Na-CMC-amended clay: effect of mixing method on hydraulic conductivity and polymer elution

Abstract

Desiccation-induced cracks in reactive soils reduce their mechanical strength and increase their hydraulic conductivity (k). Polymer additives have demonstrated efficacy in improving resistance of clay against desiccation cracking and retaining low k when exposed to saline solutions. However, the risk of polymer elution from treated mixtures and its effect on the durability of gains have received little attention. This study evaluated polymer leaching during consolidation and permeation in reconstituted mixtures. Sodium carboxymethyl cellulose (Na-CMC) was added to Na-bentonite via wet mixing (WM) and dry mixing (DM). Conducting a series of k tests on amended and unamended samples, polymer retention and elution were assessed using thermogravimetric (TGA) and total organic carbon (TOC) analyses. Na-CMC incorporation under DM reduced k by approximately 60%. DM exhibited higher levels of polymer leaching compared to WM, increasing permeability over time. Nevertheless, despite polymer loss, k values for both DM and WM specimens remained lower than untreated bentonite for up to 100 days of permeation. Furthermore, introducing a slit-film geotextile as a potential remedy for leaching did not significantly enhance polymer retention in DM samples. However, it reduced the polymer content in the effluent, suggesting that the geotextile, not the bentonite, could have retained the polymer.