Knowledge Gap: The aggregation of clay minerals-layered silicate nanoparticles-strongly impacts fluid flow, solute migration, and solid mechanics in soils, sediments, and sedimentary rocks. Experimental and computational characterization of clay aggregation is inhibited by the delicate water-mediated nature of clay colloidal interactions and by the range of spatial scales involved, from 1 nm thick platelets to flocs with dimensions up to micrometers or more. Simulations: Using a new coarse-grained molecular dynamics (CGMD) approach, we predicted the microstructure, dynamics, and rheology of hydrated smectite (more precisely, montmorillonite) clay gels containing up to 2,000 clay platelets on length scales up to 0.1 mu m. Simulations investigated the impact of simulation time, platelet diameters (6 to 25 nm), and the ratio of Na to Ca exchangeable cations on the assembly of tactoids (i.e., stacks of parallel clay platelets) and larger aggregates (i.e., assemblages of tactoids). We analyzed structural features including tactoid size and size distribution, basal spacing, counterion distribution in the electrical double layer, clay association modes, and the rheological properties of smectite gels. Findings: Our results demonstrate new potential to characterize and understand clay aggregation in dilute suspensions and gels on a scale of thousands of particles with explicit representation of counterion clouds and with accuracy approaching that of all-atom molecular dynamics (MD) simulations. For example, our simulations predict the strong impact of Na/Ca ratio on clay tactoid formation and the shear-thinning rheology of clay gels.

Energy piles are highly favored for their excellent, low energy consumption in providing heating for public residences. The temperature field changes the activity of the diffuse double electric layer (DEL) on the particle surface, thereby altering the distribution of the stress field in the soil and ultimately affecting the mechanical properties of the interface between the energy pile and the soil. Therefore, studying the influence of water content on the mechanical behavior of the soil-structure interface in the temperature field is crucial for energy pile safety. This study used a modified temperature-controlled direct shear apparatus to obtain the influence of water content and temperature on the shear behavior of the soil-structure interface. Then, the test results were analyzed and discussed. Finally, three results were obtained: (1) The water content of bentonite (wbent) had a significant impact on the shear stress-shear displacement curve of the soil-structure interface; when the wbent was less than the wp of the bentonite, the tau-l curve exhibited a softening response, then displayed a hardening response. (2) The shear strength of the soil-structure interface gradually decreased with the increase of wbent. (3) The shear strength of the soil-structure interface increased with increasing temperature under various wbent and vertical loads.

Soil contamination by organic and hazardous substances is a critical environmental issue, particularly in developing countries. This study investigates the limitations of double-layer theory for bentonite-organic contaminant interactions through experimental and numerical analysis. Using NaCl and KCl as salts and acetone, isopropyl alcohol, and glycerol as organic contaminants, the research explores the rheological properties of Na-bentonite dispersions. The double-layer theory, particularly Stern's model, has limitations in accurately representing the interaction between bentonite and organic contaminants. The research aims to validate the double-layer equations and investigate the impact of viscosity and cation hydrated radius on the rheological properties of Na-bentonite. The novelty lies in introducing a range of viscosities into the pore fluid to challenge existing double-layer equations. Numerical calculations based on double-layer theory were used to analyze the total interaction energy. The study found that without salt, bentonite showed similar rheological behavior in acetone and alcohol but higher yield stress in glycerol. NaCl up to 0.1 M increased yield stress, while 0.5 M reduced it. KCl had a more pronounced effect on rheological properties than NaCl, highlighting the importance of cation hydrated radius. In soil-organic mixtures, lower viscosity organic chemicals increased yield stress. Despite similar dielectric constants, acetone showed higher yield stress than glycerol at lower concentrations, but at higher concentrations, dielectric constant differences became dominant. The study confirms the limitations of double-layer theory in bentonite-organic contaminant interactions, particularly regarding pore fluid viscosity, though it remains reliable at high contaminant concentrations.

Salt weathering is a common deterioration phenomenon that affects outdoor cultural properties, and it is important to precisely predict the heat, moisture, and salt transfer in porous materials to suppress salt weathering. Osmosis and osmotic pressure were considered in the field of soil research, especially in clay research, but not in the field of outdoor cultural properties and building materials, which are the main target of salt weathering. Osmosis in clay is supposed to be caused by its surface charge. However, it has been suggested that sandstones and bricks that constitute cultural properties and buildings also have surface charge as clay. Thus, osmosis and osmotic pressure can occur in building materials, which may lead to materials degradation. In this study, we derive basic equations, based on nonequilibrium thermodynamics, for the simultaneous heat, dry air, water vapor, liquid water, cation, and anion transfer in building materials by considering osmosis. This equation was compared with existing model for heat and moisture transfer equations as well as models that considered the salt transfer. Based on the previous research for osmosis in clay, we summarized conditions under which osmosis occurs in building materials and presented an outlook for modeling the physical properties of materials related to osmosis.

The mechanical properties of loess are strongly dependent on the environment where it is deposited. To investigate the effects of acidic, alkaline, and saline environments on the strength and deformation properties of compacted loess, the consolidation test and direct shear test were carried out on loess samples contaminated with different concentrations of acetic acid, sodium hydroxide, and sodium sulfate. In addition, changes in zeta potential, mineralogy, chemical composition, and microstructure of the loess samples at different chemical environments were also measured. The results show that the reduction in the thickness of the diffuse double layer for the loess contaminated with acetic acid leads to the aggregation of clay particles, laying the foundation for the expansion of loess pores, while the dissolution of carbonate cement and chemical cement makes the soil structure looser. Hence, the compacted loess has significantly lower shear strength and higher compressibility in an acidic environment. The mechanical properties in the saline environment show similar variation characteristics to the acidic environment, but this is mainly due to carbonate solubilization. In the alkaline environment, the degree of interparticle cementation of the loess is enhanced by the generation of calcite due to dedolomitization and the generation of colloidal flocs of Al(OH)3, Fe(OH)3, and H2SiO3. In addition, the pore connectivity is greatly reduced by the extensive distribution of clay particles caused by the development of a diffuse double layer. As a result, its compressibility and shear strength are improved compared to uncontaminated loess. These findings can be used as a reference for geoengineering practice in loess areas.