on a covered geomembrane.

Nonexposed (or covered) lifetime conditionshave been previously evaluated and published on a 60 mil (1.5 mm) thick high density polyethylene (HDPE) geomembrane. It used landfill incubation devices at four elevated temperatures of 185, 167, 149 and 131°F (85, 75, 65 and 55°C) to reach 50% of retained strength and elongation. Considering the three stages of (i) depletion of antioxidants, (ii) induction time, and (iii) 50% reduction in mechanical properties, the lifetime extrapolation was made down to 68°F (20°C). The half-life for this geomembrane under these conditions is approximately 450 years. Since the incubation times were 10 years, other covered geosynthetics were not evaluated under the supposition that the nonexposed situation is generally a moot point for most geosynthetics in their customary applications.

For exposed geosynthetics, however, the situation is quite different. Ultraviolet radiation, elevated temperature and full oxygen are available, which shorten the service lifetime, but by how much? For evaluation of this situation, we utilized laboratory ultraviolet fluorescent tube weathering devices per ASTM D7238 for incubation purposes. Seven different geotextiles, four turf reinforcement mats (TRMs), two geogrids and six different geomembranes were evaluated. Each different material was incubated at 176, 158 and 140°F (80, 70 and 60°C) until 50% reduction of strength and elongation occurred. The data was then extrapolated down to 68°F (20°C) for laboratory halflife values and for comparison with the nonexposed condition. The ratio of nonexposed to exposed lifetime for high-density polyethylene (HDPE) geomembranes is approximately 5.0. The calculations for the nineteen exposed geosynthetics then progressed to using site-specific radiation to obtain an equivalent field life. Phoenix, Ariz., conditions are illustrated although the procedure is applicable worldwide. Half-life predictions for the geotextiles vary from a few months for the needle-punched nonwovens to up to 10 years for monofilaments and high antioxidant formulated products. Results for geomembranes vary from 47 to 97 years, with HDPE being the highest. These exposed half-life results (which took 12 years and are ongoing) are felt to be most interesting and are presented for the first time to an international audience.

Learning objectives

Webinar participants will gain familiarity of how lifetime prediction of all polymeric materials are made, including geosynthetics. The technique is incubation at several high temperatures to accelerate degradation, measure property changes, and then to extrapolate down to site-specific (i.e., actual) temperatures to estimate lifetime.

The webinar is a result of more than 10 years of U.S. Environmental Protection Agency (EPA) funding and then 12 years of Geosynthetic Institute/Geosynthetic Research Institute research focused on providing lifetime estimates of geosynthetics. For the nonexposed (buried) situation, complete laboratory simulation is used. For the exposedsituation, laboratory fluorescent ultraviolet weathering devices are used. The former evaluates only HDPE geomembranes, the latter nineteen different geosynthetics. For the nonexposed situation, lifetimes are well beyond civil engineering application lifetimes, in this case 500 years. It is seen that the exposed situation lifetimes are within the usual civil engineering lifetime expectations.

Webinar benefits

• Learn about lifetime prediction methods for polymers
• Learn specifically about the methodology with respect to geosynthetics
• Learn about the nonexposed half-life of HDPE geomembranes
• Understand that lifetime of nonexposed geosynthetics are generally far greater than typical civil engineering applications and other components
• Learn about lifetimes of 19 different geosynthetics under simulated exposed conditions

Intended audiences

This webinar is intended for public and private regulators and facility owners, civil and industrial engineers, property developers, contractors and installers, academic and research groups, the general lay public and others desiring technically related information on this most frequently asked question.

Specific topics covered

1. Background
2. Covered Lifetime Using Lab Simulation
3. Results for Covered HDPE Geomembranes
4. Exposed Lifetime Using Weathering Devices
5. Results for 19 Different Exposed Geosynthetics
6. Summary-to-Date

Webinar instructor

George R. Koerner, Ph.D., P.E., and CQQ, is the director of the Geosynthetic Institute. He is in charge of laboratory accreditation, field certification and continuing education at the institute. He also manages several research projects and has published more than 350 technical papers in his 35-year association with polymers used in below-ground construction. Koerner’s Ph.D. is from Drexel University in geotechnical engineering. He is a registered professional engineer and a certified quality auditor. Koerner has received many awards over the years. The most notable being ATA’s Environmental Technologies Award of Excellence 1995, ASCE’s DVGI Geotechnical Engineer of the year in 2004, the title of ASTM Fellow in 2013 and GMA’s first Robert M. Koerner Lecture and Award in 2017.

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Webinars cost $200.00 for GSI and GMA members, and $250.00 for nonmembers.

Successful completion of a multiple-choice test after the webinar carries 1.5 professional development hours (PDH).

For more information or to register, visit http://www.geosynthetic-institute.org/webinar.htm.