Effect of Paste Film Thickness on Workability and Strength of Magnesium Phosphate Cement Mortar

In order to better understand the effect of compositional parameters on the properties of magnesium phosphate cement (MPC) mortar, the relationship between the thickness of paste film and the workability and strength of MPC mortar is revealed. A three-parameter filling density prediction model is adopted to study the filling density of sand with different gradations. The validity of the three-parameter filling density prediction model is validated by experimental results. The thickness of the paste film of MPC mortar is calculated with different sand gradations. The results show that the thickness of paste film has a great influence on the slump flow and strength of MPC mortar. The linear positive relationship between paste film thickness and slump flow of MPC mortar. At different sand-to-binder ratios, there is no significant linear relationship between the thickness of the paste film and the mechanical properties. But under the same sand-to-binder ratio, there is an optional thickness of paste film for the strength of the MPC mortar. Comprehensively considering the workability and mechanical properties, magnesium phosphate cement mortar’s optimal paste film thickness ranges from 73 µm to 74 µm. When designing the proportion of magnesium phosphate cement, the appropriate thickness of the paste film can be selected according to the different engineering types and construction environments.