Modelling of hygro-thermal behaviour and damage of concrete at temperature above the critical point of water

In this paper, a model for the analysis of the behaviour of concrete at temperature largely exceeding critical point of water, is presented. In this temperature range liquid phase, i.e. capillary phase, and gas phase cannot be distinguished and only the latter exists. Consequently, capillary pressure has no more physical meaning above this point and liquid water is present only as physically adsorbed water. In this work, we give a different physical interpretation to the capillary pressure and use it still for the description of the hygrometric state of concrete in the zone, where temperature exceeds the critical point of water. Considerable thermal dilatation of the liquid water and the real behaviour of water vapour close to critical temperature are taken into account. Moreover, a special switching procedure in order to avoid the Stefan- like problem, which subsequently arises, is described and employed in the calculations. Finally, several numerical examples demonstrating the robustness of the adopted solution have been shown.