Open channel flow behaviour of concrete in the presence of obstacles and mechanisms of flow blockage (OCF-Blockage)

预测新混凝土是否可以填充给定的模板而不会留下大量空隙，并且不会分离，这对建筑行业非常重要。已经进行了大量的研究，其中研究了表单填充行为。几乎所有这些作品都有一个共同点，那就是他们专注于自密实混凝土（SCC），主要将混凝土视为具有宾厄姆特性的均匀（非分离）物质，并研究了非平稳条件。相反，在拟议的研究中，应在固定条件下研究可流动的普通混凝土。提出的项目的关键目标是模拟明渠流动和混凝土的堵塞行为。因此，将在明渠中检测障碍物-障碍物流动条件下的流动行为，并通过立体光学摄像系统进行监测，从而提供流动混凝土的基本信息以供评估，这代表了一种新方法。在这个项目中获得的结果将使我们能够更详细地了解混凝土何时以及如何发生堵塞，以及如何避免这种堵塞。结合计划I资助期的研究成果，将获得实际相关分离机制的完整图景（计划I：出血和沉淀；计划II：阻塞）。其次，通过在明渠中加入不同几何形态的障碍物，并研究这些障碍物的吞没情况，获得混凝土流变特性的信息。此信息可作为新混凝土验收测试的质量测试方法。工作计划的第一步是为实验开发开放的通道。在这里，提交者可以建立在广泛的初步工作，这将概述。在接下来的工作包中，研究了在流道中插入模型障碍物（如正方形或球形物体）和没有模型障碍物时的流动特性。我们的预试验清楚地表明，通过研究这些障碍物的吞噬行为，可以得出关于混凝土流变特性的结论。在接下来的步骤中，研究了障碍物对堵塞行为的影响。因此，重点放在研究哪种混凝土成分更有可能出现堵塞，以及如何根据混凝土的流变特性预测这种风险。最后，我们的目标是开发一个流变模型，一方面，混凝土的明渠流动行为可以被量化，并用于反向分析，以确定流变参数，如屈服应力和塑性粘度从明渠流动观察。该模型的第二部分包括基于水动力学的工程方法，旨在量化可能发生堵塞的风险。

The prediction, whether a fresh concrete can fill a given formwork without leaving substantial voids and without segregating is of great importance for the construction industry. Numerous studies have been carried out, in which the form filling behaviour was studied. Nearly all of these works have in common, that they were focussed on self-compacting concretes (SCC), primarily considered concrete as a homogeneous (non-segregated) substance having Bingham properties and investigated non-stationary conditions. Contrary, in the proposed study flowable ordinary concretes shall be studied under stationary conditions. The key goal of the proposed project is to model the open channel flow and blockage behaviour of concrete. Herefore, the flow behaviour will be examined in an open channel under obstacle-obstructed flow conditions and is monitored by a stereo-optical camera system, which provides the essential information of the flowing concrete for evaluation and represents a new method. The results to be obtained in this project will allow us to get a much more detailed understanding of when and how blockage of concrete occurs and how such a blockage can be avoided. Combined with the research results from funding period FP I, a complete picture of practically relevant segregation mechanisms (FP I: bleeding and sedimentation; FP II: blocking) will be obtained. Secondly, by incorporating obstacles with different geometrical configurations in the open channel and studying the engulfing of these obstacles, information on the rheological properties of the concrete shall be gained. This information can be used as a quality test method for acceptance testing of fresh concrete. The first step of the working programme consists in developing the open channel for the experiments. Here, the submitters can build up on extensive preliminary work, which will be outlined. In the following work package, the flow behaviour without and with model obstacles – such as square or spherical bodies – inserted in the flow channel is studied. Our pre-tests clearly show, that by studying the engulfing behaviour of these obstacles, conclusions on the rheological properties of the concrete can be drawn. In the subsequent step, the effect of obstacles onto the blockage behaviour is studied. The emphasis is hereby laid onto investigating which concrete compositions are more likely to exhibit blocking and how this risk can be predicted based on the rheological properties of the concrete. Finally, it is the goal to develop a rheological model with which on the one side the open channel flow behaviour of the concrete can be quantified and used for reverse analysis to determine rheological parameters such as yield stress and plastic viscosity from open channel flow observations. The second part of the model consists of a hydrodynamics-based engineering approach, which is intended to quantify the possible risk for blockage.