Interface bonding mechanism of BFPMPC and concrete: Insights from microscopic to molecular scale

This paper investigates the action mechanism of repair interface between baslt-fiber-reinforced-polymer-modified magnesium phosphate cement (BFPMPC) and cement concrete in the microscopic and molecular insights. Firstly, to clarify the mechanical properties of interface inclusions and analyze the complex microstructure quantitatively, the nanoindentation and nanoscratch were conducted by using BFPMPC and concrete bonding specimens. Secondly, the complex chemical bonding of interface was analyzed by Raman spectroscopy. Finally, the molecular mechanism of the interfaces were investigated by molecular dynamics method. The nanoindentation test confirmed that there are three types of interface forms and the gradient of elastic modulus in the repair interface. As the position from ITZ-4 changed to ITZ-2, ITZ-3 in the middle position has the lower elastic modulus. The fracture toughness K_IC tested by nanoscratch of ITZ-2, ITZ-3 and ITZ-4 was 0.28MPa⋅m^1/2, 0.18 MPa⋅m^1/2 and 0.38 MPa⋅m^1/2. The phosphate infiltration into concrete resulted in enhanced bonding properties was confirmed by Raman spectroscopy. The forms of phosphate existed in different sub-ITZs were not consistent. The molecular dynamics simulation results showed that the polymer chain was elongated by the adhesion force of the crystal structure on both sides of BFPMPC and aggregate interface. It has strong bonding with the crystal on both sides. The polymer can effectively adhered to the surface of K-struvite (MKP) particles in the process of bonding with OPC mortar and aggregate in PCC. MKP[100] crystal surface has the strongest adhesion.