To optimize the shape stability of 3D-printed white calcium sulfoaluminate (WCSA) cement composites, oyster shell powder (OSP) and cuttlebone powder (CBP) were introduced as white admixtures to regulate rheological properties and printability. The setting behavior, rheological properties, and shape stability of the WCSA cement composites were evaluated by Vicat setting-time tests, rotational rheological measurements, three-stage thixotropic recovery tests, and structural deformation measurements, together with mechanical strength tests, XRD, and SEM analyses. The results showed that the incorporation of OSP and CBP shortened the setting time of WCSA cement composites. The initial and final setting times decreased from 41 min and 67 min to 17 min and 30 min in the WCSA cement composites with OSP, and from 42 min and 66 min to 20 min and 33 min in the WCSA cement composites with CBP, which improved printing operability. As the OSP and CBP content increases from 0% to 24%, the dynamic yield stress of WCSA cement composites increased from 48.83 Pa to 530.59 Pa and 60.30 Pa to 1085.80 Pa, respectively. The thixotropic recovery degree of WCSA cement composites increased from 57.89% to 86.46%, and 56.60% to 92.14%, respectively. As the OSP and CBP contents increase from 0% to 24%, the structural deformation decreased from 12.39% to 6.91% and 13.29% to 5.12% respectively, which improved buildability of the printed structures. In addition, although OSP and CBP reduced the mechanical strength of WCSA cement composites compared with the control group, the flexural and compressive strengths gradually recovered as the contents increased from 6% to 24% due to the enhanced filling effect and improved particle packing. This study provides a reference for the application of marine calcareous solid wastes in sustainable 3D-printed cementitious materials.

The insufficient shape stability and uncontrollable rheological behavior of 3D printed cement composites (3DPCCs) still limit their wider application in construction. In this study, graded carbonated steel slag powder (CSS1 and CSS2) was used to adjust the rheological properties of 3DPCCs based on the oscillation shear and controlled shear-rate protocols, providing a sustainable and novel strategy for improved printability and mechanical properties. The results showed that the incorporation of carbonated steel slag into 3DPCCs effectively improved the viscoelasticity and yield behavior. As the carbonation time increased from 0 d to 21 d, the dynamic yield stresses of 3DPCCs with CSS1 and CSS2 increased from 126.08 Pa and 116.38 Pa to 707.29 Pa and 509.29 Pa, respectively. In addition, the structural deformation of 3DPCCs with CSS1 and CSS2 decreased from 20.35% and 21.61% to 9.83% and 11.29%, respectively, while the 3-day compressive strength increased from 8.5 MPa and 6.0 MPa to 14.2 MPa and 13.2 MPa, respectively. In conclusion, the carbonated steel slag shows great application potential in improving the rheological behavior and printability of 3D-printed cement composites.