# Experimental Study of 3D Concrete Printing Configurations Based on the Buildability Evaluation
## 1 Introduction
[21] defined good buildability when the lower layers showed no vertical distortion, layer failure, or excessive deformation in a seven-layer printing test. To achieve good buildability, [PERSON] et al. [18] suggested that the printing materials with low- to zero- slump should be used. [PERSON] et al. [11] stated that the buildability can be improved by decreasing the material density as well as the slump. Nevertheless, the printing failure still would happen with zero-slump material due to the elastic buckling and plastic collapse. However, from the technical point of view, it is not suitable to quantify the buildability by how many layers are printed or how high the achieved structure is. It should be noted that the printing height or layers can be increased remarkably by lowering the printing speed or extending the time interval [22] without considering the bonding between layers. The range of the 3D printer also limits the printing height of one printing process. The buildability reported in the literature is evaluated based on printing 10 to 30 layers. The buildability of 3 DCP should refer to the ability to create a complex architectural object rather than simple layer stacking, meaning that the buildability is an evaluation of one printing operation rather than of the printable material. Moreover, the printing operation involves the printable material and the printing equipment. In actual printing activities, one mixed material can not be extrudable with a small nozzle tip, but be printable with a large one. It can not be stackable with fast printing speed but buildable with slow printing speed. Thus, the \"printable\" material is closely related to the 3D printer regarding the configurations. Thus, the success of printing is heavily affected by the printing device (PD), printable material (PM), and the printed object (PO). Once the PM has been developed and the PO is given, the PD configurations should be precise regarding the motion speed, extruding speed, layer thickness, etc. in the form of the toolpath, which is generated by the printing software (i.e., slicing software) with a group of configurations. Better configurations can help optimize the toolpath to achieve better printing results to fit the designed geometry of the PO. A typical printing process is illustrated in Figure 1. Unfortunately, it is hard to find guidelines among the existing studies regarding concrete printing configurations. Additionally, most of their printers utilize control boards from the plastic 3D printing technique (fused deposition modeling, FDM). The toolpath generator (TPG) needs a configurable set of melting temperature, filament diameter, filling pattern, and maximum speed. However, they are not suitable for concrete printing. Therefore, it is urgent to clear the current confusion to guide 3D concrete printing activities. To establish standard criteria for the printing configuration guidelines, the following three methods were proposed:  
* Building index (_BI_): It evaluates the geometry-keeping ability. The _BI_ can help determine the parameters for the material development and the printing configuration based on the printing scale and the material mix. The buildability can be quantified as the range of _BI_ for one printable material;
* Height reduction test (HRT): This quantifies the slumping criteria of the printed filaments in terms of height reduction ratio (_HRR_) instead of the traditional slump test; and
* Leaning angle (LA): It is the angle between the vertical line and the filament-stacking direction to quantify the buildability of the material for printing complex geometry. 3 DCP must be a system that combines materials, devices, and software. Studies should be conducted both on the material and printing equipment. This study proposes buildability evaluation methods for a printing operation in terms of the PM, PD, and PO.