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International audience; It is essential to model the behavior of the interfaces between steel reinforcement and concrete in order to understand the stress transfer between these two components in reinforced concrete structures. The interface models commonly used include several parameters whose identification is based on pull-out tests, for which sensitivity to a number of parameters is not fully explained. In this contribution, the steel-concrete interface is studied at the mesoscopic scale through the simulation of pull-out tests. The three dimensional numerical reinforced concrete samples are first generated by applying a procedure, in which each sample is made up of concrete surrounding a ribbed or smooth bar embedded in the center of a cubic sample. The detailed geometry of the ribs of the steel bar is modelled with different possible shapes. Then, the finite element code Cast3M is used to perform the pull-out numerical simulations on the generated samples, using Mazar’s damage approach with regularization to describe cracking in concrete. The steel-concrete interface is modelled by combining a modified cohesive zone model (CZM) based on Tvergaard’s approach and a frictional model accounting for the frictional behavior in the damaged part of the interface. This is done by modifying an initial approach, by replacing the Crisfield’s damage model by the more adapted Tvergaard’s model and modifying the corresponding stresses to account for its exponential behavior. The interface is divided into an undamaged part where the CZM model applies and a damaged part where the frictional model dominates. The total stress is then the addition of the two corresponding stresses, and is equivalent to the CZM stress when the interface is initially undamaged, and fully equivalent to frictional model’s stress when the joint element is finally fully damaged. The overall response is studied in terms of the damage near the steel bar, the applied force versus displacement curves, and free end displacements. The results of mean bond stress versus the free end displacement are compared to available experimental data.

International audience

The behaviour of novel cementitious materials (low clinker cement CEM II/C and CEM VI) exposed to CO2 is simulated and investigated with a simplified model in this paper. Based on studies of the evolution of the phase assemblage obtained from GEMS, the carbonation process is simplified into the dissolution of one combined Cacontaining phase and the precipitation of calcite phase. The purpose is to quantify some physical variables representative of the reactive transport properties: saturation degree for drying, porosity, calcite and Ca-containing phase content for carbonation. The dissolution rate of the Ca-containing phase and corresponding precipitation of calcite are assumed to be determined by the saturation degree, the partial pressure of CO2, and the concentration of calcium in solid phases. The carbonation process is assumed to be ruled by two phenomena: the water migration through the connected porosity and the diffusion of carbon dioxide in the gaseous phase, which are governed by two mass conservation equations. This model is solved by the finite element code Cast3M, and is verified using experimental data from carbonation depth measurements using a pH indicator, portlandite and carbonate profiles from thermogravimetric analysis and drying experiments on mortar and concrete.

International audience

International audience

International audience; Concrete is an important constitutive material of nuclear power plants and waste storage structures whose mainrole is to ensure high level of performance regarding the required middle to long-term containment function. Assuch, creep and microcracking are known significant factors affecting the mechanical properties and the long termbehavior of concrete, and may call into question the safety of nuclear facilities. The accurate modelling of thesephenomena including their coupled effects have then to receive a special attention. We propose in this study toapply the relatively recent method making use of a phase field approach to reproduce the initiation and propagationof microcracking in concrete. This method rests on a diffuse description of the microcrack surfaces by one scalarvariable whose values result from a specific balance equation. As a main contribution, it is extended here andcoupled to a linear viscoelastic behavior to mimic the creep (and possibly shrinkage) of the material. A classicalgeneralized Maxwell model is retained for modelling this viscoelastic behavior. At first, an energy-based formulationis developed to express the equations governing both viscoelastic mechanical and phase field problems. In this firstattempt, only cracking due to extensions is considered. Different simple fracture criteria based on positive stressesor strains with and without threshold are applied and tested. The resulting approach is next implemented in the FEcode Cast3M so as to solve both systems of equations. Applications to a homogeneous material subject to loadingwith various durations and intensity are then analyzed and discussed with regard to the different crack driving statefunctions. In a second stage, 3D simulations of heterogeneous concrete samples made up of elastic aggregatesdispersed in a mortar matrix concentrating the viscoelastic behavior are performed. These numerical specimensare generated with polyhedral aggregates having various size and shapes, and which are randomly distributed in abox. The effects of the aggregate shape on the microcracking development and the macroscopic behavior ofsamples subject to creep loading are investigated. To this aim, different specimens are created with elongated andflattened polyhedral aggregates with given aspect ratio, and the obtained results are analyzed and confronted inparticular in terms of microcrack patterns.

Colloque avec actes et comité de lecture. Internationale.; International audience; Dans le contexte de calcul thermo-hydro-mécanique de structure, nous proposons une estimation de la perméabilité induite par la fissuration. A l'échelle micro, les paramètres des fissures sont estimés par un modèle discret. Le tenseur de perméabilité associé à la fissuration est estimé par homogénéisation. Un modèle macroscopique THM est alors utilisé pour caractériser et prédire le comportement et les transferts de fluide dans un béton soumis à un chargement thermo-hydrique modéré.