Mechanical Properties and Anisotropy of 3D-Printed Concrete Modified with Multiscale Materials Based on Optimized Printing Process Design (2025-09)¶

The layer-by-layer extrusion process of 3D-printed concrete (3DPC) often leads to insufficient interlayer bonding strength, which compromises the overall mechanical performance and intensifies anisotropy. To address this issue, this study systematically enhances the mechanical properties of 3DPC through the optimization of printing parameters and multiscale material modification. First, key printing parameters, including nozzle diameter, extrusion speed, and layer height, are optimized based on extrusion compactness and print quality. On this basis, a multiscale composite modification system comprising nano silica (NS, 0–3%), polypropylene fibers (PP, 0–0.6%), and calcium carbonate whiskers (CW, 0–3%) is established. The effects of different dosages on compressive and flexural strength anisotropy, as well as interlayer defect evolution during curing, are systematically investigated. SEM-EDS and X-CT analyses reveals that CW enhances matrix strength by filling pores and deflecting cracks, NS improves structural compactness through nucleation effects, and PP fibers bridge cracks to increase energy dissipation. The combination of 1% NS, 1% CW, and 0.2% PP exhibits the best overall performance, significantly reducing anisotropy and enhancing mechanical strength and toughness, with the lowest porosity reaching 1.1%. This study provides both theoretical and experimental support for the synergistic toughening mechanisms of multiscale functional materials and the optimization of 3DPC printing processes, demonstrating strong potential for practical engineering applications.