# 3D-Printed Lightweight Foamed Concrete with Dispersed Reinforcement
## 2 Materials and Methods
### Methods
#### 2.3.2 Stability and Buildability Assessment of Stability and Buildability  
Printability tests were conducted using the gantry-style 3D printer shown in Figure 3. The printer featured a print volume of 1000 mm (X-axis), 500 mm (Y-axis), and 500 mm (Z-axis), with a print head capable of achieving a maximum speed of 80 mm/s. The experimental setup incorporated a print head equipped with a 20 L hopper and a screw feeder with a length-to-diameter ratio of 3.5, ensuring consistent material flow during extrusion.  
Material extrusion was carried out using a nozzle with a diameter of 20 mm. The printed layers were set at a height of 8 mm, with a line width of 20 mm. For comparative analysis, foamed concrete was also cast in rectangular molds measuring 40 \(\times\) 40 \(\times\) 160 mm. The printing speed during the experiments was maintained at 40 mm/s, with a material extrusion rate of approximately 6400 mm\({}^{3}\)/s.  
Each material sample was printed in two parallel lines over five layers, forming structures measuring 40 \(\times\) 40 \(\times\) 480 mm. After hardening, the printed samples were cut to size for direct comparison with the cast specimens. This approach enabled a thorough evaluation of the printability and material properties under both printing and casting conditions. To ensure reproducibility and validity of the results, three specimens were prepared for each formulation. The quality control process during printing involved continuous monitoring via a camera positioned in the corner of the printing area, complemented by visual inspection of each deposited layer. The consistency of the printing process was also evaluated based on the uniformity of layer deposition, the stability of the extruded material, and the adhesion between printed layers. Any visible defects, such as excessive deformation, uneven layer distribution, or printing discontinuities, were documented and analyzed. During the experiments, several process variations were considered to evaluate the robustness of the 3D printing method. One of the key challenges encountered was nozzle blockage, which occurred predominantly in formulations containing 1 wt.% polypropylene fibers and rigid coconut fibers. These blockages were attributed to fiber entanglement within the extrusion system, necessitating multiple printing attempts to achieve successful specimens. To mitigate this issue, adjustments in material preparation and feeding consistency were made, including optimizing the fiber dispersion within the mixture before extrusion. Furthermore, to maintain uniform material properties, each formulation underwent a rheological evaluation using the flow table test prior to printing.  
Figure 3: Three-axis gantry-based 3D printing system.  
This ensured that all mixtures exhibited comparable workability, preventing inconsistencies in the extrusion process. The ambient conditions during printing, such as temperature and humidity, were also recorded, as these factors can influence the setting behavior and final mechanical properties of foamed concrete. These measures ensured the reliability and comparability of the printed and cast specimens, allowing for an accurate assessment of mechanical performance across production methods. The comprehensive documentation of printing parameters, process challenges, and quality control strategies contributes to the reproducibility of this study, providing a valuable reference for further advancements in 3D-printed fiber-reinforced foamed concrete. The assessment of concrete extrusion efficiency utilizing the aforementioned printer has been extensively discussed in the authors' prior research [52].