Form filling ability of fresh concrete: A time and hydration dependent approach

本项目旨在分析新鲜胶凝材料（砂浆、混凝土）的模板填充能力，并基于流变模型提供模板填充能力的数值模拟。该模型考虑了流变特性（触变性）随时间的变化及其对水化过程引起的剪切速率的依赖。流变参数来源于初始材料的物理性质以及混合成分。流变参数屈服应力、粘度和触变性根据SPP中心项目中指定的参考混合物而变化。通过适当调整混合料组成，一次只改变一个流变参数。这种方法可以量化材料特性对流变参数的影响，然后可以在流变模型中实现。为了验证关于模板填充能力的流变学模型，流变学测量与砂浆和混凝土在箱型和l型模型模板中的填充能力的研究相结合。在计算流体力学CFD中引入流变模型，以便对任意模板中材料的流动和填模能力进行数值计算。利用老化壳粒子相互作用模型（micro DEM）计算流变输入参数，进一步发展了该方法。微观DEM模型在颗粒水平上模拟了水泥水化休眠阶段发生的过程。这些过程与实验确定的胶凝体系的随时间变化的流变行为有关，特别是触变结构的形成。然后将结果用作中观和放大CFD建模的输入。因此，触变结构的形成包含在CFD模拟中，并与粒子水平上的过程和相互作用有关。因此，模板填充能力的CFD模拟可以在颗粒水平上考虑到混合成分、材料特性和水化过程的影响。通过设计一个满足最佳模板填充要求的试验混凝土组合，证明了这种建模方法仅从配合比来预测模板填充能力的能力。采用微型DEM模型，结合升级后的CFD模拟计算了混凝土的模板填充能力，并与相应的试验结果进行了比较。

The project aims to analyse the formwork filling ability of fresh cementitious materials (mortar, concrete) and provide a numerical simulation of formwork filling ability based on a rheological model. The model takes changes in the rheological properties (thixotropy) with time and their dependence on shear rate due to hydration processes into account. The rheological parameters are derived from the physical properties of the initial materials as well as mix composition.The rheological parameters yield stress, viscosity and thixotropy are varied with respect to a reference mix specified in the SPP central project. By suitable adjustment of the mix composition, only one rheological parameter at a time is varied. This approach enables quantification of the effect of material characteristics on the rheological parameters which can then implemented in a rheological model.In order to verify the rheological model with regard to formwork filling ability, the rheological measurements are accompanied by investigations of the formwork filling ability of mortar and concrete in box and L-shaped model formworks. The rheological model is implemented in computation fluid dynamics CFD in order to numerically calculate the flow and formwork filling ability of the material in any desired formwork. This method is developed further by calculating the rheological input parameters with the help of an aging shell particle interaction model (micro DEM). The micro DEM model simulates the processes occurring during the dormant phase of cement hydration at the particle level. These processes are related to the experimentally determined, time-dependent rheological behaviour of the cementitious systems, in particular the formation of thixotropic structures. The results are then used as input for the meso and up-scaled CFD modelling. Thus the formation of thixotropic structures is included in the CFD simulation and related to the processes and interactions at the particle level. The CFD simulation of formwork filling ability is therefore able to take the effects of mix composition, material properties and hydration processes at the particle level into account. The ability of this modelling approach to predict formwork filling ability from the mix composition alone is demonstrated by designing a test concrete composition which fulfils the requirements for optimum formwork filling. The formwork filling ability of the concrete is computed using the micro DEM model with the upscaled CFD simulation and compared with the corresponding test result.