MODELING OF THERMOCHEMOMECHANICAL COUPLINGS OF CONCRETE AT EARLY AGES

This paper explores the theory of reactive porous media in the modelin g of thermochemomechanical couplings of concrete at early ages. The fo rmulation is based upon thermodynamics of open porous media composed o f a skeleton and several fluid phases saturating the porous space. It accounts explicitly for the hydration of cement by considering the the rmodynamic imbalance between the chemical constituents in the constitu tive modeling at the macrolevel of material description. In particular , the diffusion of water through the layers of hydrates is considered as the dominant mechanism of the hydration with respect to the kinetic s of two apparent phenomena: aging and autogeneous shrinkage-the first related to the formation of hardened cement gel, the latter induced b y capillary effects related to the formation of menisci due to water c onsumption through hydration. The intrinsic relations concerning heat generation, aging, and autogeneous shrinkage are so derived. Furthermo re, it allows to make precise the decoupling hypothesis in order to cl arify the linkages between different aging models: solidification theo ry and maturity models. In particular, it is shown that hydration degr ee, autogeneous shrinkage, and maturity are equivalent state variables , provided that stress and temperature evolutions do not effect the th ermodynamic imbalance of hydration.