Physicochemical and Mechanical Properties of Polymer-Amended Kaolinite and Fly Ash–Kaolinite Mixtures

Abstract

Environmentally and ecologically friendly biopolymers (xanthan gum, chitosan) and synthetic polymers (polyethylene oxide, polyacrylamide) were employed as novel binders to improve the engineering performance of kaolinite and fly ash–kaolinite mixtures. The floc size, microstructure, physicochemical properties (pH, electrical conductivity, and zeta potential) of polymer-amended kaolinite were investigated, which provided in-depth understanding of the improvement of mechanical properties (Atterberg limits, compaction characteristics, thermal conductivity, and shear strength) from micro to macro. Based on the laboratory observations, it is demonstrated that polyethylene oxide (PEO), chitosan, and polyacrylamide (PAM) induced higher degree of face-to-face (FF) aggregated microfabric through polymer bridging and charge neutralization while xanthan gum led to more edge-to-edge (EE) particle associations. The addition of fly ash was found to reduce the plasticity index, increase the maximum dry unit weight, and decrease the optimum water content of kaolinite, while the organic agents were found to increase the liquid limit and decrease the maximum dry unit weight. The thermal conductivity of fly ash–kaolinite mixtures was found relatively low compared to pure kaolinite, which decreased continuously as the polymer content increased. The unconfined compressive strength (UCS) of organically modified soil increased slightly as the xanthan gum content increased. However, the UCS decreased with the further increase of polymer content (>0.1% by weight).