Shear Wave Velocity and Its Anisotropy of Polymer Modified High-Volume Class-F Fly Ash–Kaolinite Mixtures

This study investigated the effects of polymers on the small-strain stiffness behavior of high volume Class-F fly ash–kaolinite mixtures. The shear wave velocity ($V_s$) and its anisotropy of organically modified fly ash–kaolinite mixtures were evaluated using a self-developed floating wall type consolidometer bender element (BE) testing system. Both synthetic polymers [polyethylene oxide (PEO)] and biopolymers (xanthan gum and chitosan) were used to modify the stiffness of fly ash–kaolinite mixtures. Shear waves generated and received by bender elements were measured to quantify the small-strain stiffness of the organically modified fly ash–kaolinite mixtures in three orthogonal directions, i.e., $vh$, $hv$, and $hh$. The results suggested that (1) as the fly ash content increased, $V_s$ increased, while the $V_s$ anisotropy, in terms of shear wave velocity ratio $V_{s-hh}/V_{s-vh}$, decreased; (2) a threshold fly ash content concept, which corresponds to the onset of continuous contact chains between fly ash particles throughout the specimen, was used to distinguish the kaolinite-dominated zone from the fly ash-dominated zone of $V_s$ and $V_s$ anisotropy behavior; (3) the introduction of fly ash was also found to enhance the cross-anisotropy of fly ash–kaolinite mixtures; (4) the addition of PEO and chitosan increased the $V_s$ of the fly ash–kaolinite mixtures, while the addition of xanthan gum decreased the $V_s$; and (5) all three polymers were found to decrease the $V_s$ anisotropy of the fly ash–kaolinite mixtures.