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

预测新拌混凝土是否能够填充给定的模板而不留下大量的空隙并且不分离对于建筑行业是非常重要的。已经进行了许多研究，其中研究了形式填充行为。几乎所有这些作品都有一个共同点，即它们都集中在自密实混凝土（SCC）上，主要认为混凝土是一种具有宾汉性质的均匀（非隔离）物质，并研究了非稳态条件。相反，在拟定的研究中，应在静止条件下研究可流动的普通混凝土。拟议项目的主要目标是模拟明渠水流和混凝土堵塞行为。因此，流动行为将在一个开放的渠道障碍物阻塞的流动条件下进行检查，并通过立体光学摄像系统进行监测，它提供了流动的混凝土的基本信息进行评估，并代表了一种新的方法。在这个项目中获得的结果将使我们能够更详细地了解何时以及如何发生混凝土堵塞以及如何避免这种堵塞。结合资助期FP I的研究结果，将获得实际相关隔离机制（FP I：出血和沉淀; FP II：阻塞）的完整图片。其次，通过在明渠中加入不同几何形状的障碍物并研究这些障碍物的吞没，可以获得混凝土流变特性的信息。该信息可用作新拌混凝土验收测试的质量测试方法。工作方案的第一步是为试验开辟公开渠道。在这里，提交者可以建立在广泛的初步工作，这将概述。在下面的工作包中，研究了在流道中插入模型障碍物（如方形或球形物体）时的流动行为。我们的预测试清楚地表明，通过研究这些障碍物的吞没行为，可以得出关于混凝土流变性能的结论。在随后的步骤中，障碍物对阻塞行为的影响进行了研究。因此，重点放在调查哪些混凝土组合物更有可能表现出阻塞，以及如何可以预测这种风险的基础上的混凝土的流变性能。最后，它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一个基于流体动力学的工程方法，旨在量化可能的堵塞风险。

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.