ABSTRACT

Proper disposal of waste has been a challenge in the world today due to its effect on the ecosystem, as the gases emitted to the atmosphere poses a huge problem to the ozone layer. In a bid to remediate this, several techniques have been developed which includes proper waste recycling and incineration methods. Studies have shown that Sawdust, a waste material from wood processing industries in its Ash form poses a certain percentage of cementitious properties, which can be used in re-engineering and improving the strength properties of problematic lateritic soils and hence this study is aimed at treating weak lateritic soil materials using sawdust ash and developing a mathematical model to predict the Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) of the lateritic soil treated with sawdust ash for sustainable earthwork constructions. The geotechnical properties of the soil were examined, and the soil and saw dust ash were characterised using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The lateritic soil was stabilized using percentage saw dust ash of 0%, 2%, 4%, 8% and 10% and the UCS and CBR of the stabilized soil were examined. Multi-linear regression of the UCS and CBR of the stabilized soil was investigated using the historical design of Response Surface Methodology (RSM) in design expert software. The results indicated that the lateritic soil contains SiO₂, Al₂O₃, Fe₂O₃, CaO, MgO, Na₂O, K₂O, SO₂, P₂O₅ and MnO. The SEM result for the lateritic soil showed clumped particles made of Al₂O₃, SiO₂, and Fe₂O_3, while the saw dust ash SEM indicated a brittle surface with a high surface area. The XRD patterns of the unstabilized of lateritic soil and saw dust ash indicated that quartz (Qz) is the predominant mineral. The highest CBR of 15.3% was achieved at 4% SDA content. The measure of the unconfined compressive strength cured after 7, 14 and 28days showed that an increase in the SDA increased the UCS of the soil with maximum value of 195.60 kN/m³, 197.92 kN/m³ and 202.48 kN/m³ UCS obtained at 7 days, 14 days and 28 days curing respectively. The multiple linear regression for the stabilization of the lateritic soil gave linear regression models with R-squared of 0.991852 with adjusted R-Squared of 0.97963 for CBR and an R-squared of 0.989856 with an adjusted R-Squared of 0.97464 for UCS. It was recommended that cement requirement for road work could be substantially reduced to an optimum level and partially replaced by sawdust ash for road work to reduce the cost of materials.