## 3 Results and Discussion
### Fresh Paste Properties  
The results of the slump test and initial shape retention tests provide important knowledge about the effect of the additives used. Low deformation of the paste cylinder in the slump cone test promises good dimensional stability and qualifies the composition of the paste for extrusion by hand. Here, particular attention has to be paid to ensuring that there is a uniform flow of material and that the individual layers/strands do not deform after deposition. Results are checked visually according to the criteria above and are used to improve the composition of the pastes. These preliminary tests enable the material to be tested on a small size and prevent it from being wasted by mixing unsuitable pastes on a large scale. The underwater printing is also simulated by hand. To observe the increase in strength over time, a penetration test is carried out with a pen at intervals of several days. Table 8 describes the effects of the tested additives on the behavior of the paste. The mass proportions and how the percentage values are calculated can be found in Table 4. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No** & **Additive** & **Effect and Content** & **Suitability to 3D** \\  & & **Printing** \\ \hline \multirow{4}{*}{1} & \multirow{4}{*}{Plasticizer} & After addition, a significantly more resistance-free flow behavior is observed in the paste. & \multirow{4}{*}{Yes} \\  & & Proportions from 0.04 to 0.1\% are tested. The best results are achieved with an addition of 0.05\%. & \\ \hline \multirow{2}{*}{2} & \multirow{2}{*}{Burned clay} & An attempt is made to add 1.24 to 3\% of burnt clay, but no improvement in the properties can be observed at any proportion. & No \\ \cline{1-1}  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Evaluation of used additives. Figure 8: Composition of fly ash: (**a**) elemental composition; (**b**) oxide composition. Several other studies confirm the suitability of different additives for AM of fly ash-based geopolymers. [PERSON] et al. used microgllass fiber and attalpurite clay [48], as well as actigel and cellulose [49]. These additives are often used in combination with GGBFS and silica fume (SF). Since both SF and GGBFS are geopolymer precursors and react actively, they are added up to 6%, while pure thixotropic additives account for 0.5 to 0.8%. It is noticeable that in this work with superplasticizer and xanthan gum, more additives are used in percentage terms. In the printable paste mixtures, 1.1 to 1.5% additives are present in relation to the total weight. A high proportion of additives can lead to a deterioration in mechanical strength [29]. In the next steps, particular attention was given to printable compositions: #20 AB and #21 AB. The slump cone test confirmed that paste mixtures #20 AB and #21 AB have very good dimensional stability. As can be seen from the top perspective, the cone widens uniformly by 0.45 to 0.55 cm in each direction. Figure 9 shows the changes compared to the original basic diameter of 10 cm. A low slump rate is desirable as it guarantees high dimensional accuracy of the subsequently printed body. It also makes it easier to place the individual layers precisely on top of each other. However, it must be ensured that the paste remains extrudable, otherwise, lumpy behavior can occur with insufficient bonding between individual layers. The slump cone test confirmed the dependence of the \"stability\" of the paste on additives and liquid admixtures. Variations in the amount of solution added, of as little as 2%, lead to considerable differences in slumping behavior, which determines the extrusion and shape retention properties of the paste. This is consistent with findings from other studies [50].