Rheology and shape stability control of 3D printed calcium sulphoaluminate cement composites containing paper milling sludge

The shape instability and uncontrollable rheological properties of 3D printed calcium sulfoaluminate cement composites (CSACCs) limit its application in the field of architecture. In this study, paper milling sludge (PMS) was adopted to control the rheological properties using the oscillation and rotation shear protocols, aiming to control the printed structures accurately and achieve the resource utilization. Experimental results show that the incorporation of PMS in the 3D printed CSACCs can effectively improve the viscoelasticity, static yield stress and thixotropy. It should be noted that the thixotropy is the key influencing factor to affect the 3D printed structures. Similarly, according to the rotation variation of Lissaju-Bowditch (L-B) curves, it is confirmed that the thixotropic reconstruction of paste during the cycle can significantly affect the shape stability. Additionally, when the contents of PMS and pre-treated PMS (PPMS) reach 15%, the 3D printed CSACCs present better extrudability and shape stability, and the structure deformation decreases to 9.5% and 7.1%, respectively. In conclusion, the use of PMS and PPMS provides great potential for 3D printed CSACCs with improved rheology and shape stability.