The aim of the research project is to assess the potential of microfibers on degradation in high-performance concrete under cyclic loading with regard to microcrack width limitation. To this end, the composite behavior of fibers for bridging microcracks and their effect on the development of microcracks during cyclic loading were investigated in particular during the first funding period. Similarly, experimental analyses were carried out on the influence of aggregate on the fatigue resistance of high-strength concrete. This has resulted in initial findings on the stage of the damage process at which the microfibers exert their effect. Furthermore, it was investigated whether an increase in the number of microcracks primarily takes place under highly cyclic compressive loading or whether microcracks that have already developed propagate continuously. Focusing on the cyclically induced damage processes, it was also investigated to what extent microcrack formation and development in the concrete is influenced by the aggregate and in the hardened cement paste by its homogeneity (capillary pores, microair pores). Building on the findings of the 1st funding period, further investigations are to be carried out in the 2nd funding period. The experimental results obtained so far confirm the hypothesis pursued in the project, according to which material fatigue in high-strength concrete is to be considered and modeled as a multi-scale, stochastic process on different spatial levels. The modeling strategy based on this hypothesis therefore requires experimental analysis of both microstructural changes at the CSH level and cycling-induced changes in the concrete microstructure due to microcracking at the meso-scale level. Another important research objective in the second phase is to experimentally investigate and model the effect of different fiber types on the fatigue behavior of high-strength concrete under high-cycle loading. In addition to the influence of carbon and microsteel fibers on microcrack development, the effectiveness of carbon nanotubes (CNTs) in bridging potential nanodefects/cracks will also be investigated. The damage processes are recorded experimentally in relevant laboratory investigations as well as described by structure-oriented numerical models - in the Experimental Virtual Lab - in order to map microcrack formation as well as damage accumulation in the course of cyclic loading.
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Last update: Nov 25, 2022
