Fresh and hardened state properties, reaction kinetics, and microstructure of potassium, ammonium, and sodium magnesium phosphate cements: A comparative study

Magnesium phosphate cements (MPCs) are advanced inorganic binders gaining prominence in specialized engineering due to their rapid setting and high early strength. These properties make them exceptionally suitable for a wide range of applications beyond ordinary Portland cement (OPC), including the rapid repair of critical infrastructure, waste encapsulation, soil stabilization, and the development of refractory and corrosion-resistant coatings. While the properties of MPCs based on ammonium and potassium phosphates are well-documented, a systematic study including sodium dihydrogen phosphate is notably absent from the literature. This study presents a comprehensive comparative investigation of MPCs formulated with three different phosphate salts: potassium dihydrogen phosphate, sodium dihydrogen phosphate, or ammonium dihydrogen phosphate. The research methodology was designed to evaluate and contrast key characteristics of these cements, including their reaction kinetics, workability in the fresh state, physical characteristics, and mechanical strength in the hardened state. To elucidate the underlying mechanisms governing performance, a detailed microstructural analysis was conducted using Scanning Electron Microscopy (SEM), while the reaction products were characterized through X-ray Diffraction (XRD) and attenuated total reflectance–Fourier transform infrared (ATR-FTIR). The findings from this comparative analysis are crucial for identifying the most suitable phosphate salt for specific applications, thereby enabling the informed development and optimization of MPCs for advanced and sustainable construction. Funding: This work was supported by the Russian Science Foundation (Grant No. 24-79-10320, https://rscf.ru/en/project/24-79-10320/).