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

TP 3的目标是开发一个计算模型，以预测混凝土结构中ASR引起的损坏，特别是在各种环境条件下，降解条件和混凝土混合物类型的混凝土路面。数值和分析子模型的开发和验证，通过密切的协同互动与实验小组内的子项目。该项目的第一阶段是关于完整的和预损坏的混凝土中的水分和碱的耦合传输的建模。一个多尺度的战略，连续微观力学的基础上运输的孔隙流体和碱在完整的和预损伤混凝土已开发和实施的框架内的多相有限元法。该模型具有考虑扩散微裂纹和水泥基体相互作用的能力。与现有的模型相比，所开发的模型证实了实验观察的离子扩散率的阈值。在第二阶段，除了扩展运输模型，考虑到循环机械负荷对碱和流体运输的影响，主要重点将是表征ASR引起的损害。将采用与第一阶段类似的建模策略，其特点是充分考虑各种运输和损害机制的空间和时间尺度。通过微观力学表征的局部损伤和周围的反应性聚集体，在宏观尺度上，该模型应该能够考虑到本地化的ASR引起的损伤过程的影响，通过适当的均匀化方案，以及外部载荷的逆影响微裂纹的演变。运输和ASR损伤模型的组合和集成到多场有限元程序中，将使混凝土结构在各种情况下，如环境条件或特定的混凝土混合物的预期未来退化的预测。除了用于ASR耐久性预测的模型开发和软件设计外，该项目还旨在更深入地了解受ASR影响的混凝土结构中的影响（外部循环荷载，环境因素）与运输和损坏过程之间的相互作用。

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.