Modelling of concrete exposed to high temperature

In the present paper a fully coupled transient three-dimensional thermo-hygro-mechanical model for concrete is discussed. The model is formulated in the framework of continuum mechanics based on the principles of the irreversible thermodynamics. Distribution of moisture, pore pressure, temperature, stresses and strains are calculated by employing a three-dimensional transient finite element analysis of implicit type. The mechanical strain, which is due loading, temperature induced stresses and pore pressure, is calculated by employing temperature dependant microplane model for concrete. To investigate failure mechanism of explosive spalling of high strength concrete under high temperature, the extensive 3D finite element parametric study of concrete wall exposed to high temperature is carried out. In the analysis are varied concrete mechanical properties, permeability, porosity, humidity and heating rate. The results indicate that relatively high pore pressure together with local instabilities (geometrical non-linearity), due to compressive stresses that are generated in direction parallel to the heated concrete surface, are main reasons for explosive spalling. It turns out that permeability is the most sensitive concrete property with respect to the risk of an explosive spalling. The risk significantly increases with decrease of permeability.