Strength Growth as Chemo-Plastic Hardening in Early Age Concrete

Abstract

This paper is concerned with modeling, identification, and experimental determination of thermo-chemo-mechanical couplings in early age concrete for the prediction of deformation and cracking on account of strength growth as chemo-plastic coupling within the theory of elastoplasticity. By applying the thermodynamic framework of reactive porous media to concrete at early ages, the coupling terms result from Maxwell symmetries. They lead to account for autogeneous shrinkage; hydration heat; and strength growth due to chemo-mechanical, thermo-chemical, and chemo-plastic coupling with a minimum of material parameters of clear physical significance and accessible by standard material tests. Furthermore, the diffusion of water through the layers of hydrates already formed is considered as the dominant mechanism governing the kinetics of hydration. To integrate this micromechanism in the macroscopic modeling, the “normalized affinity” is identified as an intrinsic kinetic function that characterizes the macroscopic hydration kinetics of concretes. Finally, by way of example, a Drucker-Prager criterion with isotropic chemical hardening is worked out that takes into account the evolution of the plastic properties (crack threshold and hardening/softening properties) with the hydration advancing.