This study investigates the durability of cassava starch-stabilized lateritic soils subjected to cyclic wet–dry loading, using unconfined compressive strength (UCS) and indirect tensile strength (ITS) retention as key durability measures. Lateritic soils, widely used in tropical subgrade construction, suffer strength loss due to moisture fluctuations. Conventional stabilizers like cement and lime, although effective, have significant environmental drawbacks. Cassava starch, a biodegradable and abundant biopolymer, offers a sustainable alternative with promising soil-binding properties. Twelve mix designs, incorporating varying proportions of lateritic soil, cassava starch (0–10%), and water-to-solids ratio (12–16%), were prepared and cured for 28 days before undergoing 12 wet–dry cycles to simulate environmental stress. UCS retention ranged from 69.68% to 91.24%, and ITS retention from 71.79% to 92.91%, with the best-performing mix surpassing ASTM and AASHTO durability criteria and Nigerian subgrade strength requirements. Scheffé’s (3,2) mixture regression models accurately predicted durability outcomes, achieving R² values above 99% and passing F-tests for model adequacy at a 5% significance level. These findings confirm cassava starch’s effectiveness in enhancing the mechanical resilience and moisture durability of lateritic soils, supporting its application as a green stabilizer for sustainable infrastructure. The study presents a validated, data-driven framework for optimizing bio-based soil stabilization, advancing eco-friendly geotechnical practices and climate-resilient road construction.

This study evaluates the indirect tensile strength (ITS) of rice husk ash (RHA)-based geopolymer-stabilized deltaic clay soil, characterized by high plasticity (liquid limit 76.5%, plasticity index 35.3%) and low bearing capacity (CBR 3.99%). Using a quarter fractional factorial design with 32 runs, seven key mix parameters were screened: alkaline activator-to-RHA ratio (0.20–0.40), sodium silicate-to-sodium hydroxide ratio (1–3), sodium hydroxide concentration (8–14 M), curing period (4–72 hours), curing temperature (40–120°C), water-to-solid ratio (20–25%), and compaction delay (0–180 minutes). After 28 days curing, ITS ranged from 0.49 to 0.66 MPa, indicating substantial improvement over untreated soil. Effect analysis revealed compaction delay had a significant negative impact on ITS (effect = –0.0869, t = –9.379), while sodium silicate-to-sodium hydroxide ratio (effect = 0.0220, t = 2.381) and sodium hydroxide concentration (effect = 0.0210, t = 2.237) positively influenced strength. Among interactions, only the alkaline activator-to-RHA ratio combined with sodium silicate-to-sodium hydroxide ratio was significant (effect = 0.0230, t = 2.453), highlighting the critical synergy between precursor content and activator composition. These findings underscore the importance of optimizing compaction delay, activator composition, and precursor ratio to enhance geopolymerization and tensile strength through sodium aluminosilicate hydrate (N-A-S-H) gel formation. This research addresses a crucial gap in tensile strength characterization of geopolymer-treated deltaic clays and supports sustainable agro-industrial waste valorization for geotechnical applications.