Effect of wollastonite content on rheology and mechanical properties of 3D printed magnesium potassium phosphate cement-based material of MgO-SiO2-K2HPO4

Magnesium potassium phosphate cement-based material (MKPCs) of MgO-SiO2-K2HPO4 with varying wollastonite powder (WS) contents (0-20 %) were developed. Rheological performance (thixotropy, yielding behaviours and viscoelasticity) and mechanical strength were studied. Test results show that the addition of 15 % WS improved the thixotropy significantly. A thixotropy index was introduced to model the variation of static yield stress, which increased with increasing content of WS but decreased with the resting time. The fast fluctuation of thixotropy changes in early age was in favor of decreasing the structure deformation of bottom layer. The critical stress and the LVR were enlarged with the increasing WS contents. The Lissaju-Bowditch curves show that the inclusion of WS changed the rotation variation of curves from elliptic to straight-line, representing the slurry behave as elastic-solid state. The strength of mixture with 15 % WS reached to the maximum value, but excessive 20 % WS showed adverse effect on strength. It was verified mixture modified by suitable amount of 15 % WS would generally favor the excellent strength and printability. Detailed SEM images and rheological plots effectively illustrated the microstructural changes and flow behavior, enlarging the understanding of MgO-SiO2K2HPO4 for 3D printing applications.