Stabilization of expansive Ankara Clay using conventional, chemical, and waste-derived additives. A two-stage experimental investigation

Abstract

Expansive soils present major geotechnical challenges due to their pronounced swell–shrink behaviour and associated volumetric instability, which can compromise foundations, pavements, and embankments. This study examines the stabilization of Ankara expansive clay using eight conventional, chemical, and waste-derived additives through a structured two-stage laboratory program. In Stage 1, all stabilizers were applied at a uniform dosage of 30% by dry weight and evaluated in terms of index properties, Standard Proctor compaction characteristics, and one-dimensional swelling behaviour. The results show that stabilizer type strongly governs the moisture–density relationship and swelling response. Composite systems, particularly concrete demolition waste (CDW) combined with lime or gypsum and cement–gypsum blends, achieved the greatest reductions in plasticity and swell potential, whereas gypsum alone exhibited limited effectiveness. Based on Stage-1 performance, lime and CDW were selected for Stage-2 testing at 10% and 20% dosages. A clear dosage-dependent response was observed: CDW slightly outperformed lime at lower dosage due to mechanical restraint and particle interlocking, while lime showed marginally superior swell suppression at higher dosage through intensified physicochemical reactions. Both stabilizers significantly enhanced shear strength via distinct mechanisms. The findings highlight the effectiveness of waste-derived and hybrid stabilization strategies for sustainable expansive soil improvement.