Mechanical performance and life cycle assessment of a Persian gum-waste carpet fiber soil composite for landfill bottom liners

This study investigates a Persian gum-waste carpet fiber (PG-WCF) composite as a stabilizer for silty soil intended for landfill liner applications and compares its performance with the soil stabilized using ordinary Portland cement (OPC) and lime. The test program comprised unconfined compressive strength (UCS), Brazilian tensile strength (BTS), three-point flexural strength (TFS), hydraulic conductivity, microstructural observations, and life-cycle assessment. The optimum PG-WCF composite (3 wt% PG + 3 wt% WCF) achieved UCS of 708 kPa, comfortably exceeding the 200 kPa liner criterion, and a hydraulic conductivity of 9.68 × 10^-10 m/s, meeting the 1 × 10^-9 m/s requirement. Design checks based on BTS and TFS yielded factors of safety greater than 1.5 for the adopted tensile and flexural demands, indicating robust resistance at service levels. The optimum composite showed energy absorption of 50.84 kJ/m³-1.9× OPC-stabilized soil and 3.1× lime-stabilized soil-consistent with the complementary roles of PG (stiffness/strength) and WCF (deformability) in mitigating settlement-induced cracking for liner service. LCA gives a GWP of 65.6 kg CO₂-eq·m^-3 (≈ 49% below OPC) and water use of 0.44 m^-3 m^-3 (24% below OPC). Overall, the PG-WCF composite is presented as a novel, lower-impact stabilizer that attains the mechanical and hydraulic targets for liner applications while offering superior energy absorption and practical sustainability compared with traditional additives.