Influence of Mg(OH)2 on the Hydration Process and Properties of Magnesium Phosphate Cement

The magnesium raw material for magnesium phosphate cement (MPC) is mainly dead-burned MgO. However, the high-temperature calcination required for producing dead-burned MgO results in high costs and excessive carbon emissions. magnesium hydroxide (Mg(OH)2) is abundant, has low production costs, and is environmentally safe and pollution-free. Mg(OH)2 is a rich source of low-cost, non-polluting, safe and environmentally friendly, which is of great significance to alleviate the problem of high cost of use and carbon emissions if it can be adopted in large quantities. Therefore, in this work, Mg(OH)2 was used instead of partially dead-burned MgO, by means of tests such as X-ray diffraction, thermal analysis, scanning electron microscopy and energy spectrum analysis, the effects on workability, hydration process, strength development and mi-crostructure were investigated. The results showed that the incorporation of Mg(OH)2 accelerated the hydration process of MPC, the fluidity of the slurry was reduced and the setting time was shortened. In this paper, the working properties are improved by retardation means such as water glass heat treatment modification. The hydration temperature and pH of magnesium phosphate cement decreased significantly with the incorporation of Mg(OH)2, increased number of K-struvite crystals in the later 28 d, compressive strength decreases with increasing Mg(OH)2 content. When Mg(OH)2 is doped within 50%, its late strength decreases in the range of 15%, with the increase of Mg(OH)2 doping, more hydration products are formed by the reaction of Mg(OH)2. When Mg(OH)2 doping accounted for 66.6%, the reactivity of dead-burned MgO was reduced from an average value of 22% to 7%. In conclusion, the preparation of magnesium phosphate cement with large amount of Mg(OH)2 is feasible and can ensure that the later mechanical properties of the material can meet the requirements of engineering applications. It has potential applications for reducing the cost of magnesium phosphate cement use and carbon emissions. © 2024 Cailiao Daobaoshe/ Materials Review. All rights reserved.