Modeling of Thermochemomechanical Couplings of Concrete at Early Ages

Abstract

This paper explores the theory of reactive porous media in the modeling of thermochemomechanical couplings of concrete at early ages. The formulation is based upon thermodynamics of open porous media composed of a skeleton and several fluid phases saturating the porous space. It accounts explicitly for the hydration of cement by considering the thermodynamic imbalance between the chemical constitutents in the constitutive 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 kinetics of two apparent phenomena: aging and autogeneous shrinkage—the first related to the formation of hardened cement gel, the latter induced by capillary effects related to the formation of menisci due to water consumption through hydration. The intrinsic relations concerning heat generation, aging, and autogeneous shrinkage are so derived. Furthermore, it allows to make precise the decoupling hypothesis in order to clarify the linkages between different aging models: solidification theory and maturity models. In particular, it is shown that hydration degree, autogeneous shrinkage, and maturity are equivalent state variables, provided that stress and temperature evolutions do not effect the thermodynamic imbalance of hydration.