Behaviour and mineralogy changes in lime-treated expansive soil at 20 °C

Abstract

A comprehensive series of laboratory tests were conducted on a highly expansive clay soil treated with lime in order to study the lime–soil reaction over a short term and the progression of the pozzolanic reaction over a longer term. Therefore, the results of this study allow determination of the minimal concentration of lime reacting with clay minerals in order to induce a substantial long term improvement in the treated clay soil. The tests were performed with different percentages of hydrated lime (0–20%) at the room temperature of 20 °C. Plasticity Index, swelling pressure, unconfined compressive strength, wave velocity, pH, electrical conductivity and lime consumption were used to monitor the progression of the lime–clay reactions. X-ray diffraction tests were carried out in an attempt to identify the mineralogical changes and the reaction products formed in the treated soil. The experimental results indicate that 5% lime is sufficient for a short term reaction involving cation exchange, in this soil. This quantity corresponds to the amount needed for optimum change in soil properties after treatment. The excess of lime added promotes pozzolanic reactions and produces new minerals, such as calcium aluminate hydrates (CAH). This new mineral is identified by X-ray diffraction and its characteristic reflections intensities increase with lime added and curing time. Soil properties continue to be improved with lime addition. Finally, this study shows clearly that lime treatment can be used even for extremely expansive soil.