# 3D-Printed Lightweight Foamed Concrete with Dispersed Reinforcement
## 1 Introduction
### Foam Concrete in 3D Printing  
Numerous studies have investigated the strength properties of 3D-printed concrete, focusing on recycled materials, hybrid compositions with geopolymers, fiber-reinforced concrete, and foam concrete. Foam concrete, in particular, aligns with the growing demand for energy-efficient building materials. Its lightweight composition, excellent thermal insulation, and high fire resistance make it a promising option for sustainable construction.  
However, foam concrete remains underutilized in 3D printing due to two significant challenges: the preparation of the foamed mixture and its subsequent pumping.  
The commercial production of foam concrete primarily employs two methods for generating technical foam: pre-foaming and mixed foaming [26; 27]. The pre-foaming method involves preparing a foam solution that generates air bubbles, which are then combined with separately prepared cement mortar to achieve a homogeneous texture. In contrast, the mixed foaming method directly introduces foaming agents into the concrete mix [26; 28]. The final density of foam concrete depends on several factors, including the proportions of the mix components, the water content, and the concentration of the foaming agent. Achieving an optimal surfactant concentration is critical for maintaining foam stability during the extrusion process, ensuring a consistent pore structure, and minimizing bubble collapse.  
Pumping foam concrete, particularly over long distances, poses additional challenges by affecting foam stability and pore size distribution within the material [28; 29; 30; 31]. Maintaining the appropriate consistency and ensuring the stability of printed elements are essential for successful layer deposition [29]. The fluidity of the foam concrete mix and the effects of extrusion on foam stability are recognized as primary obstacles in 3D printing applications [27]. Consequently, the optimal mixture composition must balance reliable printability with minimal risk of bubble rupture during the printing process [28].  
Research by [PERSON] et al. demonstrated that the inclusion of hydroxypropyl methylcellulose enhances the ability to build successive layers of foam concrete by promoting the formation of large flocculates that aggregate cement particles. Additionally, silica ash has been shown to improve foam stability by absorbing free water and forming flocculates between silica fume (SF) particles and between SF and cement particles, thereby restricting water movement and increasing the stability of the printed structure [32].  
For optimal performance in 3D printing, the aggregate fraction diameter should be within the range of 2-4 mm, as this size ensures compatibility with the extrusion process, facilitates smooth layer deposition, and enhances precision in the printed output. The use of coarser aggregates may result in technical complications, including nozzle clogging and structural inconsistencies. To reduce weight and increase porosity in 3D-printed foam concrete elements, lightweight aggregates such as expanded perlite have been utilized [33]. In these applications, foam is typically generated by diluting a 30% concentration foaming agent with water at a 1:60 ratio. Research has demonstrated that substituting fine aggregates, such as sand, with perlite decreases the required foam content while maintaining the material's density and improving both its fresh and hardened properties. To enhance the mechanical properties and impact resistance of foam concrete, the incorporation of reinforcing fibers has been identified as an effective approach. Dispersed fibers mitigate challenges associated with conventional steel reinforcement in 3D printing, thereby improving durability and structural integrity. The growing body of research on fiber-reinforced foam concrete highlights its potential to address these challenges, further advancing its applicability in additive manufacturing.