Study on the Rheological Properties and Printability of Multi-Scale Material Modified Mortar for 3D Printing (2025-08)¶

While 3D-printed concrete (3DPC) improves material utilization, construction speed, and sustainability (reducing waste/emissions), its practical use is hindered by difficulties in controlling rheological properties and printability. This study systematically investigates the synergistic effects of nano-silica (NS), calcium carbonate whiskers (CW), and polypropylene fibers (PP) on the rheology and printability of 3DPC. Based on the theories of water film thickness and thixotropy, the mechanisms by which multiscale materials regulate rheological behavior are elucidated. Based on experimental results, a “rheology box” framework is proposed for printable mix design. The combined incorporation of NS, CW, and PP significantly increases paste viscosity and yield stress, enhances structural build-up rate, and improves shape stability and print quality. NS exhibits the most pronounced effect by promoting flocculation and hydration, while CW and PP improve rheology through fiber networking and micro-aggregation. A “Critical Fiber Dosage Theory” is introduced, identifying optimal thixotropic recovery rates at dosages of NS ≤ 2 %, CW ≤ 1 %, and PP ≤ 0.2 %. The established rheology box defines an optimal printable window—viscosity of 32.74–60.06 Pa·s, yield stress of 379.2–1081.03 Pa, and thixotropic area of 20.38–60.58—providing theoretical and practical guidance for the mix design and performance optimization of 3DPC materials.