Mineralogical and Geotechnical Characterization of Maiduguri Black Cotton Soil by X-Ray Diffraction (XRD), X-Ray Photoelectron (XPS) And Scanning Electron Spectroscopy (SEM)

摘要

The focus of this paper is to characterize clayey soil samples along the Maiduguri-Gamboru Road, Borno State, Nigeria using advanced characterization techniques in order to improve the soil engineering properties for road pavement construction and foundations. Soil samples were mineralogically characterized using X-ray Powder diffractometry (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Spectroscopy (SEM), soil index properties (Atterberg Limits) and strength tests. X-ray powder diffraction analysis detected the presence of four minerals: Quartz, SiO2; Calcite, CaCO3; Larnite, Ca2SiO4; and a clay mineral Kaolinite, Al2(Si2O5)(OH)4. XPS peak analysis by CasaXPS software confirmed the availability of eight (8) elements with Percentage Atomic Concentration as: Oxygen (65.14%), Silicon (15.79%), Aluminium (7.53%), Carbon (5.96%), Magnesium (2.11%), Ferrous (1.96%), Calcium (0.82%) and Nitrogen (0.68%) with traces of Sodium (0.00%) and Sulphur (0.00%). The ratio of the exchangeable cation Calcium / Magnesium is less than 0.5 indicating an unstable soil. The EDS chemical analysis by SEM detected eleven (11) elements. The distribution of the chemical elements by atom% in descending order is: Oxygen (63.67%), Silicon (18.66%), Aluminium (10.36%), Ferrous (3.44%), Carbon (1.66%), Calcium (0.6%), Potassium (0.52%), Tin (0.37%), Sodium (0.36%), Magnesium (0.25%), Phosphorous (0.13%), with traces of Sulphur and Barium. The Percentage Atomic concentration of carbon and aluminium given by XPS are much higher than that given by SEM (atomic %) while that of Oxygen is similar. The soil index properties: high liquid limit (68%), low plastic limit (25.3%), high plasticity index (41.7%) and free swell (50%) indicate a high swelling and highly compressible soil with an estimated uplift pressure of 151.8kN/m2. This is due to the presence of clay minerals. The soil strength characteristics: Maximum Dry Density (1708.9 Kg/m3); Un-soaked CBR (36%) and the soaked CBR (17%) fall below the minimum requirement for sub-base and base course. The frequent damages to road pavements and foundations in the area can be attributed to the chemical composition and mineral assemblage of the soil in the area. The characterization and knowledge of the chemical assemblage will make possible the effective stabilization as chemical stabilization will be directed at the different chemical compounds in the soil.