This lecture is about concrete at high temperature. In this case we need to treat concrete as a multiphase material model, which I shall explain now.
As I said, concrete is treated as multiphase material, that means that we have a solid face, then we have a liquid phase, and gas phase, which is composed by dry air.
We assume that concrete has locally thermodynamic equilibrium and we take into account hygro-thermo-mechanical coupling, we take into account all the phase changes and the hygro-thermal and mechanical reflected high temperature.