A twin-pipe pumping system has been developed to overcome the conflicting requirements in 3D concrete printing between pumping and deposition. In the twin-pipe pumping system, a helical static mixer, consisting of a series of mixing elements, is used to blend a cement-based mixture and a limestone-based mixture right before extrusion. As these two mixtures go through the static mixer, non-moving mixing elements continuously blend the materials in a flow-division pattern. However, the blending performance of the helical static mixer used for twin-pipe 3D concrete printing has not yet been reported. This paper presents the results of an experimental study on the relation between the mechanical behavior and the blending efficiency of the helical static mixer. Based on the binary images of the polished specimens printed with a different number of mixing elements, the blending performance was characterized by the coefficient of variation of the row-wise intensity distribution. A reasonable linear relationship was established between the mechanical strength (flexural strength and tensile strength) and the mixing homogeneity of the two mixtures. In addition, a higher number of mixing elements was observed to lead to a more dense pore structure, most probably due to the better compaction of the material by the higher pumping pressure.

已开发出一种双管泵送系统，以克服 3D 混凝土打印中泵送和沉积之间的冲突要求。在双管泵送系统中，螺旋静态混合器由一系列混合元件组成，用于在挤出前混合水泥基混合物和石灰石基混合物。当这两种混合物通过静态混合器时，非移动混合元件以分流模式连续混合材料。然而，用于双管 3D 混凝土打印的螺旋静态混合器的混合性能尚未见报道。本文介绍了螺旋静态混合器的机械性能与混合效率之间关系的实验研究结果。基于使用不同数量混合元素打印的抛光试样的二值图像，混合性能由变异系数的逐行强度分布。两种混合物的机械强度（弯曲强度和拉伸强度）与混合均匀度之间建立了合理的线性关系。此外，观察到更多数量的混合元件会导致更密集的孔隙结构，这很可能是由于更高的泵送压力更好地压实材料。