Fluid Indicator Test (FIT) for Screening the Hydraulic Conductivity of Enhanced Bentonites to Inorganic Aqueous Solutions

Abstract

Over the past 30 years, geosynthetic clay liners (GCLs) have been demonstrated to be a valuable barrier technology in numerous environmental containment applications. However, past research has also shown that the hydraulic conductivity (k) of GCLs is sensitive to the electrolyte concentration of the permeant liquid. At low effective stresses, a sufficiently high electrolyte concentration has the potential to result in a multiple order of magnitude higher k than the same GCL exhibits to water. To expand the boundaries of GCL functionality, recent research has focused on the use of enhanced (e.g., polymer modified) bentonites (EBs) for improving the resilience of bentonites, and GCLs, subjected to high concentration electrolyte solutions. These EBs have frequently incorporated anionic polymers (e.g. sodium polyacrylate) into the bentonite using a plethora of methods, (e.g. dry mixing, wet mixing, in-situ polymerization.) However, existing standard indicator tests (swell index, fluid loss, modified Atterberg limits) for GCL k may not always be effective for EB-GCLs. A rapid fluid indicator test (FIT) for screening high k versus low k of EB-GCLs and unmodified sodium bentonites, is proposed. Preliminary tests were conducted on granular sodium bentonite and an EB (bentonite polymer composite). Results of the FIT were compared with the swell index and k for these materials over a range of CaCl₂ solutions. The results support that a passing FIT generally correlates to low k for the same fluid under low stress conditions.