This research explores the stabilization of clay soil through the application of geopolymer binder derived from silicomanganese slag (SiMnS) and activated by sodium hydroxide (NaOH). This research aims to evaluate the effects of key parameters, including the percentage of slag, the activator-to-stabilizer ratio, and curing conditions (time and temperature), on the mechanical properties of the stabilized soil. Unconfined compressive strength (UCS) tests were conducted to assess improvements in soil strength, while scanning electron microscopy (SEM) was employed to analyze the microstructural changes and stabilization mechanisms. The results demonstrated that clay soil stabilized with SiMnS-based geopolymers exhibited significant strength enhancement. Specifically, the sample stabilized with 20% SiMnS and an activator-to-slag ratio of 1.6, cured at room temperature for 90 days, achieved a UCS of 27.03 kg & frasl;cm2. The uniaxial strength was found to be positively correlated with the SiMnS content, activator ratio, curing time, and temperature. Additionally, the strain at failure remained below 1.5% for all samples, indicating a marked improvement in soil stiffness. SEM analysis revealed that geopolymerization led to the formation of a dense matrix, enhancing soil particle bonding and overall durability. These results emphasize the potential of SiMnS-based geopolymers as a sustainable and effective soil stabilizer for geotechnical applications.

The stability of soil in high-altitude regions is significantly affected by freeze-thaw cycles, which alter its mechanical and physical properties. This study investigates the impact of 12 consecutive freeze-thaw cycles on poorly graded sandy-silt soil collected from Arunachal Pradesh. To enhance soil resistance, a bio-slurry containing urea (60 g/L) and calcium chloride (111 g/L), along with vetiver and bamboo fibers (by soil weight), was introduced as a stabilizing agent. The durability of the treated soil was evaluated by measuring the weight fluctuations after each cycle and assessing unconfined compressive strength (UCS) after 5, 10, and 12 cycles. The results revealed that untreated soil experienced a 50% reduction in UCS, while bioslurry-treated soil retained 70-80% of its original strength after 12 freeze-thaw cycles. The greatest strength retention was observed in soil treated with bioslurry and bamboo fiber, which retained 80% of its strength, followed by vetiver-treated soil at 75% strength retention. Weight loss measurements indicated that untreated soil samples lost 9.5% of their initial mass, whereas bioslurry-treated samples exhibited only a 3-5% weight loss. The findings of the study highlight the potential of bioslurry and natural fibers in mitigating freeze-thaw-induced soil degradation, making them suitable for applications in geotechnical engineering in cold-climate regions.

Cement mixing techniques are widely used to improve the mechanical properties of weak soils in geotechnical engineering. However, due to the influence of various factors such as material properties, mixing conditions, and curing conditions, cement-mixed soil exhibits pronounced spatial variability which is greater than that of natural soil deposits, introducing additional uncertainty into the measurement and evaluation of its unconfined compressive strength. The purpose of this study is to propose a novel framework that integrates image analysis with Bayesian approach to evaluate the unconfined compressive strength of cement-mixed soil. A portable scanner is used to capture high-quality digital images of cement-mixed soil specimens. Mixing Index (MI) is defined to effectively evaluate mixing quality of specimens. An equation describing the relationship between water cement ratio (W/C) and unconfined compressive strength (qu) is introduced to estimate the strength of uniform specimens. To estimate the strength of non-uniform specimens, the equation is developed by integrating MI with the strength of uniform specimens. The coefficients of equations are obtained using Bayesian approach and Markov Chain Monte Carlo (MCMC) method, which effectively estimating the strength of both uniform and non-uniform specimens, with coefficients of determination (R2) of 0.9858 and 0.8745, respectively. For each specimen, a distribution of estimated strength can be obtained rather than a single fixed estimate, providing a more comprehensive understanding of the variability in strength. Bayesian approach robustly quantifies uncertainties, while image analysis serves as a convenient and non-destructive method for strength evaluation, providing accurate method for optimizing the mechanical properties of cement-mixed soil.

Geopolymers are recently recognized as superior sustainable alkali-activated materials (AAMs) for soil stabilization because of their strong bonding capabilities. However, the influence of freeze-thaw cycles (FTCs) on the performance of geopolymer-stabilized soils reinforced with fibers remains largely unexplored. In the current study, for the first time, the durability of polypropylene fiber (PPF) reinforced clayey soil stabilized with fly ash (FA) based geopolymer is investigated under FTCs, evaluating its performance during prolonged seasonal freezing. The effects of repeated FTCs (0, 1, 3, 6, and 12 cycles), different contents of alkali-activated FA (5 %, 10 %, and 15 %), varying PPF percentages (0 %, 0.4 %, 0.8 %, and 1.2 % with a length of 6 mm), and curing time (7 and 28 days) on the properties of stabilized samples have been determined through tests including standard Proctor compaction, unconfined compressive strength (UCS), mass loss, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The results revealed that a 0.4 % PPF concentration maximized strength in FA-based geopolymer samples by restricting crack propagation, irrespective of FA content, number of FTCs, or curing time. However, higher PPF contents lowered UCS values and Young's modulus due to fiber clustering and increased failure strain, respectively. Generally, an initial increase in UCS, Young's modulus, and resilience modulus (MR) of stabilized samples occurred with more FTCs because of their dense structure, delayed pore formation, and continued geopolymerization process and followed by a constant or decreasing trend in strength after 6 (or 3 in some cases) FTCs due to ice expansion in created air voids. Longer curing time resulted in denser samples with improved resistance to FTCs, especially under 12 FTCs. Moreover, samples with 10 % alkali-activated FA demonstrated the least susceptibility to FTCs. While initial FTCs caused no mass loss, subsequent cycles led to increased mass loss and remained below 2 % for all samples. Microstructural analysis results corroborated UCS test results. Although the primary chemical composition remained unchanged after 12 FTCs, these cycles induced morphological changes such as critical void formation and cracking within the gel structure. The stabilization approach proposed in this study demonstrated sustained UCS after 12 FTCs, promising reduced maintenance costs and extended service life in regions with prevalent freeze-thaw damage.

The integration of industrial and biogenic waste materials in soil stabilization provides an environmentally sustainable alternative to conventional binders. This study evaluates the influence of mussel shell powder (MSP) on both untreated, cemented, and recycled soils, where the recycled soil was initially stabilized with calcium carbide residue, cured for one year, ground into powder, and then re-treated with MSP. Unconfined compression, ultrasonic pulse velocity, and direct shear tests were conducted to assess the strength, compaction, and shear behavior of MSP-stabilized pure, recycled, and cemented soils. The results indicate that MSP addition reduced plasticity and improved soil workability. In recycled soils, 5% MSP provided optimal strength enhancement, while in cemented soils, 20% MSP was required for significant strength gains due to its role in secondary cementation. Freeze-thaw tests demonstrated that MSP-treated soils exhibited up to a 40% reduction in strength loss compared to untreated samples, improving durability in cold climates. The ultrasonic pulse velocity measurements showed strong correlations with unconfined compressive strength, confirming its potential as a nondestructive assessment method for stabilized soils. These findings highlight the potential of MSP as a sustainable stabilizer for improving soil mechanical properties, durability, and resistance to freeze-thaw cycles.

The accumulation of waste glass (WG) from construction and demolition waste is detrimental to the environment due to its imperishable nature; therefore, it is crucial to investigate a sustainable way to recycle and reuse the WG. To address this issue, this study examined the mechanical strength, microstructural characteristics, and environmental durability-specifically under wet- dry (WD) and freeze-thaw (FT) cycles-of WG obtained from construction and demolition waste, with a focus on its suitability as a binding material for soil improvement applications. Firstly, sand and WG were mixed, and an alkali solution was injected into the mixture, considering various parameters, including WG particle size, mixing proportions, sodium hydroxide (NaOH) concentration, and curing time. Subsequently, the effect of WG grain sizes on micro- morphology characteristics and mineralogical phases was evaluated before and after the treatment through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and ultrasonic pulse velocity (UPV). The results revealed that reducing the WG particle size and increasing the WG/S ratio significantly improved the strength of the WG-treated samples. Additionally, decreasing the NaOH concentration and extending the curing time also positively influenced their strength. The UCS test results indicate that the particle size of WG significantly influenced the strength development of the samples, as the maximum compressive strength increased from 1.42 MPa to 7.82 MPa with the decrease in particle size. Although the maximum UCS values of the samples varied with different WG particle sizes, the values exceed the minimum criterion of 0.80 MPa required for use as a road substructure, as specified in the ASTM D4609 standard. Moreover, as WG grain size decreased, more geopolymer gels formed, continuing to fill the voids and making the overall structure denser, and the changes during geopolymerization were confirmed by XRD, SEM, FTIR, and UPV analysis. The optimum WG/S ratio was found to be 20 %, with strength increasing by approximately 3.88 times higher as the WG/S ratio shifted from 5 % to 20 %. In addition, the optimum NaOH concentration was determined to be 10 M, as higher molarities led to a decrease in strength. Moreover, UPV results indicate that WG-treated sand soils exhibited UPV values 9.4-13 times greater than untreated soils. The WD and FT test results indicate that WG-treated samples experienced more rapid disintegration in the WD cycle than in the FT cycle; however, a decrease in WG particle size resulted in reduced disintegration effects in both WD and FT conditions. In both the FT and WD cycles, the declining trend exhibited a stable tendency around the eighth cycle. Nevertheless, the WD cycling damage considerably intensified disintegration, causing a profound deterioration in the structural integrity of the samples. As a result, repeated WD cycles lead to the formation of microcracks, which progressively weaken soil aggregation and reduce the overall strength of the samples. Consequently, this green and simple soil improvement technique can provide more inspiration for reducing waste and building material costs through efficient use of construction and demolition waste.

Red mud is a kind of solid waste, which can be used as engineering roadbed filler after proper treatment. Due to the special physical and chemical properties of red mud, such as high liquid limit and high plasticity index, it may affect the stability of soil. Therefore, red mud can be improved by adding traditional inorganic binders such as lime and fly ash to improve its road performance as roadbed filler. Red mud-based modified silty sand subgrade filler will be affected by dry-wet alternation caused by various factors in practical application, thus affecting the durability of the material. In order to study the strength degradation characteristics and microstructure changes of red mud, lime and fly ash modified silty sand subgrade filler after dry-wet cycle, the samples of different curing ages were subjected to 0 similar to 10 dry-wet cycles, and their compressive strength, microstructure and environmental control indexes were tested and analyzed. The results show that the sample cured for 90 days has the strongest toughness and the best ability to resist dry and wet deformation. With the increase of the number of dry-wet cycles, the mass loss rate of the sample is in the range of 6 similar to 7 %, and the unconfined compressive properties and tensile properties decrease first and then increase. There are continuous hydration reactions and pozzolanic reactions in the soil, but the degree of physical damage in the early stage of the dry-wet cycle is large, and the later cementitious products have a certain offsetting effect on the structural damage. The internal cracks of the sample without dry-wet cycle are less and the structure is dense. After the dry-wet cycle, the microstructure of the sample changed greatly, and the cracks increased and showed different forms. Through SEM image analysis, it was found that the pore structure of the sample changed during the dry-wet cycle, which corresponded to the change law of mechanical properties. After wetting-drying cycles, the leaching concentration of heavy metals in the modified soil increased slightly, but the overall concentration value was low, which was not a toxic substance and could be used as a roadbed material. The study reveals the influence of dry-wet cycle on the strength characteristics and microstructure of red mud, lime and fly ash synergistically improved silty sand, which provides a technical reference for the engineering application of red mud-based materials.

In cold regions, and considering the increasing concerns regarding climate change, it is crucial to assess soil stabilisation techniques under adverse environmental conditions. The study addresses the challenge of forecasting geotechnical properties of lime-stabilised clayey soils subjected to freeze-thaw conditions. A model is proposed to accurately predict the unconfined compressive strength (UCS) of lime-stabilised clayey soils exposed to freeze-thaw cycles. As the prediction of UCS is essential in construction engineering, the use of the model is a viable early-phase alternative to time-consuming laboratory testing procedures. This research aims to propose a robust predictive model using readily accessible soil parameters. A comprehensive statistical model for predicting UCS was developed and validated using data sourced from the scientific literature. An extensive parametric analysis was conducted to assess the predictive performance of the developed model. The findings underscore the capability of statistical models to predict UCS of stabilised soils demonstrating their valuable contribution to this area of study.

Soil treatment with natural materials is an effective method to improve the mechanical properties of the original soil for recycling engineering construction. This research aims to evaluate the synergistic effects of lignin fiber and cement on sandy clayey silt stabilization. A factorial experimental design was employed, testing five lignin fiber contents (0%, 2%, 4%, 6%, and 8%) and three cement contents (0%, 2%, and 4%) across four curing periods (1, 7, 14, and 30 days). Unconfined compressive strength (UCS) tests were conducted in triplicate for each combination (total *n* = 180 samples), and failure surfaces were analyzed using Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM-EDX). Results indicate a critical lignin fiber threshold of 4%, beyond which UCS decreased by 15-20% due to increased void ratios. Statistical analysis (ANOVA, *p* < 0.05) confirmed significant interactions between lignin fiber, cement content, and curing time. For instance, 4% lignin fiber and 4% cement yielded a 139% UCS increase after 30-day curing compared to untreated soil. SEM-EDX revealed that lignin fiber networks enhance ductility by bridging soil particles, while cement hydration reduced particle detachment. These findings provide a quantitative framework for optimizing lignin fiber-cement stabilization in sustainable geotechnical applications.

The cement-stabilization technique is employed on natural and recycled granular materials to improve their mechanical properties. The strength of these materials is assessed by the unconfined compressive strength on laboratory compacted specimens, typically after 7 days of curing. Standards and technical specifications specify different values of specimen height and diameter and different loading modes of testing. This makes the comparison between different materials and with the acceptance limits of technical specifications difficult. The research investigates the effect of specimen size and loading mode on the unconfined compressive strength of both natural and recycled cement-stabilized granular materials. The results revealed significant differences in strength due to variations in specimen size and loading mode. As expected, an increase in specimen slenderness resulted in a decrease in compressive strength. A linear regression model was developed to quantify the effect of the experimental variables on the compressive strength of the two cement-stabilized materials.