Plastic shrinkage and cracking of 3D printed mortar with recycled sand

This study focused on the plastic shrinkage and cracking of 3D printed mortar mixed with recycled sand as fine aggregates. The test methods for free and restrained plastic shrinkage were designed and improved to simulate the plastic shrinkage of 3D printed mortar. The shrinkage and the development of cracks under constraints were measured by image processing, and the effect of recycled sand was evaluated. 3D printed natural sand mortar and 3D printed recycled sand mortar with replacement ratios of 25%, 50%,75%, and 100% were tested and analyzed. Results showed that the plastic shrinkage of the 3D printed mortar increased with the increase of recycled sand content. With the higher replacement ratio of recycled sand, the plastic cracking of 3D printed mortar under restraint conditions showed a higher cracking depth. It can be concluded that the 3D printed mortar mixed with recycled sand shows a minor plastic shrinkage rate under a 50% replacement ratio. When a 100% replacement ratio of recycled sand is reached, the 3D printed recycled sand mortar needs additional consideration of shrinkage compensation design to avoid early-age cracking in the plastic stage.