Magnesium phosphate cement (MPC) hardens rapidly and gains high strength in a short time, ranging about several hours to the level of normal strength of ordinary Portland cement concrete. The magnesium phosphate cement binder is produced from the reaction between magnesium oxide and phosphate in water at room temperature.
The magnesium phosphate cement binder offers several advantages compared with ordinary Portland cement binder. Not only does it set quickly but also possesses great strength and satisfactory durability.
The MPC is able to bond with different substrates like concrete, metals, wood, asphalt, and various plastics. The MPC binder systems are used mainly for dry shotcrete mixes, for rapid setting and hardening patching mortar or dry-mix products, and protective coatings.
Handling MPC Mixture
Magnesium phosphate cement concrete mixture releases substantial heat. That is why the utmost precautions shall be considered during material handling. The setting of MPC in or on equipment once it has been mixed with water shall be avoided. That is why it is advised that water not be added to the dry MPC mix till ready for material placement.
Setting times of 10 to 20 min are most common which may give an early strength development of 14 MPa within 2 hr, which may be increased to 45 to 60 min at room temperature for mixtures with retarders.
Properties of MPC
There are several desired engineering properties that concrete produced using the MPC would provide:
- Good durability
- High strength
- Low shrinkage rates
- Low permeability
- Abrasion resistance is similar to that of ordinary Portland cement concrete
- Resist impact and scratch
- Low electrical conductivity
- Good thermal conductivity
Advantages
- Sustainable technology is used in the production of MPC.
- Sets quickly and gain strength early. Rapid repairs of patches may be economically achieved by MPC.
- Excellent freeze and thaw resistance.
- Little shrinkage properties and hence shrinkage cracks are eliminated.
- Resist water penetration due to the formation of insoluble complexes. This insoluble formation is generated when a soluble of phosphate is mixed with MPC concrete
- Non-combustible and resist fire
- Bond with wide range of ingredients and substrates
- Corrosion resistance
Disadvantages
- The reaction of carbonated surfaces (calcareous aggregates) with the phosphoric acid produces carbon dioxide (CO2) that weakens the paste aggregate bond. MPC reacts chemically with the dust of the fracture or carbonated zone and causes a reduction in bond strength at the bond interface.
- MPC cannot be placed in a dry pack condition (water content cannot be adjusted for this placing method) and hard troweling is not possible.
- Any variation of the water content from that specified by the manufacturer reduces both the strength and the durability of the MPC mortar.
- MPC can be easily washed off with plenty of water while still wet or within 10-15 minutes of application, but it is very difficult to remove once it has set.
Applications
- Fast patching mixes for bridges/roads; repair of reinforced concrete structure.
- Hazardous waste/nuclear waste encapsulation
- Shotcrete applications
- Mortar for carbon fiber reinforced applications
- Permafrost, low-temperature applications
- Corrosion protective overlays, coatings
- Production of a magnesia-based refractory concrete for fireproofing coatings Applications
- Improving the water-resistance of Sorel cement.
- Production of a high early strength concrete.
