Self-consolidating earth concrete (SCEC) addresses the long construction process of conventional earthen constructions and their structural limitations, while further efforts are needed to enhance its sustainability. This study explores the development of a kaolinite-based self-consolidating earth paste (SCEP) due to their blended powder system, incorporating raw and treated (calcined and ground-calcined) kaolinite under various activation techniques, such as water hydration, sodium hexametaphosphate (NaHMP), and sodium hydroxide (NaOH) activation. The synergistic effect of calcination and mechanosynthesis on rheological, mechanical, structural, and microstructural properties of SCEP were investigated. Mechanically treated kaolinite increased yield stress, plastic viscosity, storage modulus evolution, and build-up index, while delayed the strength development compared to the calcined kaolinite samples. Among the investigated activators, NaOH resulted in more promising structural build-up, storage modulus, and compressive strength development. These findings were elaborated with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), calorimetry, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM).

This research compares the stabilization efficiency of kaolinite and montmorillonite clayey soils using two industrial and agricultural by-products, namely fly ash (FA) and rice husk ash (RHA), activated by sodium hydroxide (NaOH). To this end, various proportions of FA and RHA (i.e., 0%, 5%, 10%, 15%, and 20%), along with NaOH solutions at 2 M and 4 M concentrations, are utilized to treat both low-and high-plasticity clayey soils. The resulting geopolymers are then subjected to a wide range of mechanical and micro-structural tests, including standard compaction, unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), swelling potential, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Results show that incorporating both FA and RHA into kaolinite and montmorillonite clays up to their respective optimal contents significantly enhances all their mechanical properties. However, FA-based geopolymers exhibit superior mechanical properties compared to RHA-based ones under similar additive contents and curing conditions. Accordingly, the optimal FA content is found to be 15%, while for the RHA-based geopolymers, the peak UCS is observed at 15% and 10% RHA for kaolinite and 10% and 5% RHA for montmorillonite when treated with 2 M and 4 M NaOH solutions, respectively. The results also suggest that FA is more effective than RHA in controlling the swelling potential of both kaolinite and montmorillonite soils. Microstructural analyses further corroborate the findings of macro-scale experiments by showcasing the comparative occurrence of geopolymerization, as well as the formation of cementitious gels, and synthesis of new chemical products.

The effective stress principle is the fundamental theory of soil mechanics. The effective stress transmitted between particles dominates the mechanical properties of soil, such as strength, deformation, and drainage. However, there remains a paucity of research on the effective stress in the compression of nano-scale clay minerals. This study explored the application of the effective stress principle in the consolidation behavior of kaolinite through the Molecular Dynamics method. The calibration and correction for micro effective stress and pore water pressure were first proposed. Micro-effective stress is the stress on the mineral itself in the contact part of two particles, while micro-pore water pressure always represents that on the weakly bound and free water in the same part. The strongly bound water film between particles can indirectly transmit the micro-effective stress through the electrical double-layer repulsion. The calculation of micro stress has been corrected according to the derivation of macro theory, and the results obtained corresponded well with that in the macro experiment. Moreover, the evolution of effective stress was analyzed by observing the interparticle water film. The increase in effective stress during consolidation was mainly due to the compression of the strongly bound water and the drainage of weakly bound and free water.

Conventional biochar-based fertilizers, which typically consist of a mixture of biochar, chemical fertilizers, and additives, offer benefits but often exhibit rapid nutrient release, limiting their long-term effectiveness. Herein, we explored the enhancement of slow-release performance in biochar-based compound fertilizers by incorporating a kaolinite-infused polyvinyl alcohol/starch (K-PVA/ST) coating, resulting in a new formulation denoted as KPVA/ST-BCF. The results demonstrated that, compared to traditional NPK fertilizers, nitrogen leaching from KPVA/ST-BCF in soil column leaching tests was reduced to 19.1 % over 29 days, while phosphorus and potassium leaching were reduced to 48.5 % and 72.3 %, respectively. Mechanistic investigations revealed that the inclusion of kaolinite in the PVA/ST matrix reduces swelling, improves water retention, and enhances mechanical properties, leading to a more gradual and sustained release of nutrients. Field trials on reclaimed land showed that KPVA/ST-BCF increased wheat yield by up to 100 % compared to conventional NPK treatment. It also enhanced soil nitrogen content and organic matter, with organic matter reaching 22.7 g/kg at grain maturity. The economic assessment indicated that despite higher initial production costs compared to conventional NPK fertilizers, K-PVA/ST-BCF offers higher nutrient use efficiency, reduced management costs, and a net profit increase of $1525.86 per hectare.

The influence of modern soil ameliorants such as anionic potassium humates (PHums) and cationic poly(diallyldimethylammonium chloride) (PDADMAC) as well as their interpolymer complexes (IPCs) on rheological behavior of water-saturated kaolinite was studied. Modification of kaolinite with anionic biologically active and bio-stimulating PHums was shown to result in a decrease of storage modulus G(0)' and shear stress amplitude tau(0) corresponding to linear viscoelasticity region as well as storage modulus G' cross and shear stress amplitude tau cross at crossover point by 0.5 - 1.0 order of magnitude. Modification of the clay with cationic PDADMAC was accompanied by the opposite effect, that is, an increase in the above rheological characteristics by 1.5 - 2.0 orders of magnitude. PDADMAC/PHums IPCs with the molar ratio of cationic and anionic groups in the range 0.1 - 10 demonstrated the influence on the rheological parameters in the same manner as individual PDADMAC. This result was considered as the original procedure to provide simultaneous addition of stabilizing PDADMAC and biologically active PHums. In this case the reinforcing action of PDADMAC on the kaolinite is fully realized and the weakening action of PHums is fully suppressed. For individual polymers, the results are discussed in terms of kaolinite structural transformations caused by the interaction of charged macromolecules with negatively charged clay particles. For IPCs/kaolinite samples, rheological behavior was attributed to the exchange reactions between IPCs and clay particles. The data obtained are important for predicting the mechanical properties of wet clay soils modified with polymers and IPCs, as well as optimizing methods for introducing bio-stimulating and anti-erosion polymer additives into soils.

Foundation elements with rough (textured) surfaces mobilize larger interface shear resistance than ones with conventional smooth or random rough surfaces when sheared against soils under monotonic loading. The overall performance of foundation elements such as piles supporting offshore wind turbines, suction caissons supporting tidal energy converters, soil nails, and soil anchors installed in cohesive soils could be enhanced through utilizing rough (textured) surfaces to resist applied static and/or cyclic loading. This paper describes the shear behavior of smooth and rough (textured) surfaces in kaolinite clay and kaolinite clay-sand mixture soils under static and cyclic axial loading. The experimental investigation presented herein consists of a series of interface shear tests performed on 3D printed rough (textured) surfaces and a 3D printed smooth reference surface utilizing the Cyclic Interface Shear Test system. The paper includes a description of the interface testing system components, cohesive soil specimens' preparation procedure, smooth and rough (textured) surfaces details, testing procedure, and results of static and cyclic tests. Test results indicate that kaolinite clay-sand mixture soil mobilized larger static and post-cyclic interface shear resistance and volume contraction relative to kaolinite clay soil when sheared against the smooth reference surface. When tested against rough (textured) surfaces with variable asperity height, larger shear resistance was mobilized and larger soil dilation greater than that mobilized by the reference untextured surface in both soils. The results also indicate rough (textured) surfaces exhibited a prevalent frictional anisotropy increases with asperity angle and height in cohesive soils, the surfaces mobilized larger shear resistance and volume change in one direction (i.e., against the asperity right-angled side) than the other direction (i.e., along the asperity inclined side).

One of the major environmental problems in hot and arid locations is the production of dust. This study presents green slurries based on nanoclay-and blast furnace slag for stabilizing desert sands. The slurries introduced contain bentonite and kaolinite mineral nanoclays, along with blast furnace slag powder. Unconfined compressive strength, moisture content, and wind tunnel tests were conducted to evaluate the performance of the compounds in stabilizing sand and increasing its water-holding capacity. The mass percentages of bentonite nanoclay and blast furnace slag in the stabilizer slurry were optimized at 1-3% and 1-5%, respectively. The optimized mass percentages of kaolinite nanoclay and blast furnace slag slurry were 1-1% and 3-1%. The study found that soil stabilized with slurries increased compressive strength by three times compared to unstabilized soil. Additionally, the addition of stabilizers improved soil moisture retention by 50%. Sand surfaces stabilized with nanoclays and slag demonstrated excellent resistance to wind erosion, even at wind speeds of up to 100 km/h. Furthermore, there was no wind erosion observed at 60 degrees C. The suggested slurry compounds have shown a strong ability to enhance the mechanical properties of soil, increase soil water retention, and reduce wind erosion of sandy soil.

This paper proposes a new, computationally efficient, approach to modelling the anisotropy of surface charge on kaolinite particles in particle-scale simulations. We represent each kaolinite particle as a flat ellipsoid and calculate the total interaction energy/force between two ellipsoids as a weighted sum of face-to-face, edge-toedge, face-to-edge, and edge-to-face interactions. The weightings of these interactions are smooth functions of the relative orientations of the particles. This model was employed in coarse-grained molecular dynamics simulations of virtual samples under isotropic compression to investigate the influence of the pore water pH on microfabric formation and the mechanical behaviour of kaolinite. The simulations effectively captured the influence of pore water pH on microfabric formation and compressive behaviour, as previously reported in experimental research. The virtual sample with a pore water pH of 4 (acidic pore water) formed an aggregated and flocculated microfabric and exhibited higher compressibility during isotropic compression. In contrast, the virtual sample with a pore water pH of 8 (alkaline pore water) formed a dispersed and deflocculated microfabric and showed lower compressibility. The efficacy of the model is demonstrated here through coarse-grained molecular dynamics simulations, but it could also be implemented in a discrete element method code.

This study investigates the potential of xanthan gum (XG) to serve as a biopolymer binder for improving the rheological, mechanical, and 3D printing properties of earth-based concrete, aligning with the pressing need for sustainable, low-carbon construction materials. Experimental results indicate that XG could disperse kaolinite clay particles, which likely arises from the highly negative charges of both kaolinite and XG. Rheological parameters display two trends with increasing XG concentration: initially decreasing yield stress, viscosity, and storage modulus owing to XG's dispersing effect, followed by an increase due to polymer overlapping. The same trend is observed in 3D printing experiments, where the kaolinite clay suspensions exhibited enhanced buildability with increasing XG concentration and eventually achieved a Printable state at 5 % XG. Additionally, compressive strength was observed to steadily increase with increasing XG content, for instance, nearly tenfold with 2.4 % XG compared to 0 % XG (0.34 MPa to 3.58 MPa). This exploration highlights the pivotal role of XG as a dual-functionality agent, acting as a robust binder and a promising rheology modifier.

Electrokinetic-Permeable Reaction Barrier (EK-PRB) coupled remediation technology can effectively treat heavy metal-contaminated soil near coal mines. This study was conducted on cadmium (Cd), a widely present element in the soil of the mining area. To investigate the impact of the voltage gradient on the remediation effect of EKPRB, the changes in current, power consumption, pH, and Cd concentration content during the macroscopic experiment were analyzed. A three-dimensional visualized kaolinite-heavy metal-water simulation system was constructed and combined with the Molecular Dynamics (MD) simulations to elucidate the migration mechanism and binding active sites of Cd on the kaolinite (001) crystalline surface at the microscopic scale. The results showed that the voltage gradient positively correlates with the current, power consumption, and Cd concentration during EK-PRB remediation, and the average removal efficiency increases non-linearly with increasing voltage gradient. Considering power consumption, average removal efficiency, and cost-effectiveness, the voltage range is between 1.5 and 3.0 V/cm, with 2.5 V/cm being the optimal value. The results of MD simulations and experiments correspond to each other. Cd2+ formed a highly stable adsorption structure in contrast to the Al-O sheet on the kaolinite (001) crystalline surface. The mean square displacement (MSD) curve of Cd2+ under the electric field exhibits anisotropy, the total diffusion coefficient DTotal increases and the Cd2+ migration rate accelerates. The electric field influences the microstructure of Cd2+ complexes. With the enhancement of the voltage gradient, the complexation between Cd2+ and water molecules is enhanced, and the interaction between Cd2+ and Cl- in solution is weakened.