Evaluating the Interface Fracture Performance of Basalt Fiber-Reinforced Polymer-Modified Magnesium Phosphate Cement and Portland Cement Concrete by Semicircular Bending Specimens

This paper investigates the interfacial bonding mechanism between basalt fiber-reinforced polymer-modified magnesium phosphate cement (BFPMPC) and conventional cement concrete. An asymmetric semicircular bending specimen with a preset crack was designed to evaluate the fracture resistance of the repair interface. Interface fracture behavior was further analyzed using fracture parameter evaluation. In addition, the interfacial hydration morphology was characterized by scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) and backscattered electron imaging. The results showed that the compressive and flexural strengths of the BFPMPC mortar reached 46.1 and 11.2 MPa, respectively. Among the tested configurations, the interface subjected to Mode II fracture exhibited the highest flexural strength, and the minimum fracture toughness (1.711 MPa·m 1/2 ) occurred under Mixed mode I/II at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> = 0.346, indicating the lowest resistance to crack propagation. Fracture behavior was influenced by a cubic fit interaction between the fracture parameters <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>IC</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>IIC</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , which probably resulted from microstructural heterogeneity and nonlinear stress redistribution. The SEM/EDS observations revealed that the hydration products at the interface were porous and loosely structured. Among the sub-interfacial transition zones (ITZs) in the repair interface, ITZ-4 exhibited the smallest pore gradient variation, and ITZ-3 showed the loosest structure, contributing to its reduced mechanical properties.