# 3D-Printed Lightweight Foamed Concrete with Dispersed Reinforcement
## 3 Results and Discussions
### Flexural Strength Test
This contradicts previous research suggesting that printed concrete generally exhibits lower strength than cast concrete [58]. Additionally, the flexural strength of cast-foamed concrete was lower than that of printed samples due to the denser microstructure formed during extrusion. Other studies on dense fiber-reinforced 3D-printed concrete have further highlighted the influence of fiber alignment on mechanical properties. For example, flexural strength measurements in the \(X\), \(Y\), and \(Z\) directions showed notable variations, with the printed samples demonstrating anisotropic behavior. The incorporation of carbon fibers in 3D-printed concrete led to significant improvements in flexural strength, particularly at a 2.5% volume fraction, due to the directional orientation of fibers induced by nozzle movement during printing. Fiber alignment along the printing path was found to increase bending strength, particularly in the \(Y\) and \(Z\) directions, enhancing mechanical anisotropy [59]. These findings indicate that, in fiber-reinforced foamed concrete, printing-induced densification and controlled fiber orientation may play a crucial role in improving flexural strength compared to cast samples. However, further investigations are required to fully understand the interplay between fiber type, orientation, and printing parameters in optimizing mechanical performance. The extrusion process was hindered by frequent nozzle clogging, which was primarily attributed to the limitations of the printing equipment rather than the inherent properties of polypropylene fibers. Despite these processing challenges, polypropylene fibers, as hydrophobic synthetic reinforcements, have the potential to reduce water absorption and improve mechanical performance when used at optimal concentrations and under controlled processing conditions. These observations underscore the importance of optimizing the printing process for fiber-reinforced mixtures to fully harness their mechanical benefits. The flexural strength of printed samples was generally higher than that of molded samples, a difference that can be largely attributed to fiber orientation and material distribution. To demonstrate this behavior, randomly selected samples are presented in Figures 11a and 12a to illustrate these variations, highlighting that in printed samples, coconut and merino wool fibers tend to align parallel to the printing direction. The arrows indicate the arrangement of fibers in the printed (green arrows) and cast (orange arrows) samples. This alignment enhances structural integrity and improves flexural strength along the printing axis. In contrast, cast samples exhibit a more random fiber distribution, which can lead to localized stress concentrations and reduced mechanical performance. Furthermore, Figure 13 demonstrates the printed sample without fibers (B1/FA) shows a denser, more compact structure, whereas its cast counterpart exhibits significantly higher porosity, negatively impacting its structural integrity. These findings emphasize that fiber alignment in printed samples not only reinforces mechanical performance by improving load distribution but also mitigates the formation of structural weak points. In contrast, the uncontrolled fiber orientation in molded samples results in more heterogeneous mechanical properties and potential failure zones. Figure 11: Comparison of printed and cast samples containing added coconut fiber: (**a**) fiber arrangement in cross-section, (**b**) sample cross-section. the composition and type of reinforcing fibers used. The increased density of printed materials can be attributed to specific factors inherent to the 3D printing process. The layer-by-layer deposition characteristic of 3D printing minimizes pore formation, as the material is deposited in a controlled manner, enabling precise layer stacking and fusion. Consequently, the printed structure contains fewer internal voids compared to molded samples, where air entrapment during the molding process often leads to the formation of microscopic pores.