Effect of Additives on the Performance of 3D-Printing Ultra-High Performance Concrete (2025-03)¶

Developing 3D-printable (3DP) ultra-high performance concrete (UHPC) represents a significant hotspot in the concrete construction field. However, conventional UHPC cannot meet the requirements of printability, and the incorporation of additives is considered an effective strategy to solve these problems. The research on 3DP-UHPC from the perspective of additives in this field is relatively lacking. This study systematically investigates the printability and mechanical properties of 3D-printed ultra-high performance concrete (3DP-UHPC) by combining the hydrated phase, pore structure and micro-morphology of 3DP-UHPC with two different types of additives: inorganic nanomaterials (bentonite (BT)) and chemical polymers (polyacrylamide (PAM)). The results show that the fluidity and extrudability of 3DP-UHPC gradually decrease with increasing additive content while demonstrating an enhancement in buildability. Moreover, BT and PAM have different effects on the flexural strength, flexural strength and interlayer bonding strength of 3DP-UHPC. Although BT and PAM own different mechanisms of function for promoting the hydration of 3DP-UHPC, they can reduce the porosity of 3DP-UHPC and increase the mechanical properties of the matrix. This study shows that 3DP-UHCP displays better printability and mechanical properties when the BT and PAM doping are 0.5% and 0.06%, respectively.