Insights into compositional signatures and technical attributes of soils: a case of clays from tropics

Abstract In this paper, further insight has been provided on the index, geochemistry, mineralogy and compression characteristics of tropical clays. Tropical clays are vast in deposit and they are commonly encountered by practitioners and applied for diverse engineering applications. This was achieved by conducting index and physical tests, microstructural and elemental analyses using scanning electron microscope equipped with electron dispersive spectrometry SEM/EDS, geochemical analysis through X-ray fluorescence XRF, mineralogical analysis using X-ray diffraction XRD and oedometer tests on clay samples from Nigeria, Cameroun, Democratic Republic of Congo and South Africa. The mean particle size (D 50 ), fines content (Fc), coefficient of uniformity (Cu) and plasticity index (Ip) are 0.15 mm, 40.25%, 18.63 and 7.7% respectively, and this indicates that clays are relatively coarse, well-graded and have low plasticity. Clay fabrics are isotropic, homogeneous and characterized by separate particles and particle aggregation forming clusters with inter-particle and inter-cluster voids. Silicon, aluminum and iron are the major elemental compositions in clays with an average proportions of 54.07%, 23.30% and 13.22% respectively. The chemical compositions of clays are predominantly silica, alumina and hematite with an average proportions of 52.45%, 24.12% and 14.30% respectively. The mineralogy of clays is dominated by quartz, kaolinite and clinochlore with an average proportions of 51.01%, 48.43% and 15.75%. The clays have convergent behaviour and narrow range of initial specific volume (v) from 1.521 to 1.695. Clays have low compressibility (Cc) ranging from 0.15 to 0.20 which could be linked to chemical and mineralogical compositions. Compressibility of clays has strong effects on the intensity of weathering of clays.