Durability and Mechanistic–Empirical Performance Implications of Bamboo Leaf Ash–Stone Dust Stabilised Lateritic Subbase under Moisture Exposure and Traffic Loading

Lateritic soils are widely used in tropical pavement construction but often exhibit high fines, plasticity, and moisture susceptibility that undermine long-term performance. This study synthesizes engineering, chemical, and microstructural evidence from a lateritic soil stabilized using stone dust (SD) and bamboo leaf ash (BLA) to assess (i) moisture-related durability indicators and (ii) mechanistic–empirical (M–E) performance implications relevant to cyclic traffic loading. Lateritic soil was treated with SD (0–30% at 5% intervals) and with combined SD-BLA blends (BLA: 3 to 9%; SD: 5 to 20%) and tested for Atterberg limits, compaction (BSL/WAS/BSH), soaked and unsoaked CBR, UCS, and shear strength. XRF confirmed the pozzolanic character of SD and BLA (SiO₂+Al₂O₃+Fe₂O₃ = 85.51% for SD; 66.71% for BLA), while XRD/SEM evidenced microfabric densification and cementitious bonding in stabilized blends. The combined SD–BLA blend provided the best overall performance, with an optimum at 10% SD + 3% BLA (by dry soil mass), reducing plasticity (PI down to ~10%) and increasing strength. Moisture durability improved substantially: under British Standard Heavy (BSH) compaction, soaked California bearing ratio (CBR) increased from ~18% (natural) to ~65.48% (SD-BLA optimum) and the CBR retention ratio (soaked/unsoaked) improved from ~0.44 to ~0.71. For M-E interpretation, resilient modulus was conservatively estimated from CBR using a standard correlation, indicating a marked increase in wet-condition stiffness and reduced rutting susceptibility, thereby improving seasonal performance of subbase layers. These results support SD-BLA as a low-carbon stabilizer system for lateritic pavement layers, while highlighting the need for follow-on repeated-load and wet-dry cycling to fully quantify cyclic durability.