## 3 Results
### Temperature Rise Under Parameter Variation  
In the following, the heating curves for the varying stress levels, frequencies and the two concretes are presented. In the diagrams, the heating curves on the center of the surface are displayed in each case. This represents the maximum temperature rise which was measured in all tests. As shown in Table 1, three frequencies (3/10/20 Hz) were tested for the UHPC 1 and three different maximum stress levels (\(\sigma_{\rm o}\) = 0.6/0.7/0.8) were applied at each frequency. The diagrams in Figure 5 present the heating curves over the number of load cycles for all 27 tests. The influences of the load-dependent parameters on the temperature increase of the UHPC 1 under fatigue stress can be seen clearly. It should be noted, that a change in the scaling for the number of load cycles at 200,000 load cycles takes place in the X-axis in all diagrams (marked by two small oblique strokes). Thus it is possible to make the courses of curves with an early and a late failure visible in one graphic. Please also note that the scaling of the Y-axes is different. Figure 4: Temperature development of one test specimen made of UHPC 1; test conditions: test frequency f\({}_{\rm P}\) = 10 Hz, relation between lower and upper stress level S\({}_{\rm c,min}\)/S\({}_{\rm c,max}\) = 0.1/0.7. Basically, all tests show a temperature increase of the UHPC samples. The characteristics of the curves indicate a strong dependence of the heating of the samples on the two load-dependent parameters. The diagram (a) of Figure 5 shows the curves for the lowest frequency of 3 Hz. At 3 Hz, a higher maximum temperature is reached with increasing maximum stress level. Not only the maximum temperature, but also the steepness of the curve of heating increases is maximally. At an upper load level s\({}_{\rm c,max}\) of 80% of concrete strength, the specimens failed during the temperature rise, which was in 2 of 3 cases nearly linear over the whole test. In these two trials, the specimens achieve both a temperature increase of less than 10 K. The failure occurred very early due to the high fatigue damage. At s\({}_{\rm c,ma}\) = 0.7, a maximum temperature difference of about 8 K was recorded after 20 to 25 thousand cycles. The temperature then remained almost constant. Two of three specimens reached the break-off criterion of 2 million load cycles without failure, where a minimal temperature drop could be noticed. At s\({}_{\rm c,max}\) = 0.6, the curves are similar to the 0.7 ones. However, the maximum temperature differences were with only 5 K even lower. Each test was finished after 2 million load changes as stated in Section 2.4. Figure 5: Temperature development of all UHPC 1 specimens for maximum stress level of 0.6, 0.7 and 0.8 (a) frequency of 3 Hz; (b) frequency of 10 Hz; (c) frequency of 20 Hz. The rise of the temperature curves was dependent on the maximum stress level also at 10 Hz, as can be seen in the diagram (b) of Figure 5. However, the temperature maxima achieved were significantly higher than for the slower loading. Again at s\({}_{\rm c,max}\) = 0.6 a maximum value was reached at approximately 80 thousand load cycles. From this point on, the temperature difference to the starting temperature of all three specimens remained at approximately 12 K and no failure of the test specimen occurred until the tests were stopped. All attempts with higher stress level shows a steady increase in temperature until failure. At s\({}_{\rm c,max}\) = 0.8, the increase was again the steepest, but the total temperature increase of round about 24 K (in average) was approximately 11 K less than the average value for cyclic loading with the mean level of s\({}_{\rm c,max}\) = 0.7. In addition, the tested 0.8 specimen failed already near 20 thousand load cycles, whereby the same temperature of the test specimens with s\({}_{\rm c,max}\) = 0.7 was first reached at a little under 50 thousand load cycles on average.