Degradation processes in high-strength concrete due to multistage compressive fatigue loading

• Applicant: Dr.-Ing. Nadja Oneschkow
• Subject Area: Construction Material Sciences, Chemistry, Building Physics ; Applied Mechanics, Statics and Dynamics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 514560569

It is well-known from literature that multistage compressive fatigue loading of concrete can lead to sequence effects which are insufficiently approximated by the damage accumulation hypothesis of Palmgren-Miner. The application of the Palmgren-Miner-hypothesis in the fatigue design of concrete can lead to unsafe results. Concurrently, only few investigations are documented which focused on the underlying degradation processes. Thus, the degradation processes are not yet understood. Furthermore, the data basis available for the development of efficient modelling approaches which allow for the prediction of the fatigue behaviour is currently not sufficient. In this project, the degradation processes in high-strength concrete due to multistage compressive fatigue loading are investigated. The objectives of this project are the determination and understanding of the particular mechanisms of the degradation processes due to multistage compressive fatigue loading leading to the development of a model conception and the modification of the Palmgren-Miner-approach based on the new findings. Specifics of the degradation processes are made visible and are determined in multistage compressive fatigue experiments. Within this project, the focus lies on three selected aspects of multistage fatigue loading: (i) sequence effect of different maximum stresses, (ii) different conditions of microstructure at change of loading and (ii) change of the test frequency (rate dependency). Using a cross-scale damage analysis, the measured damage indicators are analysed together with visualisations of damage in the microstructure (microscopy) leading to new knowledge concerning the ongoing damage processes in addition to the already available knowledge concerning onestage fatigue loading. Based on the new findings a model conception concerning the cross-scaled damage processes in concrete microstructure is further developed and the Palmgren-Miner hypothesis is examined and adjusted. Furthermore, the collected data will serve as basis for the development of efficient concrete fatigue damage models which not only allow for the description but also for the prediction of the concrete fatigue behaviour.

• DFG Programme: Research Grants