Eco-friendly materials have gained significant attention for soil stabilization and reinforcement in road construction and geo-environmental infrastructure, as traditional additives pose notable environmental concerns. In this study, three concentrations of Chitosan Biopolymer (CBP) (1.5 %, 3 %, and 4.5 %) as a bio-stabilizer, three proportions of Rice Husk Biochar (RHB) (0.5 %, 1 %, and 1.5 %) as a waste-derived filler, and three dosages of Hemp Fiber (HF) (0.2 %, 0.4 %, and 0.6 %) as reinforcement were used to treat sand-kaolinite mixtures (SKM). The samples were cured for 1, 7, 14, 21, and 28 days and subjected to varying numbers of freeze-thaw (F-T) cycles. A diverse range macro-scale laboratory tests, encompassing compaction, unconfined compressive strength (UCS), indirect tensile strength (ITS), F-T durability, ultrasonic pulse velocity (UPV), and thermal conductivity (TC), were performed on the treated samples. In addition, microstructural analyses using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR) were conducted to correlate mechanical behavior with micro- scale properties. The optimal dosages of CBP and RHB were first determined through UCS tests, with 3 % CBP and 1 % RHB proving the most effective. These dosages were then used to analyze their impact on other mechanical properties. Results showed that the compressive and tensile strengths of the bio-stabilized soil at the optimum contents of additives increased by 2410.7 kPa and 201.2 %, respectively, compared to the control samples. Incorporating HF into the SKM-CBP-RHB mixtures significantly enhanced their F-T durability after 10 consecutive cycles, reducing strength deterioration and performance degradation compared to the untreated soil. The optimum composition (3 % CBP, 1 % RHB, and 0.4 % HF) led to a 6.1-fold increase in ITS and a minor 2 % reduction in performance after 10 F-T cycles. Moreover, HF incorporation improved the failure strain and reduced the brittleness of the stabilized soil. UPV and TC tests revealed that incorporating HF at levels up to 0.4 %, combined with the optimum CBP-RHB mixture, enhanced soil stiffness by 963.7 MPa and reduced thermal conductivity by 0.76 W & sdot;m-1 & sdot;K-1. The microstructural analysis confirmed these findings, showing enhanced interlocking between SKM and fibers via hydrogel formation. Overall, the study demonstrates that the CBP-RHB-HF composite markedly enhances soil strength and durability, making these additives highly suitable for applications like landfills, embankments, and slopes.

This study focuses on bio-based natural fiber-reinforced polymer composites (NFRPCs). In this work, bio-polybutylene succinate (bio-PBS) reinforced with hemp fibers (HF) varying at 10 wt%, 20 wt%, and 30 wt% were developed via microwave-assisted compression moulding (MACM) technique. The mechanical properties, crystalline properties, dynamic mechanical analysis, and soil degradation behaviour of these composites were analysed. The study demonstrated that composites with 30 wt% hemp fiber content exhibited the most optimal mechanical properties, with crystallinity increasing by 22%. These composites achieved the highest storage modulus of 13,349 MPa, while their loss modulus was found to be 110% higher compared to neat bio-PBS. Additionally, soil burial experiments revealed that the 30 wt% HF/bio-PBS composites underwent the greatest weight loss after 60 days of soil exposure, indicating superior biodegradability compared to the pure bio-PBS matrix. The work further concluded that hemp fiber-reinforced bio-PBS composites showcased improved mechanical performance, crystallinity, biodegradability, and processing characteristics, surpassing other bio-composite alternatives.

Reinforcement of soils with fibers generally increases the mechanical properties of the fiber-reinforced soil (FRS) system. However, published literature is limited to investigating the undrained response of clay and synthetic fibers, with few studies targeting natural clay and natural fibers under drained conditions. There is a need to study the response of fiber-reinforced clay systems under drained conditions to assess long-term stability. This paper investigated the drained shear strength and durability of clays reinforced with natural hemp fibers using isotropically consolidated drained triaxial tests, in which the fiber content, confining pressure, and compaction water content were varied. Results showed that the incorporation of hemp fibers improved the deviatoric stress at failure by up to 60%, which increased the drained cohesion and friction angle of the FRS by 7-10 kPa and 3-7 degrees, respectively. The increase in cohesive intercept was not affected by the compaction water content, while the increase in friction angle was pronounced in specimens compacted at optimum water content (w = 18%). Durability tests showed that the improvement in strength due to hemp fibers diminishes after 3 weeks of curing prior to drained testing, indicating the dramatic negative impact of degradation of natural fibers on the mechanical performance of fiber-reinforced clay and the need for industrial treatment of the fiber.