Bonding properties and mechanism of magnesium phosphate cement mortar-normal concrete interface

Magnesium phosphate cement (MPC) has mostly been employed as a repairing and reinforcing material for normal concrete (NC) structures. This research investigates the bonding properties and mechanisms of the MPC material-NC interface. To improve the repair effect of MPC materials, with the help of pull-off test and bi-surface shear test, modified MPC (SMMPC) mortar and polymer repair mortar (PRM) were used as comparative materials to analyze the effects of the type of repair material, the age of curing, and the method of interfacial treatment on the mechanical properties of the bonded interface. The microstructure of the bonded interface was investigated by scanning electron microscopy (SEM) technique and mercury in pressure (MIP) method. The results showed that SMMPC mortar had greater bonding performance than PRM, and the microstructure at the interface between the former and the NC substrate was denser. The shearing resistance of the bonded interface was greatly increased by chipping, reaching a maximum value of 53.2 kN. Compared with other brittle interfaces, the planting rebar interface showed good ductility during loading, and the failure slip of the relevant specimens was able to reach 2.51 mm, which was 20.7%–1041 % higher than that of the other specimens. Additionally, the method was put forward to calculate the bonding strength at the SMMPC mortar-NC interface.