The present work focuses on the impact of the chemical degradations of cementitious materials such as Delayed Ettringite Formation (DEF) on the overall material properties. DEF is an endogenous pathology due to the crystallization of ettringite within voids and cracks. The crystallization pressure in the porous cement paste induces swelling and cracking by differential expansion. The study aims to characterize the evolution of effective material properties (diffusion coefficient, apparent tenacity) with respect to DEF. A non-linear chemo-mechanical modeling is proposed where the entire diffusion-precipitation-pressurization-crack process is solved in a staggered approach. The diffusion-precipitation mechanism is translated by a rough chemical model. The resulting local volume fraction of ettringite is estimated by a finer micro-mechanical-based model using the effective elastic properties of the cement paste. The crack initiation and propagation is estimated with a dedicated cohesive zone model including pressure effect. Some applications of the model are presented.

Ce travail présente une modélisation chimio-mécanique du béton reposant sur le couplage entre le transport réactif et la réponse mécanique du système afin d'évaluer l'évolution des paramètres apparents du béton. Ce modèle repose sur une représentation d'un milieu poreux fissuré, dont la fissura-tion est traitée par un modèle de Zone Cohésives Frottantes. Il est étudié en particulier les réactions de gonflements dont les pores et les fissures sont mis sous pression. Une application à la Réaction Sulfatique Interne (RSI) est présentée mettant en avant l'impact de la granulométrie sur le gonflement du béton.

In the context of lifetime extension of nuclear power plants, the french Institut de Radioprotection et deSûreté Nucléaire (IRSN) conducts researches to predict the aging of cementitious materials. The presentwork is focusing on the impact at the mesoscale of the chemical sulfate attacks on the overall materialproperties. The sulfate attacks are characterized by the ettringite precipitation that induces great pressurein the porous cement paste. The effect of the local swelling of cement paste on concrete, conducts somecracking by differential deformation. These cracks become preferred loci for ions diffusion and furtherettringite precipitations. These strongly coupled phenomena suggest a non-linear chemo-mechanicalmodelling where diffusion, precipitation, pressurization and crack process should be simultaneouslyinvolved:1. Species diffusion: diffusion is modeled by Fick’s law in a cracked porous medium [1] [2];2. Chemical reactions: knowing species concentrations in solution, different types of reactions suchas aqueous, solid and sorption reactions [3] are modelled in order to estimate the amount of ettringitevolume;3. Mechanical: knowing the created solid volume, a local pressure is calculated in the poro-mechanicalmodel and in the cracks. The crack initiation, propagation and pressurization are based on a dedicatedCohesive Zone Model [4].The presented applications will focus on the impact of material properties, such as matrix composition,on strain kinetics. The impact of the clinker composition is estimated by a dedicated hydration computingwithin an analytical homogenization framework.REFERENCES[1] J.M. Segura and I. Carol. On zero-thickness interface elements for diffusion problems. InternationalJournal for Numerical and Analytical Methods in Geomechanics, 28:947 – 962, 2004.[2] L. Bichet. Taking into account the transport mechanisms in the fracture of heterogeneous materials:application to the nuclear power plant aging. PhD thesis, Univ. Montpellier II, 2017.[3] C. de Dieuleveult, J. Erhel, and M. Kern. A global strategy for solving reactive transport equations.Journal of Computational Physics, 228:6395 – 6410, 2009.[4] 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, 75:3378 – 3398, 2008.