## 3 Results
### Temperature Decrease with and without Previous Fatigue Damage  
As explained under point 2.1., one aim of the investigations was to find out whether fatigue damage changes the temperature release capacity, i.e., also the thermal diffusivity of UHPC. For this purpose, the test specimens PK 1T to PK 3T were subjected to cyclic loading after cooling in the testing machine. The loading was continued until a target temperature (15, 25, or 30 \({}^{\circ}\)C, compare Table 1) was approximately reached. The generation of different temperatures required different numbers of load changes before the next stop and cooling. Thus, a different degree of pre-damage was ensured. In Figure 7, the upper diagram shows cooling without pre-damage for all three samples and the lower diagram shows cooling after cyclic loading. Again, both the absolute temperatures and the heating rates are shown. All displayed data were recorded by the sensors inside the specimen. Due to the long time required for the entire sample to cool down completely, the tests were stopped in very small ranges of the cooling rate. Figure 6: (**a**) Cooling of the PK 4T test specimen between the thermal insulation plates; (**b**) data of the sensors in the middle of the height of PK 2T in detail. The curves for PK 1T and PK 3T in Figure 7a show a very similar character, both in terms of heating rate and temperature. The cooling rates increase up to about 800 s in each sample. After reaching a maximum value, all curves dropped to the same extent in all experiments until the ambient temperature was reached. In Figure 7b, the temperature curves between the test specimens differ according as planned. As listed in Table 1, the target temperature at the start of the second cooling was deliberately chosen differently. A remark to cylinder PK 3T: During the cyclic loading, only a temperature difference of 28.5 K was achieved instead of the intended 30 K. Up to +28.5 K, there were considerably more load changes required than for the other samples. So, the test was stopped a bit earlier than planned because of the highly estimated risk of failure. For our investigation, the comparison of the temperature rates between the first and second cooling is decisive above all, not between the individual samples. The maximum cooling rates achieved were higher for samples with cyclic pre-damage. However, it must be taken into account that from the beginning there was already a difference between the internal and external temperature in the second cooling and thus the delay as in the first diagram does not occur. When heating up in the oven, the temperature in the core is lowest, which is exactly the opposite of the temperature gradient in the cross section when heating up due to fatigue load [21]. Figure 7: (**a**) Cooling inside test specimens after heating in oven; (**b**) Cooling inside test specimens after heating due to fatigue load. In addition, the fastest cooling rates were achieved at different absolute temperatures in the two scenarios. In order to eliminate the influence of temperature on thermal conductivity when comparing the results, the cooling speed for each test was determined at the same absolute temperature for the first and second cooling, as shown in the diagrams by the dotted lines for an absolute temperature of 40 \({}^{\circ}\)C as an example. Table 3 shows the values for each sample at 40 \({}^{\circ}\)C and at 30 \({}^{\circ}\)C.  
At 40 \({}^{\circ}\)C, inside the test specimen, only the PK 2T shows a clear change between the first and second cooling: The release rate after the cyclic loading was higher. In the PK 1T and PK 3T tests with approximately the same maximum heating, on the other hand, the values remained almost constant, where the values were slightly higher once for the first and once for the second cooling. In this regard it should be noted that these test specimens without significant changes were subjected considerably longer to cyclic loading than PK 2T.