Polymer-modified bentonite-silt composites to improve the hydro-mechanical properties of landfill mineral sealings

Compacted clay layers are widely used in landfill barrier systems, relying on low-permeability soils to prevent leachate migration. When local soils like silts lack sufficient sealing properties, bentonite is added to enhance impermeability due to its swelling capacity and self-healing properties. The additional use of polymers shows significant potential in further modifying bentonite-silt mixtures, maintaining low permeability while improving mechanical properties. Moreover, incorporating local soil can help reduce the amount of bentonite required, making the sealing system more cost-effective, or alternatively, increasing the bentonite content can enhance the hydraulic conductivity of natural soil. While the interaction between bentonite and polymers has been widely studied, little is known about the effect of an increased silt content on hydro-mechanical properties of the polymer-soil-composite. This study systematically investigates the hydro-mechanical behaviour of polymer-modified bentonite-silt composites. The polymers Xanthan gum (XAN) and polyacrylamide (PAA) were tested in mixtures of bentonite with 30% or 70% silt, respectively. Oedometer tests were performed in the saturated state to assess stiffness and flexibility, and permeability was estimated using Terzaghi’s theory. The results indicate that polymer modification increases compressibility in silt-dominated mixtures, whereas the opposite effect is observed in mixtures with lower silt content. Furthermore, polymer modification reduces hydraulic conductivity in silt-dominated mixtures but increases it in bentonite-dominated mixtures. These findings highlight the potential of polymer additives for optimizing the hydro-mechanical properties of bentonite-silt composites in landfill sealing applications.