Comparative Analysis of Varying Proportions of Sawdust Ash on a stabilized Lateritic Soil for Road Pavement

This study investigated the performance of lateritic soil stabilized with varying proportions of sawdust ash (SDA) for pavement applications. Representative lateritic soil was obtained from Malete, Moro Local Government Area, Kwara State, Nigeria. The natural soil was characterized using particle-size distribution and Atterberg limits, while Standard Proctor compaction and California Bearing Ratio (CBR) tests were conducted on the control soil and mixtures containing 1, 3, 5, 7, 9, 10, 11, 13, 15, 17, 19 and 20% SDA by dry mass. Sawdust was sun-dried and open-burnt at Malete before the ash was further calcined at 600°C for 1 h at the Foundry Section of the University of Ilorin workshop. All geotechnical tests were carried out at the Soil Engineering Laboratory, University of Ilorin. The natural soil contained 70.4% sand and 29.6% fines, with liquid limit, plastic limit and plasticity index values of 25.0, 16.4 and 8.6%, respectively. It was classified as SC under USCS and A-2-4 (0) under AASHTO. The maximum dry density increased from 1.95 g/cm³ for the untreated soil to 2.00g/cm³ at 9% SDA, while the optimum moisture content decreased from 9.5 to 8.5% at 9–10% SDA. Unsoaked and 24-h soaked CBR values increased from 23 and 14% for the natural soil to peak values of 53 and 26%, respectively, at 10% SDA.Beyond 10% SDA, compaction and bearing performance declined. The results identify 10% SDA as the optimum overall content and support its use for improving lateritic soil intended for pavement subgrade. The measured soaked CBR does not establish direct suitability for subbase or base course without additional treatment and confirmatory testing. Keywords Lateritic soil · Sawdust ash · Soil stabilization · Compaction · California Bearing Ratio · Pavement subgrade ·Sustainable highway infrastructure