Rheology-tailored 3DP-UHPC: From enhanced printability to impact performance

This study investigated the effects of nano-clay (ANC), hydroxypropyl methylcellulose (HPMC), and other factors on the flowability and slump of 3D printed ultra-high performance concrete (3DP-UHPC). The results indicated that the incorporation of ANC and HPMC, along with an increase in aggregate particle size, leads to reduced flowability and enhanced yield stress. Consequently, a 3DP-UHPC with a dense microstructure and favorable pumpability, extrudability, and constructability was developed. In terms of mechanical properties, the compressive strength of the printed specimens exceeded 160 MPa, outperforming cast specimens with the same mix proportion. Impact tests were conducted to analyze the impact performance and failure modes of 3DP-UHPC under low-energy repeated impacts and high-energy single impact. At a lower impact energy of 20 J, the number of impacts resisted by the 3DP-UHPC in the Z and Y directions was 4–6 and 5–7, respectively, surpassing the 3–4 impacts endured by the Cast-UHPC. Under a higher impact energy of 60 J, the specimens completely fractured after a single impact. The energy absorption capacity of 3DP-UHPC was higher than that of Cast-UHPC, primarily due to the aligned steel fibers induced by the extrusion process. A statistical analysis of the in-plane directional distribution of the fibers was conducted to quantify this effect. These findings highlight the potential of 3DP-UHPC as a viable material for applications requiring both high structural performance and impact resistance in construction.