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Modélisation multi échelle des phénomènes de retrait et de fluage dans les matériaux cimentaires : approches numériques couplant les éléments finis et la méthode de Lattice-Boltzmann

Abstract : In pre-stressed concrete structures, creep and shrinkage tend to reduce the pre-stress forces which are initially produced so as to maintain concrete in a state minimizing traction forces and then cracks. Understanding and predicting these phenomena through models are thus highly important for the design and durability of civil engineering structures, such as containment buildings in nuclear power plants.The objective of this thesis is to develop a micromechanical modeling framework to describe shrinkage and creep in cementitious materials in a unified manner. For this purpose, the study focuses on the scale of the porous structure of the C-S-H gel where the intrinsic mechanisms of delayed strains are active. A computational homogenization approach is developed to model these phenomena in porous structures with arbitrary morphologies. An explicit description of the porous network and of the liquid phase of water during the drying/humidification process is taken into account. The mechanisms related to delayed strains in the solid phase are modeled by the microprestress-solidification theory (MPS). The simulations at the microscale are conductedbased on an original approach coupling the Lattice Boltzmann method (LBM) and the finite element method (FEM). The LBM is used to describe the distribution of capillary water in the porous structure, whereas the FEM serves as modeling the strain of the solid skeleton under the capillary water effets and a macroscopic load.The proposed method allows, by means of the simulations, to better understand the mechanisms related to the capillary effects in the porous structure. More specifically, taking into account realistic morphologies of microstructures and of the formed menisci lead to different regimes of shrinkage/swelling. Then, the effects of capillary pressure intensity, of surface tension and of morphologies of capillary surfaces on the elastic response of the solid skeleton are evaluated. Finally, the above approaches are extended to the case of a viscoelastic solid deformed under the action of the capillary water. From numerical observations, we propose a model is proposed to describe the creep and shrinkage of C-S-H gel in a unified way
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Submitted on : Tuesday, April 3, 2018 - 12:45:08 PM
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Jean-Luc Adia. Modélisation multi échelle des phénomènes de retrait et de fluage dans les matériaux cimentaires : approches numériques couplant les éléments finis et la méthode de Lattice-Boltzmann. Génie civil. Université Paris-Est, 2017. Français. ⟨NNT : 2017PESC1013⟩. ⟨tel-01757055⟩

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