Printability and rheological properties of 3D printing ultra-high ductility magnesium phosphate cement-based composites

With the aim to develop a 3D printing ultra-high ductility magnesium phosphate cement-based composites (3DP-UHDMC), the effects of thixotropic agent type and dosage, magnesium-phosphate ratio (M/P), water-solid ratio (W/SO), powder-binder ratio (P/B), borax-MgO ratio (BO/M) and PE fiber volume content on the printability and rheological properties were studied. Furthermore, a correlation between printability parameters (filament width, tan θ ) and rheological characteristics (yield stress, consistency coefficient) was established to predict printability under varying rheological behaviors. The optimal mixture proportion for 3DP-UHDMC was identified and a comparative analysis of the mechanical properties of cast and printed specimens was then completed. Experimental results indicated the optimum mixture proportion for 3DP-UHDMC as below: attapulgite content of 10%, M/P of 2.5, W/SO of 0.10, P/B of 0.35, BO/M of 0.3, and PE fiber volume content of 1.5%. The relationship between the filament width and the dynamic yield stress is a negative power function. The tan θ and static yield stress, as well as the spread diameter and dynamic yield stress, exhibit a negative exponential function relationship. Printability factors can be characterized by rheological parameters and optimal printability occurs within specific rheological parameters ranges: dynamic yield stress (284.87-541.09Pa), static yield stress (3379.78-4996.16Pa), and consistency coefficient (643.99-1016.41Pa·s n ). Compared with cast specimens, printed specimens exhibited reduced compressive strength and lower ultimate tensile stress, yet exhibited enhanced ultimate tensile strain.