Rheological properties of sensitive marine clays stabilised by inorganic salts - impact of anion and cation

This study investigates (1) the applicability of parallel plate rheology for assessing quick clay stabilisation by inorganic salts and (2) the short-term stabilising effects of selected cation–anion combinations. Quick clay from the Tiller-Flotten geotechnical test site was treated with salt solutions containing Na + , K + , Ca 2+ and Mg 2+ paired with Cl − , OH − , SO 4 2− and CO 3 2− at concentrations between 0.037 and 0.6 M. A dedicated rheometer protocol enabled extraction of dynamic and static yield shear strengths and structural build-up, revealing non-Newtonian shear-thinning behaviour. Dynamic yield strength from the upwards flow curve was used as the primary parameter and showed good correlation with falling-cone shear strength, with rheology offering higher precision, reproducibility, and reduced sample size. Increasing salt concentration consistently enhanced shear strength, with clear ion-specific trends. Divalent chlorides (CaCl 2 , MgCl 2 ) were most effective at low concentrations but reached a plateau near 0.2 M, while monovalent chlorides continued to increase the strength, with KCl outperforming NaCl at higher concentrations due to the smaller hydration shell and stronger adsorption of K + . Anion effects were strongly governed by pH: Cl − and SO 4 2− (neutral pH) promoted flocculation at low concentrations, whereas OH − and CO 3 2− (high pH) required higher cation concentrations to counteract initial deflocculation. Ca(OH) 2 produced the highest shear strength overall. The geotechnical stability criterion of 0.33 kPa was reached for all K-salts and for Ca(OH) 2 . Overall, the results show that short-term stabilisation of quick clay is controlled by cation valence, hydration radius, and anion-dependent pH, providing a mechanistic basis for designing more efficient binders for rapid ground improvement.