# 3D-Printed Lightweight Foamed Concrete with Dispersed Reinforcement
## 2 Materials and Methods  
### Materials  
The mixture was prepared using sand with a particle size distribution of 0.5 to 1.4 mm and CEM IV 42.5 cement, known for its reduced CO\({}_{2}\) emissions, supplied by Lafarge Polska (Holcim Group, Malogoszcz Cement Plant, Malgoszcz, Poland). The CEM IV/B (V) 42.5 N--LH/NA cement is a pozzolanic cement classified under PN-EN 197-1 [47], characterized by a compressive strength of \(\geq\)42.5 MPa after 28 days, low heat of hydration (LH), and reduced alkali content (NA). The initial setting time is \(\geq\)75 min, while the expansion in the Le Chatelier test does not exceed 10 mm. The pH of a cement-water mixture (1:2 ratio, 20 \({}^{\circ}\)C) ranges between 11 and 13.5. The cement's density falls within 2.75-3.20 g/cm\({}^{3}\), with a bulk density of 0.9-1.5 g/cm\({}^{3}\). The soluble hexavalent chromium content remains below 2 mg/kg, adhering to regulatory requirements. The material exhibits low solubility in water (0.1-1.5 g/L) and a particle size distribution between 5 and 100 \(\upmu\)m. Due to its limited alkali content (Na\({}_{2}\)Oeq \(\leq\) 0.6%), it effectively mitigates the risk of alkali-silica reaction, making it particularly suitable for durable concrete applications [48]. To enhance sustainability, 5% of the cement content was substituted with fly ash sourced from the Krakow CHP Plant (PGE Energia Ciepla S.A., Krakow, Poland), while 20% of the aggregate was replaced with slag obtained from the Puchaczow power plant (Leczynska Energetyka Spolka z o.o., Puchaczow, Poland) (Table 1). The prepared mixtures were reinforced with various fibers, including coconut, basalt, glass, merino wool, and polypropylene, incorporated at dosages of 1% and 0.5% by weight, as detailed in Table 2 and illustrated in Figure 1. The selection of fiber contents (1 wt.% and 0.5 wt.%) was based on an extensive literature review described above, aiming to examine the highest feasible concentrations that could be practically applied in large-scale 3D printing for construction purposes. Since the ultimate objective of this research is to develop a material suitable for real-world construction applications under varying environmental conditions, these values were chosen to assess the performance of foamed concrete reinforced with dispersed fibers at extreme concentration levels. The choice of fiber types--basalt, coconut, glass, polypropylene, and merino wool--was guided by their distinct mechanical properties, durability, and potential benefits in both structural and insulating applications. Basalt fibers, known for their high tensile strength and chemical resistance, enhance crack resistance and overall durability in foamed concrete. Coconut fibers, as a sustainable and flexible natural alternative, provide good water resistance, impact resistance, and energy absorption, making them particularly useful in lightweight and insulating applications. Glass fibers improve tensile strength and minimize shrinkage cracking, enhancing the structural stability of foamed concrete, especially in load-bearing applications. Polypropylene fibers contribute to ductility, toughness, and resistance to plastic shrinkage cracking, making them well suited for lightweight reinforcement. Merino wool fibers, a bio-based material with excellent thermal and acoustic insulation properties, offer potential for improving the energy efficiency of non-load-bearing construction elements. By investigating this diverse selection of fibers, this study aimed to identify the most effective reinforcement strategies for 3D-printed foamed concrete, balancing mechanical performance with insulation properties to optimize its application in large-scale construction. Foaming of the mixtures was achieved using a synthetic foaming agent, Pianotwor, mixed in a 1:1 ratio (Table 3). A total of 24 distinct mixtures were formulated, including reference samples that excluded fiber reinforcement.