Additive Manufacturing of Ultra-High-Performance Concrete: From Mechanical Characterization to Large-Scale Application

In this work, extensive experimental investigations were conducted on 3D printable Ultra-High-Performance Concrete (UHPC) at multiple scales. Initially, nanomodification techniques were employed to transform the self-leveling nature of UHPC into a more viscous mix using nanomaterials such as nano clay, which showed no detrimental effects on the mechanical performance of cast samples tested under uniaxial compression, split tension, and notched three-point bending. The developed mix then underwent a comprehensive experimental program to evaluate its rheological performance and was subsequently tested using various 3D printing systems featuring different automation setups, extrusion mechanisms, pumps, and nozzle configurations. To assess mechanical performance without compromising the integrity of printed features, novel surface preparation techniques were introduced, unlike conventional approaches that typically involve cutting or coring printed elements. Additionally, innovative interlayer enhancement methods were implemented to mitigate the anisotropic behavior characteristic of layered structures. Large-scale experiments were also conducted on two-way 3D printed laminated slabs with varying layer orientations. The results revealed that printability is not solely a material property but also a process-dependent characteristic. The novel capping method provided optimal conditions for mechanical testing while preserving the integrity of printed features. Furthermore, the proposed interlayer enhancement techniques significantly improved interlayer bonding and effectively prevented failure at the interfaces. Overall, the laminated 3D printed slabs exhibited excellent mechanical performance, outperforming their traditionally cast counterparts.