Propriedades de solos vermelhos do Estado da Paraíba

Abstract

The study carried out during this investigation presents a critical review on the definition, genesis and classification of laterized red soils. Based on this review a definition is suggestd and a useful classification from the civil engineering piont of view is indicated. A field and laboratory study of three soils selected from the geological formations of Barreiras and Serra dos Martins is presented. From the field study, a theory of formation for the three deposits is formulated and later substantiated by the laboratory study on the properties of these soils. The laboratory study consisted of: chemical analysis, thermal analysis, both differential and termogravimetry, scanning electron microscopy and determination of specific surface. The samples for the study were arbitrarily separated in concretion and soil fractions and these futher divided in four size ranges. Tests were carried out on all the specimens obtained by separation in the different size ranges. The results allowed to study the distribution of silica, alumina and iron oxides as a funtion of size. It is shown that iron oxides and amorphous silica are the main cementing agents and that geothite, hematite, prehematite and amorphous iron oxides are present as main components, as well as kaolinite in most of the specimens corresponding to different size ranges. The study of microstructure revealed mostly ramdom geometrical arrangements with aggregations cemented by the amorphous materials. The round shapes, typical of the prehematite stages, were found in most of the concretion specimens and the internal structure of prehematite was very clearly revealed. Some engineering properties were studied on the light of the nature of the laterized soils and qualitative mechanisms were formulated to explain these properties.