Sustainable Stabilization of Expansive Clay Using Lime and Steel Slag

Expansive clays undergo moisture‐induced swelling and shrinkage that can cause serviceability loss in lightly loaded structures and pavements. In Bangladesh, stabilization of such clay is a geotechnical concern, while steel slag generated from local steel industries remains an underutilized calcium‐rich by‐product. Although lime is a well‐established calcium‐based stabilizer, its energy‐intensive production motivates evaluation of steel slag as a complementary stabilizing agent. This study evaluates lime, steel slag, and equal‐mass lime–steel slag blends for stabilizing a high‐plastic expansive clay from Char Bishwanath, Sirajdikhan, Munshiganj, classified as fat clay (CH) according to the Unified Soil Classification System (USCS). A dosage‐resolved, replicate‐based program included index and shrinkage tests, free swell index (FSI), one‐dimensional swelling up to 90 days, unconfined compressive strength (UCS), pH, and scanning electron microscopy (SEM). Additives were mixed at 3%–15% by dry soil mass. UCS and one‐dimensional swell specimens were compacted at the untreated soil’s optimum moisture content and maximum dry density, sealed, and cured at 25°C ± 2°C; FSI was measured separately on uncured oven‐dried mixtures after 24 h immersion. Results are reported as mean ± standard deviation from three replicates, with untreated soil as the control. The FSI decreased from 90.0% ± 5.0% to 7.1% ± 0.8% with 15% lime, 21.4% ± 2.5% with 9% steel slag, and 9.1% ± 1.0% with the 6% total lime–steel slag blend (3% lime + 3% steel slag). After 90 days, treated specimens reached swell strains of 0.1%–0.2% and swell pressures of 1.71–5.85 kPa, compared with 53.07% and 96.47 kPa for untreated soil. UCS improved relative to untreated clay but varied nonmonotonically with curing time. SEM showed densification, aggregation, pore filling, and gel‐like products morphologically consistent with cementitious bonding. Lime most consistently reduced FSI at high dosage, steel slag minimized long‐term swell pressure, and optimized blends provided balanced performance.