3D concrete printing (3DCP) is an emerging intelligent construction technology that enables the direct transformation of digital models into physical components, thereby facilitating the precise fabrication of complex geometries. This study investigates the anisotropic mechanical properties and construction applicability of low-carbon 3D printed concrete for reusable formwork systems. Axial compression, flexural, and splitting tensile tests were conducted to examine mechanical anisotropy, and the effects of steel slag and iron tailings replacement levels on mechanical performance were evaluated. Carbon emission analysis was also performed. Using the coefficient-of-variation TOPSIS method, an optimal printable low-carbon mixture was identified, comprising 30% steel slag, 40% iron tailings sand, and 0.3% fibre content, balancing both mechanical performance and environmental benefits. To address the challenges associated with printing large monolithic formwork units, such as excessive weight and demoulding difficulties, three connection strategies for curved wall modular reusable formwork were designed. Finite element analyses were conducted to assess the strength and stiffness of each strategy, and an optimized connection configuration was proposed. The findings demonstrate the feasibility of accurately fabricating complex architectural components using low-carbon 3D printed concrete, providing theoretical and practical support for the industrialized production of large-scale, geometrically complex structures.

Low-carbon and highly printable cementitious materials are crucial for the practical application of extrusion-based three-dimensional concrete printing (3DCP). This study develops and optimizes a one-part alkali-activated concrete suitable for 3D printing through an integrated experimental and evaluation approach. An orthogonal experimental design was employed to investigate the effects of precursor ratio (ground granulated blast-furnace slag, GGBFS, to fly ash, FA), water-to-binder ratio, activator dosage, and retarder content on fresh-state properties, rheological behavior, setting characteristics, and mechanical performance. The optimal mixture was determined using the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) multi-criteria decision method. The mixtures exhibited suitable rheology, with a yield stress of 90–141 Pa and a plastic viscosity of 3.5–7.2 Pa·s, a setting time of 40–96 min, and mechanical performance with compressive and flexural strengths of 29–71 MPa and 4.2–6.9 MPa, respectively. The optimal mixture provided a 95-min printing open time and an acceptable pumping pressure of 1.77 MPa, while full-scale tests confirmed stable extrusion and good print quality. Furthermore, within the defined cradle-to-gate, materials-stage boundary and the adopted inventory factors, the optimized alkali-activated mixture exhibited an embodied CO₂ emission of 0.113 kg CO₂/L, which is approximately 61% lower than that of the reference cement-based printable mixture. The proposed approach provides a systematic framework for designing low-carbon, high-performance one-part alkali-activated materials for extrusion-based 3D concrete printing applications.