Integrated assessment of magnesium phosphate cement repaired concrete from the perspective of mechanical, geometric and electrochemical compatibility

Abstract

Magnesium phosphate cement (MPC) has gained more and more attention in the field of rapid repair and strengthening of normal concrete and reinforced concrete structures. Although the performance of MPC itself is of great concern, its compatibility with existing concrete is poorly understood. An effective testing method is necessary to assess the reliability of utilizing MPC mortar repairing construction comprehensively. In this work, systematic assessment methods regarding the mechanical, geometric and electrochemical compatibility between MPC repair mortar and concrete substrate were proposed. Five interesting repaired patterns were designed. The observed results showed that the composite system demonstrates excellent interfacial bonding and overall mechanical properties. The 3-h bond strength of the vertical repair interface repaired pattern reached 3.1 MPa, and comparable or even higher flexural strength was observed in the horizontal interface and compound interface repaired patterns. A novel MPC-NC ring was employed to monitor the interface bond stress evolution, which is a time-dependent function that develops rapidly in the early stages and is affected by relative humidity. The steel rebar in the repaired system (half repair mortar/half concrete substrate) exhibited superior corrosion protection even after 180 days of exposure in 3.5 wt% NaCl solution. The electrochemical compatibility mechanism can be contributed to the passivation process and the inhibition of charge transfer in the repaired area. This study lays a solid foundation for applying MPC repair material in practical engineering and carries out a compatibility evaluation.