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

新拌混凝土的成型填充能力：依赖于时间和水化的方法

• 批准号: 387065993
• 负责人: Professor Dr.-Ing. Christoph Gehlen
• 金额: --
• 依托单位: Centrum Baustoffe und Materialprüfung (cbm)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/387065993?language=en
• 关键词: Form; filling; ability; fresh; concrete

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.

该项目的目的是分析新的胶凝材料（砂浆，混凝土）的模板填充能力，并提供一个基于流变模型的模板填充能力的数值模拟。该模型考虑到流变特性（触变性）随时间的变化及其对剪切速率的依赖性。流变参数是从初始材料的物理性质以及混合料组成推导出来的。流变参数屈服应力、粘度和触变性相对于SPP中心项目中规定的参考混合料而变化。通过适当调节混合物组成，每次仅改变一个流变参数。这种方法可以量化的流变参数，然后可以在流变model.To验证流变模型与模板填充能力的材料特性的影响，流变测量是伴随着调查的模板填充能力的砂浆和混凝土在箱形和L形模型formworks。流变模型在计算流体力学CFD中实现，以便数值计算材料在任何期望的模板中的流动和模板填充能力。该方法进一步发展，通过计算的流变输入参数的帮助下，老化壳颗粒相互作用模型（微观DEM）。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。这些过程与水泥体系的实验确定的时间依赖性流变行为有关，特别是触变结构的形成。然后将结果用作中尺度和放大尺度CFD建模的输入。因此，触变结构的形成包括在CFD模拟中，并与颗粒水平的过程和相互作用有关。因此，对模板填充能力的CFD模拟能够考虑混合物成分、材料性质和颗粒水平的水化过程的影响。通过设计满足最佳模板填充要求的测试混凝土组合物，证明了这种建模方法预测模板填充能力的能力。采用微观离散元模型结合CFD模拟计算了混凝土的充模能力，并与相应的试验结果进行了比较。