3D Printability of Recycled Steel-Fiber-Reinforced Ultra-High-Performance Concrete (2025-01)¶

3D printing ultra-high performance concrete (UHPC) can be used for additive construction of structural components, which significantly reduces the reliance on steel reinforcement. This study investigates the effects of water-to-binder (w/b) ratios, recycled steel fibre (RSF) volume fraction and thickener content on the rheological behaviour, flowability, extrudability, buildability and shape retention ability of 3D printing RSF-reinforced UHPC. The results show that decreasing the w/b ratio, RSF incorporation and thickener incorporation increase the static and dynamic yield stress of the mixture. The dynamic yield stress of the mixture increases by 27.37 % when the volume fraction of RSF is increased from 1 % to 3 % at the same w/b ratio and thickener content. The addition of thickener increases the extrudability and buildability of 3D printing RSF-reinforced UHPC, which is mainly related to the adsorption of the thickener on the surface of the cementitious material particles and the introduction of bridging forces in the system of neighbouring cementitious material particles. The shape retention ability of 3D printing RSF-reinforced UHPC can be improved by increasing RSF volume fraction and thickener content. In addition, the mixture with a w/b ratio of 0.16, RSF volume fraction of 3 % and thickener content of 0.1 % shows the best printability.