## 4 Conclusions  
This paper investigated the fatigue behavior of TRC and of sandwich panels with faces made of TRC. Uniaxial tests were performed on rectangular TRC coupons, in total 27 specimens were fabricated and tested, divided into four series: one reference series and three series which were cyclically preloaded up to different stress levels (0.5 MPa, 1.0 MPa, and 2.0 MPa). In addition, 13 sandwich beams were tested by means of a four-point bending test. Three different series were considered: one reference series and two series cyclically preloaded up to the corresponding stress level (1.0 MPa and 2.0 MPa) in the tensile face of the sandwich beam. Afterwards, all specimens (incl. the reference specimens) were loaded up to failure. All tests, both cyclic and static, were monitored with DIC to map the cracking patterns and to measure the actual crack widths.  
A large similarity was observed between the experiments on the material level and the experiments on the element level. One could conclude that the fatigue behavior of the sandwich panels was strongly dependent on the fatigue behavior of the TRC faces. No degradation was observed in the core, nor in the interface between core and faces. The sandwich beams were less sensitive to the formation of cracks and degradation of the mechanical behavior compared to the TRC coupons. Possible reasons could be found in the different anchorage length of the textiles and in the presence of EPS-core; the bond between EPS and TRC restricted the crack widths.  
Fatigue parameters as cycle modulus and dissipative energy were investigated. All of them were related to the occurrence of cracks, which was the only observed damage mechanism: if no cracks were formed during the loading-unloading cycles, the parameters remained constant. In the presence of cracks, a decrease of the modulus and an increase of the dissipative energy and residual accumulative strains was observed. The modulus/stiffness and dissipative energy evolved in the opposite direction. Once a crack originated during the cyclic loading, its width grew during the first subsequent cycles but evolved asymptotically. The formation of cracks was governed by the maximum cycle stress. The higher the latter, the larger the probability of the occurrence of cracks.  
The residual capacity of the cyclically preloaded specimens was compared to a virgin reference behavior, obtained with identical experimental set-ups. Samples which remained uncracked after being subjected to the repeated loading conditions had a residual behavior equal to the reference behavior. The presence of cracks was reflected in the residual behavior by a lower initial modulus/stiffness. After being fully saturated with cracks, the remaining modulus is only dependent on the modulus of the fibers. This modulus remained unaffected leading to the conclusion that the fibers were not degraded by the cyclic preloading. The ultimate capacity was degraded little after subjection to repeated loading conditions. No clear relation was observed between the occurrence and number of cracks and the loss of ultimate capacity.  
Figure 19: The maximum crack width observed in the sandwich beams per series.  
**Author Contributions:** Conceptualization, M.D.M, T.T. and O.R.; methodology, M.D.M., J.W. and T.T.; formal analysis, M.D.M.; investigation, M.D.M.; writing--original draft preparation, M.D.M.; writing--review and editing, T.T., J.W., J.V.; M.E.K.; P.K.; visualization, J.V.; supervision, T.T., J.W. and O.R.; project administration, M.D.M. and T.T.; funding acquisition, M.D.M, T.T. and O.R.  
**Funding:** This research was funded by Agentschap voor Innovatie en Ondernemen (VLAIO) and CRH Structural Cngrant number 150251.  
**Acknowledgments:** The authors gratefully acknowledge Agentschap voor Innovatie en Ondernemen (VLAIO) and CRH Structural Concrete Belgium nv for funding the research of the first author through a Baekeland mandate.  
**Conflicts of Interest:** The authors declare no conflict of interest.