Controlling structural deformation is essential for the structural stability of 3D-printed cement composites. In this paper, carbonated recycled aggregate (CRA) was incorporated into 3D-printed magnesium phosphate cement composites (MPCCs) to control rheology and improve buildability. Experimental results show that CRA increased the static yield stress from 2210.96 to 6238.18 Pa and the storage modulus. When the incorporation of CRA was more than 15%, the phase angle was less than 45°, indicating predominantly solid-like behavior. Additionally, due to the higher porosity, the compressive strength and flexural strength of 3D-printed MPCCs decrease with the increasing CRA content; however, the decline tendency becomes significantly more pronounced when CRA content exceeds 10%. Structural deformation decreased from 14.39% to 6.91%, attributed to the rough surface of CRA, which promotes more uniform stress transfer during stacking. This study demonstrates a simple upcycling route that improves the printing stability and sustainability of 3D-printed magnesium phosphate cement composites (MPCCs).

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.

This study addresses the recycling of construction waste wood and the development of thermal insulation materials by developing a high-belite sulfoaluminate cement-based recycled wood powder thermal insulation mortar (HRTM). High-belite sulfoaluminate cement (HBSC) and building gypsum (GY) were used as hydraulic binders, and recycled wood powder (RWP) was used as a full substitute for natural fine aggregate. The effects of the RWP-to-binder ratio (R/B) and GY replacement ratio on workability, mechanical properties, thermal insulation performance, water resistance, and drying shrinkage behavior were systematically investigated. The hydration products, pore structure, and microstructural evolution were characterized by thermogravimetry-differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and low-field nuclear magnetic resonance. Increasing R/B reduced dry density and thermal conductivity while improving water retention. The maximum water retention rate was 99.22% at R/B = 1/6 and 15% GY. The mechanical properties and drying shrinkage behaviour varied across the GY series and were influenced by GY replacement, water content, and PCE dosage. At R/B = 1/9 with 10% GY, HRTM exhibited a dry density of 992.19 kg/m³, a thermal conductivity of 0.253 W/(m·K), and a 28 d compressive strength of 23.8 MPa. The microstructural results showed corresponding changes in water-bearing hydration products, matrix continuity, and the RWP–matrix interface. These findings support the use of recycled wood powder in lightweight thermal insulation mortar.

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.