Modification of fresh and hardened properties of 3D-printed recycled mortar by superabsorbent polymers

The high water absorption level of recycled sand limits the applicability of 3D-printed recycled mortar. In this study, superabsorbent polymers (SAPs) were adopted to modify the properties of both fresh and hardened 3D-printed recycled mortar. The effects of various SAP dosages, particle sizes, and addition methods were carefully examined. X-ray diffraction (XRD) and computed tomography (CT) were adopted to observe the microstructure. The test results showed that the addition of SAP effectively improved the printability of the mixed mortar. Particularly, with the addition of SAP, the autogenous shrinkage was reduced by more than 50 %, indicating that the polymer had an obvious inhibitory effect on shrinkage. Furthermore, the hydration of cementitious materials was promoted, resulting in an increase in compressive strength by 27%-69 %. Microstructural analysis further confirmed that the addition of SAP optimized the pore structure and enhanced the density of the 3D-printed mortar but did not change the types of hydration products. Generally, for the modification of 3D-printed mortar with recycled sand, it would be recommended to add SAP at a doping level of 0.4 % with a particle size of 60-100 mesh.