Simulation based modelling of time- and shear-dependent disperse and rheological properties of cement suspensions

该项目的目的是开发增强的本构模型，用于基于化学和物理颗粒和流体特性预测胶凝材料的流变性。由于其基本基础，该建模方法显示出普遍的有效性和适用性。该项目在纳米和微观尺度的化学和物理过程的基本见解与宏观流动行为之间架起了一座桥梁，为克服现有本构流变模型的局限性做出了贡献。因此，即使对于具有时变剪切历史的复杂处理步骤，如泵送、3D打印或喷涂，也能够更可靠地模拟和建模混凝土流动。为此，在CFD-DEM耦合模拟的帮助下，基于基本材料性质和相互作用，研究和模拟了水泥基悬浮液的时间和剪切相关的分散和流变特性。在模拟的帮助下，首次能够全面地模拟取决于众多化学和物理颗粒以及流体特性、混合物组成和工艺参数的基本相互作用。建立了新的含时接触模型，并将其用于CFD-DEM耦合数值模拟。通过不同的实验对仿真环境的结果进行了标定和验证。与其他工作组合作，研究了与模拟相关的颗粒和流体的性质。因此，使用了不同的反应性和非反应性技术和模型颗粒系统。对悬浮液的分散性和流变性进行了全面的表征。通过旋转和振荡流变仪试验研究了相关的颗粒和流体特性。微观结构对流变性的影响可以用颗粒团聚行为来描述。因此，在考虑和不考虑水化效应的情况下，不同剪切速率、不同时间步长和不同剪切历史下的凝聚状态和流变性是表征的。在剪切条件下，用激光背向散射法测量了浆体的粒度分布和团聚状态，并将其集成到新的同轴圆柱式流变仪中。在模拟和实验结果的基础上，将时间和剪切相关的微结构效应引入到现有的本构模型中，从而能够考虑水泥水化的触变效应和老化效应。作为本构模型和多尺度模型的关键参数，将特别关注作用于膏体相的局部剪切率的确定。该方法能够为微观尺度的模拟和实验捕捉真实的剪切参数，从而允许更可靠的放大和建模。

The aim of the project is to develop enhanced constitutive models for the prediction of rheological properties of cementitious materials based on chemical and physical particle and fluid characteristics. Due to its fundamental basis the modelling approach exhibits a general validity and applicability. Bridging the gap between fundamental insights into chemical and physical processes at nano as well as micro scale and the macroscopic flow behavior, the project makes a contribution for overcoming limitations of existing constitutive rheological models. Thereby, a more reliable simulation and modelling of concrete flow even for complex processing steps with time-variant shear history, such as pumping, 3D printing or spraying, is enabled. To that end, the time- and shear-dependent disperse and rheological properties of cementitious suspensions are investigated and modelled based on fundamental material properties and interactions with the help of coupled CFD-DEM simulations. With the help of the simulations, the basic interactions depending on numerous chemical and physical particles and fluid characteristics, mixture composition and processing parameters can be modelled comprehensively for the first time. New time-dependent contact models are developed and used for the coupled CFD-DEM simulations. The results of the simulation environment are calibrated and validated by different experiments. The properties of particles and fluid relevant for the simulations are investigated in cooperation with other working groups. Therefore, different reacting and non-reacting technical and model particulate systems are used. The disperse and the rheological properties of the suspensions are characterized comprehensively. Relevant particle and fluid characteristics are investigated by rotational and oscillation rheometer tests. The microstructure effect on the rheological properties is described by the particle agglomeration behavior. Therefore, the agglomeration state and the rheological properties are characterized for different shear rates, time steps and shear histories with and without regard for hydration effects. The particle size distribution and the agglomeration state of the pastes are determined under shear conditions by a laser backscattering method integrated into a new coaxial cylinders rheometer setup. Based on the simulation and experimental results the time- and shear-dependent microstructure effects are implemented into existing constitutive models enabling the consideration of thixotropic effects and ageing effects due to cement hydration. Being a key parameter for constitutive models and multi-scale modelling, a special focus will be on the determination of local shear rates acting on the paste phase. The approach enables to capture realistic shear parameters for the simulations and experiments at micro scale, hence allowing a more reliable scale-up and modelling.