Effect of metakaolin on the fresh and hardened properties of 3D printed cementitious composite

3D concrete printing (3DCP) receives worldwide attention, however, incorporating metakaolin (MK) as rheology modifier to develop 3D printed cementitious composites (3DPCC) is limited. In this study, the effect of MK was studied from the perspectives of both fresh and hardened properties. Results showed that compared with control, static yield stress, dynamic yield stress, and viscosity increase by 285.4%, 129.5%, and 49.2% with 10% MK. The increase in the thixotropic area showed that the addition of MK improves the buildability. Meanwhile, the specimens added with MK exhibited increased maximum stress and elastic modulus under unconfined compression, indicating that MK could enhance the early performance of the 3DPCC. Moreover, the stiffness development process of 3DPCC was observed from its failure pattern at fresh state, and MK was found to accelerate the failure pattern change from plastic failure to shear failure. Besides, MK also showed improved 3DPCCs' mechanical properties and the inhibition of the drying shrinkage because of its pozzolanic activity and filling effect. It is believed that MK positively affects both fresh and hardened properties of the 3DPCC and is therefore recommended to be utilized in 3DCP.