Soft soil foundations need to be reinforced because of their low bearing capacity and susceptibility to deformation. Ordinary portland cement (OPC) is widely used in foundation treatment due to its strong mechanical properties. However, the production process for OPC curing agents involves high energy consumption and significant CO2 emissions. Given these problems, this paper proposes a fly ash-slag-based geopolymer to replace OPC curing agents, which can solidify soil while reducing OPC consumption. Another issue is that variability in environmental conditions influences the strength of soil solidified with fly ash-slag-based geopolymer, leading to subpar mechanical properties. However, by adding desulfurized gypsum as an admixture, the rich SO42- can react with Ca2+ and active silicate in the geopolymer to form Aft, thereby improving the mechanical properties. In the experiment, desulfurized gypsum is added as an admixture to a fly ash-slag-based geopolymer curing agent, and the resulting solidified soil is investigated through various macroscopic and microscopic tests. These tests include unconfined compressive strength measurements, water stability tests, scanning electron microscopy analyses, and X-ray diffraction tests. The results of these tests are combined with the response surface method to optimize the alkali-solid ratio, the modulus of the alkali activator, and the amount of desulfurized gypsum to 0.6%, 0.809%, and 15.96%, respectively. On this basis, an optimal mixing ratio was proposed and applied to form a geopolymer-solidified soil. The compressive strength and microstructure of this soil were then investigated using the single-variable method. An unconsolidated undrained triaxial test was performed on geopolymer-solidified soils of different curing times to investigate their shear performance. The water stability test was carried out to explore the influence of soaking time on the strength of solidified soil. Through microscopic observation, it was found that the fly ash-slag-based geopolymer generated significant amounts of (N, C)-A-S-H and C-S-H in solidified soil. With the addition of desulfurized gypsum, soil particles become filled with Aft and the solidified soil becomes more brittle instead of plastic, resulting in a significant increase in compressive strength. In addition, the cohesion and internal friction angle increase with curing time. With the increase of soaking time, the softening effect of long-term water soaking reduced the strength of the solidified soil.

Natural paper-based materials are desirable candidate materials for disposable hygiene products due to their environmental sustainability, cost-effectiveness, and biodegradability. However, their practical application is often hindered by poor water stability and limited functional properties. In this study, we developed a wet-laid web formation and hot-pressing technique to produce porous, layered paper-based materials with high porosity, flexibility, water stability, and antibacterial properties. These materials were created using naturally derived components, including kapok fiber, carboxymethyl cellulose (CMC), and cationic starch (CS). The synergistic interaction between CMC and CS significantly enhances the mechanical properties and water stability, achieving a 146.09 % improvement compared to materials without CMC/CS. The resulting paper-based materials also exhibit water stability for up to 30 days. Kapok fibers contribute excellent antimicrobial properties, with >95 % inhibition of both Escherichia coli and Staphylococcus aureus. Furthermore, the materials are biodegradable in soil, completely degrading after 60 days. This study provides novel insights into the valorization of kapok fiber and presents a sustainable approach to producing high-performance paper-based materials for disposable hygiene products applications.

The soil construction materials cured with biopolymers are gradually being recognized and widely used in engineering areas, such as roadbeds or foundation fills. The strength of biopolymer-solidified soils (BSS) is easily influenced by the change of internal residual moisture content (RMC), however, the quantitative relationship between them remains unclear. Xanthan gum, as a representative of biopolymer, was used in this study to enhance the mechanical properties of silty sand dredged from the Yellow River under different initial water contents and curing temperatures. The unconfined compressive strength (UCS), curing time, water stability and microscopic properties of BSS were investigated via a series of indoor experiments. Results show that the proposed method for quantitatively evaluating the BSS strength using different RMC values was found to be workable compared to that of the traditional cement-treated method under different curing ages. The curing time required for BSS to reach a certain target strength, i.e. 2900 kPa, is reduced to 9.3 h at a higher curing temperature of 90 degrees C. Moreover, BSS exhibits the self-healing properties of strength recovery after re-temperature drying, with a strength recovery ratio above 45%. The control raw soil samples completely disintegrate in water within 10 s, and even lower xanthan gum biopolymer dosages, such as 0.5%, improved stability in water by reducing permeability by sealing the internal voids of the soil. SEM results indicate that the initial water content and curing temperature mainly affect the distribution of effective xanthan gum linkages, and thus significantly improve the strength and water stability of BSS. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

In recent decades, rapid urbanization has generated a large amount of waste soft soil and construction debris, resulting in severe environmental pollution and posing significant challenges to engineering construction. To address this issue, this study explores an innovative approach that synergistically applies recycled fine aggregate (RFA) and soil stabilizers to improve the mechanical properties of soft soil. Through laboratory experiments, the study systematically examines the effects of different mixing ratios of RFA (20%, 40%, 60%) and soil stabilizers (10%, 15%, 20%) with red clay. After standard curing, the samples underwent water immersion maintenance for varying durations (1, 5, 20, and 40 days). Unconfined compressive strength (UCS) tests were conducted to evaluate the mechanical performance of the samples, and the mechanisms were further analyzed using scanning electron microscopy (SEM) and particle size distribution (PSD) analysis. The results indicate that the optimal performance is achieved with 20% RFA and 20% stabilizer, reaching the highest UCS value after 40 days of water immersion. This improvement is primarily attributed to the formation of a dense reticulated structure, where RFA particles are effectively encapsulated by clay particles and stabilized by hydration products from the stabilizer, forming a robust structural system. Unconsolidated undrained (UU) tests reveal that peak deviatoric stress increases with confining pressure and stabilizer content but decreases when excessive RFA is added. Shear strength parameter analysis demonstrates that both the internal friction angle (phi) and cohesion (c) are closely related to the content ratios, with the best performance observed at 20% stabilizer and 20% RFA. PSD analysis further confirms that increasing stabilizer content enhances particle aggregation, while SEM observations visually illustrate a denser microstructure. These findings provide a feasible solution for waste soft soil treatment and resource utilization of construction debris, as well as critical technical support and theoretical guidance for geotechnical engineering practices in high-moisture environments.

The effective utilization of phosphogypsum (PG) and industrial waste soil is of paramount importance in the real world. The combination of phosphogypsum and soil in a single mixture can simultaneously utilize both materials. In this study, a novel green road material was developed according to the concept of synergistic utilization of multiple solid wastes, which is based on conventional cement stabilized soil. The GGBS was employed to gradually replace cement to stabilize PG-soil mixtures. The curing effect of GGBS replacing cement and the modification effect of PG on stabilized soil were evaluated in three aspects: mechanical properties, water stability, and environmental performance. This evaluation was conducted using the unconfined compressive strength (UCS), softening coefficient, and ionic concentration of heavy and trace metals. Furthermore, microscopic characterization techniques, including a pH meter, UV-visible spectrophotometer, FTIR, XRD, SEM, and EDS, were used to perform further analyses of the curing mechanism. The objective was to enhance the UCS of stabilized soil by incorporating an optimal amount of PG, avoiding the necessity for a complex and costly pretreatment process for PG. The UCS reached approximately 8 MPa in 7 days without immersion in water curing and 4 MPa in 7 days with 1 day immersion in water curing. Despite the decline in water stability resulting from the incorporation of PG, the stabilized soil exhibits superior mechanical properties compared to the majority of studies on the application of PG to stabilized soils. The monitoring of contaminant ions in the stabilized soil over a period of 28 days demonstrated compliance with EPA requirements, indicating that PG-based stabilized soil does not negatively impact the surrounding environment in the presence of water. Additionally, the optimal ratio of GGBS to cement is 1:1. Meanwhile, excessively high or low cement content has a detrimental impact on the properties of stabilized soil. Lastly, the practical engineering application of this novel green road material was achieved, and its mechanical properties and economic benefit were demonstrated to be superior to those of conventional cement stabilized soil. The study of PG in stabilized soil was transformed into the utilization of realworld projects without the necessity for a complex pretreatment process for PG. Concurrently, the replacement of GGBS for cement results in a reduction in both carbon emissions and economic costs, due to an enhanced utilization of solid waste. Additionally, it offers a more detailed analysis of the curing mechanisms in stabilized soils with respect to strength, water stability, and harmful ions.

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.

The structural properties of loess are susceptible to change when subjected to external loads and complex environments, leading to various geological disasters. To investigate the mechanical behavior and strengthening mechanism of loess stabilized with biopolymers such as xanthan gum and guar gum, especially for soils with low bearing capacity and stability in engineering applications, we conducted research on the improvement of soil with xanthan gum and guar gum, tests including unconfined compressive strength, disintegration, direct shear, and microstructure tests were conducted. Among the four different dosages of biopolymers (0%, 0.5%, 1%, 2%) and four different curing ages (1 day, 3 days, 7 days, 14 days), the 2% content of biopolymer and 14 days had the greatest impact on the mechanical properties of loess, Both the compressive and shear strength, as well as the water stability of solidified loess, improve with higher content of xanthan gum and guar gum or prolonged curing time; however, the disintegration rate decreases. Microscopic analysis indicates that the biopolymers effectively fill the gaps between soil particles and attach to the particle surfaces, forming fibrous and reticular structures that improve the interparticle bonding and ultimately increase the strength and water stability of the loess. Xanthan gum and guar gum biopolymers can improve the mechanical properties and water stability of loess, enhance the erosion resistance and improve the water-holding capacity. These outcomes suggest that guar gum and xanthan gum biopolymers have the potential to serve as environmentally sustainable alternatives to conventional soil stabilizers.

Urban construction generates significant amounts of construction residue soil. This paper introduces a novel soil stabilizer based on industrial waste to improve its utilization. This stabilizer is primarily composed of blast furnace slag (BFS), steel slag (SS), phosphogypsum (PG), and other additives, which enhance soil strength through physical and chemical processes. This study investigated the mechanical properties of construction residue soil cured with this stabilizer, focusing on the effects of organic matter content (Oo), stabilizer dosage (Oc), and curing age (T) on unconfined compressive strength (UCS). Additionally, water stability and wet-dry cycle tests of the stabilized soil were conducted to assess long-term performance. According to the findings, the UCS increased with the higher stabilizer dosage and longer curing periods but reduced with the higher organic matter content. A stabilizer content of 15-20% is recommended for optimal stabilization efficacy and cost-efficiency in engineering applications. The samples lost their strength when immersed in water. However, adding more stabilizers to the soil can effectively enhance its water stability. Under wet-dry cycle conditions, the UCS initially increased and then decreased, remaining lower than that of samples cured under standard conditions. The findings can provide valuable data for the practical application in construction residual soil stabilization.

This study addresses the engineering geological disaster resulting from the degradation of mechanical properties of expansive soil due to changes in environmental humidity along the Middle Route of the South-to-North Water Transfer Project. Calcium carbide slag and slag are utilized as curing materials to improve the expansive soil. Comparative tests were conducted on the unconfined compressive strength, split tensile strength, and water stability of untreated and treated expansive soil to analyze the performance differences pre- and post-treatment. The strength enhancement mechanism of the calcium carbide slag-slag cured soil was investigated through the X-ray diffraction (XRD), electron microscope scanning (SEM), thermogravimetric analysis (TGA) test and nuclear magnetic resonance (NMR) test, revealing its microscopic mechanism of action. The results showed a significant increase in the overall strength and water resistance of the calcium carbide slag-slag composite modified cured soil with different slag dosage based on 6% dosage of calcium carbide slag, and a maximum value was reached when the slag dosage was 9%. Over time, the unconfined compressive strength and split tensile strength improved, while the water stability coefficient decreased notably. Hydration of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) generated by the hydration of calcium carbide slag-slag composite cured soil led to the formation of tightly bonded soil particles, enhancing the soil's pore structure distribution and strength. The evident effectiveness of the composite curing method for calcium carbide slag-slag treated soil suggests promising engineering applications.

Loess exhibits poor engineering properties, such as low strength and poor water stability. Conventional materials used for improving loess, such as cement and lime, result in environmental pollution issues throughout their production and application processes. To assess the efficacy of bio-based materials, including calcium alginate (CA), xanthan gum (XA), cotton fibers (CO) and flax fibers (FA) in the treatment of loess, the improved soil's strength, disintegration, and water resistance were examined. Subsequently, an optimal amendment approach was determined, and dry -wet cycle tests and microscopic observation were performed. The results show that 1.0 % calcium alginate can effectively enhance the strength of loess, significantly improving its resistance to disintegration with almost no observable disintegration; permeability is significantly reduced, and water repellency is enhanced. 2.0 % xanthan can improve the strength and disintegration resistance of loess, but the improvement in strength is lower than that of calcium alginate. Additionally, the improved soil with XA experiences a flocculent disintegration in static water, which cannot maintain the soil structure. Cotton fibers and flax fibers can enhance both compressive and tensile strength of the soil. The content of 0.45 % flax fibers is considered the optimal choice as it has no effect on water stability. Combining the above results, the combination of 1.0 % CA and 0.45 % FA has been selected to improve the loess, which effectively improves the comprehensive mechanical properties and water stability of the composite improved soil. The decrease in strength and mass loss rate are significantly reduced after dry -wet cycle tests. Microscopic tests show that calcium alginate connects soil particles by Ca2+ ionic bridges, which allows the cementing materials to fill the loess pores and exert the role of agglomeration and coagulation to enhance the integrity of the loess. This study shows that the bio-based material with calcium alginate as the main body can effectively improve the mechanical strength and water stability of the loess.