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Toward a fully coupled THM mesoscopic modelling of the behaviour of concrete at high temperature

The exposure of concrete to fire, which often leads to spalling, is a phenomenon that is not yet fully understood. Given the complexity of the thermo-hydro-mechanical phenomena and their strong interaction, a combined numerical-experimental approach is indispensable for understanding the behaviour of concrete at high temperature with respect to spalling. This study deals with the numerical modeling of moisture distribution in heated concrete, a parameter directly linked with spalling. The validation of these numerical models is usually based on experimental studies that monitor parameters such as gas pressure (P), temperature (T) and global mass loss (M). While such kind of experiments represent an important progress in better understanding the high temperature behaviour of concrete, some limitations appears due to the point-wise nature of temperature and gas pressure measurements. Firstly, the measurements might be influenced by the embedded sensors and secondly, the full-field information, which takes into account the role of concrete heterogeneity, is missing. Recently, in-situ neutron tomography experiments for measuring the distribution of moisture content in 3D have been performed. Local information obtained in this experimental study provided valuable insight to benchmark the modelling. In a first part of the paper, a homogenized continuum model has been employed for investigating various aspects, such as: speed of the drying front, moisture accumulation behind this front, experimental boundary effects etc. In a second part, a fully coupled 3D thermo-hydro-mechanical (THM) model is presented and used for simulating an experiment with a single aggregate for the purpose of investigating the influence of the aggregate on the drying front. Numerical results clearly highlight the coupling between mechanical damage on the drying front progression and built the first step toward the simulation on the concrete behaviour at high temperature taking into account the heterogeneous nature of the concrete (mesoscopic simulations).