Analysis of Time-variant Nano- and Microscopic Mechanisms for Modelling the Meso- and Macroscopic Segregation Stability of Concrete Subject to Vibration

混凝土结构中的创新加工技术，如3D打印或现代丝状混凝土结构，对所用混凝土的工作性提出了很高的要求。总体而言，混凝土施工的趋势总是朝着更柔软、更具流动性的混凝土发展。然而，混凝土的流动性和稳定性代表着相互竞争的需求，因为使用可流动混凝土增加了无意分离的风险。混凝土的流动行为和新鲜混凝土结构中由重力、泵压或振动能量等外力引起的细观和宏观分离形式(除氧、沉淀、水分分泌)构成了基于流变学的过程。流变性可以用连续相(液)和分散相(固)之间的相互作用来描述，这种相互作用取决于部分纳米级的颗粒形态、颗粒相互作用和连续相的化学性质。此外，还会发生与颗粒集合体的相互作用，这会对宏观层面产生影响。现有的描述水泥基悬浮液载荷-变形行为的模型方法是一个很有希望的基础。然而，这些都没有考虑来自微观结构的早期积累的水化产物的影响。为了描述载荷-变形行为和稳定性，现有的建模方法必须扩展到塑性成分，由早期水化产品的力学行为决定。识别纳米和微米尺度上的性质与可测量的流变性质之间的相关性是这一建议的基础。在加水后的规定时间内，载体流体的颗粒形态以及物理和电化学性质应以解析的方式确定。此外，还将研究这些纳米和微观特性如何影响粘结剂悬浮液的可测量流变性能。在混凝土浇注过程中产生的高剪应力会导致浆体相的流变特性发生重大变化，这将通过对悬浮液的结构破坏行为的描述来表示。除了糊相本身性质的影响外，它还特别影响糊相与晶间颗粒(集合体)之间的相互作用。这种相互作用将在典型的砂浆和混凝土调查中通过改变骨料的颗粒特性和通过改变级配曲线的结构来确定。由于实施了工作方案的多尺度结构，将确定所有相关因素，并将其作为概念模型的输入变量，以描述混凝土在振动影响期间的离析稳定性。

Innovative processing techniques in concrete construction, such as 3D printing or modern and filigree concrete structures, place high demands on the workability of the concrete used. In general, the trend in concrete construction is always towards softer and more flowable concrete. However, the flowability and the stability of a concrete represent competing demands, because the use of flowable concrete increases the risk of unintentional separation. The flow behaviour of the concrete and the meso and macroscopic forms of segregation (deaeration, sedimentation, water secretion) in fresh concrete structures, caused by external forces such as gravity, pump pressure or vibration energy, constitute rheology-based processes. The rheological behaviour can be described by the interactions between the continuous (liquid) and the dispersed (solid) phase which are dependent on the partially nanoscale particle morphology, the particle interactions and the chemical properties of the continuous phase. In addition, an interaction with granular aggregates occurs, which has an effect on the macroscopic level. The existing model approaches for describing the load-deformation behaviour for cementitious suspensions represent a promising basis. However, these do not take into account the influence of early-accumulating hydration products from the microstructure. For a description of the load-deformation behaviour and the stability, existing modelling approaches have to be extended by the plastic component, determined by the mechanical behaviour of early hydration products.The identification of the correlations between the properties on the nano- and microscale and the measurable rheological properties as a function of time represents the basis of this proposal. The particle morphology and the physical and electrochemical properties of the carrier fluid at defined times after the addition of water are to be determined analytically. In addition, how these nano- and microscopic characteristics affect measurable rheological properties of the binder suspension will be investigated. A high shear stress, as occurs during concrete casting during vibration effects, results in a significant change in the rheological properties of the paste phase that will be represented via the description of the structural breakdown behaviour of the suspension. Besides the resulting influence of the properties of the paste phase itself, it particularly influences the interaction between the paste phase and the intergranular particles (aggregates). This interaction will be identified during exemplary mortar and concrete investigations by varying the granulometric properties of the aggregate and by varying the structure of the graduation curve. Thanks to this implementation of the multiscale structure of the work programme, all relevant factors will be identified and will serve as input variables in a conceptual model to describe the segregation stability of concrete during vibration effects.