Performance Characterization of Recycled Carbon Fiber and Its Interfacial Bonding Properties with Cement Matrix

Recycled carbon fiber, as a novel type of solid waste, possesses high tensile strength, structural stability, and low utilization rates. Recycling carbon fiber for use in cementitious materials presents an efficient solution. However, achieving good interfacial bonding between recycled carbon fiber and cementitious materials is crucial for its high-performance application in such materials. This study first characterizes the properties of recycled carbon fiber and, for the first time, tests the interfacial parameters between recycled carbon fiber and cement matrix through single-fiber pull-out tests. The results show that the surface of recycled carbon fiber, lacking active functional groups and being relatively smooth, leads to poorer interfacial bonding with the cement matrix compared to virgin carbon fiber. The interfacial bonding strength, interfacial friction bonding strength, and chemical debonding energy are 0.65 MPa, 0.47 MPa, and 0.36 J/m², respectively. Next, based on the theoretical model of interfacial mechanics, a single-fiber pull-out model was used to predict the bridging stress curve of recycled carbon fiber. The calculations show that the bridging stress of recycled carbon fiber at volume fractions of 0.16%, 0.3%, and 0.47% are 1.25 MPa, 2.18 MPa, and 3.40 MPa, respectively. Finally, tensile tests were conducted to investigate the tensile properties of cementitious materials reinforced with recycled carbon fiber. At various fiber contents, the recycled carbon fibers provided corresponding bridging stresses at crack sites, enhancing the tensile strength of the cementitious materials by 8.8~35.48%.