Plastic shrinkage mitigation and prediction of 3D printed concrete via iron tailings powder incorporation

Due to the lack of formwork, 3D printed concrete (3DPC) is prone to plastic shrinkage at the early stage, leading to potential cracking and thus compromising the mechanical performance of printed components. To address this issue, this paper utilizes low-cost iron tailings powder (ITP) to suppress the plastic shrinkage of 3DPC without impairing its mechanical performance. The results indicate that replacing river sand with 20 vol% ITP (the ITP20 group) has the best effect in inhibiting plastic shrinkage strain of 3DPC, decreased by 55.2% compared to the reference group at 3 h. This is attributed to its rapid stiffness development and reduced capillary pressure. At 3 h, compared with the reference group, the plastic strength and elastic modulus of the ITP20 group increase by 43.8% and 92.4%, while the water evaporation degree and capillary pressure decrease by 35.3% and 72.1%, respectively. Compared with the reference group, the pore structure of the ITP20 group is refined, resulting in an increase of approximately 20% in its 28-d compressive strength in all directions. Finally, the proposed semi-empirical prediction model for plastic shrinkage of 3DPC is validated using the data from this study and other 3DPC incorporating recycled brick fine aggregate, with relative errors all less than 10%. These findings not only provide a new pathway for the utilization of iron tailings but also reduce the raw material cost of 3DPC while improving its performance.