Soil–Cement Mixtures with Fiber Reinforcement in 3D Printing: Challenges and Opportunities for Sustainable Construction

Additive manufacturing with soil–cement mixtures is emerging as a disruptive approach to advancing sustainable manufacturing processes. However, its industrial scalability remains limited by material brittleness and a lack of process standardization. This study presents an integrative literature review that critically evaluates the influence of fiber reinforcement on the 3D printing process and the mechanical performance of soil–cement mixtures within the context of sustainable construction and circular economy principles. The analysis integrates fresh-state rheological behavior with hardened-state performance, showing that an optimized fiber dosage (0.3–0.5% by volume) shifts the failure mode from brittle to quasi-ductile while reducing crack propagation by approximately 60%. Additionally, the study compares various fiber types, including synthetic and natural alternatives. The results show that synthetic fibers used at low dosages (0.5–1.0% by volume) provide the greatest improvements in tensile strength and post-cracking ductility. In contrast, natural fibers, typically used at higher dosages (8.0–13.0% by volume), mainly improve toughness and thermal performance, with more limited gains in strength. The review also identifies key gaps in the existing literature, such as a lack of standardized protocols for measuring process parameters and the need for studies that address long-term durability and comprehensive lifecycle assessments. These findings outline a clear research roadmap to support the consolidation of reinforced soil–cement as a resilient and sustainable material for next-generation additive manufacturing.