Multiscale investigation of the interfacial bonding mechanisms of magnesium potassium phosphate cement and cement concrete

The interface bonding between magnesium potassium phosphate cement (MPC) and Portland cement concrete (PCC) is critical for ensuring long-term durability and structural integrity in pavement rehabilitation. However, the underlying interfacial bonding mechanism remains poorly understood at different scales. This paper investigates the mechanism of MPC/PCC interface properties by multiscale methods with macro-microscopic tests and molecular dynamic (MD) simulation. The results demonstrated that the flexural strength of the MPC/PCC specimen was highly sensitive to both crack lengths and fracture modes. Mode II of the specimen consistently showed the superior shear-dominated resistance behaviour. The high porosity and microcracks in sub-ITZs corresponded closely with the gradient change in elastic modulus and fracture toughness, underscoring the critical role of pore distribution in interface mechanical performance. Excellent bonding behaviour and fracture resistance of MPC/PCC interface driven by the formation of phosphate-based hydration products, dense interfacial microstructures and strong interfacial chemical bonding were validated by Raman spectroscopy.