Enhancement of Magnesium Oxysulfate Cement by Acid Modifiers and Its Reaction Mechanism

To address the challenges of low mechanical strength and poor water resistance in magnesium oxysulfate cement (MOSC), this study explores the incorporation of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) and hydrolyzed polymaleic anhydride (HPMA) as modifiers. Advanced analytical techniques, including X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric differential scanning calorimetry, were employed to analyze the physical phase composition and microscopic structure of MOSC hydration products. These analyses provided insights into the enhancement mechanisms associated with PBTC and HPMA. The findings revealed that the chelation of PBTC and HPMA with Mg²⁺ influenced the hydration process of MOSC, prolonged its setting time, and facilitated the emergence of a new needle-and-rod crystalline phase (5·1·7 phase) within the hydration products. This water-insoluble phase, characterized by a three-dimensional network structure of interspersed crystals, contributed to improved mechanical strength and water resistance. When the doping level of HPMA is 2.00%, the 28-day compressive strength of MOSC reached 104.42 MPa, which exceeded that of the control sample by 127.45%. The softening coefficient was as high as 0.94. The results of this study show that PBTC and HPMA, as modifiers, can effectively improve the mechanical properties and water resistance of MOSC. Their influence on the hydration mechanism and crystallization process of MOSC provides a certain theoretical basis for the practical engineering applications and sustainable development of MOSC.