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

存在障碍物时混凝土的明渠流动行为和流动阻塞（OCF 阻塞）机制

• 批准号: 452024049
• 负责人: Professor Dr.-Ing. Michael Haist
• 金额: --
• 依托单位: Institut für Baustoffe
• 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/452024049?language=en
• 关键词: Open; channel; flow; behaviour; concrete

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.

对于建筑业来说，新混凝土能否在不留下大量空隙和不分离的情况下填充给定的模板是非常重要的预测。已经进行了大量的研究，其中研究了表格填写行为。几乎所有这些工作的共同点是，他们都专注于自密实混凝土(SCC)，主要认为混凝土是一种具有宾汉特性的均质(非隔离)物质，并研究了非静态条件。相反，在拟议的研究中，流动型普通混凝土应在静止条件下进行研究。拟议项目的主要目标是对混凝土的明渠流动和堵塞行为进行建模。因此，采用立体光学摄像系统对明渠在有障碍物条件下的流动特性进行检测，为评价流动混凝土提供必要的信息，是一种新的方法。这项工程所取得的成果，将使我们更详细地了解混凝土堵塞的时间和方式，以及如何避免这种堵塞。结合资助期FP I的研究结果，将全面了解实际相关的分离机制(FP I：出血和沉淀；FP II：堵塞)。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过程，可以获得混凝土的流变性信息。这些信息可作为新拌混凝土验收检验的质量检验方法。工作方案的第一步是为试验开辟开放渠道。在这里，提交者可以在广泛的前期工作的基础上进行积累，这些工作将被概述。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)时的流动特性。我们的预试验清楚地表明，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的结论。在随后的步骤中，研究了障碍物对堵塞行为的影响。因此，重点是调查哪些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性来预测这种风险。最后，我们的目标是开发一种流变模型，利用该模型一方面可以量化混凝土的明渠流动行为，并用于反向分析，以根据明渠流动观测确定屈服应力和塑性粘度等流变参数。模型的第二部分包括一种基于流体力学的工程方法，其目的是量化可能的堵塞风险。