Stabilisation of Lateritic Soil for Road Construction Using Banana Leaf Ash

In view of the need to stabilise poor lateritic soil for road construction, this study investigated the effects of banana leaf ash (content retained on British Standard sieve No. 40) on the strength characteristics of selected lateritic soils. This is with a view to ascertaining the possibility of using the referenced banana leaf ash (BLA) content to stabilise the soils, for road construction purpose. To achieve the aim of this study, two soil samples were collected from two identified borrow pits (one sample from each borrow pit – referred to as Sample A and Sample B respectively) in Ile-Ife, southwestern Nigeria. Using standard procedure, preliminary and geotechnical tests were conducted on the soil samples in their natural states. BLA was then prepared and introduced to the soils at varying proportions of 2 %, 4 % and 6 % by weight of dry soil. The Atterberg limits and California bearing ratio (CBR) were subsequently determined for the treated soils. For the natural soils, results showed that: the plasticity index values for Sample A and Sample B were 22.91 % and 26.60 % respectively; the specific gravity values were 2.71 and 2.75 respectively; the optimum moisture content (OMC) and maximum dry density (MDD) for Sample A were 26.50 % and 1.325 Mg/m3 respectively, while for Sample B the values were 19.80 % and 1.643 Mg/m3 respectively; and the CBR values were 6.85 % and 11.36 %, respectively. With the addition of BLA: plasticity index generally reduced with the lowest values (4.89 % and 6.24 % for sample A and Sample B respectively) at 6 % BLA content; the CBR steadily increased until optimum values (10.23 % and 22.73 % for Sample A and Sample B respectively) were obtained at 4 % BLA content. The study concluded that: BLA could be used to improve the properties of lateritic soils for road construction purpose; and the particle size of BLA used does not diminish the quality of BLA as a soil-stabilising agent.