Experimental Evaluation of Lateritic Sub-Base Soil Stabilized with Cement and Charcoal
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Premature pavement failures in Nigeria are often linked to weak lateritic subgrades, which typically show high plasticity and soaked CBR below 10%. Cement stabilization is effective but costly and carbon-intensive at high dosage, and little evidence exists on using Iroko Wood Charcoal (IWC) as a partial cement replacement. This study stabilized a lateritic soil from Ibadan with nine blends of 0–6% CEM I Portland cement and 0–6% IWC, evaluating index properties, compaction, 24-hour soaked CBR, and Unconfined Compressive Strength (UCS) at 3 and 7 days. The 6% cement, 2% IWC blend produced the lowest plasticity index, highest CBR (15.63%), and highest UCS (313.27 kPa), a sixteen-fold strength gain over the untreated soil, before performance declined beyond 2% IWC due to the charcoal's high water demand. This optimum blend exceeded the general subgrade CBR requirement of 10% but fell short of the Federal Ministry of Works and Housing (FMWH) stabilized sub-base thresholds for CBR and UCS. The stabilization is therefore suited to lower-tier applications, meaning pavement layers placed below the sub-base, such as improved subgrade and capping layers, that require a soaked CBR of at least 10%. Only 6% cement with 2% IWC (15.63%) or 4% IWC (15.56%) reached this level, and higher binder content is needed for full sub-base compliance.
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