Effect of M/P ratio, w/c ratio, and additive contents on rheological properties of seawater mixed magnesium phosphate cement system

Abstract

Rheological properties play a crucial role in determining the grouting effectiveness of magnesium phosphate cement (MPC) slurry. This study aims to investigate the effects of the magnesia-to-phosphate (M/P) ratio, water-to-cement (w/c) ratio, fly ash (FA), and metakaolin (MK) on the rheological properties of seawater-mixed MPC slurries using rheological tests and low-field 1H nuclear magnetic resonance (NMR). Two methods for incorporating FA were explored to modulate the rheological properties of the MPC. The results demonstrated time-dependent viscosity changes with two distinct phases, including a plateau and a subsequent period of sudden change, with the minimum apparent viscosity occurring as hydration progressed. The apparent MPC viscosity was influenced by the MgO-particle content and the theoretical water consumption, with M/P = 3 exhibiting the lowest apparent viscosity within a w/c range of 0.14–0.2. Moreover, the addition of FA increased the minimum apparent viscosity of the MPC slurry. During the pre-hydration stage, using FA as an MPC substitute yielded better rheological properties than using FA as an MgO substitute. The MK increased the apparent MPC viscosity considerably and adversely affected its rheology.