The printable and hardened properties of nano-calcium carbonate with modified polypropylene fibers for cement-based 3D printing

Cement-based 3D printing (3DP) technology shows an extensive prospect in the practical application of engi-neering. Yet, the 3DP material is one of the main factors restricting its rapid development in civil engineering. This study applies the nano-CaCO3 (NC) with modified polypropylene (PP) fibers to modify the cement-based material, and the printable and hardened properties of the mixture are tested. The results indicate that NC can reduce the pastes' fluidity and increase the pastes' yield stress, and significantly enhance its printable and hardened performances. When the NC content is 2 wt%-3 wt% of the binder, the printable and hardened properties of the mixture are the best. In particular, the compressive strength of the 3DP specimens with 3 wt% NT content is the best, which is 34% higher than that of the blank group. Yet, the splitting tensile strength of the 3DP specimens with 2 wt% NT content is the best, and the interlayer-direction tensile strength of each group is smaller than the vertical-direction tensile strength. Interestingly, when the NC content is 2 wt%-3 wt% of the binder, compared with the cast specimens, the printed specimens present superior physical-mechanical prop-erties, which indicates the superiority of 3DP technology. The scanning electron microscope (SEM) observation reveals that NC can improve the adhesion on the surface of modified PP fiber, which is also beneficial to the improvement of the hardened properties of the specimens. Besides, the microstructure analysis shows that NC can refine the pore structure, accelerate the hydration process and reduce the mic-cracks.