Impact of Clay Mineralogy and Dispersing Agents on Particle Size Analysis of Fine-Grained Soils

Abstract

Hydrometer analysis is a widely used method for determining the particle size distribution of fine-grained soils. However, its accuracy depends on assumptions of Stokes’s law, and influence by other parameters such as temperature, type and concentration of dispersing agents and specific gravity etc. Furthermore, clay minerals exhibit distinct swelling and shrinkage behaviors, their interaction with dispersing agents directly influences sedimentation and particle size distribution. This study investigates how clay mineralogy influences the effectiveness of the dispersing agents and its implications for the classification of fine-grained soils. For the present study, six soil samples were analyzed for index properties (specific gravity, grain size distribution, free swell index, and Atterberg limits), chemical properties (pH and electrical conductivity), elemental composition (X-ray fluorescence), and surface charge (zeta potential). The findings reveal that conventional hydrometer analysis, which relies on assumed sedimentation behavior, often inaccurately represents actual mineralogical characteristics, underscoring its limitations. The results show that soil dispersion behavior varies considerably depending on mineral composition, as reflected by wide ranges in liquid-to-solid (L/S) ratios (2-50), pH (7.38-10.20), EC (0.027-0.522 mS/cm), and FSI (0-250%). Among the tested samples, sodium bentonite exhibited the highest dispersion efficiency, achieving a maximum zeta potential of (-48.7 mV). This study emphasizes the necessity of mineralogy-specific dispersion strategies to enhance the precision of fine-grained soil classification.