Strength and resilient performance of expansive subgrades stabilized with apricot kernel shell ash

Expansive subgrades pose significant challenges for road pavements due to their poor engineering properties. To address this issue using a sustainable waste-derived material, this study, for the first time, investigated the stabilization of expansive subgrades of different origins with apricot kernel shell ash (AKSA). Two expansive soils, a high plasticity clay (CH) and a low plasticity clay (CL), were treated with 0–15% AKSA by dry mass. A comprehensive program comprising compaction, unconfined compressive strength (UCS), direct shear, fall cone, California bearing ratio (CBR), resilient modulus (Mr), and scanning electron microscopy (SEM) was conducted, alongside Mr prediction using artificial neural networks (ANN) and finite element analyses in Plaxis 2D. AKSA reduced the maximum dry density and increased optimum moisture content, while mechanical performance improved up to an optimum AKSA content (≈ 6% for CH and ≈ 9% for CL). Peak UCS gains at 28 days reached ~ 107% (CH) and ~ 98% (CL); CBR increased by ~ 47% (CH, 6% AKSA) and ~ 71% (CL, 12% AKSA). Mr rose by ~ 1.47× (CH, 6% AKSA) and ~ 1.50× (CL, 9% AKSA). SEM revealed denser, less porous microstructures with evidence of cementitious gel formation. The ANN outperformed multiple regression in predicting Mr (R²_test ≈ 0.96). Plaxis 2D simulations indicated reduced deformations and shear strains for optimally stabilized subgrades. Furthermore, compared to cement stabilization, the AKSA-based specimen can minimize carbon emissions by approximately 40 and 43 tons for 1000 m³ of CH and CL soils, respectively, when replacing 3% cement, highlighting its significant environmental and practical advantages. These results demonstrate that AKSA is a promising, low-carbon stabilizer for expansive subgrades and supports circular use of agricultural waste. Future work should address variability in AKSA composition, durability under wet–dry cycles, and environmental leaching.