Numerisches Modell zur Beschreibung von Alkalientransport und AKR-induzierter Schädigung in Beton

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The goal of TP3 is the development of a computational model to predict ASR induced damage in concrete structures, specifically in concrete pavements for various environmental conditions, conditi-ons of degradation and types of concrete mixture. The numerical and analytical sub-models are developed and validated through close synergetic interaction with experimental sub-projects within the research group. The first phase of the project was concerned with modeling of the coupled transport of moisture and alkalis in intact and pre-damaged concrete. A multi-scale strategy based on continuum micromechanics for transport of pore-fluid and alkali in intact and pre-damaged concrete has been developed and implemented within the framework of a multiphase finite element method. The model has the capability to take into account the interactions of diffuse microcracks and the cement matrix. In contrast to existing models, the developed model confirms experimental observations for a threshold value for ion diffusivity. In the second phase, in addition to extending the transport model to take into account the influence of cyclic mechanical loads on alkali and fluid transport, the main focus will be on characterizing ASR induced damage. A modeling strategy similar to the first phase will be adopted, characterized by the adequate consideration of the spatial and temporal scales of the various transport and damage mechanisms. Through a micromechanical characterization of local damage in and around the reactive aggregate, at the macroscopic scale, the model should be capable of taking into account the influence of localized ASR induced damage processes through appropriate homogenization schemes as well as the inverse influence of external loads on micro-crack evolution. The combination of the transport and the ASR damage model and integration into a multifield finite element program will enable prognoses of the expected future degradation in concrete structures for various scenarios such as environmental conditions or the specific concrete mixture. In addition to model development and software design for durability predictions due to ASR, the project aims to gain a deeper understanding of the interactions between the effects (external cyclic loads, environmental factors) and the transport and damage processes in ASR affected concrete structures.