Understanding fresh concrete flow by advanced rheological characterization

通过高级流变表征了解新拌混凝土流动

• 批准号: 403524381
• 负责人: Professor Dr.-Ing. Hans-Joachim Schmid
• 金额: --
• 依托单位: Lehrstuhl für Partikelverfahrenstechnik
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/403524381?language=en
• 关键词: Understanding; fresh; concrete; flow; advanced

The overall objective of this project proposal is to significantly enhance the fundamental understanding of the flow behaviour of fresh concrete. Therefore, it aims to perform a rheological characterization of concrete including particle sizes up to the centimetre scale. Today, profound rheological measurement methods are only available for cement pastes and to a limited extent for mortar. For concrete, only ‘relative’ characterization methods are available, i.e. allowing only a qualitative comparison of different types of concrete. In contrast, this project aims for ‘absolute’ measurements, i.e. delivering rheological properties of concrete, which are transferable and can be used directly for simulation of concrete flow in arbitrary geometries.To achieve this, an appropriate coaxial concrete rheometer will be developed and built. It will be equipped with a movable non-interfering ultrasonic image velocimetry (UIV) system for on-line monitoring of the flow profile or even the particle distribution during measurements. This system will allow for real rheological measurements, which offer unbiased, measurement system independent rheological parameters and flow curves while the validity of the system is checked in-situ. Since wall slip is a fundamental problem for all concrete rheometers, different 3D-printed wall geometries will be analysed and improved for the best possible results. It is expected to find different geometries for different concrete compositions.In addition, comparative measurements of the different concrete phases - cement, mortar and concrete – will be carried out. This aims to understand the influence of the coarse grains on the rheology of concrete. Since simulations are often based on flow properties of the cement phase only, these measurements will help to understand current problems and limitations in simulations and acquire a more profound understanding of concrete flow in general.Furthermore, the rheometer will be used to evaluate the performance of different simulation methods of other members in the priority program. The rheometer can be used for all 3 phases of common concrete suspensions, i.e. cement, mortar and concrete, and provides measured flow/concentration profiles via UIV. Therefore, experimental data will allow for detailed comparison with simulations. This should lead to a validation of simulation models and a precise calibration of model parameters. Finally, comparative measurements with classical (i.e. ‘relative’) concrete viscometers will be performed. Combined with UIV measurements and simulations this will allow for a better understanding of the phenomena occurring in these classical set-ups. Thus, experimental data gained with the new rheometer can even help to implement new model based evaluation methods to improve data interpretation from classical viscometers.

本项目提案的总体目标是显著提高对新拌混凝土流动特性的基本认识。因此，其目的是进行混凝土的流变学表征，包括高达厘米级的颗粒尺寸。今天，深刻的流变测量方法仅适用于水泥浆体，并在有限的范围内适用于砂浆。对于混凝土，只有“相对”表征方法可用，即只允许对不同类型的混凝土进行定性比较。相比之下，本项目的目标是“绝对”测量，即提供混凝土的流变特性，这些特性是可转移的，可以直接用于模拟任意几何形状的混凝土流动。为了实现这一目标，将开发和建造一台合适的同轴混凝土流变仪。它将配备一个可移动的非干扰超声图像测速系统，用于在线监测流量剖面，甚至是测量过程中的颗粒分布。该系统将允许进行真实的流变测量，其提供无偏的、独立于测量系统的流变参数和流动曲线，同时现场检查系统的有效性。由于壁滑移是所有混凝土流变仪的基本问题，因此将分析和改进不同的3D打印壁几何形状，以获得最佳结果。预计将发现不同混凝土成分的不同几何形状。此外，还将对不同混凝土相-水泥、砂浆和混凝土-进行比较测量。这旨在了解粗颗粒对混凝土流变性的影响。由于模拟通常仅基于水泥相的流动特性，因此这些测量将有助于了解当前模拟中存在的问题和局限性，并对混凝土流动有更深入的了解。此外，流变仪将用于评估优先计划中其他构件的不同模拟方法的性能。流变仪可用于普通混凝土悬浮液的所有3个阶段，即水泥、砂浆和混凝土，并通过UIV提供测量的流量/浓度曲线。因此，实验数据将允许与模拟进行详细比较。这将导致模拟模型的验证和模型参数的精确校准。最后，将进行与经典（即“相对”）混凝土粘度计的比较测量。结合UIV测量和模拟，这将允许更好地理解这些经典设置中发生的现象。因此，使用新流变仪获得的实验数据甚至可以帮助实施新的基于模型的评估方法，以改善传统粘度计的数据解释。