The protective effect of magnesium phosphate cement on steel corrosion

This study aims at evaluating the protective effect of magnesium phosphate cement (MPC) on steel corrosion in the repair of reinforced concrete (RC) structures. Steel substrates covered with thin magnesium ammonium phosphate cement (MAPC), magnesium potassium phosphate cement (MKPC) and ordinary Portland cement (OPC) paste were designed, respectively. Specimens were suffered from accelerated corrosion tests. The protective properties and mechanisms of MPC were explored compared to those of OPC by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, and mass loss methods. The experimental results show that corrosion initiation of steel substrates in MAPC, MKPC and OPC took place after 9, 6 and 2 cycles of accelerated corrosion tests, respectively. After 12 cycles, steel substrates in MPC exhibited much lower corrosion current density and mass loss rate than those in OPC. This study clearly revealed that MPC exhibits excellent protective effect on steel corrosion, which might be attributed to a newly formed protective film on the steel surface. Furthermore, the interaction between phosphates and Fe2+ ions could play an important role in the formation of protective film and effectively reduce the corrosion rate. (C) 2020 Elsevier Ltd. All rights reserved.