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.

Clayey sand soils require improvement in civil engineering projects due to their low density, high porosity, and inadequate shear behavior. On the other hand, the extensive use of cement in soil stabilization is associated with environmental concerns such as high COQ emissions. In this study, the effect of partial replacement of cement with zeolite (up to 50 %) and the addition of polyvinyl alcohol (PVA) fibers (up to 0.8 wt%) on improving the mechanical, microstructural and environmental properties of clayey sand soil was investigated. Samples were prepared with different cement contents (3 and 6 %) and, after 7 and 28 days of curing, were subjected to compaction, unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV), scanning electron microscope (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and toxicity characteristic leaching procedure (TCLP) tests. The compaction test results showed that maximum dry density (MDD) decreases and optimum moisture content (OMC) increases with increasing zeolite content. The performance of different mixtures showed that the optimum mixture consisted of 6 % cement, 20 % zeolite, and 0.8 % fibers, which increased UCS, ITS, and UPV by 320 %, 194 %, and 35 %, respectively, compared to unstabilized soil. Micro-structural analyses showed the formation of CSH and CAH gels and improved interfacial transition zone bonds. Also, TCLP results showed that zeolite reduced heavy metal leaching. This study, with an innovative approach, investigated the simultaneous effectiveness of zeolite, cement, and fibers and introduced the potential of the UPV method as a non-destructive method for evaluating the mechanical performance of stabilized soil.

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.

This study explores the mechanical properties and synergistic mechanisms of silty sand modified with guar gum (GG) and polypropylene fiber (PP fiber) through a series of unconfined compressive strength (UCS) tests, direct shear tests, and direct tensile tests. The test results reveal that the unconfined compressive strength (UCS) of silty sand can be dramatically improved by incorporating GG, boosting its strength by up to 23 times compared to the natural soil. Adding PP fiber further enhances the UCS and effectively mitigates brittle failure. GG dominates the increase in shear strength by enhancing cohesion, while the PP fiber optimises the shear stability by increasing the internal friction angle. The shear strength of the GG-PP fiber-enhanced soil can be boosted by 235% compared to natural soil. The synergistic effect of GG and PP fibers enables the tensile strength of the improved silty sand to reach 122.75 kPa, representing a 34.15% increase compared to soil with only GG incorporated. However, if the fiber content is too high (> 0.5%), the tensile strength will decrease due to increased porosity. The study found that GG enhances the cohesion between soil particles through hydrated gel, and the PP fiber inhibits crack propagation and improves ductility through the bridging effect. The two form a bonding-bridging synergistic system, which significantly optimises the mechanical properties of the soil. This combined improvement scheme has both high strength and high ductility and can replace traditional inorganic cementitious materials, providing new ideas and methods for the application of silty sand in roadbed engineering, slope reinforcement, and other fields.

The construction of high-speed railway in Southwest China must traverse extensive regions of red mudstone. However, due to the humid subtropical monsoon climate in Southwest region, the red mudstone is often exposed to a high-water content or saturated state for extended time, and the poor mechanical properties under such condition cannot satisfy the requirements of high-speed railway subgrade. This paper proposes the use of lime and cement to improve the saturated unconfined compression strength (UCS) of the red mudstone fill material. Comprehensive tests, including UCS tests and scanning electron microscopy, were conducted on cement-lime modified red mudstone. Results show that lime stabilisation can significantly enhance the UCS and elastic modulus with the increase of dry density and modifier content. For the specimens with 4% lime and 6% cement, both peak strength and elastic modulus of the modified samples are more than 10 times higher than those of the untreated ones. The modulus exhibits nonlinear degradation with the development of shear stress, but the degradation can be improved with the increase of dry density and modifier content. At 60% of initial tangent modulus, the corresponding stress for untreated soil, lime stabilised and cement-lime modified filler are 0.74, 0.92 and 0.99. As for the energy evolution, the increasing dry density can enhance elastic and dissipated energies through denser particle arrangements, while a higher modifier content raises total energy. When the cement content is 6%, the total energy is more than 8 times higher than that of the untreated material, reflecting increased brittleness to a sudden fracture. The improvements are attributed to the formation of acicular and platy hydration products, which can tighten the pore structure. The study underscores the importance of lime and cement in ensuring subgrade stability for high-speed railways in Southwest China's red bed regions.

This research investigates the use of waste stone dust, a crushing industries byproduct, in combination with cement to enhance the engineering properties of high-plasticity silt. The investigation focuses on evaluating improvements in soil consistency, compaction characteristics, microstructure, and long-term strength behavior. Results indicate that the addition of waste stone dust significantly improves plasticity and compaction characteristics, while the combination of cement and stone dust enhances shear strength more effectively than either material alone. The unconfined compressive strength of untreated soil, initially 57.3 kPa after one day of curing, increased up to 19.4 times after 90 days with 10 % cement addition, with further improvements observed when stone dust was incorporated. Moreover, non-linear regression analysis reveals that strength improvement follows a sigmoidal relationship with cement content and a logarithmic trend with curing time. Furthermore, insights from Consolidated Undrained Triaxial tests and Scanning Electron Microscopy provide further strengthen the stabilization mechanisms of the treated soil. The triaxial results show that adding 6 % cement in natural soil slightly increases the friction angle from 20 degrees to 22 degrees and increases the cohesion from 28 kPa to 60 kPa. However, further addition of 30 % stone dust and 6 % cement slightly improved friction angle and reduced the cohesion from 60 kPa to 26 kPa, which infers that cement primarily increased cohesion, whereas stone dust increases inter-granular friction. More importantly, this study offers a cost-effective solution to enhance behavior, addresses environmental concerns, and improve infrastructure resilience for high-plastic-silt-related problems.

The use of various sustainable materials and cement is a frequent and successful strategy for stabilizing problematic soil. The current research discusses the potential use of discarded millet husk ash (MHA) and cement (C) as subgrade ingredients to improve the geotechnical qualities of soil (S). MHA and cement are mixed in different proportions and the engineering characteristics of the stabilized soil are studied. The study involves examining fundamental properties, such as specific gravity and Atterberg's limits, as well as engineering properties, including Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) tests. These evaluations are conducted to assess the feasibility of using the MHA-cement blend as a construction material. Additionally, FTIR & SEM analysis shows the addition of MHA-cement blend effectively couples with the soil. The test findings demonstrate that adding MHA to soil lead to decreased liquid limits and plasticity indices. The maximum dry density (MDD) was observed to decrease when MHA was mixed with soil. When 8% cement was incorporated to the S:MHA (84.5:7.5) combination, the UCS value rose even higher reaching 1600.1 kPa. The S:MHA:C arrangement in the ratio of 84.5:7.5:8 had the greatest California bearing ratio (CBR). Fourier transform infrared spectroscopy (FTIR) elucidated the various types of bond formations present within the soil composite and deeper peaks depicted greater presence of cementitious compounds after curing period. SEM analysis exhibited a greater density of N-A-S-H and C-A-S-H gels in comparison to natural soil samples. The findings suggest that the MHA-cement blend can effectively enhance the geotechnical properties of problematic soils, while addressing issues of agricultural waste management. This research contributes to several Sustainable Development Goals (SDGs), including SDG 9 (Industry, Innovation, and Infrastructure) by promoting innovative construction materials.

Complex adverse weather conditions such as rain erosion and frost are frequently encountered in practical construction projects, particularly in the Inner Mongolian region of China. In this study, a new biopolymer (GGPAM) with an interpenetrating crosslinked network structure was developed by chemically modifying GG to address the poor resistance of soil to rainwater erosion, frost, and other complex environmental conditions in open-air construction buildings. First, GG-PAM was synthesized by chemically modifying guar gum (GG) through graft copolymerization, and thermogravimetric (TG) analysis confirmed its favorable thermal stability. Subsequently, experiments were conducted to investigate the mechanical properties and microstructural characteristics of GG-PAM-solidified soil. Then, using GG as a control, dry-wet cycle and freeze-thaw cycling tests were performed to compare the changes in unconfined compressive strength (UCS) of GG- and GG-PAM-solidified soil. Finally, water erosion, crack propagation, and permeability tests were conducted to evaluate the resistance of GG-PAM-solidified soil to external forces. The results indicated that the mechanical strength, durability, and erosion resistance of the GG-PAM-solidified soil were significantly superior to those of GG. When the GG-PAM content reaches 1 %, both the mechanical strength and erosion resistance of the solidified soil are significantly improved. These findings provide a theoretical basis for the construction and maintenance of roadbeds.

The purpose of this study was to evaluate the sustainability benefits of Class F fly ash (FA), lime sludge (LS), and ground granulated blast furnace slag (GGBS)-based geopolymer-stabilized Edgar plastic kaolin (EPK) clay using the sustainability index (ISus) approach. Geotechnical engineering operations usually precede most infrastructural projects, making pavement construction an integral contributor to various environmental effects, due to the production of enormous quantities of greenhouse gas emissions through soil stabilization activities. To nip these concerns in the bud, effective integration of these environmental implications must be achieved during the geotechnical planning phase. The life cycle assessment (LCA) method was used to assess a wide range of environmental effects of a project, from raw material procurement, manufacturing, transportation, construction, and maintenance to final disposal. It is a well-recognized tool for designing environmentally sustainable projects. Experimental results from the geopolymer-stabilized EPK clay showed a notable improvement in unconfined compressive strength of the geopolymer-stabilized clay with 15% (FA + LS) and 5% (FA + GGBS) contents of up to 697% and 464%, respectively, after 28 days of curing at elevated temperature, 70 degrees C. The sustainability index (ISus) of geopolymer and lime treatment methods was analyzed based on the concept of environmental, resource consumption, and socioeconomic concerns, which quantifies the sustainability through greenhouse gas emission, environmental impacts, and the cost of utilizing FA, LS, and GGBS in soil stabilization compared with traditional lime. LCA was conducted for traditional lime treatment, FA-LS, and FA-GGBS geopolymer-stabilized subgrades to determine the most sustainable treatment method. From the sustainability analysis, using FA, LS, and GGBS as geopolymer stabilizers for kaolin clay reduced the global warming potential by 98.03% and 77.55% over the traditional lime stabilizers at 8% dosage. More importantly, results from the sustainability index (ISus) computations showed that FA-LS (ISus = 12.88) and FA-GGBS (ISus = 29.72) geopolymer treatment methods of EPK clay subgrade soils are more sustainable alternatives compared to the traditional lime (ISus = 48.07) treatment method.

This paper assesses the performance of biopolymers (agar gum and guar gum) for soil stabilization and the self-healing properties of these materials using non-destructive ultrasonic pulse velocity (UPV) and unconfined compressive strength (UCS) tests. Scanning electron microscopy (SEM) tests were performed to investigate the microstructure of the stabilized soil during the self-healing process. The results showed that adding biopolymers to the soil significantly improved the soil's mechanical properties and self-healing properties. The self-healing indexes of sandy soil stabilized with 1% of guar gum and agar gum were 45% and 18%, respectively, at the curing time of 14 days. Increasing the internal bonds and reducing cracking caused by hydrogel swelling are the significant advantages of using biopolymers in soil stabilization. The UPV provides a quick and accurate estimate of changes in the properties of the stabilized soil. The UPV of the samples increased after the self-healing period. The UPV of the sandy soil stabilized with 1% guar gum and agar gum increased by 17% and 13%, respectively, at the curing time of 7 days. The SEM results showed that the swelling of biopolymers led to crack repair after the self-healing period, the creation of new bonds between grains, and the increase of the contact surface of soil particles.