Ivanova Irina, Mechtcherine Viktor
Institute of Construction Materials, TU Dresden, 01069 Dresden, Germany.
Materials (Basel). 2020 Mar 27;13(7):1551. doi: 10.3390/ma13071551.
With increasing interest in the use of additive manufacturing techniques in the construction industry, static rheological properties of fresh concrete have necessarily come into focus. In particular, the knowledge and control of static yield stress (SYS) and its development over time are crucial for mastering formwork-free construction, e.g., by means of layered extrusion. Furthermore, solid understanding of the influences of various concrete constituents on the initial SYS of the mixture and the structural build-up rate is required for purposeful material design. This contribution is concentrated on the effect of aggregates on these rheological parameters. The volume fraction of aggregates was varied in the range of 35% to 55% by volume under condition of constant total surface area of the particles. The total surface area per unit volume of cement paste was equal to 5.00, 7.25 and 10.00 m²/L, conditioned on the constant volume fraction of aggregates. Both variations were enabled by changing the particle size distributions of the aggregates while holding the cement paste composition constant for all concrete mixtures. To characterise the SYS and the structural build-up, constant shear rate tests with a vane-geometry rotational rheometer were performed. It was found that in the ranges under investigation the variation in volume fraction had a more pronounced effect on the static rheological properties of concrete than did the variation in surface area. An accurate mathematical description of the relationship between the initial SYS of concrete and the relative volume fraction of aggregate based on the Chateau-Ovarlez-Trung model was proposed. Challenges in deriving a similar relationship for the structural build-up rate of concrete were highlighted.
随着建筑行业对增材制造技术的兴趣日益浓厚，新拌混凝土的静态流变特性必然成为关注焦点。特别是，对于静态屈服应力（SYS）及其随时间的发展的了解和控制，对于掌握免模板施工（例如通过分层挤压）至关重要。此外，为了进行有针对性的材料设计，需要深入了解各种混凝土成分对混合物初始SYS和结构形成速率的影响。本文着重研究骨料对这些流变参数的影响。在颗粒总表面积恒定的条件下，骨料的体积分数在35%至55%的范围内变化。在骨料体积分数恒定的情况下，每单位体积水泥浆的总表面积分别为5.00、7.25和10.00 m²/L。通过改变骨料的粒径分布，同时保持所有混凝土混合物的水泥浆组成不变，实现了这两种变化。为了表征SYS和结构形成，使用叶片式旋转流变仪进行了恒定剪切速率测试。结果发现，在所研究的范围内，体积分数的变化对混凝土静态流变特性的影响比表面积的变化更为显著。基于Chateau - Ovarlez - Trung模型，提出了混凝土初始SYS与骨料相对体积分数之间关系的精确数学描述。文中强调了推导混凝土结构形成速率类似关系时面临的挑战。
