# 3D-Printed Lightweight Foamed Concrete with Dispersed Reinforcement
## 1 Introduction
### Fiber Reinforced Foam Structures  
Fiber-reinforced foamed concrete structures represent a compelling area of materials engineering, combining the lightweight and insulating properties of foamed concrete with the enhanced mechanical performance imparted by fiber reinforcement. The incorporation of fibers into foamed concrete significantly improves its tensile and bending strengths, thereby enhancing its load-bearing capacity and resistance to dynamic loads. Despite these advantages, a considerable research gap persists regarding the adaptation of fiber-reinforced foamed concrete for 3D printing applications. Bridging this gap requires a detailed investigation of mix compositions, stability during the printing process, production methodologies, and the types of fibers used for reinforcement, along with their influence on mechanical properties and long-term durability. Addressing these challenges is crucial for advancing the use of foamed concrete in structural engineering and unlocking its full potential in additive manufacturing. A review of existing literature highlights that the inclusion of short, dispersed fibers positively influences the mechanical properties of foamed concrete. The preparation of fiber-reinforced foamed concrete typically involves mixing the fibers with cement mortar before the introduction of foam. Fibers can be added either to the dry ingredients or to the pre-mixed cement mortar to ensure uniform dispersion. For example, [PERSON] et al. developed a process to prevent fiber clumping by mixing cement and basalt fibers in a drum for two minutes, adding two-thirds of the water for one minute, and then the remaining water for an additional five minutes before incorporating the pre-foamed mixture and stirring for five minutes at 100 rpm [34]. Similarly, [PERSON] et al. and [PERSON] et al. employed methods in which cement and water were mixed at ratios of 0.4 and 0.6, respectively, before adding fibers and mixing for uniform distribution. Foam was then introduced, with its volume carefully controlled to achieve the desired density [35]. Experimental studies have further demonstrated the efficacy of various fiber types in enhancing the mechanical properties of foamed concrete. For instance, [PERSON] et al. found that adding 0.4% (by volume) of polypropylene (PP) fibers increased compressive strength by 35% [36]. Similarly, incorporating 1.5% carbon fibers improved compressive strength by 36%, with the combination of PP fibers yielding even greater enhancements [37]. [PERSON] et al. investigated poly(vinyl alcohol) (PVA) fibers, PP fibers, and recycled fibers from damaged wind turbine blades (comprising glass fibers and resin). Their findings revealed that 0.25% PVA fibers increased compressive strength to 1.50 MPa, whereas excessive PP fiber content led to agglomeration, negatively impacting strength. Recycled fibers improved strength to a lesser extent due to their larger diameter and uneven dispersion, which reduced their reinforcing effectiveness [38]. Despite these challenges, fiber reinforcement in foamed concrete mitigates key limitations, such as reducing the number and size of pores. However, excessive fiber content may puncture air bubbles during mixing, compromising foam stability [39]. Additional studies have indicated that incorporating basalt fibers and marble powder enhances the physico-mechanical properties of foamed concrete while reducing drying shrinkage [40; 41]. Foamed concrete, a cement mortar mixed with a foaming agent, offers significant advantages due to its reduced density and high thermal efficiency. However, its application in 3D printing is often constrained by structural deformations in the lower layers caused by the weight of successive layers. Fiber reinforcement has been shown to enhance the stability of foamed concrete during the printing process by mitigating cracking and distortion, improving surface quality, and minimizing material settlement.