This study investigates the optimization of recycled coarse aggregate (RCA) in 3D concrete printable ink by partially replacing natural coarse aggregates in 20% increments from 0% to 100%. The recycled concrete aggregate (RCA) was characterized for its morphological and physical properties. The rheological parameters of the ink such as viscosity, yield stress, and thixotropy were evaluated. Furthermore, extrudability, printability, and shape retention were assessed to determine the 3D printing performance of the ink. Mechanical performance was determined through compressive, flexural, and ultrasonic pulse velocity (UPV) tests. Durability was assessed using the Rapid Chloride Penetration Test (RCPT) and water absorption. Characterization results showed that the processed aggregates had a predominantly spherical morphology, enhancing the workability of the 3DCP ink. The study identified a yield stress range of 1.5–2.5 kPa as the optimal printability window, ensuring a balance between pumpability and buildability in 3D printable inks. At 40% RCA replacement, the ink achieved 82.76% structural recovery in thixotropy, indicating superior shape stability after shear, along with an open time of 60 min. The 28-day compressive strength of inks with 40% RCA and 40% RFA showed increases of 17.08% and 17.17%, respectively, compared to the control ink attributed to improved particle packing. Furthermore, the RCPT charge passed was significantly lower at this replacement level, indicating reduced chloride ion permeability. Overall, the findings establish 40% RCA replacement as the optimal proportion, providing an effective balance of rheological behavior, mechanical performance, durability, and microstructural refinement for 3D printable concrete applications.