Controlling compressibility in oil-contaminated soils using alkali-activated slag: a sustainable approach

Oil-contaminated soil (OCS) poses significant environmental and geotechnical challenges, necessitating effective remediation strategies. One promising approach for OCS treatment is stabilization/solidification using alkali-activated materials (AAMs), which are recognized as an environmentally sustainable alternative to cement and lime. Despite extensive research on AAM applications, the compressibility behavior of OCS stabilized with AAMs remains largely unexplored. This study aims to address this gap by investigating the effectiveness of alkali activation of granulated blast furnace slag (GBFS) in mitigating the compressibility of OCS while simultaneously contributing to slag waste reduction, and cost-effectiveness. A comprehensive experimental program was conducted, incorporating pH, electrical conductivity (EC), cation exchange capacity (CEC), organic matter content, unconfined compressive strength (UCS) tests, ultrasonic pulse velocity (UPV) measurements, one-dimensional consolidation tests, and microstructural analyses. The findings demonstrated that alkali-activated slag (AAS) effectively stabilized and solidified OCS by inducing the formation of cementitious phases. This treatment resulted in a minimum 180% increase in UCS, a reduction in compressibility by at least 40%, and a decrease in the permeability coefficient by over 90%. Moreover, replacing 8% cement with the alkaline activation of 15% slag led to a 55% reduction in CO₂ emissions, while also lowering energy consumption and cost by 52% and 46%, respectively, to achieve a compressive strength of 1 MPa. Additionally, the study underscored the critical role of calcium content in enhancing the mechanical properties of AAS-stabilized OCS. In conclusion, AAS improves OCS geotechnical properties, making it a sustainable and viable material for construction and infrastructure development.