Mechanical and microstructural performance of expansive clay stabilised using recycled pottery waste and lime

This study investigates the mechanical and microstructural performance of expansive clay stabilised using recycled pottery waste (PW) and lime, with emphasis on moisture sensitivity, swelling control, and strength enhancement. Geotechnical tests included Atterberg limits (WL, PL, PI), DFS, and standard Proctor compaction (OMC and MDD), while pavement-related performance was assessed using UCS, soaked CBR, and resilient modulus (MR). Microstructural and mineralogical characterisation was performed using SEM and XRD. PW significantly reduced plasticity (PI reduced from 26.64% to 7.01%) and eliminated swelling (DFS = 0% at ≥ 22% PW) by diluting active clay minerals and suppressing diffuse double-layer activity. An optimum PW content of 22% was identified, which also reduced OMC and enabled stable compaction behaviour. Lime addition further enhanced stabilisation, with 3% lime identified as the optimum dosage, resulting in a 28-day UCS increase from 343.3 kPa to 1270.01 kPa, soaked CBR improvement from 1.83% to 9.42%, and resilient modulus enhancement from 18.3 MPa to 73.74 MPa, demonstrating substantial gains in load-bearing capacity and elastic stiffness suitable for pavement subgrades. Higher lime contents (≥ 4%) caused over-flocculation, density reduction, and partial reappearance of swelling. SEM revealed the transformation from a loose PW-clay fabric to a dense, well-bonded matrix at 3% lime, while XRD confirmed attenuation of clay-related peaks and formation of poorly crystalline hydration products, validating pozzolanic transformation. Overall, a 22% PW + 3% lime blend provides an optimised low-carbon stabilisation, showing recycled pottery waste can function as an engineered stabilisation constituent rather than an inert filler for sustainable pavement subgrade applications.