Caractérisation physicochimique des aluminosilicate (argile et bauxite) de Kindia, Guinée: application dans la formulation des mortiers hydrauliques et des compositions céramiques

Abstract

This work assessed the potential uses of two types of clays and a bauxite quarried in Kindia (Guinea). They were firstly characterised by chemical and mineralogical composition, specific surface area, plasticity, particle size distribution, thermal behaviour, evaluation of pozzolanicity and determination of the amount of amorphous phase. Kaolinite and muscovite were found as the main clay minerals in clays, 57.40% and 27% against 55.10% and 19.90% respectively in addition to non-plastic minerals, precisely quartz with fine particles, goethite, hematite, anatase and gibbsite in traces. The two clays have high plasticity index that is consistent with the small size and broad particles size distribution. During heating up to 1200°C, the fluxing behaviour of both clays was pointed out through sintering with effective densification as result of significant quantity of muscovite and reactive fine quartz. Both clays exhibited limit firing shrinkage, 4.5% and 3.5% respectively. The study of ceramic test-discs physical and mineralogical properties led to conclude that these clays are suitable for dense ceramic compositions which require sufficient plastic ability and more dimensional stability during firing. Regarding the bauxite, it is gibbsite-rich 69.50% and contains 45.06 wt.% of alumina, 23.80 wt.% of iron oxide, and 1.74 wt.% of silica. This chemical composition fulfil that required for bauxites used in refractory cement formulations. During heating, this bauxite sample undergoes high densification with low linear shrinkage, suggesting its potential use in dense ceramic compositions with high thermal stability. The correlation between pozzolanicity, amorphous phase content, and specific surface area indicated that the raw bauxite and its calcined product at 600°C present an interesting reactivity exploitable in alternative cement formulations. Accordingly, mortars were manufactured by replacing 5 – 25 wt.% of Portland cement with raw bauxite and its 600 °C calcined product respectively. The both additives favoured the reduction of the workability and setting time of mortars. In the case of calcined bauxite, ettringite and monosulfoaluminate coexist regardless the rate of substitution due to the higher reactivity of alumina, whereas for raw bauxite, ettringite is only found at 5% and 10%. Heterogeneous microstructures and increased porosity are revealed with the rate of cement replacement for raw bauxite, whereas for calcined bauxite, the porosity decreases. Definitively, even the minimum compressive strengths of both series of mortars enable their application as construction materials. Favouring the porosity increase, raw bauxite is more appropriate for applications in porous materials development.