Influence of constitution and mixture treatment of cationic polymers on modified bentonite

Polymers are used to control clay-water interaction and related engineering properties in geotechnical and geoenvironmental applications. The interaction between polymers and clay solids is highly dependent on polymer characteristics and the preparation method. However, the significance of the polymer chain length and charge properties as fundamental characteristics of polymers has not been studied with respect to the macroscopic behaviour of modified clay. The current study addresses the significance of polymer chain length, charge density and the effect of drying and grinding after mixing on the volumetric behaviour of polymer-enhanced bentonite. Unconfined suction-controlled shrinkage tests and one-dimensional compression tests were performed on a series of wet-mixed bentonite-polymer intercalates. Part of the samples was dried and ground after wet mixing. The bentonite used was a natural sodium bentonite (MX80), and the polymers were cationic copolymers based on acrylamide of different chain lengths and cationicity. The results show that the impact of cationic polymers on the shrinkage and compression behaviour of wet-mixed bentonite arises from polymer bridging and modification of smectite surface properties. It is demonstrated that post-mixing treatment of wet-mixed bentonite by drying and grinding yields a significant change in the shrinkage and compression behaviour.