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Geosynthetic clay liners (GCLs) comprising sodium bentonite (NaB) have been shown to exhibit significant membrane behavior, whereby contaminants are restricted from passing through the clay due to electrostatic repulsion, potentially enhancing long-term containment performance. Recent membrane behavior research has focused on evaluating membrane efficiency () of enhanced bentonites (e.g., bentonite polymer composites) and testing under more complex conditions (e.g., elevated temperatures, unsaturated conditions), often drawing comparisons with earlier published data on NaB-GCLs. However, the validity of comparing NaB-GCL results across studies and from earlier work remains unclear. No prior study has evaluated the variability in reported values for the same type of NaB-GCL manufactured in different years. In this study, multistage membrane behavior tests were performed on specimens of the same NaB-GCL type manufactured at different dates. One specimen (GCL1) was taken from a NaB-GCL roll manufactured in the last five years. Another specimen (GCL2) was taken from a NaB-GCL roll that had been stored in a laboratory since 2005. Values of were measured for both specimens, and also compared to results reported in 2002 for the same type of NaB-GCL (GCL3). To support interpretation of the results, cation exchange capacity, mass per unit area, and swell index tests also were performed. For the same salt solution concentrations, GCL2 exhibited significantly lower than GCL1 and GCL3. Lower values of corresponded to lower bentonite mass per unit area. The results have important implications regarding limitations in comparing results of current membrane behavior research on enhanced materials and testing conditions to commonly cited literature data.
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This content will become publicly available on February 27, 2026
Evaluating Diffusion through Geosynthetic Clay Liners Using a Modified Dialysis-Leaching Test Method
Geosynthetic clay liners (GCLs) used in waste and chemical containment applications exhibit high swell and low hydraulic conductivity to water (e.g., k < 10−10 m/s), such that diffusion dominates contaminant transport occurring through the barrier. Thus, knowledge of expected diffusion coefficients for GCLs under relevant environmental conditions is required for performance-based design and accurate assessment of the barrier system. Unfortunately, diffusion testing for bentonites can be challenging and time consuming, limiting data availability for GCL diffusion coefficients. The dialysis leaching test (DLT) method has been utilized in recent studies for simple, time-efficient diffusion measurements for bulk sodium bentonites (NaB), enhanced bentonites, and NaB pastes. This study used a new, modified version of the DLT method for measuring diffusion in GCLs comprising NaB. Diffusion tests were performed using dilute (20 mM) and aggressive (100 mM) calcium chloride (CaCl2) solutions to measure apparent diffusion coefficients (Da) for chloride for the GCLs. Values of Da were in the range of 10−10 m2/s, consistent with expectations from the literature for longer-term traditional testing. Diffusion coefficients increased as CaCl2 concentration increased, as expected due to cation exchange and suppression of the diffuse double layer in the bentonite in the GCL. The results of the study demonstrate the potential use of a new, time-efficient test method for assessing diffusion properties of GCLs, further improving our ability to predict contaminant transport through barrier systems.
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- Award ID(s):
- 2143145
- PAR ID:
- 10608892
- Publisher / Repository:
- American Society of Civil Engineers
- Date Published:
- ISBN:
- 9780784485699
- Page Range / eLocation ID:
- 356 to 363
- Format(s):
- Medium: X
- Location:
- Louisville, Kentucky
- Sponsoring Org:
- National Science Foundation
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