Effects of Aluminum Silicate on Mechanical Strength and Microstructural Improvement of Magnesium Phosphate Cement Mortar

This study explored the role of aluminum silicate (AS) on the water stability performance and microstructural properties of magnesium phosphate cement (MPC) composites. Five consecutive dosages of AS were introduced in MPC composites as a substitute for magnesium oxide. It was revealed that MPC composites containing 3% AS exhibited a compressive strength (CS) of around 108.2, 97.1, and 103.4 MPa and a flexural strength (FS) of about 14.9, 13.9, and 14.3 MPa at 28 days in open air, full immersion and cover by wet cloth, respectively, and these results were higher than control and other surrogate mixtures. Additionally, electron microscope, X-ray diffraction, and energy dispersive spectrometer observations confirmed the formation of intermediate crystals along with struvite minerals, which explained the dense microstructure, by reducing the micropores. Moreover, thermogravimetric analysis and differential thermal analysis results demonstrated that crystal water in struvite was lost at around 97.35°C, which was the primary issue behind losing the solid mass of the composite paste in a high heat environment. The outcomes of the study might play a role in field applications of MPC composites blended with AS.