Magnesium Phosphate Cement Commonly Used Mineral Admixtures

Magnesium phosphate cement (MPC) is a special cementitious material, also known as chemically bonded ceramics. It has the advantages of fast setting speed, high early strength, low volume shrinkage, good wear resistance, and can be constructed under low temperature conditions. Crack repair, solid waste heavy metals, biological materials, etc. have a wide range of application value.

1. Fly Ash

Fly ash (FA) is a powder waste produced during coal combustion. Its main mineral composition is glass, and its main chemical composition is SiO2, Al2O3, Fe2O3, CaO, etc.

Adding FA to MPC can prolong its setting time and improve workability. One is that the retarder mainly reacts with MgO particles and adsorbs on the surface of the MgO particles, hindering the reaction of MgO with phosphate. After FA replaces part of MgO, the total amount of MgO decreases and the relative content of retarder increases. The heat of hydration will be reduced, thereby prolonging the setting time. The second is that FA itself can absorb PO43-, preventing the production of K-Struvite, thereby slowing down the coagulation speed of MPC. In addition, in the process of freshly mixed MPC slurry, since the fine glass particles in FA have a certain lubricating effect, the fluidity of MPC can be improved.

2. Slag

The full name of slag is granulated blast furnace slag (GGBS), which is the waste slag produced during the smelting of pig iron in iron and steel plants. Its main chemical components are CaO, SiO2, Al2O3, etc.

In the MPC system, because GGBS is a very active admixture, it can usually shorten the setting time of MPC. In addition, GGBS and MPC form a good particle gradation, and the particle effect improves the fluidity of MPC slurry.