Rybczynski, SebastianSebastianRybczynskiSchaan, GunnarGunnarSchaanSchmidt-Döhl, FrankFrankSchmidt-DöhlRitter, MartinMartinRitterDosta, MaksymMaksymDosta2026-10-292026-10-292026Springer 978-3-032-19394-0: 225-247 (2026)https://hdl.handle.net/11420/65599Given the increasing demand for sustainable and lightweight concrete structures, the application of ultra-high-performance concrete (UHPC) has gained significant relevance. However, in contrast to static loading conditions, cyclic loads are more prevalent in real-world scenarios. Despite the superior mechanical properties of UHPC, it may exhibit a different resistance to cyclic loading. Consequently, this study focuses on both experimental and numerical analyses to investigate the primary mechanisms responsible for crack initiation at the meso-, micro-, and nanoscale. Following mechanical fatigue testing, microstructural alterations were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). To extend these findings to the mesoscale, a novel rheological model was developed. The results suggest that fatigue damage originates from nanoscale transformations of ettringite, combined with a densification of the cementitious matrix. Moreover, an increased content of unhydrated cement clinker within the matrix enhances fatigue resistance. At the mesoscale, stress concentrations around aggregate particles intensify with increasing load cycles, propagating into the binder matrix and contributing to further material degradation.enTechnology::620: EngineeringBook Part10.1007/978-3-032-19394-0_11