Study on the Effects of Nozzle Proximal Carbonation Mixing and Vacuum Dewatering on the Printability and Mechanical Properties of the 3D Printed Construction Mortar

This paper investigates the printability and mechanical properties of 3D printed construction mortar (3DPCM) through the methods of vacuum dewatering and carbonation mixing, wherein flowability and extrudability serve as critical indicators of mortar printability. The results demonstrate that for mortar with a low water-to-binder ratio, both carbonation mixing and vacuum dewatering significantly reduce its rheological properties. Although a reduction in rheological performance is also observed in mortar with a high water-to-binder ratio by 7%, the effect is less pronounced. Furthermore, either carbonation mixing or vacuum dewatering effectively enhances printability, enabling highly flowable mortar to exhibit favorable printing performance while also markedly accelerating the hardening rate, thereby improving the shape retention of printed specimens. Additionally, the compressive strength can be enhanced by 4.1–4.6%. The printing process incorporating carbonation mixing or vacuum dewatering can enhance the interlayer bonding strength of mortar with high flowability; however, when both methods are applied simultaneously, the interlayer strength may decrease due to excessively rapid hardening. The final results indicate that vacuum dewatering and carbonation mixing can effectively improve the printability and buildability of more fluid mortar, providing feasibility for directly applying a wider range of mix proportions in printer-based manufacturing.