Mickaël Thiery

Poroelastic Analysis of Partial Freezing in Cohesive Porous Materials

We revisit the poromechanics set up by Olivier Coussy for better understanding of the mechanical effect of partial freezing in cohesive porous materials. This approach proves to be able to quantitatively predict swelling even if the in-pore liquid does not expand when solidifying. In this case, dilation results from the so-called cryosuction process that dominates thermal shrinkage under cooling, as shown in our analysis conducted on the historical experiment run by Beaudoin and MacInnis (1974, “The Mechanism of Frost Damage in Hardened Cement Paste,” Cem. Concr. Res., 4, pp. 139–147) on benzene saturated 24-h old cement paste. Both mechanisms are also at work when freezing water saturated early age cement paste with air voids. In this case, the cryosuction process results in shrinkage and should be added to the thermal shrinkage, their respective amplitudes being temperature dependent but, a priori, of the same order of magnitude.

Application of the reliability theory to the assessment of carbonation-induced corrosion risk of rebars

Deterministic approaches for the prediction of the carbonation penetration have limitations related to the high variability of the input data. This paper deals with two carbonation models which are developed in the framework of a probabilistic approach. The random input data are presented, i.e. materials, environment and engineering design properties. The evaluation of the time-dependent probability of carbonation-induced reinforcement corrosion is assessed by calculating the reliability index for three studied concretes. This probabilistic approach provides a framework for a sensitivity analysis which enables one to identify the most influencing model parameters which have to be determined carefully in order to improve the accuracy of the prediction and to determine the parameters whose variability should be reduced to enhance the durability. Furthermore, a probabilistic approach provides a tool to design the thickness of the concrete cover in order to avoid oversizing. Les modélisations déterministes de la carbonatation présentent des limites, essentiellement liées à la forte variabilité des données d’entrée des modèles. Le présent article porte sur deux exemples de modèle de carbonatation qui sont assortis d’un cadre probabiliste. Les données d’entrée des modèles sont présentées et assorties de lois de probabilité. La sécurité, vis-à-vis du risque de carbonatation, est donneé avec un niveau de confiance. L’approche probabiliste offre aussi un cadre pour une analyse de sensibilité de ces deux modèles permettant de dégager les paramètres les plus influents qui devront être déterminés avec soin pour améliorer la justesse de la prédiction et ceux pour lesquels la variabilité devra être réduite afin d’améliorer la durée de vie. De plus, les modèles probabilistes constituent des outils d’aide au dimensionnement de l’enrobage, notamment lorsque les approches normatives conduisent à un surdimension-nement.

Extension of Petersen matrix to the modelling of chemical equilibrium involved in concrete carbonation

Concrete is a porous material in which several chemical reactions may develop. One way to handle such a complex set of reactions is to use a modified form of Petersen matrix notation which is described in the paper. This formulation of Petersen matrix is able to handle the case where some of the reactions involved in the set of reactions have no analytical expression, but are described by chemical equilibrium. In order to handle this new situation, the reaction rate is tuned during the simulations in such a way that the chemical equilibrium remains verified. This tuning is performed thanks to a numerical proportional integral (PI) controller technique. This extension of the Petersen matrix is applied to the case of concrete carbonation modelling. The PI coefficients are given for each equilibrium controlled kinetics. The simulation results obtained thanks to a finite-difference solver are compared to experimental results taken from the literature.