Internal dynamics in concrete and model systems of concrete: 3D particle tracking, flow and concentration profiles.

混凝土内部动力学和混凝土模型系统：3D 粒子跟踪、流量和浓度分布。

• 批准号: 387100398
• 负责人: Dr. Günter K. Auernhammer
• 金额: --
• 依托单位: Institut Physikalische Chemie und Physik der Polymere
• 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 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/387100398?language=en
• 关键词: Internal; dynamics; concrete; model; systems

The flow of concrete is of enormous importance in the modern building technology. Despite intense studies over the last decades, still many fundamental questions concerning understanding of the flow process are still under debate. Cementitious materials (cement pastes, mortars and concrete) are suspensions of particles with a size distribution that spans several orders of magnitude (ranging from nano-metric additives over micro-metric cement particles to milli-metric sand and gravel particles). These particles have very specific influences on the flow properties, even in simple situations, like the flow of a model mortar containing only cement nd sand particles during the dormant period of the hydration reaction. The aggregation of the cement particles generates a yield stress that has to be overcome to allow flow. When the concrete is flowing the concentration of the sand particles is reduced close to walls, due to flow-induced particle migration. The combination of both processes leads to the formation of a plug-like shear profile, with a thin strongly sheared lubrication layer close to the walls. Spatially highly resolved optical studies of this process are naturally hindered by the opacity of cementitious materials. The aim of the proposed project is to elucidate the interplay between the processes behind the formation of a lubrication layer. To do so, a highly transparent model system shall be developed and carefully cross-checked to exhibit all relevant properties of real cementitious material (particle interactions and concentrations, density difference, macroscopic flow properties and flow profiles). Such a model system will then allow the investigation with high spatial and temporal resolution. We will apply non-destructive and fast 3D imaging techniques and use single particle tracking at two length scales. The flow of the sheared model cement paste (particle diameter typically between 10 µm and 50 µm) will be investigated by high-speed confocal microscopy. This will result in series of 3D images from which the trajectories of almost all particles can be extracted. The knowledge of the particle trajectories allows to elucidate the relation between particle interaction, flow profile and size and structure of the aggregates. The analysis of the motion of sand particles follows similar lines. However, the imaging technique will be different. A thin laser sheet will be used to illuminate and image the sample layer by layer. Within the SPP we will validate our experimental approach through comparisons to other experimental and theoretical groups in the program. Our experimental approach will be enhanced through the exchange of results between the different groups and combination of experimental methods on the same sample. We intend to provide insight in the interplay between the different processes behind the formation of a lubrication layer.

混凝土的流动性在现代建筑技术中非常重要。尽管在过去的几十年里进行了深入的研究，但仍然有许多关于流动过程的基本问题仍在争论中。胶凝材料（水泥浆、砂浆和混凝土）是颗粒的悬浮液，其尺寸分布跨越几个数量级（从纳米添加剂到微米水泥颗粒到毫米沙子和砾石颗粒）。这些颗粒对流动性能具有非常具体的影响，即使在简单的情况下，如在水合反应的休眠期期间仅包含水泥和砂颗粒的模型砂浆的流动。水泥颗粒的聚集产生屈服应力，必须克服该屈服应力以允许流动。当混凝土流动时，由于流动引起的颗粒迁移，靠近壁的砂粒浓度降低。这两个过程的结合导致形成一个塞状剪切剖面，与薄的强烈剪切润滑层接近的墙壁。空间高分辨率的光学研究，这一进程自然阻碍了水泥材料的不透明性。拟议项目的目的是阐明润滑层形成背后的过程之间的相互作用。为此，应开发高度透明的模型系统，并仔细进行交叉检查，以显示真实的胶凝材料的所有相关特性（颗粒相互作用和浓度、密度差、宏观流动特性和流动剖面）。这样的模型系统将允许以高空间和时间分辨率进行调查。我们将应用非破坏性和快速3D成像技术，并在两个长度尺度上使用单粒子跟踪。将通过高速共聚焦显微镜研究剪切模型水泥浆（粒径通常在10 µm和50 µm之间）的流动。这将产生一系列3D图像，从中可以提取几乎所有粒子的轨迹。颗粒轨迹的知识允许阐明颗粒相互作用、流动剖面和聚集体的尺寸和结构之间的关系。对沙粒运动的分析也遵循类似的思路。然而，成像技术将是不同的。 将使用薄激光片逐层照射样品并成像。在SPP中，我们将通过与该计划中的其他实验和理论组进行比较来验证我们的实验方法。我们的实验方法将通过不同小组之间的结果交流和对同一样品的实验方法的组合得到加强。我们打算提供洞察力的润滑层的形成背后的不同过程之间的相互作用。