Leaner, more filigree, and resource-saving constructions are the development goal of the in the building industry. In reinforced concrete construction, a ultra-high strength concrete was developed to achieve these goals. Due to its use and requirements, this very pressure-resistant material is no longer only exposed to static loads. In applications such as wide-span bridges, machine foundations and wind turbines, the susceptibility to vibration is also significant. Research into the fatigue behavior of the new building material is therefore very important. In this article we will discuss the effect of heating up of high performance concretes under fatigue stress. The thesis is that warming up, which was already observed by several research groups, has an influence on the fatigue strength. Changes in the strength of the concrete or residual stresses generated by heating can lead to early failure. The aim is to find the reasons for the heating and the grade of influence on the fatigue strength. A systematic test program was developed to investigate the influencing parameters maximum stress level, frequency, and maximum grain size of the concrete. Thirty fatigue tests were carried out; the results will be presented here. The influence on the temperature increase as well as on the heating rate for the individual parameters will be discussed. The results show that all three discussed parameters have a significant influence on the temperature rise. Whereas the maximum temperature reached depends strongly on the frequency, the other two parameters mainly influence the heating rate.

Smarter, more filigree, and resource-saving buildings are the aim of developments in the construction industry. In reinforced concrete construction, ultra-high strength concretes have been developed to achieve these goals. Due to their use and requirements, these highly pressure-resistant materials are increasingly exposed to cyclically occurring and high-frequency loads. Examples of this are applications in long-span bridges or wind turbines. Research into the fatigue behaviour of the new construction material is therefore very important for the standardization and practical introduction of the high performance material. In this article, we want to investigate the heating process of ultra-high performance concrete (UHPC) under fatigue stress in more detail. In previous investigations in this project, an influence of the heating on the fatigue strength could be determined. A systematic parameter study has defined decisive load configurations for a maximum heating process. The aim is now to better understand the heating process. For this purpose, the temperature generation rate and the temperature release, which probably influences the overall temperature development, are investigated. A test program with eight experiments gives information about the temperature release during the experiment and the heating rate with and without pre-damage in the sample. In addition, the causes of failure caused by temperature are investigated with additional insulated tests. The results are presented, discussed, and conclusions are drawn in the article. For instance, fatigue damage affects the rate of temperature increase, but not the thermal conductivity of the material. In the different configurations, the test specimens essentially overlap at the maximum temperature reached in the inner test specimen. In addition to the assumed influence of the temperature gradients in the cross section as a cause of premature failure due to additional constraint stresses, the maximum temperature in particular turns out to be decisive, independent of the gradient.

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The heating up of high-performance concretes under fatigue load in cyclic pressure threshold test raises the question of the mechanisms and influences of this heat development. Of particular interest is how the heating affects the fatigue strength and what the causes of this are. In order to be able to answer this basically, two test series-one with an HPC and one with a UHPC-were carried out in which the temperature influence on the static compressive strength in a range of À25 C to 90 C was determined. In addition, different storage conditions are being considered in order to question previous findings. In this article, the state of the art is briefly presented and the test program based on it. Then, the production and storage of the specimen, their preparation and the used measurement technique are explained. The results obtained are presented with regard to concrete strength, type of storage, moisture content and, in the main part, the influence of temperature. A discussion of the results in relation to the state of knowledge follows. General insights are acquired, which will be very helpful for further work in the field of fatigue research on high performance concretes.

The heating of high‐performance concrete during high‐frequency cyclic loading strongly influences the fatigue strength and has a negative influence on them. This is particularly noticeable in fatigue tests for the standardization of high‐performance concretes. In order to understand the causes and to be able to consider the strength change, effects of different parameters have to be investigated. Both the loading speed and the applied fatigue stress have a strong influence on the speed of heating up. However, from measurements during fatigue tests result curves that show not only the temperature generation but also the temperature release, making it difficult to assess the individual aspects. For this reason, a purely measurement‐based method is being developed with which the cooling can be calculated continuously over the temperature curve and thus the pure heating can be determined. This enables a better understanding of the experiments carried out so far. In this paper, the previous test results are presented, and the evaluation method is explained and applied. This partially corrects the previous understanding of the parameters. The new findings from the evaluation method on the frequency influence are verified and confirmed with three additional tests with thermal insulation.