Interlayer reinforcement of 3D printed concrete by the in-process deposition of U-nails

3D concrete printing has tremendous potential for construction manufacturing; however, weak interface bonding between adjacent layers remains a well-known issue that affects the mechanical properties of printed structures. The layers introduce anisotropy and reduce the capacity to resist tensile and shear loads. Reinforcements, inserted perpendicular to the printed layers to traverse the interfaces, can improve these limitations, but the insertion of reinforcements is difficult to achieve in practice, and there are few published studies exploring appropriate methods. This study presents a promising approach using U-shaped nails inserted into concrete during the printing process. The bridging effect and dowel action of the applied U-nails are visualised and analysed to elucidate the toughness improvement. The ultimate tensile strength and shear strength of 3D printed concrete are significantly increased by 145.0% and 220.0%, respectively. U-nails with a filament thickness of 2–2.5 mm are recommended to yield optimal improvement in the interlayer strength

Technology readiness: A global snapshot of 3D concrete printing and the frontiers for development

Since the inception of 3D concrete printing (3DCP) in the early to mid-2000's, the commercial landscape for this technology has expanded rapidly in parallel with developments of relevant materials, production technologies and knowhow. To benchmark the state-of-the-art of 3DCP technology in the construction field, this study presents a systematic review and analysis of 3DCP's development and applications based on information from articles, patents and publicly available data. An estimation of Technology Readiness Level (TRL) for 3DCP has been formulated through expert review, and the evidence suggests this is in the region of TRL6-7 similar to that reported for polymer-based fused deposition modelling processes. A new schema for the TRL assessment process is suggested and applied to two case studies: 1) the production of decorative works; 2) the fabrication of dwellings. Finally, we have identified four frontiers for research and development that should be exploited to raise the TRL of 3DCP