Coconut shell fiber for reinforcing lime-stabilized soil: A sustainable approach to improve resilience

Lime-stabilized soils often exhibit brittleness and limited durability under environmental loading. This study investigates coconut shell fiber (CSF) as a sustainable, cost-effective reinforcement for enhancing mechanical and durability performance of lime-stabilized clayey soil. Laboratory tests with 1–9% lime and 0.25–1.0% CSF assessed compaction, permeability, strength, wet–dry and freeze–thaw durability, and microstructure. The results show that permeability decreased from 8.0×10⁻⁸ to 3.0×10⁻⁸ cm/s with 9% lime, but rose slightly to 5.0×10⁻⁸ cm/s at 0.75% CSF. Optimum performance was at 3% lime, 3 cm fiber length, and 0.75% CSF, yielding UCS of 4795.7 kPa and tensile strength of 9.0 Pa after curing 60 days. CSF addition transformed failure from brittle to ductile and enhanced long-term strength. After the first wet–dry cycle, UCS increased 30.9–53.4% for lime-only and 61.7–79.9% for CSF-reinforced specimens. After six cycles, UCS and mass losses were 40.0–71.3% and 6.2–31.1% (lime-only) versus 18.0–53.4% and 5.0–29.9% (CSF-reinforced). Under freeze–thaw, UCS losses were 6.3–62.3% (lime-only) and 5.9–54.5% (CSF-reinforced). Microstructural analysis showed improved matrix integrity, reduced porosity, and greater hydration product formation with CSF. Overall, CSF improved strength by up to 89.9% under standard curing, 58.0% under freeze–thaw, and 112.2% under wet–dry conditions, demonstrating its effectiveness as a low-carbon reinforcement for resilient infrastructure.