Effect of Chemical Composition of Woodash and Lime on Stabilization of Expansive Soil

Abstract

Stabilizing effect of combined woodash and lime on expansive soil from south-eastern Nigeria has been evaluated. The evaluation followed subjecting industrial woodash to X-ray fluorescence (XRF) to determine its chemical composition while an expansive soil underlain by the Coniacian Awgu Group was subjected to X-ray diffraction (XRD) to determine the mineralogy of the soil. The plasticity index (PI), linear shrinkage (LS), free swell index (FSI) and unconfined compressive strength (UCS) of the soil was determined to ascertain the geotechnical properties of the natural soil. The soil was then mixed with woodash in varying proportions viz: 0% woodash and 100% soil; 6% woodash and 94% soil; 12% woodash and 88% soil; 18% woodash and 82% soil; 24% woodash and 76% soil. The PI, LS, FSI and UCS of each woodash-soil admixture was determined to ascertain how these geotechnical properties varies amongst the admixtures and thus the soil improvement of the various woodash proportions. The woodash-soil admixture that gave the best improvement quality was further mixed with 2%, 4%, 6% and 8% lime and PI, LS, FSI and UCS of each woodash-soil-lime admixture also determined to ascertain the amount of lime that gives the best improvement to the woodash-soil admixture. The XRF result revealed that the woodash was dominated with CaO and some other oxides in minor quantities. The XRD result revealed that the soil contains clay minerals. The geotechnical properties of the woodash-soil admixtures indicate that 18% woodash and 82% soil showed the best improvement in PI, SL, FSI and UCS of the soil while the addition of 4% lime to this best improved woodash-soil admixture further improved only the FSI and UCS. Results show that the stabilizing effect of both the woodash and combined woodash and lime is controlled by the chemical composition of the woodash.