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<p>The excessively rapid setting of Magnesium Potassium Phosphate Cement (MKPC) limits its broader engineering application, necessitating the development of environmentally benign and effective retarders. This study investigates the influence of gypsum on MKPC hydration kinetics, setting behavior, and phase evolution to clarify its retarding mechanism. Gypsum significantly extends the initial setting time while preserving or improving early-age strength, outperforming borax in mechanical performance. Hydration heat measurements show that gypsum decouples the overlapping exothermic peaks of MgO dissolution and K-struvite crystallization, indicating suppressed early hydration. XRD, DTG, and Rietveld refinement confirm that Ca<sup>2+</sup> released from gypsum reacts with H<sub>2</sub>PO<sub>4</sub><sup>−</sup> to form brushite, which inhibits MgO dissolution. Concurrently, brushite formation releases H<sup>+</sup>, lowering pore-solution pH and suppressing KDP dissolution. These findings reveal a coupled chemical-physical mechanism governing gypsum-induced retardation and demonstrate gypsum’s potential as a sustainable retarder for MKPC.</p>

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Gypsum-induced retardation mechanism in magnesium potassium phosphate cement: roles of brushite formation and MgO passivation

  • 期刊论文

  • 发表日期：

    2026年5月18日

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  • Yong Wang,
  • Danlei Li,
  • Fuqiang He,
  • Lixuan Mao,
  • Jin Zhou,
  • Song Hao,
  • Jianming Yang

摘要

The excessively rapid setting of Magnesium Potassium Phosphate Cement (MKPC) limits its broader engineering application, necessitating the development of environmentally benign and effective retarders. This study investigates the influence of gypsum on MKPC hydration kinetics, setting behavior, and phase evolution to clarify its retarding mechanism. Gypsum significantly extends the initial setting time while preserving or improving early-age strength, outperforming borax in mechanical performance. Hydration heat measurements show that gypsum decouples the overlapping exothermic peaks of MgO dissolution and K-struvite crystallization, indicating suppressed early hydration. XRD, DTG, and Rietveld refinement confirm that Ca2+ released from gypsum reacts with H2PO4− to form brushite, which inhibits MgO dissolution. Concurrently, brushite formation releases H+, lowering pore-solution pH and suppressing KDP dissolution. These findings reveal a coupled chemical-physical mechanism governing gypsum-induced retardation and demonstrate gypsum’s potential as a sustainable retarder for MKPC.