Performance of Novel Magnesium Phosphate Cement Using Sodium Dihydrogen Phosphate

Magnesium phosphate cements (MPC) are formed by reacting dead burned magnesia with soluble phosphates at room temperature, which are found to be quick setting with significant strength. The reaction is a highly exothermic process with fast hardening process. It is an acid–base reaction to form insoluble phosphate binder. It acts as an alternate binding material to normal Portland cement concrete. MPC is mostly prepared with a retarder, such as borax, to slow down the quick setting of the binder. Dead burned magnesia reacts with phosphate in the hydration of MPC produces struvite which attach onto the MgO particles which have not reacted, leading to the formation of solid particles. The strength and durability of MPC depend on the quantity and characteristics of the ingredients, water to binder ratio and admixtures. In most case of MPC, the phosphates used are dihydrogen phosphates of ammonium and potassium. This study used phosphate of sodium dihydrogen phosphate instead of phosphates of ammonium and potassium. Novel magnesium phosphate cement using dead burnt MgO and sodium dihydrogen phosphate (NaH2PO4) has been developed. Chemically inactive dead burnt MgO used was produced by sintering raw MgO at a controlled temperature of 1750 °C in rotary kiln. The MgO to NaH2PO4 ratio adopted was from 4:1 to 1:4. The study involved the mechanical properties including compressive and split tensile strength, durability and microstructure properties including scanning electron microscope and EDAX, for various proportions. The optimum mix for magnesium sodium dihydrogen phosphate cement (MNPC) was arrived as 70% dead MgO and 30% sodium dihydrogen phosphate which gave the better result in terms of strength and durability.