## 3 Results and Discussion
### 3D Printing Process  
The printing of the two paste mixtures (#20 AB and #21 AB) and the underwater printing produced results that are compared with each other and with outcomes from other sources, including printing in air--Figure 10.  
Figure 10(a) shows the extrusion test of a paste that is too liquid. It can be clearly seen that the lower layers collapse under the weight of the upper ones, and visible irregular extrusion occurs on the sides. Both individual layers and the entire volume collapse. The reason for the slow curing is the insufficient use of additives. As the geometric error is considered too high, especially after curing, the printed bodies are not used for subsequent experiments. Figure 9: Slump cone test results for mix #21 AB: (**a**) from the side; (**b**) from the top. Figure 10: Selected results of the printing tests: (**a**) Volumes printed using #20 AB; (**b**) Volumes printed using #21 AB; (**c**) Underwater print. After adjusting the paste composition, new prints are carried out (#20 AB). A very homogeneous, slight over-extrusion can be seen in picture 2 compared to the results achieved before. The individual layers are neatly laid over each other and few geometric differences are visible between the layers (Figure 11c). The lower layers remain stable, and the printed object does not sag even after multiple layers have been applied. There are gaps on the upper side of the extrusion (Figure 11c), which could cause cavities inside the component. After adjusting the previous mix, the final prints are made with paste composition #21 AB. This results in very precise extrusion and high reproducibility of the individual layers (Figure 11e). The material appears drier than #20 AB and there is less over-extrusion and wrinkling on the top of the component. This can be seen when Figure 11c,d are compared. The print image is not ideally smooth, and there are often cracks on the surface of the strand, which lead to imperfections, particularly on the top of the object. When printing underwater, the visibility of the results is sometimes limited. Nevertheless, it became apparent that the material tends to tear during extrusion and that it is not possible to create smooth surfaces and edges. The behavior is the same between the layers, and the deposition of another layer shifts the existing one considerably. By increasing the flow, more material could be added to close potential gaps. After completion of the printing process, the outlines of a relatively true-to-shape body can be guessed, but the poor visibility in the water prevents any statement on the placement of the lower layers. The most important printer components are the gentry system and the feed- and positioning units of the print head. The latter consists of the driven mixer with a connected  
Figure 11: Comparison of the printing process: (**a**) #11 AB with shape deviation; (**b**) #20 AB showing over extrusion; (**c**) #20 AB homogeneously extruded; (**d**) #21 AB with good flow rate; (**e**) #21 AB with slight sagging; (**f**) #21 AB used for UW3 dP. progressive cavity pump and the nozzle. The four-axis system proves to be suitable for the applications. It is also the more common system in the literature compared to robotic solutions. However, [PERSON] et al. [49] used a six-axis Denso robot to generate cuboids from geopolymer [49]. The lack of geometric complexity of the previously printed components makes a gantry system more attractive. A progressive cavity pump is used as the primary pumping unit in this study. Its utility is unique among comparable experiments and has advantages and disadvantages. It enables precise material extrusion and very low flow rates are also possible. However, extrusion breakage and air entrapment often occur. A round nozzle with a diameter of 20 mm is attached. In addition to round nozzles, square nozzles with 20 \(\times\) 20 mm or 30 \(\times\) 10 mm [29] dimensions are also used and can result in smoother wall finishes.