Theoretical and experimental investigations to extend the calculation basis of different types of concretes exposed to natural fire

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In this research project, the reasons for different types of high-temperature behaviour in normal-strength (CC), high-performance (HPC) and ultra-high-performance (UHPC) concrete will be explored and described at both increasing and decreasing temperatures under natural fire conditions by conducting theoretical and experimental investigations. Due to the difference in stiffness and thermal strain of concrete's cementitious and aggregate phases, mechanical and/or thermal loads cause cracks within the material, especially at points of discontinuity in the structure such as cement-aggregate-bond areas and pores. These cracks are partly reversible (e.g. by re-hydration of cement) during the cooling phase and thereby have an influence on the mechanical as well as the thermal characteristics of concrete. Firstly, to understand these changes in characteristics, this research project consists of experimental investigations into both physical and chemical processes. Thereafter small scale laboratory tests are set up to determine the thermal and thermomechanical properties which are the basis for the definition of specific values for simulations and calculations. In the next step, full scale tests are conducted. The results are compared to the small scale findings to prove whether the formerly determined specific values can also be applied to real scale structural elements. All experiments are accompanied by numerical simulations to check the specific values theoretically, run parameter studies and validate the values as basis of further calculations.