# Overview of the Development of 3D-Printing Concrete: A Review
## 3 Performance Requirements of 3D-printing Concrete Materials
### Printability of 3D-printing Concrete Materials
#### 3.1.4 Setting Time  
Setting time refers to the time that the 3D printed concrete mixture is mixed with water to maintain the printing performance. Setting time is an important parameter of the performance indicators of 3D-printing materials. A longer setting time can obtain good fluidity and extrudability, and a shorter setting time can obtain sufficient early strength. Due to the different scales of structures, the setting time of materials should be adjusted according to the scale of the printed structure to meet different needs. Therefore, the setting time of 3D printed concrete should be adjustable within a certain range.  
Setting time can be adjusted by coagulant, retarder, or by changing the gelling material. [PERSON] et al. [16] found that stirring the cementitious material can increase the setting time; by adding a retarder and a superplasticizer, respectively, the influence of the two on the setting time was obtained, as shown in Figure 7. The setting time of the superplasticizer and retarder with the dosage of 1% and 0.5% is 68 min and 100 min, respectively. [PERSON] et al. [35] mixed 60% calcium sulfoaluminate and 40% type I ordinary Portland cement to shorten the setting time of the cementitious material to 45 min. [PERSON] et al. [24] mixed 93% ordinary Portland cement and 7% sulphoaluminate cement, and the obtained mixtures had initial setting and final setting times of 110 min and 150 min, respectively. [PERSON] et al. [36] obtained an initial setting time of 163 min by adding 3% calcium chloride.  
Figure 6: Print shape adopted for evaluating the buildability. (a) Shape map. (b) Evaluation Chart. Reprinted with permission from ref. [30]. Copyright 2019 Elsevier Ltd.  
The setting time test is based on different standards, and the instruments and methods used by the researchers are not the same. [PERSON] et al. [37] started printing a strip of 800 mm \(\times\) 40 mm every 10 min after a static time of 30 min and recorded the time of rupture as the setting time. [PERSON] et al. [36] used a penetration resistance meter to test the initial setting time of the mixture based on the ASTM C403 standard, and found that the initial setting time of the mixture with 3% calcium chloride was 163 min. [PERSON] et al. [38] used a Vicat tester to measure the initial setting time of cement slurry containing limestone fillers according to ASTMC191-08, and found that with the increase of limestone content and its fineness, the initial setting time of the mixture was shortened. [PERSON] et al. [35] obtained the initial setting and final setting time of 99 min for the mixture to meet the requirements of 3D-printing through the Vicat tester. [PERSON] et al. [39] used the penetration resistance method to determine the stiffness development of the cementitious material during the coagulation process in accordance with the Chinese national testing standard GB/T50080-2002 and determined the setting time of the mixture based on the penetration resistance measured at different times. However, now the setting time of printing materials is still relatively long, which makes the advantages of 3D-printing rapid manufacturing unable to be fully utilized.