Review of methods for quantifying polymer loading of enhanced-bentonite geosynthetic clay liners

Geosynthetic clay liners (GCLs) are thin, hydraulic and chemical containment barriers with low hydraulic conductivity (<= 3 similar to 10(-11) m/s) to water or dilute chemical solutions. However, when used to contain liquids with more aggressive chemistries, the hydraulic conductivity of GCLs can be several orders-of-magnitude higher. Polymer enhanced bentonites are developed for use in GCLs to maintain low hydraulic conductivity upon exposure to liquids with aggressive chemistries. Polymer loading is an important factor affecting the hydraulic conductivity of enhanced-bentonite GCLs (EB-GCLs). Measurements of polymer loading are conducted as part of manufacturing and construction quality assurance/quality control (QA/QC) of EB-GCLs, and to assist in interpreting outcomes of hydraulic conductivity testing of EB-GCLs. Methods used to quantify polymer loading of EB-GCLs are reviewed in this paper, with focus on loss on ignition (LOI) and total carbon (TC) analyses. Both methods may be component methods in that measurement of the parameter of interest (i.e., LOI, TC) is required for the sodium bentonite and polymer components as well as the bentonite-polymer mixture. In addition, composite LOI and TC methods are described whereby the polymer content is determined directly via calibration of measured LOI or TC for an enhanced-bentonite series with different, known polymer contents. Each method can be used without direct measurement of the base materials or calibration for use in QA/QC. Examples are provided from tests conducted with poly(acrylic acid), sodium carboxymethyl cellulose, covalently crosslinked poly(acrylic acid), and a bentonite polymer composite to illustrate the application, accuracy, and limitations of the methods.