Current Research Bulletin

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.

electro-kinetic remediation, lead-contaminated soil, electrode material, unconfined compressive strength, California bearing ratio, scanning electron microscopy

1. AASHTO (1996). Standard Specification for Transportation Materials and Methods of Sampling and Testing. American Association of State Highway and Transportation Officials, Washington, D.C.
2. ASTM (1992). Standard Classification of Soils for Engineering Purposes (Unified Soil Classification System). American Society for Testing and Materials.
3. British Standards Institution (1990). BS 1377: Methods of Test for Soils for Civil Engineering Purposes, Parts 2, 4 and 7. BSI, London.
4. Butcher, F. and Sailie, E. L. (1984). Testing soils for use as road construction materials. Nigerian Society of Engineers Technical Transactions.
5. Clare, A. G. (2012). Principles and applications of scanning electron microscopy in materials characterisation. Journal of Materials Science, 47(2), 401-415.
6. Edeh, J. E. and Amadi, A. A. (2014). Geotechnical properties of lateritic soils stabilised with locally derived admixtures. Nigerian Journal of Engineering Research and Development, 7(1), 22-31.
7. Goldstein, J. (2003). Scanning Electron Microscopy and X-ray Microanalysis. 3rd ed. Springer, New York.
8. Ingles, O. G. and Metcalf, J. B. (1972). Soil Stabilization: Principles and Practice. Butterworths, Sydney.
9. Mohammad, N., Moghal, A. A. B., Rasheed, R. M. and Almajed, A. (2022). Critical review on the efficacy of electrokinetic techniques in geotechnical and geoenvironmental applications. Arabian Journal of Geosciences, 15(8), 781.
10. Molaei, M. A., Miraki, H., Morovati, M., Ghadir, P. and Javadi, A. A. (2024). Solidification/stabilization of lead-contaminated soil using alkali-activated volcanic ash. Environmental Science and Pollution Research, 31(26), 38465-38484.
11. Naseer, U., Du, Z. P., Ahmad, A., Farooq, S., Yousaf, M. and Yue, T. X. (2025). Advanced electrode materials in electrokinetic technology for remediation of heavy metal-contaminated soil: recent progress and challenges. Advanced Sustainable Systems, 9(8), 2500197.
12. Nigerian General Specifications for Roads and Bridges (2016). Federal Ministry of Works, Abuja.
13. Osinubi, K. J. and Medubi, A. B. (1997). Lime stabilisation of tropical black clay for road construction. Journal of Environmental Sciences, 1(1), 12-19.
14. Oyediran, I. A. and Enya, A. (2021). Effect of contamination on the index and geotechnical properties of remediated soils. International Journal of Geo-Engineering, 12, 4.
15. Sun, Z., Xu, S., Zhang, J., Eugene, B. D. and Li, S. (2024). Effect of electrode positioning on electrokinetic remediation of contaminated soft clay with surface electrolyte. Toxics, 12(10), 758.
16. TRRL (1977). A Guide to the Structural Design of Bituminous-Surfaced Roads in Tropical and Sub-Tropical Countries. Transport and Road Research Laboratory, Crowthorne.
17. Zheng, X., Li, Q., Wang, Z. and Chen, M. (2024). Remediation of heavy metals contaminated soil by enhanced electrokinetic technology: A review. Arabian Journal of Chemistry, 17(6), 105773.