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.

As emerging pollutants, microplastics (MPs) pose serious threats to the terrestrial ecosystems, and the long-term presence of aged MPs in soil results in toxic effects on plant growth. However, the phytotoxicity mechanisms of aged MPs remain unclear. To understand the toxic effects of aged MPs and the response mechanism of lettuce plants, we selected polyethylene (PE) and polypropylene (PP) (commonly found in soil), and then studied the effects of the two phytotoxins on the soil-plant system before and after aging of the MPs. We found that aging enhanced the toxicity of the MPs to the plants. Compared with the original MPs-treatment group, aged PE and PP particles reduced plant biomasses by 26.19%-28.44% and 25.58%-26.13%, respectively, potentially due to the effects of aged MPs on the rhizosphere soil, which further inhibited nutrient absorption in lettuce. The metabolic response of lettuce to MPs was also different. Aged PE significantly attenuated malic acid and proline concentrations in lettuce, and the reduction in these two products inhibited photosynthesis, energy metabolism, and cellular homeostasis, thereby aggravating the damage caused by aged PE. Aged PP principally affected the metabolic pathways of phenylalanine, tyrosine and tryptophan, which was postulated to be the reason why aging enhanced the phytotoxicity of PP. This study provides new insights into the assessment of the toxic effects of MPs, as well as the environmental behavior and ecological risks of aged MPs.

Building structures located in saline soil areas are more vulnerable to damage due to the combined effects of loading and sulfate erosion. Polypropylene fibers lithium slag concrete (PFLSC) exhibits good corrosion resistance, which can mitigate damage to building structures in saline soil areas. However, the eccentric compression behavior of PFLSC columns under sulfate erosion and external loading remains unclear. Therefore, in this study, an eccentric compression test was conducted on 10 PFLSC columns after exposure to combined sulfate erosion and external loading, with corrosion time and stress ratio as the research variables. The failure modes, load-displacement curves, failure loads, and strains of rebars were investigated. The results indicate that polypropylene fibers and lithium slag can effectively inhibit the corrosive effects of sulfates and significantly enhance the ductility and ultimate axial capacity of the specimens. Additionally, taking into account the prior load levels and the damage caused by sulfates to the concrete, a damage factor has been introduced to determine the strength of the concrete after undergoing loads and sulfate exposure. Ultimately, a model has been proposed to calculate the ultimate axial capacity of PFLSC columns under the coupled effects of loads and sulfuric acid. The calculated results showed excellent agreement with the corresponding experimental results. It provides reliable guidance for the durability design of PFLSC columns.

Due to their effectiveness, environmental friendliness, and economic benefits, geosynthetics are increasingly utilized in civil engineering, especially woven geotextiles for soil stabilization reinforcement. Standard strength testing assumes a constant rate of elongation for samples, but in practice, the loading rate of geosynthetics in the field is much lower. Selecting appropriate materials is crucial for the effectiveness and durability of structures. For polymeric materials like woven geotextiles, the strain rate affects their properties. Understanding these properties is essential for safe design and construction. This article explores the potential application of polypropylene geotextiles for soil reinforcement in embankments. The polymer properties are discussed, along with the methodology for strength testing of geosynthetics and the results of the research. The findings allowed for the calculation of the long-term strength of samples at different elongation rates, which was used to verify changes in the factor of safety for a slope model. The highest tensile strength was 33.44 kN/m at a stretching speed of 20 mm/min. At 2 mm/min, it was 30.35 kN/m, and at 0.2 mm/min, it was 28.70 kN/m. These results determined the factor of safety: F = 2.08 for the fastest stretched sample and F = 1.97 for the slowest. Theoretical approaches to understanding changes in strength parameters due to variations in strain rate have been presented, as well as computational approaches using the Bishop method in GEO5 software, based on the results from tensile strength tests.

The prevalent presence of microplastics in marine environments poses major ecological risks requiring innovative approaches to their management and reduction. This study addresses a knowledge gap in biodegradable microplastic alternatives by looking at the biodegradability and properties of reclaimed microplastic polypropylene (PP) blended with polylactic acid (PLA). The study lies in the systematic exploration of various PP/PLA formulations, evaluating their potential for enhanced biodegradability without significantly compromising mechanical performance. Microplastic PP and PLA blends were prepared in various ratios using the melt blending method. The blend was characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) to confirm the presence and morphology of the components. The mechanical properties were evaluated using tensile strength tests. A blend of 90% PP and 10% PLA was found to retain the highest tensile strength even after immersion in seawater. The thermal stability and degradation behavior were analyzed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). This shows that increasing PLA content affects the thermal properties of the blends. Seawater immersion and soil burial tests were used to assess the biodegradability of the blends. The results showed that the blends' biodegradation was confirmed by increases in conductivity and salinity in the seawater and weight loss in the soil burial. The major findings show that blending PP and PLA improves biodegradability while maintaining adequate mechanical properties. Tests including immersion in saltwater and soil burial were used to assess the biodegradability of the blends. The results showed that the blends' biodegradation was confirmed by increases in conductivity and salinity in the seawater and weight loss in the soil burial. The major findings show that blending PP and PLA improves biodegradability while maintaining adequate mechanical properties. Finally, this study presents a new approach to reducing microplastic pollution through the blend of reclaimed PP with biodegradable PLA, resulting in a sustainable material with improved environmental performance. Future studies should look into new formulations, biodegradable polymers, and long-term degradation tests under a variety of environmental circumstances.

In order to solve the problem of low freeze-thaw deformation strength of railway road genes in cold regions, railway subgrade soil was improved with polypropylene fibres. The failure mechanism of fibres improved foundation soil is revealed by experiments. The test results showed the following: (1) The strength decreased with the increase in the water content in the melting state and reached its maximum when the water content was 12% in the freezing state. The strength reached the maximum when fibre incorporation was 0.3% and fibre length was 15 mm. (2) The shear strength of the improved subgrade soil gradually decreased and tended to be stable with the increase in the number of freeze-thaw cycles in the frozen state. There was no significant change with the increasing number of freeze-thaw cycles in the thawing state. (3) Before and after the cyclic loading of the fibre-modified subgrade soil, the strength after cyclic loading was greater than that before. (4) Through scanning electron microscopy, the optimal fibre content was determined to be 0.3%. The research results can provide a strong reference for the improvement of railway subgrades, and they have broad application prospects.

The secondary utilization of iron tailings solid waste meets the green development requirements of road construction in the new era. Currently, there is a lack of research on the equivalent confining pressure effect of fiber, the influence of complex stress paths on the mechanical properties of modified soil, and the internal damage in soil based on energy dissipation theory. The effects of different polypropylene fiber content, confining pressure, curing age, and complex stress path on the mechanical properties of fiber cement-modified iron tailings (FCIT) were investigated by triaxial tests and energy angle. Combined with the actual subgrade engineering, the stress path test is set up, and the strength index of the FCIT under different working conditions is obtained. From the thermodynamic point of view, the failure process for the FCIT is further revealed. The results show that: (1) the optimal fiber content of FCITs is 0.75%. At this time, the mechanical properties of FCIT are optimal, the strength is high, and shear failure is not easy. The fiber has the equivalent confining pressure effect, which could provide better shear performance for FCITs so that the FCIT is resistant to collapse in embankment construction; (2) the influence of multislope stress path on the secant modulus of the FCIT is worse than that of a single-slope stress path. The influence of curing age on the secant modulus of these two kinds of stress path is consistent, and the secant modulus of the FCIT at 28-day curing is 1.2 times that at 7-day curing; (3) after 7 and 28-day curing, the dissipation energy of the FCIT was consistent when the fiber content was 1%. Due to the equivalent confining pressure of the fiber, the fiber dissipation energy of the FCIT is not affected by the curing age. The total dissipated energy of the FCIT with a stress path slope of 1.5 is 5-6 times that with a stress path slope of 2.5. The total dissipated energy of the single-slope and multislope stress paths decreases with the increase in curing age. (c) 2024 American Society of Civil Engineers.

Freeze-thaw (FT) aging can change the physicochemical characteristics of microplastics (MPs). The toxic impacts of FT-aged-MPs to soil invertebrates are poorly understood. Here the toxic mechanisms of FT-aged-MPs were investigated in earthworms after 28 d exposure. Results showed that FT 50 mu m PE-MPs significantly increased reactive oxygen species (ROS) by 5.78-9.04 % compared to pristine 50 mu m PE-MPs (41.80-45.05 ng/mgprot), whereas FT 500 mu m PE-MPs reduced ROS by 7.52-7.87 % compared to pristine 500 mu m PE-MPs (51.44-54.46 ng/ mgprot). FT-PP-MPs significantly increased ROS and malondialdehyde (MDA) content in earthworms by 14.82-44.06 % and 46.75-110.21 %, respectively, compared to pristine PP-MPs (40.56-44.66 ng/mgprot, 0.41-2.53 nmol/mgprot). FT-aged PE- and PP-MPs caused more severe tissue damage to earthworms. FT-aged PE-MPs increased the alpha diversity of the gut flora of earthworms compared to pristine MPs. Earthworm guts exposed to FT-aged-MPs were enriched with differential microbial genera of contaminant degradation capacity. FT-PE-MPs affected membrane translocation by up-regulating lipids and lipid-like molecules, whereas FTPP-MPs changed xenobiotic biodegradation and metabolism by down-regulating organoheterocyclic compounds compared to the pristine PE- and PP-MPs. This study concludes that FT-aged MPs cause greater toxicity to earthworms compared to pristine MPs.

Biopolymer treatment of geomaterials is a promising technology with green technology potential that can help reduce global warming. It offers a positive environmental impact and a wide range of applications. This paper reports the results of a study of the mechanical performance of biopolymer-treated dune-sand from the Algeria desert. The sand was mixed with varying amounts of xanthan gum biopolymer and reinforced with polypropylene fibre. The study demonstrated that xanthan gum treatment improved the Unconfined Compressive Strength (UCS) of unreinforced sand and fibre-reinforced sand. Nonetheless, the test results revealed that biopolymer-treated sand manifested higher resistance after drying. Based on the findings, the optimal quantity of xanthan gum for treating sand is 2%. The incorporation of fibre in the matrix increases the strength and failure strain. The Scanning Electron Microscopy (SEM) analysis further substantiated that the biopolymer bonds the sand particles together and the distribution of PP fibre in the mixture, thereby enhancing compressive strength and durability. The results indicate that using xanthan gum biopolymer treatment offers an environmentally friendly approach to enhancing the mechanical properties of desert sand.

The degradation of cement-stabilized soil foundations in coastal environments is primarily caused by the corrosive effects of chloride and sulfate ions. While Nano-SiO2 enhances the mechanical properties of cemented soil, it may also increase brittleness, affecting safety and cost-effectiveness. Polypropylene fibers improve ductility by inhibiting crack propagation but contribute minimally to strength enhancement. To optimize performance, this study employed 3.6% Nano-SiO2 and 0.8% polypropylene fibers. Unconfined compressive strength (UCS) tests indicate that with increasing curing time, erosion from Cl- and SO42- significantly increases the brittleness of Nano-modified cemented soil, with compressive strength initially rising and then declining. The incorporation of polypropylene fibers further enhances both compressive strength and deformation modulus. At 60 days of curing, the composite cemented soil exhibits strength improvements greater than the sum of the individual gains in various environments, with compressive strength increases of 248.9, 159.9, and 102.9% in freshwater, chloride, and sulfate conditions, respectively. Scanning electron microscopy and X-ray diffraction analyses indicate that excessive expansion products from Cl- and SO42- reduce Nano-SiO2's effectiveness. The C-S-H gel fills the indentations on the fiber surface and tightly envelops it, while Nano-SiO2 further enhances the mechanical interlocking between the fibers and the matrix, thereby improving durability in marine.