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Caractérisation du potentiel de ségrégation des particules colloidales et non-colloidales des suspensions cimentaires sous cisaillement

Abstract : The aim of this work is to study the phenomenon of segregation of colloidal and non-colloidal particles in sheared cementitious suspensions and to determine a quantitative rheometric criterion capable of evaluating their segregability during rheological characterization tests.In order to meet this objective, we apply a specific methodology allowing, on the one hand, the rheological characterization of cementitious suspensions under shear using a rheometer equipped with coaxial cylinders and, on the other hand, the monitoring of their state of stability during characterization. The experimental protocol consists of two identical cycles and different decreasing shear gradient steps, allowing the rheological characterization of the suspensions. The rheometric tests were performed systematically twice by varying the vertical gap between the mobile and the container. The rheological characterization of the suspensions has been associated with several density measurements in the different parts of the rheometer at characteristic moments of the rheometric test for monitoring the stability and quantitative evaluation of possible segregation. All the results made it possible to define a segregation criterion based solely on the rheometric measurements making it possible to quantify the segregability of the cementitious suspensions during the rheological characterization because of the shear. The rheometric results between two geometrical configurations of shearing devices were compared in order to study the influence of the geometrical characteristics of coaxial cylinder rheometers on the segregation potential of cementitious (colloidal) particles and spherical glass beads(non-colloidal). The observed differences were analyzed using numerical flow simulations in each configuration using the COMSOL MULTIPHYSICS software.It has been shown that the effect of the bottom has a significant influence on the rheometric results of the cement suspensions causing a modification of this methodology according to the configuration. In addition, for the configuration used in this work, the segregation of the particles becomes more pronounced in the second cycle instead of the 1st cycle signifying a segregation delay in this case. This delay is due to the large serrations on the walls of the cylinders compared to the horizontal gap which causes a turbulent fluid flow in the rheometer preventing the segregation of the particles. Numerical simulation has also shown that the particle segregation potential is mainly influenced by the presence or absence of grooves on the container wall. On the other hand, the introduction of glass beads, considered as non-colloidal particles, does not influence the segregation of the colloidal particles. Segregative grouts can be divided into two types: weakly segregative where segregation of the beads does not occur; highly segregative where the beads begin to segregate. These findings were confirmed by the comparative analysis of the variation of the segregability criterion during the rheometric tests between grouts with and without beads.
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Ba Tung Pham. Caractérisation du potentiel de ségrégation des particules colloidales et non-colloidales des suspensions cimentaires sous cisaillement. Matériaux composites et construction. Université de Cergy Pontoise, 2019. Français. ⟨NNT : 2019CERG1036⟩. ⟨tel-02888645⟩

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