Effects of pre-test heating temperature on microstructure, chemical and mineralogy of lateritic soil

Abstract

Pre-test drying methods are known to have a significant impact on the properties of lateritic soils. Nevertheless, there has not been sufficient investigation into the impact of pre-test drying temperature on the mineralogical and microstructural characteristics of lateritic soils, which are particularly sensitive to moisture variation. This work aims to investigate the impact of the temperature used for pre-test drying on the microstructure and mineralogy properties of three lateritic soils from Ado-Ekiti, Southwest Nigeria, which developed over different Precambrian basement complex rocks. Samples of disturbed lateritic soils were collected and tested at their natural moisture content (NMC) as well as at three other states obtained through air-drying and oven-drying at 60 °C and 110 °C. X-ray diffraction and scanning electron microscope (SEM) analyses were performed to explore the mineralogy and microstructural properties of the soils. Results show that the lateritic soils at their NMC consist mainly of kaolinite, quartz, and k-feldspar, while minerals like clinopyroxene, mica, and plagioclase feldspar, hematite are present in minor quantity. The increase in the pre-test drying temperature had no significant impact on the mineralogy or elemental composition of the lateritic soil, possibly due to the fact that the temperature was not sufficiently high to trigger mineral transformation. As the pre-test drying temperature rose, SEM micrographs indicated that the structure of the air-dried and oven-dried soil samples became increasingly aggregated and clumped, particularly when the temperature reached 110 °C. This suggests that the oven-drying process caused particle aggregation, which altered the structure of the lateritic soils and, in turn, affected properties such as plasticity and particle size distribution.