Thermo-mechanical material properties of concrete in the cooling phase

The application of natural fire models is provided in the current Eurocode as an alternative to the common ISO 834 standard fire for fire safety design. When determining the temperature-time curves, the load-bearing capacity of the building components and structures has to be ensured throughout the entire fire duration due to possible failure of the components in the cooling phase because of a delayed heating or high tensile forces. The application of natural fire models is currently associated with some uncertainties because the parameters of the material properties in the cooling phase after high temperature exposure have not been determined yet. Within a current research project funded by the German Research Foundation (DFG), the material behavior of conventional, high and ultra-high performance concrete for realistic natural fires, including a heating and a cooling phase, is investigated. For this purpose, temperature-dependent thermal and thermo-mechanical material properties of the concretes have been determined. In this paper, the determination of the thermo-mechanical material properties in the cooling phase of conventional concrete is described.