From micro to macro – fundamental concrete modelling considering local shear rate and microstructure inhomogeneities due to processing using a scale-bridging approach

从微观到宏观 â 基础混凝土建模考虑到由于使用尺度桥接方法进行处理而导致的局部剪切率和微观结构不均匀性

• 批准号: 451942209
• 负责人: Dr.-Ing. Inka Mai
• 金额: --
• 依托单位: Institut für Bauingenieurwesen
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/451942209?language=en
• 关键词: micro; macro; fundamental; concrete; modelling

During processing, e.g. pumping, concrete flow behaviour is determined by the rheological properties of the bulk material and the interface layer near the wall. Hence, modelling the macroscopic flow behaviour of concrete during processing requires a clear description of interface layer forming processes and of rheological properties of bulk and interface material. Therefore, the shear induced particle migration (SIPM) has to be taken into account as a dominating mechanism, with larger particles migrating to regions with lower shear rates. Another key issue is upscaling from cement paste to concrete modelling. Today, fundamental models are largely based on particle interactions and exist for cement paste only. However, existing concrete rheology models are largely based on continuum mechanics or DEM and validated based on empirical data. The goal of the present project is to investigate and model macroscopic concrete flow behaviour with regard to both, the influence of the interface layer at the wall and the chemical-physical particle interactions acting on cement paste. These are key issues for fundamental modelling of concrete rheology. To implement particle interactions in rheological models on macro scale, the challenge of upscaling from cement paste scale to the concrete scale has to be solved. As rheology of cement paste highly depends on its microstructure, which is mainly determined by the actual shear history, fundamental models must consider effects on microstructure formation. However, shear rates acting on cement paste at concrete level are significantly higher than the global shear rate. This so called local shear rate acting on cement paste in concrete is determined by particle packing and the relative velocity of two adjacent large particles. As larger particles are subject to SIPM, leading to largely inhomogeneous particle distributions at macro scale, the local shear rates are also varying depending e.g. on the actual solid fraction. Clearly, this inhomogeneity is more pronounced in the interface layer than in the bulk material. However, also the bulk system has to be considered as inhomogeneous, if the differences in global shear rates are prevalent.Therefore, the aim of the present project is the investigation and modelling of time- and shear-dependent microstructure and rheological properties of cementitious suspensions subjected to shear in a bottom up approach. In this project, the addressed key issues are a) SIPM, b) interface layer and its formation mechanisms, c) local shear rates induced by larger particles and d) its effect on microstructure and rheology taking particle-particle interactions into account. Only a scale-bridging approach from micro scale to macro scale enables to adequately achieve this goal, which will be realized utilizing experiments and numerical simulations.

在加工过程中，例如泵送，混凝土流动行为由散装材料和壁附近界面层的流变特性决定。因此，在加工过程中的混凝土的宏观流动行为建模需要一个清晰的描述界面层形成过程和流变性能的散装和界面材料。因此，剪切诱导颗粒迁移（SIPM）必须考虑作为一个主导机制，与较大的颗粒迁移到具有较低的剪切速率的区域。另一个关键问题是从水泥浆到混凝土模型的升级。今天，基本模型主要基于颗粒相互作用，并且仅存在于水泥浆体中。然而，现有的混凝土流变模型在很大程度上是基于连续介质力学或离散元法，并根据经验数据进行验证。本项目的目标是调查和模拟宏观混凝土流动行为方面的影响，界面层在墙上和化学-物理颗粒相互作用对水泥浆。这些都是混凝土流变学基本建模的关键问题。为了在宏观尺度上实现流变模型中的颗粒相互作用，必须解决从水泥浆尺度到混凝土尺度的升级挑战。由于水泥浆体的流变性在很大程度上取决于其微观结构，而微观结构主要由实际剪切历史决定，因此基本模型必须考虑微观结构形成的影响。然而，在混凝土水平上作用于水泥浆体的剪切速率显著高于整体剪切速率。作用于混凝土中水泥浆体的局部剪切速率由颗粒堆积和相邻两个大颗粒的相对速度决定。由于较大的颗粒受到SIPM的影响，导致宏观尺度上的颗粒分布很大程度上不均匀，因此局部剪切速率也会根据例如实际固体分数而变化。显然，这种不均匀性在界面层中比在体材料中更明显。然而，也散装系统被认为是不均匀的，如果在全球剪切速率的差异是prevalent.Therefore，本项目的目的是调查和建模的时间和剪切相关的微观结构和流变性能的水泥悬浮液剪切自下而上的方法。在这个项目中，解决的关键问题是a）SIPM，B）界面层及其形成机制，c）由较大颗粒引起的局部剪切速率和d）考虑颗粒-颗粒相互作用对微观结构和流变学的影响。只有从微观尺度到宏观尺度的尺度桥接方法才能充分实现这一目标，这将利用实验和数值模拟来实现。