Improving Marine Clay Subgrade Performance Using Cassava Peel Ash as a Sustainable Cement Substitute: An Experimental Study

This study examines the effectiveness of Cassava Peel Ash (CPA) as a partial cement substitute for stabilising Marine Clay Soil (MCS), a weak soil common in coastal areas, to improve its mechanical properties for sustainable pavement subgrades. Untreated MCS was characterised, followed by stabilisation with 8 per cent total binder (cement with 0–30 per cent CPA replacement) under curing temperatures of 40°C and 60°C. Key findings show that replacing up to 15% of cement with CPA increased the Unconfined Compressive Strength (UCS) by 30 per cent compared to untreated soil, reaching 245 kN/m². However, higher CPA content reduced UCS and raised the Free Swell Index (FSI) by as much as 65 per cent, indicating a balance between strength and swelling. Cohesion improved, whereas the angle of internal friction decreased, suggesting CPA’s pozzolanic activity enhances bonding but limits shear resistance. These results highlight CPA’s potential as a cost-effective and environmentally friendly stabiliser for low-load subgrades, thereby reducing cement consumption and CO₂ emissions. Nonetheless, the high FSI restricts its application where high swelling is a concern. This research highlights the value of CPA in sustainable infrastructure and identifies optimal CPA dosages for MCS stabilisation.