Résumé
In the context of the lifetime extension of nuclear power plants, the french Institut de Radioprotectionet de Sûreté Nuclaire (IRSN) conducts researches to predict the ageing of cementitious materials. Thepresent work is focusing on the impact of the chemical degradations such as Delayed Ettringite Formation(DEF) on the overall material properties at the aggregates scale. DEF is an endogenous pathologyrelated to the cement composition and to the early age chemical reactions where thermal conditionsinduced dissolution of primal ettringite and later moisture environment can lead to ettringite reprecipitation.The crystallization pressure in the porous cement paste thus conducts both to its swelling andsome cracking by differential strains. These cracks are preferential location for ions diffusion and furtherettringite reprecipitations. These strongly coupled phenomena suggest a non-linear chemo-mechanicalmodelling where the diffusion, precipitation, pressurization and crack process should be solved in acoupled approach. In an modelling, for each time step, one calculates:Species diffusion: to describe the environmental impact on the concrete. Diffusion is modeled by Fick’slaw in a porous medium. This model follows the framework of [1] and it takes into account the resistiveimpact of the crack on the normal flow;Chemical reactions: knowing species concentrations in solution, one models different types of reactionssuch as aqueous, solid and sorption reactions [2]. Thus, the amount of ettringite volume is evaluated;Mechanical: knowing the solid volume, a local pressure is calculated in the poro-mechanical model andin the cracks. The crack initiation, propagation and pressurization are based on a dedicated CohesiveZone Model [3].The presented applications will focus on the impact of material properties, such as volume fraction ofinclusion and matrix composition, on strain kinetics.REFERENCES[1] L. Bichet. Taking into account the transport mechanisms in the fracture of heterogeneous materials:application to the nuclear power plant aging. PhD thesis, Universit´e de Montpellier II, 2017.[2] C. de Dieuleveult, J. Erhel, and M. Kern. A global strategy for solving reactive transport equations.Journal of Computational Physics, pages 228 : 6395 – 6410, 2009.[3] F. Perales, S. Bourgeois, A. Chrysochoos, and Y. Monerie. Two field multibody method for periodichomogenization in fracture mechanics of non linear heterogeneous materials. Engineering FractureMechanics, pages 75 : 3378 – 3398, 2008.