Geosynthetics August/September 2021 - 41

GSI NEWS
GEOSYNTHETIC
INSTITUTE
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geosynthetics, and provide
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organizations.
www.geosynthetic
- institute.org
By George R. Koerner
GSI's new GCL test method
T
he Geosynthetic Institute (GSI) has a new standard test method for " Determination
of the Polymer Loading in Geosynthetic Clay Liners (GCLs). " It was developed over
several years without consensus of the membership. GSI forged ahead with it because we
see many such products in the market and believe there is a need to start the standardization
process to provide some means of quantitative assessment of these products.
This test method covers the measurement for loss of ignition (LOI) of GCL infills to
determine the polymer loading. The method also covers the measurement of moisture
content and ash content, which are required for the calculation of LOI by default.
It should be noted that the techniques described within the standard are only two of
13 methods that Schumacher (2002) suggests for the determination of total organic carbon
(TOC) in soils. The methods described have been shown to accurately identify the
amount of polymer added to a GCL infill regardless of formulation. Gustitus et al. (2020)
and Scalia et al. (2014) have identified many different types of polymers currently used to
enhance bentonite performance in GCLs. It is freely acknowledged that these methods do
not address the nature of the polymer, consideration of polymer durability, effectiveness
in reducing hydraulic conductivity long-term, polymer distribution within the GCL infill
and the potential for washout. But it is a first step.
GCLs have demonstrated excellent performance as hydraulic barrier systems that have
George R. Koerner is the
director of the Geosynthetic
Institute in Folsom, Pa.
a very low hydraulic conductivity to prevent contamination of the surrounding groundwater,
particularly when teamed with a geomembrane as a composite liner system. When
leachates have aggressive characteristics (e.g., high total dissolved solids and cations, such
as K+, Na+, Mg2+, Ca2+ and NH4
+), they may alter the bentonite and lead to an unacceptable
increase in hydraulic conductivity through ion exchange. To resist these high-ionicstrength
leachates, polymer-modified GCLs containing a blend of sodium bentonite and
various polymers have been introduced as an answer to this challenge.
Polymer-modified GCLs are typically used with marginal bentonites to enhance swell
index and fluid loss properties. These polymers are proprietary, and their long-term performance
is unknown. Bentonite in GCLs can be supplied as a natural sodium bentonite,
sodium-activated " peptized " bentonite or calcium bentonite. Polymers may be added
to improve several characteristics of a GCL; however, the nature and suitability of these
polymers needs to be evaluated on a case-by-case basis. If they are used, the manufacturer
should provide details about the polymers contained within their products and their longterm
durability performance.
Polymer-modified GCLs are being used more frequently in our industry. This new test
method will help us identify when and to what extent polymers are being used in concert
with the typical clay infill.
Gustitus, S. A., Nguyen, D., Chen, J., and Benson, C. H. (2020). " Quantifying polymer loading in bentonite-polymer
composites using loss of ignition and total carbon analyses. " ASCE Geotechnical Journal, In Press.
Scalia, J., Benson, C. H., Bohnhoff, G. L., Edil, T. B., and Shackelford, C. D. (2014). " Long-term hydraulic conductivity of a bentonitepolymer
composite permeated with aggressive inorganic solutions. " Jour. of Geotechnical and Geoenvironmental Engineering, 140(3).
Schumacher, B. A., (2002). " Methods for the determination of total organic carbon (TOC) in soils and sediments. " NCEA-C-1282
EMASC-001, U.S. EPA Environmental Sciences Division National Exposure Research Laboratory, Las Vegas, Nev. G
www.GeosyntheticsMagazine.com
41
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Geosynthetics August/September 2021

Table of Contents for the Digital Edition of Geosynthetics August/September 2021

Geosynthetics August/September 2021 - Cover1
Geosynthetics August/September 2021 - Cover2
Geosynthetics August/September 2021 - 1
Geosynthetics August/September 2021 - 2
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Geosynthetics August/September 2021 - Cover3
Geosynthetics August/September 2021 - Cover4
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 1
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Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 5
Geosynthetics August/September 2021 - GeoNashville Attendee Brochure 6
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