Anomalous matrix and interlayer pore structure of 3D-printed fiber-reinforced cementitious composites

Ordinary 3D-printed neat cement paste generally possesses a porous interface between two neighbored filaments. Our work demonstrates that the addition of glass microfibers into cementitious slurries may lead to an anomalous pore structure, i.e., the increased porosity of the inner and outer matrices in filaments and the densified interlayer between filaments in fiber-reinforced cementitious composites (FRCC). Limited glass microfiber addition (0.6%) has no benefits to the bending strength of FRCC beams, the compressive strength of filament matrix, and the bonding behaviors between filaments. The coupled mechanisms of lubrication layer and pressurized bleeding on the surface of filaments, and air-void entrapments in the matrix of filaments were proposed to account for the formation of the anomalous pore structure and strengths. Our findings would deepen the understanding of matrix-interlayer structures in 3D-printed FRCC towards better tuning and design of 3D printing-based additive manufacturing.