This study systematically investigated the pore structure response of kaolin and illite/smectite mixed-layer rich clay in a reconstituted state to one-dimensional (1D) compression by first performing oedometer tests on saturated clay slurries, followed by characterising their pore structure using multi-scale characterisation techniques, with the primary objective of advancing the current understanding of the microstructural mechanisms underlying the macroscopic deformation of such clays. Under 1D loading, the volume reduction observed at the macro level essentially represented the macroscopic manifestation of changes in inter-aggregate porosity at the pore scale. It was the inter-particle pores that were compressed, despite the interlayer pores remaining stable. Two distinct pore collapse mechanisms were identified: kaolin exhibited a progressive collapse of particular larger pore population in an ordered manner, whereas illite/smectite mixed-layer rich clay demonstrated overall compression of inter-aggregate pores. Accordingly, mathematical relationships between the porosity and compressibility parameters for these two soils were proposed, with the two exhibiting opposite trends arising from their distinct microstructural features. Approaching from the unique perspective of pore structure, quantitative analysis of pore orientation and morphology on the vertical and horizontal planes demonstrated some progressively increasing anisotropy during compression. These findings provide important insights into porescale mechanisms governing clay compression behaviour and enrich the limited microporosity database in soil mechanics.

In the reinforcement of micro-cracks and soil, cement grouting often suffers from poor injectability due to particle size limitations. While ultra-fine cement produced through physical grinding can address this issue, it significantly increases cost and energy consumption. Moreover, ultra-fine cement is prone to aging when exposed to moisture and CO2 in the air. To address these issues, this study proposes a new approach for in-situ particle size reduction of cement slurry through the mild corrosion of acetic acid. The refining effect of acetic acid on cement particles was investigated, along with its impact on mechanical properties and hydration products. The results show that acetic acid accelerates cement dissolution, promoting early-stage strength development and microstructure formation. The addition of 1.2 wt% acetic acid reduced the D90 particle size of the slurry by 36.4 %. Acetic acid also enhances the release of Ca2+ from clinker, increasing the precipitation of Ca(OH)2, CaCO3, and calcium silicate hydrate (C-S-H) at early stages, which serves as the primary source of early strength. Additionally, it raises the Ca/Si ratio of the early-formed C-S-H gel. However, excessive acetic acid can inhibit the further development of strength at later stages. The research demonstrates that premixed acetic acid activation is an effective approach for enhancing the performance of cementitious grouting materials, with promising potential to reduce energy consumption associated with physical cement grinding.

A significant amount of open-pit-mine broken sandstone (OMBS) is produced during open-pit mining. The mechanical strength of the loose sandstone is critical for ensuring dump slope stability and sustainable mine construction. This study investigates the modification of OMBS using artemisia sphaerocephala krasch (ASK) gum to enhance its engineering properties. Unconfined compressive strength, shear strength and permeability tests were conducted to quantitatively analyze the modification effect. And the stability was evaluated using FLAC3D simulation methods. The modification mechanism was characterized through SEM, FT-IR, XRD. The results demonstrated that the addition of 2 % ASK gum significantly improved OMBS mechanical performance and reduced permeability. Meanwhile, the failure mode of OMBS changed with the ASK gum content increasing. The simulation result indicated the stability of modified dump slope was better under the drying-wetting cycle. From the perspective of microstructure and chemical characteristics, the addition of ASK gum created new hydrogen bonds through intermolecular interactions with the hydrophilic groups between OMBS particles and formed a dense and stable structure through three reinforcement modes: surface encapsulation, pore filling, and bonding connection. This study provides a new idea for resource saving and environmentally friendly mining area development.

This study investigated the impact of optimum dosages of nano-calcium carbonate (nano-CaCO3) and nanosilica on the engineering behavior of black cotton soil. The desired percentage of nano-addition, 2%, for both nanomaterials, was determined by analyzing the plasticity-compaction characteristics and the relative strength index values of treated samples. The study unveiled that the entire clay microstructure was transformed into a nanocrystalline matrix after treatment. The deviatoric strength enhancement with confining pressure and curing period was significant after treating the soil with either nano-CaCO3 or nanosilica. The nanosilica treatment was found to be more effective in improving the California bearing ratio (CBR) strength of black cotton soil samples compared with nano-CaCO3 stabilization. The addition of nanomaterials induced the formation of nanocrystalline hydrate gels and silica gel, resulting in an increased resistance to volumetric deformation under compressive stresses. The hydraulic conductivity of nano-treated samples dropped due to the highly tortuous networks between pores in the nano-crystalline structure. The experimental results were substantiated by analyzing the microstructure of nano-treated soils using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) techniques.

In situ resource utilization of lunar regolith provides a cost-effective way to construct the lunar base. The melting and solidifying of lunar soil, especially under the vacuum environment on the Moon, are the fundamentals to achieve this. In this paper, lunar regolith simulant was melted and solidified at different temperatures under a vacuum, and the solidified samples' morphology, structure, and mechanical properties were studied. The results indicated that the density, compressive strength, and Vickers hardness of the solidified samples increased with increasing melting temperature. Notably, the sample solidified at 1400 degrees C showed excellent nanohardness and thermal conductivity originating from the denser atomic structure. It was also observed that the melt migrated upward along the container wall under the vacuum and formed a coating layer on the substrate caused by the Marangoni effect. The above results proved the feasibility of employing the solidified lunar regolith as a primary building material for lunar base construction.

Waste red layers have the potential to be used as supplementary cementitious materials after calcination, but frequent and long-term dry-wet cycling leads to deterioration of their properties, limiting their large-scale application. In this study, the feasibility of using calcined red layers as cement replacement materials under dry-wet cycling conditions was analyzed. The damage evolution and performance degradation of calcined red layer-cement composites (RCC) were systematically evaluated via the digital image correlation (DIC) technique, scanning electron microscopy (SEM) analysis and damage evolution mode. The results show that the calcined red layer replacement ratio and number of dry-wet cycles affect the hydration and pozzolanic reactions of the materials and subsequently affect their mechanical properties. Based on the experimental data, a multiple regression model was developed to quantify the combined effects of the number of dry-wet cycles and the replacement ratio of the calcined red layer on the uniaxial compressive strength. As the number of dry-wet cycles increases, microcracks propagate, the porosity increases, and damage accumulation intensifies. In particular, at a high substitution ratio, the material properties deteriorate further. The global strain evolution process of a material can be accurately tracked via DIC technology. The damage degree index is defined based on strain distribution law, and a damage evolution model was constructed. At lower dry-wet cycles, the hydration reaction has a compensatory effect on damage. The pozzolanic reaction of the calcined red layer resulted in an increase in the number of dry-wet cycles. The RCC samples with high replacement ratios show significant damage accumulation with fast damage growth rates at lower stress levels. The model reveals the nonlinear effects of dry-wet cycling and the calcined red layer replacement ratio on damage accumulation in RCC. The study findings establish a scientific foundation for the resource utilization of abandoned red layers and serve as a significant reference for the durability design of materials in practical engineering applications.

In this study, carbide slag, fly ash, cement, and sodium sulfate were used to stabilize silt from the Yellow River Alluvial Plain. An orthogonal test was conducted to evaluate the optimal mix design for soil stabilization. The mechanical properties, hydration products, and microstructure of the stabilized silt were examined. The effects of stabilizer concentration, compaction, and moisture content on the mechanical properties were investigated. Based on mechanical performance, the optimal stabilizer mix was found to consist of 30% cement, 13.6% carbide slag, 54.4% fly ash, and 2% sodium sulfate. The results indicated that the California Bearing Ratio (CBR), unconfined compressive strength, and splitting tensile strength of the stabilized silt increased with higher stabilizer dosage and compaction degree. In the early stages, the hydration products of the stabilized silt were primarily calcium hydroxide, ettringite, and C-S-H, which exhibited a loose structure. Over time, the microstructure densified, and more crystalline C-S-H was formed. This study provides valuable insights into the use of industrial by-products for soil stabilization, offering a sustainable and cost-effective solution to improve the strength and stability of silt in construction projects.

Freeze-thaw cycles pose a serious threat to the protection and preservation of earthen sites. To investigate the effects of freeze-thaw cycles on the shear strength and permeability of site soil, this study took artificially prepared site soil as the research object. Through triaxial shear tests and permeability tests, the strength and permeability characteristics of site soil under different sticky rice slurry content, sticky rice slurry density and freeze-thaw cycles were analyzed. In addition, the mineral composition, chemical structure, and microstructural characteristics of the samples were investigated by combining X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) tests. The results showed that the addition of sticky rice slurry could increase the shear strength and decrease the permeability coefficient of the soil, while the opposite effect was exhibited after freeze-thaw cycle. The optimum ratio of loess to sticky rice slurry was 95:5, and the optimum density of sticky rice slurry was 1.04 g/cm3. The addition of sticky rice slurry and the increase in the number of freeze-thaw cycles did not significantly change the mineral composition of the soil. The SEM results showed that the morphology and arrangement of soil particles became complex after freeze-thaw cycle, the inter-particle connections became loose, and the pore morphology became irregular. The surface porosity of the soil increased, and the proportion of large and medium pores increased. The directionality of the pores was enhanced, and the complexity of the pores increased. The pore arrangement became relatively stable after 15 freeze-thaw cycles. These findings can provide a reference for the restoration of ancient sites in loess areas.

Climate change increases the frequency of extreme weather events, intensifying shallow flow-type landslides, soil erosion in mountainous regions, and slope failures in coastal areas. Vegetation and biopolymers are explored for ecological slope protection; however, these approaches often face limitations such as extended growth cycles and inconsistent reinforcement. This study investigates the potential of filamentous fungi and wheat bran for stabilizing loose sand. Triaxial shear tests, disintegration tests, and leachate analyses are conducted to evaluate the mechanical performance, durability, and environmental safety of fungus-treated sand. Results show that the mycelium enhances soil strength, reduces deformation, and lowers excess pore water pressure, with a more pronounced effect under undrained than drained conditions. Mycelium adheres to particle surfaces, forming a durable bond that increases cohesion and shifts the slope of the critical state line, significantly enhancing the mechanical stability of fungus-treated sand. The resulting strength parameters are comparable to those of soils reinforced with plant roots. Fungus-treated sand remains stable after 14 days of water immersion following triaxial shear tests, with no environmental risk from leachate. These findings demonstrated that fungal mycelium provides an effective and eco-friendly solution for stabilizing loose sand, mitigating shallow landslides, and reinforcing coastlines.

The socio-economic growth of a nation depends heavily on the availability of adequate infrastructure, which relies on essential materials like river sand (RS) and cement. However, the rising demand for RS, combined with its excessive extraction causing ecological damage, and its increasing cost, has raised significant concerns. At the same time, the production of cement contributes significantly to environmental damage, especially through CO2 emissions. In this scenario geopolymer technology has emerged as a sustainable alternative to cement, offering environmental benefits and reducing the carbon footprint of construction materials. This study investigates the impact of replacing RS with copper slag (CS) and laterite soil (LS) in geopolymer mortar (GM) on key properties such as setting time, flowability, compressive strength, and microstructure. The results showed that as LS content increased, setting time and flowability decreased considerably, while increasing CS content caused a reduction in these values. Unlike the other observed parameters, the compressive strength values showed no distinct upward or downward trend. Moreover, the microstructural analysis, including SEM, EDS, XRD, FTIR, TGA and BET, provided valuable insights to support the observed results across various mix designs. Overall, the findings highlight that optimised binary blends of CS, LS and RS not only improved the compressive strength but also enhanced the microstructural characteristics of geopolymer mortar, reinforcing their potential as sustainable and high-performance alternatives to conventional fine aggregates.