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

混凝土施工中的创新加工技术，如3D打印或现代和细丝混凝土结构，对所用混凝土的可加工性提出了很高的要求。总的来说，混凝土施工的趋势总是朝着更柔软、更易流动的混凝土发展。然而，混凝土的流动性和稳定性代表了相互竞争的需求，因为使用可流动混凝土会增加意外分离的风险。混凝土的流动行为以及新混凝土结构中由重力、泵压力或振动能量等外力引起的中观和宏观形式的离析（脱氢、沉降、水分泌）构成了基于流变学的过程。流变行为可以通过连续相（液体）和分散相（固体）之间的相互作用来描述，这种相互作用部分取决于纳米级颗粒形态、颗粒相互作用和连续相的化学性质。此外，还与颗粒聚集体发生相互作用，对宏观水平产生影响。现有的描述胶凝悬浮物荷载-变形特性的模型方法具有良好的基础。然而，这些都没有从微观结构上考虑早期水化产物的影响。为了描述载荷变形行为和稳定性，现有的建模方法必须由早期水化产物的机械行为决定的塑性成分扩展。确定纳米和微观尺度上的性质与可测量的流变性能作为时间函数之间的相关性是本建议的基础。在加水后，载液在规定时间内的颗粒形态和物理及电化学性质将用解析法测定。此外，这些纳米和微观特征如何影响粘合剂悬浮液的可测量流变特性将被研究。在混凝土浇筑过程中，在振动作用下产生的高剪切应力会导致膏体阶段流变特性的显著变化，这将通过悬浮液的结构破坏行为的描述来表示。除了膏体相本身性质的影响外，它还特别影响膏体相与粒间颗粒（聚集体）之间的相互作用。这种相互作用将通过改变骨料的粒度特性和改变分级曲线的结构，在砂浆和混凝土的示范研究中被识别出来。由于工作方案的这种多尺度结构的实施，所有相关因素都将被确定，并将作为概念模型的输入变量，以描述振动作用下混凝土的离析稳定性。

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.