Mix design and rheological properties of magnesium potassium phosphate cement composites based on the 3D printing extrusion system

The magnesium potassium phosphate cement composites (MPCCs) with rapid setting, high early strength and low shrinkage performances show considerable potential for 3D printing. In this study, the synergistic effects of magnesium to phosphate (M/P) mass ratio, borax content and fly ash content on the the initial setting time and rheological properties of 3D printed MPCCs (3DP-MPCCs) were investigated using response surface methodology (RSM). The dynamic yielding behaviours are obtained based on Herschel-Bulkley model. The effects of mix design on deformation rate and compressive strength of 3DP-MPCCs were discussed. The results showed that the initial setting time of 3DP-MPCCs was prolonged to 30 min to 90 min by optimizing the mix design and decreased with the increase of M/P mass ratio. The incorporation of borax significantly reduced the consistency factor, which was beneficial to the extrudability of 3DP-MPCCs. High M/P mass ratio was the critical factor for the better buildability of 3DPMPCCs, which can be further improved by increasing the FA content. Finally, the 3DP-MPCCs with M/P mass ratio of 3.0, 40% borax and 25% FA was determined as the optimal mix design, showing the minimum deformation rate of 0.28% and highest compressive strength of 32.59 MPa, respectively. ? 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study investigated the effects of mix design on the performance of magnesium potassium phosphate cement composites (MPCCs) for 3D printing, focusing on initial setting time and rheological properties. By optimizing the mix design, the initial setting time was prolonged and the compressive strength was improved.