Abstract: This research explores the effectiveness of geopolymer-based soil stabilization enhanced by natural coir fiber reinforcement, using Ground Granulated Blast Furnace Slag (GGBFS) as the main aluminosilicate precursor and sodium hydroxide as the alkaline activator. A methodical experimental strategy was implemented, starting with the adjustment of GGBFS content (5–25%) to identify its optimal level, followed by the optimization of sodium hydroxide concentration (2M–14M), and ultimately, the integration of coir fiber in different percentages (0.5–2%). The ideal mixture—20% GGBFS, 10M NaOH, and 1% coir fiber—was subjected to Unconfined Compressive Strength (UCC), California Bearing Ratio (CBR), and Atterberg limit assessments. The results indicated notable enhancements in compressive strength and load-bearing capacity, with the peak UCC reaching 112.77 kN/m². Curing effects were also examined under various conditions, showing improved strength with prolonged curing time. The inclusion of coir fibers enhanced ductility and crack resistance, while the utilization of industrial by-products and natural fibers promotes environmental sustainability. The results affirm that fiber-reinforced geopolymer stabilization presents a feasible, eco-friendly alternative to traditional soil enhancement methods.

Keywords: Geopolymer soil stabilization, ground granulated blast furnace slag, coir fiber reinforcement, sodium hydroxide activator, unconfined compressive strength, California bearing ratio, Atterberg limits, sustainable construction, eco-friendly stabilizers, alkali-activated binders.

| DOI: 10.17148/IARJSET.2025.12739