In-Silico Investigation of Mechanical Behavior of Hydrated Na-Montmorillonite Tactoid

Swelling clay minerals, exemplified by Na-montmorillonite (Na-Mt), are vital constituents in expansive soils and hold significant relevance in geotechnical engineering. Comprehending their distinctive swelling behavior upon hydration is imperative for managing potential damage to civil infrastructure. Conversely, this swelling property gives rise to numerous advantageous applications, including using these clays in barrier materials and nanocomposites. The hierarchical structure of montmorillonite, consisting of clay mineral layers, tactoids, aggregates, and assemblies of aggregates, plays a pivotal role in the swelling behavior of expansive clays. This investigation employs molecular dynamics (MD) and steered molecular dynamic (SMD) simulations to explore the nanomechanical properties of hydrated Na-Mt tactoids at various hydration levels. It provides insights into their responses to compression, tensile, and shear deformation. This study reveals increased hydration levels increase interlayer spacing in clay structures, resulting in higher average d-values. Water molecules drive attractive electrostatic interactions with clay mineral layers, predominantly mediated by sodium ions, highlighting the complex interplay between interlayer hydration and tactoid stability. Higher hydration enhances tactoid compressibility, reducing the stress required for deformation by compressing water molecules and clay mineral layers in the interlayer space. The study also demonstrates a notable reduction in tensile modulus with increasing hydration, signifying the significant impact of even minimal hydration on interlayer cation-clay layer interactions. Hydrated tactoids exhibit altered mechanical responses in shear deformation compared to dry ones, requiring lower shear stress to detach the top clay layer from the tactoid. The presence of water molecules impedes the locking of clay mineral layers, further influencing mechanical properties. The results and insight provided by this work will contribute to a better understanding of the impact of interlayer hydration on the stability and response of swelling clay minerals.