# Experimental Study of 3D Concrete Printing Configurations Based on the Buildability Evaluation
## 5 Conclusions  
Traditional material testing methods may not be suitable for this printing technique. This study proposed the height reduction test (HRT), building index (_BI_), and leaning angle (LA) to guide the configuration of cementitious printing based on the existing material mixtures OSS1, OSS2, and OSS3 and a laboratory printing device with a nozzle size of \(\mathcal{O}\)15 mm. More studies should be conducted when the material mix proportion and extruding mechanism vary. The main conclusions are summarized as follows:  
1. Building index (_BI_) was proposed to evaluate the layer stacking ability of the PM and PD by counting how many layers were printed in the initial setting time. _BI_ can be used to guide the printing configuration and material development. The acceptable  
Figure 19: Four decorative printings with same-layer height printing: **(a)** a 40 cm high vase, **(b)** a 30 cm high vase, **(c)** a 120 cm high vase, and **(d)** a decorative hollow sketch with a real height of 1498 mm from a designed height of 1500 mm, requiring 150.5 min and 40 Kg of OSS3 material.  
Figure 18: The application of this study in the process of 3D concrete printing. This study is at point _p0_. _P1_ compares the LA from the designed PO and the existing PM and PD, and feeds back to optimize the PM or the designed PO, as well as _p2_ and _p3_. Based on updated configurations, the final PO would be printed at _p4_, from the newly generated toolpath.  
ranges of \(BI\) for mixes OSS1, OSS2, and OSS3 in this study were 0-19.1, 0-61.1, and 0-99.4, respectively.
* The height reduction test (HRT) measures the height reduction percentage (height reduction ratio) of a PO. It is suitable for the slump evaluation of printed filaments, with more practical significance for the development of PM than the common slump test. Theoretical calculation and numerical simulation verified that the criteria _HRR r_ and gap height tolerance (GHT) \(\delta\) have a relationship of \(r=\frac{\delta}{\delta+1}\) for a PM, and 0.167 is the criteria value for regular geometry printing with \(\delta=0.2\).
* Leaning angle (LA) tests guide the design of CAD sketches to increase the buildability of applications.
* _BI_, _HRR_, and LA can work as the meta parameters of the 3 DCPT to guide material development and printing configurations, including the printing speed and layer height.  
Conceptualization, X.C.; Formal analysis, X.C.; Funding acquisition, H.C. and Z.L.; Investigation, Y.L., X.C. and M.H.; Methodology, H.C. and X.C.; Project administration, H.C.; Resources, Y.L. and M.H.; Software, Y.L.; Supervision, H.C.; Visualization, Y.L.; Writing--original draft, X.C.; Writing--review and editing, H.C., W.T. and Z.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Shenzhen Research Grant (KQTD20200909113951005), the Science and Technology Development Fund, Macau SAR (FDCT-0083/2018/A2), and Multi-Year Research Grant, University of Macau (MYRG2019-00135-IAPME).  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
The authors declare no conflict of interest.