Dressler Inka, Freund Niklas, Lowke Dirk
Institute of Building Materials, Concrete Construction and Fire Safety, TU Braunschweig, 38106 Braunschweig, Germany.
Materials (Basel). 2020 Jan 14;13(2):374. doi: 10.3390/ma13020374.
Recently, the progress in 3D concrete printing has developed enormously. However, for the techniques available, there is still a severe lack of knowledge of the functional interaction of processing technology, concrete rheology and admixture usage. For shotcrete 3D printing technology, we present the effect of accelerator dosages (0%, 2%, 4% and 6%) on fresh concrete properties and on interlayer strength. Therefore, early yield stress development up to 90 min is measured with penetration resistance measurements. Deformation of layers under loading is investigated with digital image correlation and a mechanical testing machine. One point in time (10 min after deposition) is examined to quantify vertical buildability of elements depending on the accelerator dosage. Four different interlayer times (0, 2, 5 and 30 min), which occur for the production of small and large elements as well as due to delay during production, are investigated mechanically as well as quantitatively with computed tomography regarding the formation of cold joints. With increased accelerator dosage, an instantaneous increase in early age yield stress and yield stress evolution was observed. An increase in interlayer time leads to a reduced strength. This is mainly attributed to the observed reduced mechanical interlocking effect of the strands. Finally, a model to describe interlayer quality is presented. In the end, advantages as well as limitations of the findings are discussed.
最近，3D混凝土打印技术取得了巨大进展。然而，就现有技术而言，对于加工工艺、混凝土流变学和外加剂使用之间的功能相互作用仍严重缺乏了解。对于喷射混凝土3D打印技术，我们展示了促凝剂用量（0%、2%、4%和6%）对新拌混凝土性能和层间强度的影响。因此，通过贯入阻力测量来测定直至90分钟的早期屈服应力发展情况。利用数字图像相关技术和一台机械试验机研究加载下层的变形情况。考察一个时间点（浇筑后10分钟），以量化取决于促凝剂用量的构件竖向可建造性。研究了四种不同的层间时间（0、2、5和30分钟），这些时间出现在生产小构件和大构件时以及生产过程中的延迟期间，通过机械性能测试以及利用计算机断层扫描对冷缝形成情况进行定量分析。随着促凝剂用量增加，观察到早期屈服应力和屈服应力发展瞬间增加。层间时间增加会导致强度降低。这主要归因于观察到的股线机械联锁效应降低。最后，提出了一个描述层间质量的模型。最后，讨论了研究结果的优点和局限性。
