## 4 Summary, Conclusion and Outlook  
In the first part of the presentation of the results, the experiments on temperature release are presented, in which the test specimens were only slightly fixed in the test setup until they were completely cooled down, after having been heated in an oven. It was shown that the temperature is released mainly via the surfaces of the steel load introduction plates. Thus, the reduction of the temperature in the centre of the concrete cylinders was faster than the reduction at the surface. When the heat was prevented from dissipating via the steel, homogeneous cooling occurred at all measuring points, but this now lasted twice as long as when cooling via steel and ambient air. The investigation of pre-damage influences by cyclic loading on the temperature release was carried out by heating via fatigue loading and renewed cooling under the same boundary conditions. Load cycle numbers of approx. 25%, 60%, and 90% of the mean load cycles from [24] under the same load parameters showed an influence on cooling only when the initial values of \(-0.94\times 10^{-2}\) K/s to \(-1.50\times 10^{-2}\) K/s were considered. This influence can be attributed to the changed thermal conductivity of concrete at different temperatures [20]. When comparing the temperature rates before and after loading and taking into account the different pre-damages, no systematic influence could be found if the comparison was carried out at the same absolute temperatures. The same experiments were used to investigate the influence of pre-damage on heat generation. In principle, all tests showed a significant increase in the heating rate after the cyclic preloading compared to the rate at the first loading. However, the pre-damage had no visible influence on the number of load cycles achieved. In comparison, the same maximum temperature difference of almost 50 K was noticed in all tests. The second loads remained, as the results in [22; 24], below the expected value according to fib Model Code 2010 [30] under this load configuration. This confirms the results in [22; 24] that the temperature is essentially related to premature failure. The verification of the assumption of temperature gradients in the cross section as an essential influencing factor was confirmed by comparing tests with different measured differences between inside and outside temperature. However, the reduction of the difference due to insulation showed that the gradient is not the only decisive factor. Insulation causes a reduced release capability via the environment, a minimized gradient and thus a faster and higher absolute temperature in UHPC. The samples with insulation failed faster than the non-insulated ones. The reason for this is considered to be the influence of temperature increase on the compressive strength of concrete. According to [31], a reduction for HPC was found with increasing temperature. If the strength is also reduced for UHPC, the related concrete stress would increase over the duration of the test. This would result in a faster damage accumulation and cause an earlier failure. A comparison of all test results of this test program shows that under the different test conditions, the failure temperatures inside the test specimen are all in similar ranges: 55 K for the insulated samples PK 7 TI/8 TI, 49 K for the samples PK 1T-3T (second fatigue loading after thermal pre-loading by heating in a furnace and by a first cyclic loading) and 45 K for the cylinders PK 5T/6T (single cyclical exposure without insulation). Under the parameter configuration investigated here, a type of failure temperature can be assumed for the used UHPC. If the results of the temperature release tests are related to the tests with and without insulation, assumptions can be made about the influence of cooling on the heating process. Although the temperature is also clearly dissipated via the steel plates, a temperature reduction via the ambient atmosphere already changes the heating rate significantly.