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.

该项目旨在分析新拌水泥基材料（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）随时间的变化以及水合过程对剪切速率的依赖性。流变参数源自初始材料的物理特性以及混合物成分。流变参数屈服应力、粘度和触变性相对于 SPP 中央项目中指定的参考混合物而变化。通过适当调整混合成分，一次仅改变一个流变参数。这种方法能够量化材料特性对流变参数的影响，然后在流变模型中实现。为了验证流变模型在模板填充能力方面的效果，在流变测量的同时还研究了箱形和 L 形模型模板中砂浆和混凝土的模板填充能力。流变模型在计算流体动力学 CFD 中实现，以便对任何所需模板中材料的流动和模板填充能力进行数值计算。通过借助老化壳颗粒相互作用模型（微型 DEM）计算流变输入参数，进一步发展了该方法。微型 DEM 模型模拟了颗粒水平上水泥水化休眠阶段发生的过程。这些过程与实验确定的、随时间变化的水泥体系流变行为有关，特别是触变结构的形成。然后将结果用作细观和放大 CFD 建模的输入。因此，触变结构的形成包含在 CFD 模拟中，并且与颗粒水平的过程和相互作用相关。因此，模板填充能力的 CFD 模拟能够在颗粒水平上考虑混合物成分、材料特性和水化过程的影响。通过设计满足最佳模板填充要求的测试混凝土成分，证明了这种建模方法仅根据混合成分预测模板填充能力的能力。使用微型 DEM 模型和放大的 CFD 模拟计算混凝土的模板填充能力，并与相应的测试结果进行比较。