Flow-induced particle migration in cement-based materials at high shear rates

高剪切速率下水泥基材料中流动引起的颗粒迁移

• 批准号: 387095311
• 负责人: Professor Dr.-Ing. Viktor Mechtcherine
• 金额: --
• 依托单位: Institut für Baustoffe
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/387095311?language=en
• 关键词: Flow; induced; particle; migration; cement

The flow of heterogeneous, cementitious suspensions at high shear rates induced by pumping is a complex process greatly influenced by material composition and its ability to generate a lubricating layer (LL) which reduces the friction at the pipe wall-to-concrete interface. Pumping behaviour depends both on the rheological properties and the thickness of such lubrication layer and on the rheological properties of the concrete bulk. The formation of the lubricating layer is mostly related to flow-induced particle migration (FIPM) under high shear rates. To date there are no in-depth insights on FIPM in concrete under high shear rates and its effect on lubricating layer formation; existing investigation approaches are insufficient. The project at hand is to enable the attaining of a clear understanding of causality and underlying mechanisms of FIPM in concrete and eventually to apply this knowledge to realistic description and prediction of pumping process. The consequences of FIPM on the formation of LL and on the resulting material flow behaviour, with the focus on pumpability, are to be established as the basis for purposeful analysis of the concrete pumping process and its implementation in numerical simulation. These main objectives will be accomplished stepwise by first developing adequate approaches for experimental coverage, fundamental analysis and description of particle migration in concrete at high shear rates followed by experimental investigation of the effects of rheological properties of the suspending medium, i.e., paste of cement and fines, on FIPM. Next, the effects of particle size shape, size distribution and packing density on FIPM will investigated and the analysis of cause-effect relationships between particle migration, formation of LL, flow pattern and pressure-flow rate function will be performed. The obtained data and insights will be then used for developing a numerical representation of FIPM for CFD analysis, which will be applied in predicting the pumping behaviour of concrete in the pipeline. For validation the results of full-scale pumping experiments performed in an earlier research project will be used. Accordingly, the work program is comprised of a comprehensive combination of appropriate experimental methods, novel measuring techniques and new approaches to mimic particle migration adequately, enriched by a strong link to numerical simulation. It consists of three segments: 1) experimental investigations focusing on the qualitative and quantitative analysis of FIPM, formation of LL, and the rheological properties of LL and concrete bulk; 2) numerical simulation based on implementation of the FIPM into existing CFD-model to calculate the thickness and rheological properties of LL and, consequently, of pumping behaviour; 3) consideration of the pumping process, in which the prediction of concrete flow can be compared with the available results of full-scale pumping experiments.

泵送引起的非均质胶凝悬浮液以高剪切速率流动是一个复杂的过程，受材料成分及其产生润滑层（LL）的能力的很大影响，LL可以减少管壁与混凝土界面的摩擦。泵送行为取决于流变特性和这种润滑层的厚度以及混凝土体的流变特性。润滑油层的形成主要与高剪切速率下的流致颗粒迁移有关。到目前为止，还没有深入了解高剪切速率下混凝土中的FIPM及其对润滑层形成的影响；现有的调查方法是不够的。目前的项目是使人们能够清楚地了解具体的FIPM的因果关系和潜在机制，并最终将这些知识应用于抽水过程的实际描述和预测。FIPM对LL的形成和由此产生的物质流动行为的影响，重点是可泵性，将作为有目的分析混凝土泵送过程及其在数值模拟中的实施的基础。这些主要目标将通过首先开发足够的实验覆盖方法，基本分析和描述高剪切速率下混凝土中的颗粒迁移，然后对悬浮介质（即水泥膏体和细粉）流变特性对FIPM的影响进行实验研究来逐步实现。接下来，将研究粒径形状、粒径分布和堆积密度对FIPM的影响，并分析颗粒迁移、LL形成、流型和压力-流量函数之间的因果关系。获得的数据和见解将用于开发FIPM的数值表示，用于CFD分析，这将用于预测管道中混凝土的泵送行为。为了验证在早期研究项目中进行的全尺寸泵实验的结果，将使用。因此，工作计划包括适当的实验方法，新颖的测量技术和充分模拟粒子迁移的新方法的综合组合，并通过与数值模拟的紧密联系来丰富。包括三个部分：1)实验研究，重点是FIPM的定性和定量分析，LL的形成，LL和混凝土体的流变特性；2)基于FIPM在现有cfd模型中实现的数值模拟，以计算LL的厚度和流变特性，从而计算泵送行为；3)考虑泵送过程，其中混凝土流动的预测可以与全尺寸泵送实验的现有结果进行比较。