Study on interfacial defect fracture behavior of mortar and potassium magnesium phosphate composites

Abstract Potassium magnesium phosphate cement (MKPC) has important application value in rapid structural repair engineering due to its fast hardening and high strength. To further explore the bonding mechanism of the Mortar‐MKPC interface, the three‐point bending (TPB) test combined with digital image correlation (DIC) technology was used to systematically study the influence mechanism of the defect scale effect and MKPC hydration process on interface bonding performance. By quantitatively analyzing the strain field evolution and crack initiation characteristics of composite materials under different curing cycles (3d, 7d, and 28d) and defect parameters ( a 0 is 0.1, 0.2, and 0.3, respectively), we found that the interfacial bond strength increases significantly with the curing age. Based on the finite element method, the complex stress intensity factor of the interface crack tip of the bi‐material was calculated. The results showed that the parameters of the interface crack of the specimen are mainly dominated by the normal stress ( K 1 ), and the shear stress ( K 2 ) had little effect. The microstructure of the interface was characterized by SEM‐EDS, and the densification and gel phase of hydration products increased with the increase of age. The interfacial bonding strength and elastic modulus of B28‐4 are 2.3 and 1.2 times that of B3‐4, respectively. Mortar‐MKPC composites showed higher crack propagation resistance ( W pre ) in the middle stage (7d), and its value was 45.7% higher than that of MKPC samples when a 0 was 0.1. By analyzing the coupling mechanism of hydration development and defect evolution of materials in interface failure, it is helpful to provide a theoretical basis for the rapid repair of civil infrastructure and sustainable applications.