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SUMMARYIn the context of radioactive waste storage, underground concrete structures may be subjected to external sulfate attack due to penetration of sulfate combined with leaching. This paper proposes a coupled chemo-mechanical modeling relying on a simplified chemical description of the solid phase composing the cement paste to address this issue. The sulfate and calcium species diffusing through the pore solution are supposed to completely control the chemical system, in particular the precipitation of gypsum and ettringite, which may lead to significant macroscopic expansions and cracking. The crystallization pressure generated by the growing crystals is introduced in the modeling through a poroelasticity analogy. Based on a representation of the cement paste of the matrix-inclusion type, the application of the Mori-Tanaka (MT) scheme provides estimates of the mechanical and diffusive properties and of the interaction coefficient as a function of the degradation state. The obtained coupled system is applied to two-dimensional numerical simulations of laboratory tests; the confrontation between experimental and computational results shows a good agreement in terms of both hydrated product evolutions as a function of time and macroscopic cracking appearance.

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This study aims at generating numerical 3D samples of concrete so as to study the effects of the granular inclusions shape on the macroscopic kinetics of reactive transport phenomena.Two types of mesostructure configurations are considered: the first one is composed of a matrix of mortar in which are randomly distributed inclusions corresponding to the concrete coarse aggregates, and the second one also includes a steel rebar. The choice of a mesoscopic modeling for the mortar matrix is based on the need to obtain numerical structures of reasonable size. In particular, the Interfacial Transition Zones (ITZ) are ignored, as this hypothesis seems acceptable for coarse aggregates. This study is applied to the case of drying and atmospheric carbonation by using simplified models solved by the finite element code Cast3M. The purpose is to quantify the influence of the aggregate shape on the kinetics of macroscopic transfer and the isovalue lines for some physical variables representative of the reactive transport problems: saturation degree for drying, and porosity, calcite and portlandite concentrations for carbonation. Basic aggregates shapes are studied (spheres, cubes), as well as more complex ones (Voronoi particles) which are supposed to be more representative of real aggregates. The effects of 'non-isotropic' shapes (oblate and prolate ones) are also investigated. It is shown that the influence of the aggregate shapes appears negligibly small on macroscopic indicators, except for oblate shapes with aspect ratios of 3. This latter case also exhibits substantial local delayed effects and a more important variability, which may have some importance for a precise description and estimation of degradation processes related to steel rebar corrosion.