Geosynthetics June/July 2023 - 41

after 30, 60, 90 and 120 days' immersion
via tensile properties, differential scanning
calorimetry and visual observations.
It appears that predictable minor changes
of the above properties take place under
the experimental conditions with 10 ppm
chlorine dioxide (ClO2) at 122° (50°C).
This solves the vexing issue of arriving
at a standard leachate and furthermore
models a harsh scenario.
This practice also covers a procedure
for the accelerated aging of geomembranes
with double 180° folds (i.e., a star
fold). See Figures 1-3 for the typical
sample coupon and situation with the
immersion container (mason jar) and
constant temperature water bath. The
types of geomembranes that this practice
is focused on are ideally relatively thin
geomembranes (less than 30 mil or 0.75
mm). The procedure could allow for the
examination of the effect of ClO2 concentration
(3, 5 or 10 ppm) at 122°F (50°C).
The downside is that one can't use higher
temperatures due to the accelerated consumption
of ClO2. Even at 122°F (50°C),
the solution needs to be changed once a
week so that proper concentration can
be maintained (controlled via pH = 6.8
+/- 0.1 monitoring).
The performance trends show that the
choice of resin type plays a key role in the
longevity of the geomembranes. In addition,
the stabilizer packages contributed
to better resistance to degradation in
chlorinated water.
Many factors affect the performance
of the geomembrane, including diffusion,
density and thickness. The simultaneously
increasing material embrittlement
and the consumption of active antioxidant
molecules imply an apparent
unselective reaction of ClO2 with the
polymer and the stabilizers' molecules.
Moreover, the radical nature and the high
reactivity of ClO2 leads to the formation
of carbon-chlorine species, which are
assumed to originate from degraded antioxidant
molecules. Our results are consistent
with those reported by Abdelaal
et al. (2019).
Geomembranes have shown themselves
to function well as landfill liners
and covers. However, our goal is to never
stop improving. Such laboratory accelerated
aging tests are of value in comparing
different products or different formulations
of the same product. The process
can also be used to contrast against a
given specification. It is the Geosynthetic
Institute's intention to update GRI
Standard GM24, Standard Practice for
Incubation and Subsequent Evaluation
of Single 180° and Double 180° Folding
of Geomembranes, and GRI Test Method
GM16, Standard Test Method for Observation
of Surface Cracking of Geomembranes.
These updated standards will be
critical to address the new wave of highperformance
geomembranes.
References
Abdelaal, F. B., Morsy, M.S., and Rowe, R. K. (2019).
" Long-term performance of a HDPE geomembrane
stabilized with HALS in chlorinated water. " Geotextiles
and Geomembranes, 47(6), 815-830, 24, https://mc06.
manuscriptcentral.com/cgj-pubs.
Hsuan, Y. G., Schröder, H. F., Rowe, R. K., Müeller, W.,
Greenwood, J. H., Cazzuffi, D., and Koerner, R. M.
(2008). " Long-term performance and lifetime prediction
of geosynthetics, " Proc. 4th European Conf.,
Edinburgh, Scotland.
Koerner, R. M., Halse, Y. G., and Lord, Jr., A. E. (1990).
" Long-term durability and aging of geomembranes. "
Proc. Waste Containment Systems: Construction,
Regulation and Performance, R. Bonaparte, ed.,
Geotechnical Special Publ. No. 26, ASCE, 106-134. G
>> For more, search GSI at
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FIGURE 1 Star fold coupon
FIGURE 2 Immersion bath
FIGURE 3 Specimen preparation
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