Tough, Ductile, and Strong Hard-Soft Cementitious Composite Enabled by Multi-Material Additive Manufacturing

Abstract

Monolithic cementitious materials lack fracture resistance and are brittle. Advancements in additive manufacturing techniques and architected designs have remained limited in degrees of freedom to use of single (cement-based) constituent. This work charts a new pathway for manufacturing and designing tough, ductile, and strong architected cement-based materials by proposing a multi-material additive manufacturing (MMAM) technique, an integrated manufacturing-design-engineering approach. Cementitious mortar with elastomeric constituents (silicone and polyurethane) are exemplified, through a layered hard-soft architected design, inspired by the microstructure of a sea sponge (glass sponge Euplectella aspergillum). The MMAM technique alternates extrusion of hard-soft composites, enabling systematic control over geometry and constituents of resulting structures. The results demonstrate layered mortar-silicone composites achieved up to 3.9-and 8.8-fold enhancements in fracture toughness and up to 11.7-and 12.4-fold enhancements in ductility relative to monolithic 3D-printed (3DP) and cast mortars, respectively. A coupled large-deformation phase-field-cohesive-zone (PF-CZM) framework was used to systematically probe soft-layer thickness and bulk soft-material properties. Simulations revealed that combining higher-stiffness soft layers with reduced thickness can yield up to a 24-fold increase in work-of-fracture while recovering load-bearing capacity of monolithic mortar. Guided by numerical predictions, experiments on thin, stiffer polyurethane interlayers validated the numerical predictions and provides additional experimental evidence that the proposed (Mortar-PU) composites achieve 82-and 187-fold higher fracture toughness, 22.6fold more ductile, relative to 3DP and cast monolithic references while recovering the flexural strength to levels statistically comparable to those counterparts. These large gains arise from three synergistic mechanisms: crack arrest/deflection, crack bridging, and discontinuous layerwise crack re-nucleation, activated by the layered hard-soft architecture and supported by DIC/AE fracture analyses). The proposed MMAM-enabled fabrication-design-engineering approach can unleash entirely new properties, pathways, and perspectives for imagining next-generation concrete structures.

Keywords: Multi-Material Additive Manufacturing, Tough Hard-Soft Architected Cementitious Composites, Fracture Toughness, Finite-Element, Phase-Field and Cohesive Zone Model Framework