# 3D-Printed Lightweight Foamed Concrete with Dispersed Reinforcement
## 3 Results and Discussions
### Microscopy Observations  
The microscopic images (Figure 17a-k) present cross-sectional analyses of 3D-printed foamed concrete samples reinforced with various fiber types. Sample (a) incorporates coconut fibers, a natural reinforcement material known for its high hydrophilicity and elevated lignin content, which impart flexibility, durability, and resistance to microbial decomposition. However, these fibers exhibit lower tensile and flexural strength compared to synthetic fibers. The natural surface irregularities of the coconut fibers contribute to a heterogeneous pore distribution, particularly in regions adjacent to the fibers, resulting in a non-uniform pore structure that adversely affects the mechanical performance of the material. The fracture surface of the sample (b) illustrates the spatial orientation and fiber distribution induced during the extrusion-based additive manufacturing process. Sample (c) contains basalt fibers, an inorganic reinforcement material renowned for its exceptional tensile strength, thermal stability, and low water absorption capacity. These properties promote effective fiber-matrix adhesion, thereby minimizing interfacial void formation. Consequently, the pore architecture in this sample is notably more homogeneous compared to coconut fiber-reinforced composites. The fractured image of sample (d) confirms the consistent dispersion of basalt fibers, which are observed to localize in distinct regions due to the flow dynamics of the printing process. Sample (e) incorporates glass fibers, characterized by their smooth surface texture, which reduces their potential for capillary water absorption and limits interfacial bonding with the cementitious matrix. This results in moderate flexural strength and a relatively low water absorption coefficient. The pore structure, marked by irregular geometries, correlates with these fiber-matrix interactions. The fracture image (f) reveals fiber agglomeration, suggesting insufficient dispersion during mixing, likely due to the retention of the as-manufactured fiber configuration. Samples (g) and (h) contain merino wool fibers, a natural material exhibiting high hygroscopicity and low chemical affinity with the cement matrix, leading to poor interfacial adhesion. This results in elevated porosity, as evidenced by the irregular and enlarged pore morphology observed in the microscopic images. The contrast-enhanced micrograph (g) distinctly highlights the dimensions and dispersion of the merino wool fibers, while the fracture surface image (h) provides further insight into the weak bonding characteristics. Microstructural analysis confirmed that sheep wool fiber-reinforced concrete exhibited good bonding between fibers and the matrix, with low void content, supporting mechanical improvements [63; 64]. Despite the high porosity, prior studies have indicated that wool fiber inclusion enhances ductility and sustainability, aligning with environmental goals by repurposing waste materials and promoting resource conservation. Sample (i), reinforced with polypropylene (PP) fibers, exhibits a pore structure dominated by uniform, near-spherical voids. Polypropylene fibers are associated with the lowest porosity among all tested specimens, which directly correlates with superior mechanical properties, enhanced durability, and a minimal water absorption coefficient. The fracture surface confirms a homogeneous fiber distribution, contributing to the uniformity and structural integrity of the composite. The reference sample (k), composed of foamed concrete without any fiber reinforcement, serves as the control for comparative evaluation. Its homogeneous pore structure provides a baseline for assessing the impact of fiber inclusions on pore morphology, mechanical strength, and water absorption properties. Figures 18 and 19 present selected samples that exhibit significant variations in results between printed and cast specimens.