Engineering mechanics of bio-inspired architected cementitious materials (ACM) and composites (ACC) enabled by digital fabrication

Concrete is inherently weak and brittle under tension, making it susceptible to cracking under mechanical and environmental loading. Recent advances in digital fabrication enable control over spatial arrangements of cementitious materials across meso-to-macro length scales, shifting cementitious design from passively formed microstructures to intentionally engineered architecture. This review introduces two emerging classes of cementitious materials: architected cementitious materials (ACMs), formed by spatially arranging a single cementitious constituent (e.g., paste, mortar, concrete or fiber-reinforced counterparts), and architected cementitious composites (ACCs), formed by arranging multiple constituents such as concrete and polymer phases. We synthesize progress in bio-inspired ACMs and ACCs over the past decade, designed to improve mechanical and functional properties through digital and advanced manufacturing processes. Fundamental design principles, beyond mimicking geometry, inspired by several biological systems such as mantis shrimp, coelacanth fish scales, seashells, cortical bone, sea sponge, and nacre are discussed and pertinent engineered underlying (dissipative) toughening mechanisms are highlighted, including crack twisting, deflection, interlocking, arrest, re-nucleation and polymer bridging/deformation, and tablet sliding. Key corresponding novel fabrication pathways enabling the design of ACMs and ACCs are highlighted, including 3D-printing, hybrid 3D-printing/casting, multi-material fabrication, and laser processing. Experimental, theoretical, and numerical approaches are synthesized to demonstrate how spatial arrangements and multi-materiality link design variables to toughening mechanisms. Key findings illucidate that controlled spatial arrangements and multi-materiality enabled in ACMs and ACCs demonstrate a range of several-fold to two-orders-of-magnitude enhanced fracture toughness compared to conventional cement-based counterparts, while maintaining or improving flexural strength. However, future progress requires resolving size effects, process-induced defects, reinforcement integration, and durability to enable scalable, high-performance ACMs and ACCs for infrastructure applications.