Enhancing Printability of 3D Printed Concrete by Using Metakaolin and Silica Fume (2025-04)¶

This study investigates the effects of incorporating metakaolin (MK) and silica fume (SF) on the fresh and hardened properties of 3D printed concrete (3DPC). Five mix designs were prepared with MK replacement levels of 0%, 10%, 12.5%, and 15%, along with one mix containing 10% MK and 5% SF. Key performance metrics include flowability, green strength, pumpability, shape retention, buildability, extrudability, compressive strength, and interlayer bond strength. The results showed that increasing MK content generally enhanced early strength gain, shape retention, and buildability; however, a high MK dosage (15%) negatively affected extrudability and caused visible cracking. The mix with 10% MK and 5% SF (MK10SF5) demonstrated the best overall performance, achieving excellent shape retention (S1 = 0.99), the highest buildability (72 printed layers), and the highest compressive strengths: 85.4 MPa for cast specimens and 78.8, 64.4, and 73.0 MPa in the X, Y, and Z directions, respectively, for 3D printed specimens. It also recorded the highest interlayer bond strength of 2.14 MPa. The superior performance of MK10SF5 is attributed to the synergistic effects of MK and SF, which enhance particle packing, cohesion, and pozzolanic reactivity. These findings highlight the potential of MK and SF in optimizing 3DPC for improved printability and mechanical performance.