# 3D-Printed Lightweight Foamed Concrete with Dispersed Reinforcement
## 3 Results and Discussions
### Water Absorption  
Water absorption tests, conducted in both vertical and horizontal orientations, relative to the printing direction, provide significant insights into the anisotropic properties of printed samples and the influence of various fibers and additives on water behavior within the concrete matrix. These observations not only highlight differences in absorption behavior but also provide clues on the underlying mechanisms driving these differences and suggest potential strategies for performance enhancement. In the vertical orientation, water absorption rates were significantly higher across all samples, regardless of the composition and type of reinforcing fibers used. Samples containing coconut fibers (CO) and glass fibers (G) exhibited the highest absorption rates, 65-70 kg/m\({}^{3}\) after 168 h. This elevated absorption can be attributed to the fibrous nature of these additives, which increase matrix porosity and promote capillary action, thereby facilitating water ingress. Coconut fibers, being natural and highly porous, are inherently hydrophilic, making them prone to absorbing water. Glass fibers, while not hydrophilic, may create microvoids in the matrix that enhance water permeability. Additives such as polypropylene (PP) and merino wool (M) demonstrate intermediate water absorption rates. Polypropylene, a synthetic and hydrophobic fiber, contributes to absorption primarily through voids or gaps created during the printing process. Merino wool, although more hydrophilic than polypropylene, absorbs less water compared to coconut and glass fibers due to its smoother and less porous structure. The compact nature of merino wool enhances water resistance by creating a more impermeable concrete matrix. In contrast, the horizontal orientation relative to the printing direction consistently exhibits lower water absorption coefficients across all samples, with maximum values ranging between 20-25 kg/m\({}^{3}\). This reduction highlights the anisotropy introduced by the 3D printing process. The lower absorption rates in the horizontal orientation can be attributed to stronger material compaction along the layers during printing. As the extruded material undergoes self-compaction under its own weight, fewer voids are formed, resulting in tightly bonded layers. This increased compaction also aligns with the higher density observed on the horizontal cross-section of the samples. The differences in water absorption between vertical and horizontal orientations are particularly pronounced, underscoring the role of anisotropy in printed samples. Vertical absorption is more pronounced due to weaker interlayer bonding, a characteristic feature of the layer-by-layer deposition process inherent in 3D printing. Interlayer interfaces, with their reduced adhesion, create microcracks or voids that act as capillary pathways for water ingress. In contrast, horizontal absorption benefits from stronger intralayer cohesion, as the continuous deposition within each layer promotes more uniform material bonding. Fibrous additives such as CO, G, and M further influence water absorption by introducing irregularities into the concrete matrix. These fibers disrupt the continuity of the cementitious material, increasing overall porosity and creating pathways for water penetration. Natural fibers like CO amplify this effect through direct water absorption, compounding the challenges posed by increased porosity. In printed samples, the extrusion process often exacerbates this issue, as inconsistent material distribution around fibers can further elevate porosity. The hydrophilic or hydrophobic nature of additives plays a critical role in governing water absorption. Natural fibers (e.g., CO) are highly hydrophilic and actively absorb water, whereas synthetic fibers (e.g., PP) are hydrophobic but may still increase water absorption by disrupting matrix cohesion. Process parameters during printing, including printing speed, nozzle size, and extrusion pressure, significantly influence the uniformity of material deposition.