Scale-bridging Modeling of Microstructural Changes in Concrete and Damage Analysis of Concrete Structures for the Identification of Coda Signals

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The high sensitivity of the coda waves to weak microstructural changes in concrete opens the perspective to identify early-stage damage events that precede macrocracking and severe failure of concrete structures. Detecting such precursor damage in concrete and reinforced concrete structures can serve as an early warning system to take precautionary retrofitting measures to avoid expenses for extensive rehabilitation of engineering infrastructure. However, the state of the coda wave technology for the assessment of the structural integrity of concrete structures is at its early stages. Within the framework of this Research Group FOR 2825, the objective of Subproject RUB1 is to establish a model-based characterization of the degradation of concrete at multiple scales and to enable a classification of the level of damage using simulated and measured coda data. In the first phase of the project, RUB1 developed a tool to generate realistic concrete microstructures and a multiscale reduced-order model for simulating concrete damage. Synthetic coda waves obtained from sampling the virtual concrete specimens were used to train a classifier and to identify specific stages of microstructural changes such as reversible deformation, distributed microcracking and localized macrocracks. In the second phase of the project, first the reduced-order multiscale model for damage simulation will be extended to consider environmental loads such as temperature and moisture. Second, the material scale damage classifier will be extended and enhanced with additional attributes to filter environmental and boundary effects. The third major area of focus is the transfer of coda-characteristics (damage-class and loading-type identifiers) derived at the material scale and specimen scale to the structural scale. Finally, the capability of the model-based framework for the identification of damage will be validated by application to the demonstrator projects.