Shrinkage and Cracking Performance of PP/PVA Fiber-Reinforced 3D-Printed Mortar

Compared with conventional cast-in-place mortar materials, three dimensional (3D)-printed mortar has the characteristics of high cementitious material consumption, low aggregate-cement ratio, and large water evaporation area, which makes 3D-printed materials and structures more prone to plastic shrinkage and cracking. In this study, polypropylene (PP) fiber and polyvinyl alcohol (PVA) fiber were used to optimize the shrinkage and crack resistance of 3D-printed mortar. The effects of PP and PVA fibers on the printability, mechanical properties, shrinkage, and crack resistance of 3D-printed mortar were tested, and the regulation mechanism was explored. The results show that the optimal content of PP fiber for cracking resistance is 0.3%; the corresponding 28-day compressive strength and flexural strength are 39.2 and 6.9 MPa, respectively, and the shrinkage of the material can be reduced by 13.8% after 120 days. A content of PVA fiber higher than 0.2% is recommended for cracking resistance; the 28-day compressive strength and flexural strength reach 41.3 and 8.0 MPa, respectively, and the shrinkage of the material can be reduced by 13.3% after 120 days. Hence, PVA fiber is recommended to control the shrinkage and cracking of 3D-printed mortar.