Time dependent changes of material properties of FRC due to intensive heating

Studies on porous media, particularly on fiber-reinforced concrete (FRC), which is exposed to various temperature conditions, are of great concern for engineers and researchers in wide scale of civil and underground construction. The problem consists in a relatively very complicated description of processes which the concrete undergoes during the change of loading conditions, such as change of temperature (fire), wetting, moistening, attack by chemical substances, etc. There are too many variables which should be observed and their mutual effect should be taken into consideration. If a structure is loaded by a change of temperature on one boundary surface, a texture of the concrete varies and the phases inside the concrete adopt the temperature conditions. In this paper, a numerical study based on 3D finite elements, and an experimental one based on the effect of various conditions of temperature, degree of saturation of gaseous and water parts in pores and vapor are carried out. The parameters in the numerical study are tuned according to the results from the experiments. The theory is established based on thermodynamic laws, Fourier’s law, Fick’s law, balance conditions, etc. An immediate application of the results from this paper is in underground structures, mainly in concrete (FRC) linings of tunnels. More general applications are much wider.