This Ph.D. thesis aims at characterising and modeling the mechanical behavior of
concrete at the mesoscopic scale. The more general scope of this study is the development
of mesoscopic model for concrete ; this model is to represent the concrete as a heterogeneous medium, taking into account the difference between aggregate and cement paste respecting the grading curve, the model parameters describe the mechanical and thermal behavior of cement paste and aggregates. We are interested in understanding the concrete behaviour, considered one structure.
A program of random granular structure valid in 2D and 3D has been developed. This
program is interfaced with the Finite Element code CAST3M in order to compute the
numerical simulations. A method for numerical representation of the inclusions of concrete
was also developed and validated by projection of the geometry on the shape functions,
thus eliminating the problems of meshing that made the representation of all aggregates
skeleton almost impossible, particularly in 3D.
Firstly, the model is studied in two-dimensional and three-dimensional in order to optimize
the geometrical model of the inner structure of concrete in terms of the meshing
strategy and the smallest size of the aggregate to be taken into account. The results of
the 2D and 3D model are analyzed and compared in the case of uniaxial tension and uniaxial
compression. The model used is an isotropic unilateral damage model from Fichant
[Fichant et al., 1999]. The model allows to simulate both the macroscopic behavior but
also with the local studies of the distribution of crack and crack opening. The model
shows interesting results on the transition from diffuse to localized damage and is able
to reproduce dilatancy in compression. Finally, the mesoscopic model is applied to three
simulations : the calculation of the permeability of cracked concrete ; the simulation of
the hydration of concrete at early age and finally the scale effect illustrated by bending
computation on notched beams.