# 3D-Printed Lightweight Foamed Concrete with Dispersed Reinforcement
## 1 Introduction
### Fibers in 3D Printing  
As 3D printing technology continues to advance, its potential to transform the construction industry is becoming increasingly evident. The ability to produce complex geometries, customize designs, and minimize material waste are among its most notable advantages. Despite these promising applications, 3D concrete printing still faces significant challenges. One of the primary concerns is ensuring the structural integrity of the lower layers during the additive manufacturing process. Precise control over the concrete mix is critical for maintaining homogeneity and consistency, as the layer-by-layer deposition characteristic of 3D printing can result in inconsistencies and weak interlayer bonding, potentially compromising the overall strength of the printed structure. To address these challenges, exploring alternative reinforcement methods compatible with 3D printing technologies is essential for achieving the requisite strength and durability. Fiber incorporation in concrete has emerged as a promising approach to maintaining form stability during printing, contributing to more precise and accurate structures. However, fiber addition also affects the rheological properties of the concrete mix, influencing its fluidity, pumpability, and printability--particularly when small nozzle sizes are employed. Research has demonstrated that the inclusion of fibers alters extrusion dynamics and interlayer adhesion, with varying outcomes depending on fiber type, length, and concentration. For instance, studies indicate that incorporating 0.5-1 wt.% basalt fibers can support efficient extrusion while maintaining printability [3; 4; 5]. Similarly, [PERSON] et al. investigated the effects of glass fibers with lengths of 3 mm, 6 mm, and 8 mm and concentrations ranging from 0.25% to 1%. Their findings revealed that fiber contents exceeding 2% significantly increased viscosity, leading to nozzle clogging and reduced fluidity, which can negatively impact the performance of printed structures [6; 7]. These insights underscore the necessity of balancing fiber content to optimize both material properties and the printing process. The impact of different fiber types on the overall properties of 3D-printed concrete extends beyond its fluidity and remains a critical area of study. Fiber reinforcement offers the added benefit of addressing challenges associated with incorporating traditional steel reinforcements into printed elements. A diverse range of short fibers has been explored in the context of 3D concrete printing. Among these, steel fibers are the most widely studied [8]. Other fiber types, including carbon [9; 10], basalt [9], glass [11; 12], wollastonite [13], polyethylene (PE) [14], polypropylene (PP) [15], poly(vinyl alcohol) (PVA) [16], and polymethyl methacrylate (PMMA) [17], have also been investigated. Furthermore, researchers have analyzed recycled rubber fibers [18], natural fibers such as flax [19], jute [20], and sisal [21], as well as combinations of elastic and rigid fibers [22]. These investigations highlight the versatility of fiber reinforcement in enhancing the mechanical and structural properties of 3D-printed concrete. However, they also emphasize the need for continued research to better understand the interplay between fiber type, concentration, and the specific requirements of 3D printing. Advancing this knowledge will not only improve the performance of 3D concrete printing but also support its broader adoption as a transformative construction technology. An effective strategy to enhance the strength of concrete mixes for 3D printing involves incorporating fibers during the raw material preparation phase. This approach ensures the uniform distribution of fibers throughout the concrete matrix, facilitating the smooth passage of short fibers through the nozzle and mitigating the risk of clogging. Fibers, particularly those oriented perpendicularly to potential crack paths, play a pivotal role in inhibiting crack initiation and propagation.