Geosynthetics June/July 2023 - 40

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By George R. Koerner
Updated accelerated aging test
for geomembranes
he accelerated aging process is based on the relationship between temperature and
chemical reaction rate, in which the reaction rate increases as temperature rises. Most
accelerated aging tests use higher temperatures to accelerate the aging process by representing
real-time aging artificially. A good accelerated aging test should simulate real-time aging by
using elevated temperatures to speed up the aging process.
Accelerated aging is often a specification endurance requirement for geomembranes,
which will hopefully be related to real-time aging and actual service life performance of the
product in question.
The anticipated service lifetime due to general material degradation is invariably asked
by owners, regulators and designers, as well as the suppliers, manufacturers and installers
that are involved. Other than intentional or accidental damage, the possible degradation
mechanisms identified by Hsuan et al. (2008) are as follows:
* ultraviolet radiation, oxidation, hydrolysis, chemical, radioactive, biological, migration
and temperature.
Each mechanism only has relevance depending on the site-specific conditions as well as
George R. Koerner, Ph.D.,
P.E., CQA, is the director of
the Geosynthetic Institute
in Folsom, Pa.
the specific type of geosynthetic resin and the formulation from which the geomembrane
was made. If indeed a specific mechanism is involved, testing organizations have appropriate
standards for such laboratory evaluation. The results of such testing, however, are usually of
a " go-no-go " nature insofar as a final selection of material. They are not meant to be lifetime
prediction methods in themselves. The most frequently asked question regarding all types
of geomembranes is: " How long will they last? "
For most geomembranes, the answer is governed by the following: the formulation, fabrication,
shipping and handling, proper design, installation, exposure environment and how
well the geomembrane was maintained. To answer the lifetime question, the use of several
different tiered elevated temperature incubations, followed by extrapolation to lower (presumably
site-specific) temperatures, is utilized. Such Arrhenius modeling has been described
by Koerner et al. (1990) and others; however, it cannot be routinely specified or checked.
Hence, we have a quandary. Do we have aging tests that can quickly assure us that we
have durable geomembranes for most applications? For HDPE geomembranes we have relied
on ASTM D5397 Stress Crack, ASTM D5721 Oven Aging and ASTM D7238 QUVA in the
GRI-GM13 standard to satisfy this challenge. However, HDPE formulations have gotten
so good over the past few years that these tests are no longer aging the material quickly
enough. Therefore, we need a test that can age the material in less than 90 days and still be a
good indicator of performance. We have dabbled with exposing these systems under stress
(autoclave or burst); however, neither has given us the acceleration effect that we are looking
for in the 90-day time frame.
Supported by the work on accelerated aging of HDPE geomembranes exposed to the
leachate at 122°F (50°C) (EPA 9090 and then ASTM D5322), we believe that an incubation
exposure may be in order. The change of properties as a function of aging can be assessed

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Geosynthetics June/July 2023

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