Charles Toulemonde

A critical comparison of several numerical methods for computing effective properties of highly heterogeneous materials

Modelling transport and long-term creep in concrete materials is a difficult problem when the complexity of the microstructure is taken into account, because it is hard to predict instantaneous elastic responses. In this work, several numerical methods are compared to assess their properties and suitability to model concrete-like microstructures with large phase properties contrast. The methods are classical finite elements, a novel extended finite element method (@m-xfem), an unconstrained heuristic meshing technique (amie), and a locally homogenising preprocessor in combination with various solvers (benhur). The benchmark itself consists of a number of simple and complex microstructures, which are tested with a range of phase contrasts designed to cover the needs of creep and transport modelling in concrete. The calculations are performed assuming linear elasticity and thermal conduction. The methods are compared in term of precision, ease of implementation and appropriateness to the problem type. We find that xfem is the most suitable when the mesh if coarse, and methods based on Cartesian grids are best when a very fine mesh can be used. Finite element methods are good compromises with high flexibility.

Three-dimensional morphological modelling of concrete using multiscale Poisson polyhedra

This paper aims at developing a random morphological model for concrete microstructures. A 3D image of concrete is obtained by microtomography and is used in conjunction with the concrete formulation to build and validate the model through morphological measurements. The morphological model is made up of two phases, corresponding to the matrix, or cement paste and to the aggregates. The set of aggregates in the sample is modelled as a combination of Poisson polyhedra of different scales. An algorithm is introduced to generate polyhedra packings in the continuum space. The latter is validated with morphological measurements.

Upscaling concrete properties: a rational approach to account for the material complexity and variability

Life management of electric hydro- or nuclear power plants requires estimating long-term concrete properties on concrete facilities for obvious safety and serviceability reasons. Decades-old structures are foreseen to be operational for several more decades. Operational time-scale is thus far more extended than laboratory test duration. Additionally, tests on rather old concrete can hardly be done again due to the difficulties of finding genuinely representative cement or aggregates and, as far as dams are sometimes concerned, to the large size of the coarse aggregates. In order to estimate long-term mechanical properties upscaling techniques offer an interesting alternative. Two approaches are described in the sequel: 0D analytical and semi-analytical simulation based on homogenisation techniques and 3D numerical simulation.

3D morphological modeling of concrete using multiscale Poisson polyhedra

This paper aims at developing a random morphological model for concrete microstructures. A 3D image of concrete is obtained by microtomography and is used in conjunction with the concrete formulation to build and validate the model through morphological measurements. The morphological model is made up of two phases, corresponding to the matrix, or cement paste and to the aggregates. The set of aggregates in the sample is modelled as a combination of Poisson polyhedra of different scales. An algorithm is introduced to generate polyhedra packings in the continuum space. The latter is validated with morphological measurements.

Three-dimensional morphological modelling of concrete using multiscale Poisson polyhedra: 3D MORPHOLOGICAL MODELLING OF CONCRETE

This paper aims at developing a random morphological model for concrete microstructures. A 3D image of concrete is obtained by microtomography and is used in conjunction with the concrete formulation to build and validate the model through morphological measurements. The morphological model is made up of two phases, corresponding to the matrix, or cement paste and to the aggregates. The set of aggregates in the sample is modelled as a combination of Poisson polyhedra of different scales. An algorithm is introduced to generate polyhedra packings in the continuum space. The latter is validated with morphological measurements.