## 3 Results
### Heating Rate of the Concrete  
The steepness of the warming up curves can be used to estimate how strong the increase in temperature was during the test. In order to quantify this heating rate, the heating curves can be derived. This was done for the attempts at \(\mathrm{s_{c,max}}\) = 0.7 for the UHPC 1 concerning both the number of load cycles and the duration. Figure 8 shows the speed of the temperature increase for one attempt each at 3 Hz, 10 Hz and 20 Hz. As an example, the test that reached the temperature in the middle of the respective configuration was selected for the representation. The diagram (a) in Figure 8 shows the rates of temperature increase per load cycle. The fastest rise of \(10^{-3}\) K/lc was recorded in the attempt with the lowest total temperature difference reached at 3 Hz. It was measured directly at the beginning of the test. In relation to a load change, more force is applied to the test specimen over time as the length of the load change increases. For 3 Hz, the longest force application is generated with 1/3 s. The speed of the temperature increase decreased rapidly afterwards. After 1,500 load cycles the point of overlap with the 10 Hz curve is reached, and after 4,150 load cycles with the 20 Hz curve. Additionally, with regard to the number of load cycles, the heating per load cycle was therefore quickly at its slowest at the lowest test frequency. After only 0.25% of the total number of load changes, this speed has already halved. The regressive curve reaches the value 0 after 75 thousand load cycles. This means that no further heating of the test specimen occurred after less than 4% of the total number of load cycles up to the break-off criterion. The experiment with 10 Hz had its maximum heating speed also at the beginning of the attempt with 0.8\(\cdot\)10\({}^{-3}\) K/lc. Then, the course did not drop to 0, though, rather at 0.35\(\cdot\)10\({}^{-3}\) K/lc a turning point after about two thirds of the overall course was reached and the heating speed increased again. The warming rate decrease at the beginning was noticeably lower than at 3 Hz and during the first 15 thousand load changes nearly linear with 1.67\(\cdot\)10\({}^{-8}\) K/lc\({}^{2}\). The increase in heating velocity was particularly strong during the last 10% of the experiment. The specimen failed at a heating speed of 0.7\(\cdot\)10\({}^{-3}\) K/lc before the initial value was reached again. Figure 8: Heating rate of UHPC 1 specimens for test frequency \(\mathrm{f_{P}}\) = 3 Hz, \(\mathrm{f_{P}}\) = 10 Hz and \(\mathrm{f_{P}}\) = 20 Hz and relation between lower and upper stress level \(\mathrm{S_{c,min}}\)/\(\mathrm{S_{c,max}}\) = 0.1/0.7, (**a**) related to the load cycles (**c**); (**b**) related to the time (s). In contrast to 10 Hz, the maximum heating speed was reached at 20 Hz for all evaluated samples that failed before the break-off criterion; the maximum speed of the temperature increase was reached immediately before the failure. In relation to the number of load changes, the rate of warming at the start is lowest with 0.5\(\cdot\)10\({}^{-3}\) K/lc. However, this starting velocity did not decrease during the test. The curve shows two turning points. After 12 thousand of 70.7 thousand load changes, a first maximum of 0.6\(\cdot\)10\({}^{-3}\) K/lc is reached. Then the speed decreased until the start value was reached again. From 12 thousand load changes, compared to the other frequencies resp. load speeds, the highest warming speed per load cycle at 20 Hz was also permanently recorded. Immediately before failure, the heating rate was 0.76\(\cdot\)10\({}^{-3}\) K/lc. The diagram (b) in Figure 8 shows the same attempts. This case, however, the heating rate is displayed in relation to the test duration in seconds instead of load cycles. The curve characteristics remain the same like described before for diagram (a). Due to the changed reference value on the X-axis, the curves are significantly compressed and stretched.