Experimental Assessment of the Strength Characteristics of Lateritic Soil Stabilized With Sawdust Ash and Plantain Peel Ash

Lateritic soils constitute important construction materials for highways, embankments, foundations, airfields, and earth-retaining structures across Nigeria. Nevertheless, some lateritic deposits possess inadequate engineering characteristics that may result in pavement distress, excessive settlement, erosion, slope instability, and seepage-related problems. Improving the engineering properties of such soils through stabilization is therefore essential for achieving satisfactory structural performance and durability. This study examined the effectiveness of sawdust ash (SDA) and plantain peel ash (PPA) as sustainable stabilizing materials for improving the engineering properties of lateritic soil classified as AASHTO A-2-6. The soil was treated using four SDA contents of 3%, 6%, 9%, and 12%, while PPA was maintained at a constant proportion of 6%. Laboratory investigations were undertaken to determine the moisture content, particle-size distribution, Atterberg limits, compaction characteristics, and California Bearing Ratio (CBR) of the untreated and stabilized soil specimens. The results demonstrated that the incorporation of SDA and PPA altered the index and strength characteristics of the lateritic soil. The Maximum Dry Density (MDD) varied non-linearly with increasing SDA content, reaching its maximum value of 1.875 Mg/m³ at 9% SDA + 6% PPA, compared with 1.780 Mg/m³ for the natural soil. The Optimum Moisture Content (OMC) similarly varied from 11.8% to 12.8% among the stabilized mixtures. The 48-hour soaked CBR increased from 10.8% for the untreated soil to a maximum of 17.6% at 9% SDA + 6% PPA. The results indicate that the combined stabilizers improved the load-bearing capacity of the lateritic soil, although performance declined when SDA content was increased beyond the optimum level. The 9% SDA + 6% PPA combination produced the most favourable overall performance and satisfied the stated minimum CBR requirement for subgrade applications. The study demonstrates that SDA and PPA can provide useful and environmentally sustainable alternatives for improving weak lateritic soils while promoting the beneficial reuse of agricultural and wood-processing wastes in geotechnical engineering.