11 Aug 2025

3D Printing of Ultra-High-Performance Concrete: Shape Stability for Various Printing Systems

Abstract: Attention is on concrete 3D printing for its potential in structure optimization, life-cycle extension, emission reduction, and cost savings. Previous studies tailor a mix to a specific printing system and evaluate printability based on measurements of pumpability, extrudability, and buildability. For this investigation, an experimental program was conducted using various printing systems on a nano-modified UHPC mix. A medium-scale gantry and a large-scale ABB robotic arm were utilized, piston-type extruder and an auger system were employed, various nozzles, including circular and rectangular designs, were tested, and a cavity and Thom-Katt pump were used. Results indicated the shape stability of the UHPC mix is influenced by the printing system. Furthermore, the use of a circular nozzle demonstrated different shape stabilities when the extrusion system was changed from a piston-type extruder to an auger system. Additionally, the method of material pumping to the extrusion system was found to be critical for shape stability of printed layers. The mix failed to maintain its shape post-extrusion when using the cavity pump, which was attributed to higher strain rates imposed on material during the pumping process. This issue was not observed when the piston-type pump was used.