<p>The resolution of environmental and engineering problems offered by conventional infrastructure materials, this research proposes a sustainable and high-performance alternative: alkali-treated pine needle geotextile (TPNG). The study employs a rigorous technical methodology, encompassing both laboratory and in-situ tests, to comprehensively characterise TPNG material properties and evaluate its performance advantages in flexible and airfield pavements. Major findings reveal that TPNG reinforcement significantly enhances the strength of the subgrade, resulting in a substantial increase in California Bearing Ratio (CBR) values (as much as 185% on the wet side) at a proper placement depth of 1&#xa0;cm. Such a marked enhancement in load-carrying capacity, especially in moisture-susceptible regions, is a significant finding. Direct shear tests demonstrate an enhanced soil-geotextile interaction, resulting in an increased angle of internal friction (ϕ) from 22° (for unreinforced soil) to 35° (for TPNG-reinforced soil), indicating a significant improvement in shear strength properties. TPNG efficacy in reducing pavement distress is emphasised under cyclic loading, as it effectively reduces pavement settling by up to 50% for high loads and thin pavement thickness. The results conclusively establish TPNG as a viable, eco-friendly, and affordable material for constructing sustainable infrastructure. The innovation supports Sustainable Development Goal 12 by valorising a significant biomass waste stream, as well as Goal 9 by encouraging sustainable construction methods, thereby closing the gap between environmental performance and engineering performance.</p> Graphical abstract <p></p>