Tailoring Ultra-High Performance Concrete for Additive Manufacturing (2026-02)¶

Tailoring printable ultra-high-performance concrete (UHPC) for additive manufacturing requires a rigorous balance between fresh-state printability and post-print mechanical and durability performance. In this study, the roles of superplasticizer (at distinct dosages of 1.93%, 2.17%, and 2.41%) and viscosity-modifying admixture (VMA) (2.5%, 3%, and 3.5%) in governing the printability-performance interplay of UHPC were systematically investigated through a three-level experimental framework by covering fresh-state properties, printability, and post-print performance. The results demonstrate that while increased superplasticizer dosage can enhance the flowability and extrudability of UHPC, it reduces water retention and shape stability, whereas VMA played an essential role in favoring water retention and buildability at the expense of flowability. The synergistic balance between superplasticizer-induced lubrication and VMA-induced cohesiveness resulted in optimal extrudability and printability in two groups (M2 with low superplasticizer and intermediate VMA, M6 with intermediate superplasticizer and high VMA), while the superior interfacial bonding, strength, and impermeability of M2 to M6 indicate that increases of superplasticizer (from 1.93% to 2.17% ) and VMA (from 3.0% to 3.5%) resulted in 26.0% lower compressive strength and 29.8% lower bulk resistivity in printed UHPC. Directional dependencies observed in strength and electrical resistivity further confirmed the anisotropic nature of 3D-printed UHPC arising from layer-by-layer deposition and interlayer interfaces. The overall findings highlight the necessity of a performance-based mixture design approach that balances the amounts of superplasticizer and VMA to maximize their synergy in jointly optimizing the fresh-state behavior, printability, hydration kinetics, and post-print mechanical and durability performance in tailoring 3D-printable UHPC.