Effects of kiln ash on the compressibility of residual Lateritic soils

The potential for the use of kiln ash as an additive to Lateritic soils to improve their engineering characteristics as road construction material was experimentally investigated. The results of laboratory tests indicate that no significant improvement of the soil properties occurred until after several weeks of curing time. In general, as the content of kiln ash in the soil was increased, the soil pH increased from 5.5 to 11.8; the maximum unconfined shear strength increased from 340 to 423 kPa (corresponding to 0-8% kiln ash content), the soil liquid limit reduced from 59 to 49% (corresponding to 0-20% kiln ash as content). No significant change in the plasticity limits of the lateritic soil was observed, in the range of 0 to 8% kiln ash content. Relative to the compressibility of the natural soil (measured in terms of the total strain), a decrease of about 3% occurred for kiln ash contents of 5, 10, and 20% within I to 7 days; and that this decrease reached about 19% for 20% kiln ash content as time progressed (to more than 177 days). These results imply that significant and desirable changes in soil compressibility can be achieved after a few months if the soils are admixed with kiln ash. Soil solution pH changes cause a time-dependent increase in soil strength, where calcium cations combine with silica and aluminum of the soil to form insoluble cementitious materials.