The Shear Strength of “Tunable” Clay-Polymer Composite under Various Ionic Concentrations

“Tunable” clay-polymer composites were created as a material that could be modified in-situ through controlled manipulation of interparticle spacings by exposing them to differing surrounding fluid chemistries. Altering interparticle spacing has a significant influence on the mechanical behavior of the composite. The purpose of this study is to investigate the stress-strain response of a kaolinite-polyacrylamide when exposed to various pore fluid conditions, namely ionic concentration (0 M and 0.3 M NaCl). The low and high ionic concentrations were chosen to promote extended and coiled conformations (polymer molecule shape). The specimens of composite and pure kaolin were pre-consolidated at 100 kPa from slurries. The undrained shear strength was determined using triaxial testing in which the specimens were isotropically consolidated to the desired stress of 100 kPa. The results show that the undrained shear strength of the pure kaolinite is controlled mainly by its initial packing density and fabric arrangement (physical effects) rather than any changes in physicochemical-induced forces at the particle level. However, the undrained shear strength of the “tunable” composite was significantly influenced by the conformation of the polymer molecules. In addition, the effective stress path depends on the fabric for pure kaolin and on polymer conformation for the composite, demonstrating the “tunable” nature of the composite.