Multi-scale characterization on behaviors of the interface between magnesium phosphate cement and portland cement

Abstract This study focused on the interfacial transition zone (ITZ) between magnesium phosphate cement (MPC) paste and Portland cement paste (PCP). Multi-scale analyses were conducted to explore bonding characteristics and interfacial shear strengths of the ITZ with an innovative composite specimen. Meanwhile, ITZ was investigated by the Nano-indentation test, the scanning electron microscope (SEM), and the energy-dispersive spectrometer (EDS). Based on the damage mechanics and the interface kinematics formula, the viscous behavior and friction behavior were coupled together for the first time to develop the constitutive relation of the interface damage. A finite element (FE) model of MPC-PCP interface shear strength was developed and conducted to validate the proposed constitutive relation of the interface damage. Sensitivity analysis of repair size was predicted by the effect of different sizes on shear strength. The 7d shear strength of the repair interface reached 5.2 MPa, which indicates that MPC has good bonding with PCP. Investigated by SEM/EDS analysis, the cracks appeared at 10 μm away from PCP edge and the width at 6 h and 3d was around 3–5 μm. According to the nano-indentation test, the elastic modulus varied greatly in the ITZ and the lowest value located 10 μm away from the PCP side. Numerical results from FE models were found consistent with the experimental results, which validates the proposed constitutive relation of the interface damage.