# 3D-Printed Lightweight Foamed Concrete with Dispersed Reinforcement
## 3 Results and Discussions
### Flexural Strength Test  
Figure 10 shows a comparison of the flexural strength of printed and molded samples. Flexural strength tests conducted after 28 days revealed that mixtures incorporating bottom slag (SL) in combination with basalt or glass fibers exhibited the highest flexural  
Figure 10: Flexural strength after 28 days: (**a**)—printed samples, (**b**)—molded samples. strength values. These results underscore the reinforcing potential of rigid fibers when utilized in conjunction with dense fillers. For instance, the B1/SL/B1 mixture achieved a flexural strength of 3.72 MPa, while B1/SL/B05 reached 4.14 MPa. Similarly, mixtures reinforced with glass fibers, such as B1/SL/G1 and B1/SL/G05, attained flexural strength values of 2.39 MPa and 2.31 MPa, respectively. Coconut (CO) and glass (G) fibers demonstrated moderate to high flexural strength, reflecting their crack-bridging properties, which enhance resistance to bending stresses. The mixture containing fly ash reinforced with merino wool fibers (B1/FA/M05) exhibited high flexural strength among the tested samples, achieving an average value of approximately 2.8 MPa for molded specimens and 4.08 MPa for printed specimens. These results are consistent with the findings of [PERSON] et al. [57], who reported that the incorporation of sheep wool fibers into cementitious mortars significantly enhanced mechanical performance and sustainability by partially substituting cement with a natural, renewable additive. Specifically, the addition of 10 g (1% by volume) of untreated wool fibers, replacing an equivalent mass of cement in plain mortar, resulted in an 18% increase in flexural strength and a 110% improvement in fracture toughness. Merino wool fibers, due to their natural composition and smooth texture, positively contributed to the matrix by facilitating better interlock and force distribution within the concrete, thereby supporting the material's mechanical integrity and compressive strength. Other fly ash-containing mixtures, such as B1/FA/B1 (reinforced with 1 wt.% basalt fibers) and B1/FA/CO05 (containing 0.5 wt.% coconut fibers), also exhibited relatively high flexural strength, exceeding 2.0 MPa. In contrast, polypropylene (PP) fibers presented significant challenges during the printing process, particularly at a concentration of 1 wt.%. Frequent nozzle clogging during extrusion hindered consistent material flow, which was primarily attributed to the physical limitations of the printing equipment rather than the intrinsic properties of polypropylene fibers. As a hydrophobic synthetic fiber, polypropylene has the potential to reduce water absorption and enhance mechanical performance when used at optimal concentrations and under suitable processing conditions. However, the challenges encountered at 1 wt.% PP highlight the importance of optimizing the printing process for fiber-reinforced mixtures to fully exploit their mechanical benefits. Furthermore, the flexural strength of printed samples was generally higher than that of molded samples across all additives, indicating the potential advantages of the 3D printing process in improving mechanical performance. In the conducted research of fiber-reinforced foamed concrete, printed samples exhibit higher flexural strength than their cast counterparts. This finding aligns with previous studies on lightweight cementitious composites reinforced with hollow glass microspheres (HGM) and polyvinyl alcohol (PVA) fibers, where the orientation of fibers perpendicular to the loading direction was found to enhance both flexural strength and overall mechanical properties, with reported increases of 8% and 40%, respectively, compared to cast samples [57]. Limited sources of research on fiber-reinforced 3D-printed foamed concrete (PVA fibers) report that cast specimens exhibited 28% (after 28 days) and 32% (after 56 days) lower strength than printed specimens when averaged across all three loading directions.