Blended Cements with Kaolinitic Calcined Clays: Study of the Immobilization of Cr(VI)
Numerous investigations on the immobilization of chromium in cement-based systems were carried out in the recent years. The aim of this study is to analyze the influence of the crystallinity of kaolinite used to make calcined kaolinitic clay when are used in pastes for immobilization of Cr(VI). In previous study, it was found that the reactivity of kaolinitic calcined clays used as partial replacement of Portland cement largely depends on the crystallinity of kaolinite in the raw clay. Calcined clays obtained from raw materials containing kaolinite with disordered structure presents a very high pozzolanic activity allowing high-percentage replacement (30 %) in blended cements. In this study, pastes of blended cement with 15 % and 30 % by mass of two kaolinitic calcined clays (order and disorder structure of kaolinite) were elaborated using a solution of 5000 ppm of K2Cr2O7 and a solution-to-cementing material ratio of 0.50. The immobilization efficiency was measurement by lixiviation test and the modifications in the hydrated phases was studied by X-ray diffraction and SEM/EDS analysis. The results shown that kaolinitic calcined clay from ordered kaolinite was more efficient than disordered kaolinite to retention of Cr(VI), reaching values higher than that of PC-paste.
KeywordsPortland Cement Pozzolanic Reaction Blended Cement Hydrated Phase Kaolinitic Clay
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