Exploring material synergies: earth-based materials and steel applications in modern construction.

This paper presents a critical review of reinforcement strategies applied to earth-based building materials for 3D printing, with a focus on both natural and metallic solutions. Several recent studies were analysed to evaluate the mechanical, thermal and environmental performance of composites reinforced with plant fibres, biopolymers and steel fibres (both industrial and recycled). Natural reinforcements have been shown to improve compressive strength, shrinkage crack control and thermal insulation; however, they have limitations in terms of long-term durability and mechanical robustness. On the other hand, steel fibres, widely used in cementitious composites, offer superior performance in tensile strength, fracture toughness and crack control, although their application in 3D printing with earth materials is still little explored. Based on the results analysed, this paper proposes the incorporation of recycled steel fibres as a promising strategy to improve both the structural reliability and sustainability of earth 3D printed components. Further experimental investigations are recommended to match fibre dimensions, treatments and volume fractions to the printable earth matrices, as well as to develop hybrid reinforcement systems combining natural and metallic fibres.