Preparation of 3D-Printed Concrete from Solid Waste: Study of the Relationship between Steel Slag Characteristics and Early Performance in 3D Printing

Using steel slag in architectural three-dimensional (3D) printing not only enhances its utilization efficiency but also significantly reduces cement consumption, thereby mitigating carbon emissions. This study evaluated the substitution of steel slag for cement in 3D printing and examined its impact on rheological properties, fluidity, green strength, and early hydration microstructure based on alkalinity level, particle-size distribution, and blending quantity. The relationship between the early properties of 3D-printed steel slag cementitious materials and their pore microstructures was investigated using low-field nuclear magnetic resonance (NMR) tests. The results showed that high-alkalinity steel slag has superior rheological characteristics and generates a larger amount of gel water within the initial 30 min of hydration. Steel slag particles ranging from 5 to 20 mu m had the most significant influence on enhancing the rheological properties of 3D-printed steel slag cementitious materials by facilitating the formation of a flocculated mesh structure during early hydration. Optimal rheological performance was achieved with a dosage level of 10% steel slag, effectively reducing porosity and improving compactness in the mortar.