Sustainable recycling of steel slag for the stabilization of dispersive soils; insights into dynamic response and erosion susceptibility

Dispersive clays are highly susceptible to erosion and structural instability, yet the effectiveness of steel slag (SS) for simultaneously improving their strength, stiffness, and dispersive behavior remains insufficiently understood. This study investigates the effectiveness of steel slag as a sustainable stabilizer for dispersive clay by evaluating its effects on mechanical strength, dynamic stiffness, erosion resistance, and dispersive behavior. Clay specimens were stabilized with 0–30% SS at 5% increments and cured for up to 56 days. UCS, bender element, disintegration, and pinhole tests were conducted to assess the engineering performance, while SEM–EDX, XRD, and XRF analyses were used to identify the underlying stabilization mechanisms. Reactions of steel slag with soils allowed to form cementitious hydration products such as calcium-silicate-hydrate (C-S-H) and ettringite, with availability of portlandite (Ca(OH) 2 ), together enhanced soil properties and promoted ion exchange producing denser soil matrix. The results demonstrated a clear dosage-dependent improvement in the engineering performance of dispersive clay. The highest UCS improvement, approximately 152%, was achieved with 25% SS after 56 days, indicating its superior strength performance and favorable balance between mechanical interlocking and chemical stabilization. Accordingly, 25% SS was identified as the optimum dosage, while the reduction in strength at 30% SS after 56 days of curing suggests that excessive slag content may adversely affect the soil matrix. Increasing steel slag content progressively enhanced the dynamic response, with the highest Vs observed at 30% SS after 56 days. A strong correlation between UCS and Vs was observed, with correlation coefficients ranging from r = 0.90–0.98 were observed across the investigated curing periods, demonstrating the potential of nondestructive bender element testing for predicting strength development and monitoring stabilization performance. In the disintegration test, 5% SS reduced mass losses from 100% to approximately 8% after 100 min, while steel slag contents of 15% and higher transformed the soil from highly dispersive (D1) to non-dispersive (ND1–ND2) after curing. In conclusion, the findings demonstrate that steel slag provides a cost-effective and sustainable approach for stabilizing dispersive soils, while reducing dependence on conventional stabilizers and enabling the beneficial reuse of industrial by-products in geotechnical engineering.