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<p>Magnesium phosphate cement (MPC) shows strong potential for protecting steel reinforcement in marine structures, yet its coupled strength evolution and corrosion-protection mechanism under natural seawater remain unclear. This study presents a 161-day medium-term immersion investigation in natural seawater, combining compressive strength tests, electrochemical measurements, XRD, SEM/EDS, PLM, and MIP to distinguish the matrix effect from the pore-solution chemistry effect. Compared with ordinary Portland cement (P.O.), MPC forms a dense struvite-based matrix that inhibits the ingress of chloride ions, water, and oxygen. Its compressive strength exhibits a distinctive dual-peak behavior, reaching 65.7&#xa0;MPa with smaller fluctuation than P.O., indicating superior environmental stability. Electrochemically, the steel rebars embedded in MPC maintain a stable corrosion potential of approximately -0.7&#xa0;V, with the corrosion current density 2-3 orders of magnitude lower than that in P.O. Protection occurs through three synergistic stages: pore blocking by dense hydrates, chemical passivation by an α-FeOOH/Fe<sub>3</sub>O<sub>4</sub> barrier, and self-repair through continued hydration and microcrack sealing. NH<sub>3</sub>/NH<sup>4+</sup> mainly derives from residual ammonium phosphate and ammonium-bearing struvite in alkaline microdomains, contributing to localized oxygen-poor/reducing conditions near steel. This mechanism overcomes pH-dependent limitations of P.O. and supports marine anticorrosive repair design.</p>

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Corrosion Protection of Steel Reinforcement by Magnesium Phosphate Cement in Seawater: Performance and Mechanistic Insights

  • 期刊论文

  • 发表日期：

    2026年7月29日

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  • Qi Chen,
  • Yan Guan,
  • Jun Chang,
  • Yingxue Teng,
  • Xiaoyang Chen,
  • Zhiqi Hu,
  • Meishuo Sun

摘要

Magnesium phosphate cement (MPC) shows strong potential for protecting steel reinforcement in marine structures, yet its coupled strength evolution and corrosion-protection mechanism under natural seawater remain unclear. This study presents a 161-day medium-term immersion investigation in natural seawater, combining compressive strength tests, electrochemical measurements, XRD, SEM/EDS, PLM, and MIP to distinguish the matrix effect from the pore-solution chemistry effect. Compared with ordinary Portland cement (P.O.), MPC forms a dense struvite-based matrix that inhibits the ingress of chloride ions, water, and oxygen. Its compressive strength exhibits a distinctive dual-peak behavior, reaching 65.7 MPa with smaller fluctuation than P.O., indicating superior environmental stability. Electrochemically, the steel rebars embedded in MPC maintain a stable corrosion potential of approximately -0.7 V, with the corrosion current density 2-3 orders of magnitude lower than that in P.O. Protection occurs through three synergistic stages: pore blocking by dense hydrates, chemical passivation by an α-FeOOH/Fe3O4 barrier, and self-repair through continued hydration and microcrack sealing. NH3/NH4+ mainly derives from residual ammonium phosphate and ammonium-bearing struvite in alkaline microdomains, contributing to localized oxygen-poor/reducing conditions near steel. This mechanism overcomes pH-dependent limitations of P.O. and supports marine anticorrosive repair design.