## 2 Materials and Methods
### Methods  
Particle size analysis was conducted using an Anton Paar PSA 1190 LD (Anton Paar GmbH, Graz, Austria). The dry method was used to analyze the sand and the more precise wet method was used for the significantly smaller fly ash particles. After carrying out three measurements to increase accuracy, the results were obtained.  
Samples were analyzed using scanning electron microscopy (SEM) to determine the structure and shape of both the sand and the fly ash, as well as the xanthan gum particles. The device used was the JSM-IT200 InTouchScope(tm) (JEOL, Tokyo, Japan). The samples were prepared by placing on a carbon pot and coating the surface with a thin layer of gold in the JEOL Smart Coater (JEOL, Tokyo, Japan).  
Figure 5: The setup for UW3 DP: (**a**) overall view; (**b**) printing process.  
The elemental and oxide analyses were carried out using an EDX-7200 from SHIMADZU (SHIMADZU EUROPA GmbH, Duisburg, Germany). Fly ash and sand were both investigated regarding their elemental and oxide composition. The analyses were conducted on powdered samples using polypropylene foil for covering. The analysis was made in air using the software PCEDX Navi (Version: EDX-7000P).  
A slump cone test, defined by the EN 12350-5 [42] standard, was performed to ensure the dimensional stability of the printed bodies. To test the shape holding of a paste, it was filled into an oiled truncated cone. After compacting and leveling the surface, the weight was removed, and the metal mold was pulled away upwards. The free-standing paste was then subjected to impact with its platform by rotating a shaft on the underside of the apparatus. By rotating it 15 times within 15 s, the test body was subjected to several hard impacts, each of which caused deformation. At the end of the test, the new dimensions were measured, i.e., how the cone deformed/slumped.  
The results of the initial shape retention tests were used to design pastes, which were then extruded by hand. Commercially available cartridge presses were filled with around 1000 g of paste, and by operating the gun as evenly as possible, layers could be deposited on top of each other, and the first extrusions were carried out.  
To investigate and compare the mechanical properties of both printed and conventionally produced samples, the prepared cubes/cuboids were tested regarding compressive and flexural strength. To achieve more representative results, three samples of each configuration were tested. Compressive strength can be described as the maximum stress that can be endured by a material before failure occurs. The tests were carried out following the EN 12390-3 [43] standard. Flexural strength was measured on a beam or slab-shaped sample, which rested on supports and was centrally loaded by a single fin, following EN 12390-5 [44]. Calculations were performed according to Formula (1).  
\[\sigma=\frac{3\cdot F\cdot l}{2\cdot d_{1}\cdot{d_{2}}^{2}} \tag{1}\]  
With:  
\(\sigma\)--Flexural strength, MPa  
F--Maximal load, N  
I--Space between supporting points, mm (140 mm)  
d\({}_{1}\), d\({}_{2}\)--Sample dimensions, mm  
The tests were carried out with a 3000 kN compression machine from Mateset (Mateset, Treviolo, Italy). To contribute to the accuracy of the results, the contact surfaces of the samples were made to be as smooth and parallel as possible. This was achieved by sanding before measurement. The dimensions of the bodies were used to calculate the final values, and also to determine the densities. The specimens were loaded with a continuous constant rate of 0.5 MPa/s, whereas for compressive strength, the starting force was 0.500 kN, and for flexural strength, it was 0.001 kN. The machine stops automatically when the maximum force applied to a sample drops by a certain percentage. This value was set at 30% for the compressive strength test and 10% for the flexural strength test. The test was considered successful if the sample failed according to a known pattern.