Sustainable stabilization of kaolin clay by waste eggshell powder & hemp fibre: Mechanical & microstructural study

• Lime–ESP–HF mix raised UCS from 357 to 4078 kPa (∼10.4 times). • HF reinforcement increased tensile strength by 542% in treated clay. • 6% lime + 25% ESP + 0.75% HF improved bonding and soil stability. • Reinforced soil showed up to 95% higher strength retention in F–T cycles • SEM/XRD confirmed C–S–H and C–A–H gel formation enhancing soil structure. Clay stabilization traditionally relies on lime to improve strength and reduce deformation, but environmental concerns have led to interest in eggshell powder (ESP) as a sustainable, eco-friendly alternative. This study investigates the stabilization of kaolin clay using varying concentrations of lime (2–8%) in combination with partial substitution by ESP (25–100%) and randomly distributed hemp fiber (HF) at 0.25–1%. Treated samples were subjected to curing periods of 1, 7, 14, and 28 days and evaluated through compaction, unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV), and freeze-thaw (F-T) resistance tests. Microstructural analysis was conducted using X-ray diffraction (XRD) and scanning electron microscopy (SEM) to verify performance via micro-scale interactions. Results indicated that substituting 25% of lime with ESP significantly increased UCS and F-T durability by over fourfold compared to lime-treated specimen. Incorporation of HF further enhanced performance, with the optimal blend (6% lime, 25% ESP, 0.75% HF) exhibiting a sixfold increase in ITS and only 5% strength loss after ten F-T cycles. SEM analysis confirmed strong interfacial bonding and the formation of Calcium silicate hydrates (C–S–H) and Calcium alumina hydrates (C–A–H) gels at the soil–fiber interface, attributed to the calcium carbonate content of ESP, which contributed to improved strength and tensile resistance. These findings demonstrate that lime-ESP-HF composites as waste materials and eco-friendly agents improve soil strength, ductility, and durability, offering sustainable and efficient solutions for civil infrastructure applications such as roads, landfills, and slope stabilization.