Strength Development and Microstructural Evolution of Electro-Kinetically Remediated Lead-Contaminated Lateritic Soil: Effect of Electrode Material

Abstract: Lead (Pb) contamination of lateritic soils used for pavement construction compromises both the environmental quality and the geotechnical performance of the material. Electro-kinetic remediation (EKR) offers a low-energy route to decontaminate such soils, but the electrode material used can itself alter the resulting mechanical behaviour. This study evaluates the effect of aluminium, carbon and graphite electrodes on the unconfined compressive strength (UCS), California bearing ratio (CBR) and microstructure of a lead-contaminated lateritic soil from Birnin Gwari, Kaduna State, Nigeria. Scanning electron microscopy (SEM) with energy-dispersive X-ray analysis (EDS) was used to relate microstructural changes to the observed strength trends. The untreated soil classified as A-7-6 (CL) with a liquid limit of 48.0% and UCS of 225.3-335.0 kN/m² across British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH) compactive efforts. After EKR, carbon-electrode treatment consistently produced the highest strength gains, raising the 7-day UCS to 364.0 kN/m² and the unsoaked CBR to 85% at BSH effort, exceeding the 80% threshold specified for lightly trafficked road bases. Aluminium-electrode treatment reduced strength relative to the untreated soil, while graphite gave intermediate performance. SEM micrographs showed a shift from the loosely aggregated, high-porosity fabric of the untreated soil toward a denser, more flocculated particle arrangement in the carbon-treated samples, consistent with the strength improvement; EDS confirmed a reduction in PbO content and enrichment in Fe2O3 accompanying carbon-electrode treatment. The results indicate that electrode selection is a controlling variable in EKR-based soil remediation for pavement applications, with carbon electrodes offering the best combination of contaminant removal and geotechnical suitability among the materials tested.