The project focuses on two topics: firstly, the examination of structural damage caused by fatigue in cementitious high performance materials using high resolution analytical electron microscopy. The correlation with the inhomogeneities within the material, for example the residues of the plasticizers in the hydrated material, is of special interest. It is our working hypothesis, that in high performance concretes without capillary porosity, the initiation of cracks is caused by such inhomogeneities, whereas in normal strength concrete the initiation of cracks is linked to capillary porosity and the pores within the transition zone. Secondly, the aim of the project is the multiscale modelling of fatigue in high performance concrete using a bonded particle model (BPM). The project concentrates on concrete without capillary pores. The analysis of the structural damage requires very small specimens Tension tests on such small specimens will be performed in a transmission electron microscope. The results of these mechanical tests will be linked to the spatial distribution of the phases within the concrete. The examination of the crack propagation is performed on macroscopic specimens damaged by fatigue. Parts of these specimens will be analyzed by FIB-tomography. This method allows a three-dimensional reconstruction of the structure with very high resolution. Therefore, a large portion of the scientific work will be the development of methods for analyzing concrete with high resolution electron microscopy. These methods will then be made available for the whole DFG priority program. In addition, these examinations will produce fundamental results with regard to structural damage, crack formation and crack propagation in the case of fatigue, for the own modelling as well as for the modelling work of other projects within the DFG priority program.The numerical research work is focused on the development of a multiscale BPM-based simulation approach and on the validation of meso- and macro-scale models for the description of fatigue behavior. The new approach should be able to predict the influence of cyclic loading on mechanical properties; consider the influence of mesoscopic concrete structure on macroscopic behavior; describe initiation and coalescence of micro- and growth of macro cracks, which lead to material destruction.The modeling of investigated samples will be performed with the self-developed simulation framework MUSEN, which will be extended with new calculation algorithms and rheological models. The validation of the simulation results and the estimation of the model parameters will be made based on data experimentally obtained for high-performance concrete and its components. Thereby, information not only about macroscopic material behavior will be used, but also data obtained from electron microscopy will be applied to create, adjust and validate the models.

Extensive advances in concrete technology have led to the development of high performance concretes with significantly expanded application possibilities. Examples include self-compacting, high-strength and ultra-high-strength concretes with steel-like strengths or fiber-reinforced and textile-reinforced concretes with highly ductile behavior. These concretes allow very slender, aesthetic and resource efficient concrete structures, which are more susceptible to vibration due to their reduced weight. Even outside of the classical construction industry, the range of applications for high-performance concretes will undergo considerable development, for example in mechanical and plant engineering, where they can become an alternative to metallic and ceramic materials. All of these structures are subjected to highly cyclical loading, so that the fatigue behavior is crucial for their design and thus for the feasibility of innovative concrete applications. However, there is any basic knowledge of material degradation of concrete under fatigue stress hardly available. Because of these gaps in knowledge, the use of modern high-performance concretes is already considerably hindered, sometimes even prevented.The designed aim of this priority program is to capture, understand, describe, model and predict the material degradation of high-performance concretes using the newest experimental and virtual numerical methods. Since the damage processes occur on a very small scale, they cannot be entirely observed during the load tests. The recording of suitable damage indicators during the experiments make the time-consuming fatigue tests already very demanding. To this extent, the desired results will be developed from a close cooperation between the building material science and the computational mechanics knowledge, which is the interconnection of experiment and computation in the Experimental-Virtual-Lab.An SPP is the perfect framework to resolve the pressing issues of material degradation across locations. The collaboration is designed in such a way that in addition to an intensive exchange of experimental techniques, damage indicators and modeling approaches, a multiple use of the experimental data and a close interaction between experiment and simulation is achieved. Due to the complex experimental technique and the necessity of a fundamental further development of material models, a strong cooperation of the participating locations is promoted with special structural arrangements. Only in this way the existing barriers to the use of fatigue-stressed high-performance concretes can be overcome and an innovation boost for building with concrete and for concrete applications outside of the classical construction industry can be triggered. The new knowledge will also enable to extend the service life of existing fatigue-stressed structures such as bridges and wind turbines.