Evolution of Microstructure-Rheology-Mechanical Properties: A Multiscale Analysis of Steel Slag Cementitious Composites for 3D Printing

抄録

Focusing on the recycling of construction waste and intelligent construction, this study investigates the application of steel slag in 3D-printed cementitious composites. The work focuses on resolving the key technical challenges of rheological regulation and the mitigation of printed component anisotropy, with the aim of achieving high-performance fabrication. Through integrated rheological testing, mechanical characterization, and microstructural analysis, the mechanisms governing rheological behaviour and the evolution of mechanical properties are elucidated. The findings reveal that the incorporation of 30% steel slag increases the static yield stress of the paste from 2140.2 Pa to 2714.8 Pa—a rise of 26.9%—whilst the dynamic yield stress increases from 231.23 Pa to 369.61 Pa, corresponding to a 59.85% enhancement. The plastic viscosity, however, exhibits only a marginal increase from 5.69 Pa·s to 5.90 Pa·s. The inclusion of steel slag retards structural build-up, resulting in diminished thixotropy. The low hydraulic reactivity of the slag and the concomitant reduction in cement content led to a decrease in the formation of C–S–H gel and a coarsening of the pore structure, with the total porosity increasing by 21.17%. Consequently, the compressive strength declines from 45.2 MPa to 41.8 MPa, a reduction of approximately 8.7%. Interlayer splitting tensile tests further indicate that the 30% steel slag substitution reduces interlayer bond strength by roughly 14.9%. Moreover, the decrease in ultrasonic pulse velocity and the increase in apparent defect ratio derived from interlayer defect analysis collectively confirm the pronounced anisotropy introduced by the printing process, with the presence of steel slag exacerbating both interlayer defects and the degree of anisotropy. This study provides a theoretical foundation for balancing the rheological benefits of steel slag in 3D-printable materials against the attendant mechanical penalties, and it underscores the necessity for future optimization through material modification and process refinement.