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.

A two-lift gradient design for airport pavements has been proposed to mitigate the functional degradation, especially the salt-frost (S-F) damage induced by deicing slat fluids. Herein, this study focuses on elucidating the mechanism and improvement of incorporating mineral admixtures in the development of a novel S-F resistant surface concrete material, which is of great significance for delaying the functional deterioration of pavement surface in northern China. The results indicated that the filling effect and secondary hydration reaction between the fly ash (FA) and silica fume (SF) and cement hydration products results in a dense spatial network structure, effectively reducing porosity and optimizing pore structure. It was found that SF can effectively improve the frost resistance and salt corrosion resistance of cement mortar, while the influence of FA depends on its content and environmental conditions. The incorporation of FA and SF significantly enhanced the structural density of cement concrete and reduced chloride ion permeability. The improvement in impermeability is most pronounced when both FA and SF are used in combination. In addition, a fitting equation between the admixture content and chloride ion permeability has been established, demonstrating good fitting results. In non-frozen saline soil areas, a large amount of FA or SF could be incorporated; in seasonally frozen areas, the priority should be given to SF to ensure salt corrosion resistance and frost resistance. The findings of this study provide a scientific basis for sustainable airport pavement construction in northern China.

The large amount of slag generated during the construction of earth pressure balance shield (EPBS) not only incurs significant disposal costs, but also exacerbates environmental pollution. To improve the utilization of the shield slag, silty clay with additive is proposed as a slag conditioner instead of bentonite. Firstly, various macroscopic properties of the bentonite and silty clay slurries are tested. Subsequently, the relationships between the macroscopic properties of the silty clay slurries containing additives and the modification mechanism are evaluated at microscopic, mesoscopic, and macroscopic scales by using infrared spectroscopy (IR), scanning electron microscope (SEM), and Zeta potential tests, respectively. Based on these tests, reasons for variations in modification effects of different slurries are identified. The results show that addition of 3 % sodium carbonate to the silty clay can effectively improve the rheological properties of the slurry. The modification mechanism of sodium carbonate involves the formation of hydrogen bonds between water molecules and inner surface hydroxyl groups within the lattice layer of kaolinite. This process significantly enhances the rheological properties of the silty clay slurry. Furthermore, sodium carbonate alters the contact relationships between the silty clay particles, which increases viscosity and reduces permeability of the slurry. Finally, sodium carbonate increases thickness of the electrical double layer of the silty clay particles. This allows the particles to bind more water molecules, therefore improving slurry-making capacity of the silty clay. This paper presents an innovative multiscale analysis of the modification process of silty clay. The substitution of recycled silty clay for bentonite as a slag conditioner not only substantially reduces the cost of purchasing materials, but also considerably decreases the expenses associated with transportation and disposal of the soil discharged by EPBS.

The modification of dispersive soils remains a prominent and challenging issue in the field of geotechnical engineering. Using lime, fly ash, and CaCl2 as benchmark materials, this study explores the potential of enzymeinduced calcite precipitation (EICP) technology to modify three kinds of dispersive soils. The modification effects of the four materials were systematically evaluated through crumb and pinhole tests. By linking the modification performance to curing time and material dosage, the study proposes a novel formula to compare the modification efficiency of the materials. To enhance practical applicability in engineering contexts, the study also investigates the impact of these materials on the mechanical properties of dispersive soils through unconfined compressive strength (UCS) tests. Furthermore, the modification mechanisms of the materials were compared using exchangeable sodium percentage (ESP) analysis, scanning electron microscopy (SEM), Energy Dispersive Spectrometer (EDS), and X-ray diffraction (XRD). The results indicate that both EICP technology and lime exhibit superior modification effects, effectively enhancing the resistance to water erosion and the mechanical properties of dispersive soils. Compared to lime, EICP technology demonstrates higher modification efficiency and greater environmental sustainability. Notably, low-concentration EICP solutions can effectively modify all three kinds of dispersive soils tested in this study.

Dispersive soil is susceptible to water erosion and could cause damage in geotechnical engineering or hydraulic engineering projects. Recycled clay brick powder (RCBP) was used as a modifier to improve the dispersivity and water stability of dispersive soil in this study. Pinhole tests, crumb tests, disintegration tests, particle analysis tests, exchangeable sodium percentage (ESP) tests, pH tests, conductivity tests, and X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were conducted to explore the modification effects and corresponding mechanisms of RCBP on dispersive soil. The results revealed that the dispersivity of the soil significantly weakened as the RCBP content increased and curing time extended. Specifically, adding 4% RCBP to the soil and curing for 7 days effectively transformed dispersive soil into nondispersive soil. Furthermore, the final disintegration time of the soil sample with 10% RCBP cured for 28 days was 273% longer than that of the soil sample without curing. Moreover, the treatment led to decreased fines content, ESP value, and pH value in the soil samples. The decrease in ESP value indicated the replacement of sodium ions adsorbed on the soil particle surfaces with calcium ions, resulting in a reduction in the thickness of the diffuse electric double layer of soil particles, and subsequently reduced soil dispersivity. Additionally, the decrease in pH also contributed to the reduction of the diffuse electric double-layer thickness. XRD and SEM analyses confirmed the formation of cementing materials between soil particles due to the modification, which filled gaps and cemented particles to create a waterproof barrier between soil particles. In conclusion, the utilization of RCBP as a modifier for dispersive soil could be a win-win measure with promising outcomes. It is recommended that more than 4% RCBP should be added in engineering applications.

Red clay exhibits characteristics such as softening owing to water absorption and cracking because of water loss, which can lead to slope instability, road cracking, and compromised structural integrity when used directly in roadbed filling. Although the addition of industrial materials such as cement is a common engineering treatment, it severely impairs soil renewability. Lignosulfonate (LS) extracted from paper plant waste fluids is a natural bio-based polymer with promising applications as a soil improver. In this study, the boundary moisture content and mechanical properties of LS-treated red clay were investigated using Atterberg, unconfined compressive strength, and direct shear strength tests. Additionally, the LS-treated red clay modification mechanism was explored at multiple scales using zeta potential analysis, X-ray diffraction, scanning electron microscopy coupled with energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. The results indicated that the LS dosage significantly affected both the water content and mechanical strength of the red clay boundaries. The optimal dosage of LS for red clay was 3 wt. %, at which the liquid limit was reduced by 32.97%, the plastic limit by 19.33%, and the plasticity index by 48.37%. The 28-day compressive strength of LS-treated red clay was increased by 378.4%, and the direct shear strength was increased by 136%. Analysis of the microstructure and mineral composition revealed that the LS-treated red clay did not form new minerals, but primarily filled pores and connected soil particles. Through the combined effects of hydrogen bonds, electrostatic interactions, and cation exchange, the LS-treated red clay reduced the size of the mineral particles and the thickness of the mineral double electric layer, resulting in increased structural densification. These results are of great scientific significance for the ecological modification of soils.

Dispersive soil is a widely distributed problematic soil in arid or semiarid areas of the world and can cause pipe erosion, gully damage and other seepage failures. This study analyzed the effect of environmentally friendly enzyme-induced carbonate precipitation (EICP) on the dispersivity of dispersive soils. This methodology was tested for the stabilization of three dispersive soil types (two high-sodium soils, two low-clay-content soils, and two soils with both high sodium and low clay contents) to examine the impact on dispersivity based on the results of pinhole tests and mud ball tests. Physical, chemical, mechanical, and microscopic tests were also conducted to investigate the effects of the components in the EICP reaction solution on dispersive soil modification. The experiments showed that the concentration of the reaction solution and the curing time required to limit the dispersivity decreased with increasing clay content in the soil. Ca2+ limited the dispersivities of dispersive soils via four distinct mechanisms. The first mechanism was ion exchange; Ca2+ decreased the percentage of exchangeable sodium ions to less than 7% while reducing the thickness of the diffuse double layer such that the spacings between soil particles were reduced and the chemical dispersivity was limited. Second, Ca2+ increased the viscosity of the solution by salting out the organic matter present in the soybean urease. Subsequently, the D1-class physically dispersive soil was converted into an ND2-class nondispersive soil. Third, Ca2+ decreased the soil pH by reducing the CO32- content, which could hydrolyze to increase the soil alkalinity. Finally, the presence of Ca2+ led to the generation of cementitious minerals through the precipitation of CaCO3 crystals that continuously generated CO32-, filling and cementing soil particles and thereby limiting their physical dispersivity. These results indicated that a low-concentration EICP reaction solution efficiently controlled the dispersivities of the three dispersive soils.

Large quantities of abandoned marine soft soil are generated from coastal engineering which cannot be directly utilized for construction without modification. The utilization of traditional binders to modify abandoned marine soft soil yields materials with favorable mechanical properties and cost efficiency. However, the production of traditional binders like cement leads to environmental pollution. This study uses a CGF all-solid-waste binder (abbreviated as CGF) composed of industrial solid waste materials such as calcium carbide residue (CCR), ground granulated blast furnace slag (GGBS), and fly ash (FA), developed by our research team, for the modification of abandoned marine soft soil (referred to as modified soil). It is noteworthy that the marine soft soil utilized in this study was obtained from the coastal area of Jiaozhou Bay, Qingdao, China. Physical property tests, compaction tests, and unconfined compressive strength (UCS) tests were conducted on the modified soil. The investigation analyzed the effects of binder content, compaction delay time, and curing time on the physical, compaction, and mechanical properties of CGF-modified soil and cement-modified soil. Additionally, microscopic experimental results were integrated to elucidate the mechanical improvement mechanisms of CGF on abandoned marine soft soil. The results show that after modification with binders, the water content of abandoned marine soft soil significantly decreases due to both physical mixing and chemical reactions. With an increase in compaction delay time, the impact of chemical reactions on reducing water content gradually surpasses that of physical mixing, and the plasticity of the modified soil notably modifies. The addition of binders results in an increase in the optimum moisture content and a decrease in the maximum dry density of CGF-modified soil, while the optimum moisture content decreases and the maximum dry density increases for cement-modified soil. Moreover, with an increase in binder content, the compaction curve of CGF-modified soil gradually shifts downward and to the right, while for cement-modified soil, it shifts upward and to the left. Additionally, the maximum dry density of both CGF-modified and cement-modified soils shows a declining trend with the increase in compaction delay time, while the optimum moisture content of CGF-modified soil increases and that of cement-modified soil exhibits a slight decrease. The strength of compacted modified soil is determined by the initial moisture ratio, binder content, compaction delay time, and curing time. The process of CGF modification of marine soft soil in Jiaozhou Bay can be delineated into stages of modified soil formation, formation of compacted modified soil, and curing of compacted modified soil. The modification mechanisms primarily involve the alkali excitation reaction of CGF itself, pozzolanic reaction, ion-exchange reaction, and carbonization reaction. Through quantitative calculations, the carbon footprint and unit strength cost of CGF are both significantly lower than those of cement.