Supplementary information files for "On the origins of anisotropy of extrusion-based 3D printed concrete: the roles of filament skin and agglomeration"

Supplementary files for article "On the origins of anisotropy of extrusion-based 3D printed concrete: the roles of filament skin and agglomeration"<br><br>One of the most significant challenges facing extrusion-based 3D concrete printing (3DCP) is the anisotropy present in the printed material: under load, the observed performance is typically lower than a cast equivalent and significantly so in certain directions. In addition, the performance is also more variable than cast material. These observations are, in part, due to surface moisture evaporation and air entrapment. Here, we investigate the hypothesis that the printed concrete comprises of agglomerated filament core and skin having distinct properties as a necessary consequence of the printing process. Through novel X-ray computed tomography measurements, we show that printed concrete comprises the core and Filament Interfacial Zone Network (FIZN) and that, in contrast to the cores, the FIZN is found to be free from pores except at boundaries where there is incomplete bonding. Through morphological, chemical and mechanical analysis, the FIZN is also found to contain 20% less sand and 60% more anhydrous cement than the filament cores, while the FIZ material was inferred to have 11% higher compressive strength, 28% lower flexural strength and 22% lower elastic modulus than the core. The findings from this work suggest that anisotropy will always exist and that care should be devoted to the material rheology, printing system and the filaments arrangement in order to produce consistent and predictable hardened material properties.<br>© The Author(s), CC BY 4.0

论文《挤出型3D打印混凝土的各向异性起源：丝材表皮与团聚的作用》补充材料

挤出型3D混凝土打印（extrusion-based 3D concrete printing, 3DCP）面临的最显著挑战之一，在于打印成型材料存在各向异性：受载时，实测性能通常低于同配比浇筑成型材料，且在特定方向上性能差距尤为显著。此外，打印混凝土的性能波动也较浇筑材料更大。上述现象部分源于表面水分蒸发与气泡截留。

本研究针对该假说开展验证：打印混凝土由经团聚形成的丝材芯部与表皮构成，二者因打印工艺的固有特性而呈现出迥异的性能特征。通过创新性的X射线计算机断层扫描（X-ray computed tomography）测量，本研究证实打印混凝土由丝材芯部与丝材界面区网络（Filament Interfacial Zone Network, FIZN）构成；与芯部不同，FIZN仅在结合不充分的界面处存在孔隙，其余区域无孔隙结构。通过形貌、化学与力学分析，本研究发现FIZN的砂含量较丝材芯部低20%，无水水泥含量较芯部高60%；经推导可知，丝材界面区材料的抗压强度较芯部高11%，抗弯强度低28%，弹性模量低22%。

本研究结果表明，各向异性现象将始终存在，因此需重点关注材料流变性能、打印系统及丝材排布方式，以获得性能稳定且可预测的硬化混凝土材料。

© 作者，CC BY 4.0 许可协议