Effect of recycling methods on microstructure and mechanical properties of carbon fiber cementitious composite

Despite extensive research on carbon fiber recycling and their application in cementitious composites, the impact of recycling methods on composite structures remains inadequately understood. This study investigates the microstructural and mechanical behavior of ball-milled carbon fibers recycled via mechanical and pyrolytic methods in cement matrices. Cementitious composites containing 0.5%, 1%, and 1.5% volumetric carbon fibers underwent SEM, XRD, FTIR analyses, and mechanical tests for compression and flexural stress. SEM results showed that mechanically recycled fibers formed agglomerates in the cement paste, while pyrolytically recycled fibers were randomly dispersed. Recycling increased fiber surface roughness, enhancing adhesion with the cement matrix. XRD and FTIR confirmed the inert nature of both fiber types, indicating no chemical reaction with the matrix. Mechanically recycled fibers improved flexural tensile stress by at least 250% over the control sample (fiber-free composite), but higher fiber content reduced this effect. In contrast, pyrolytically recycled fibers enhanced flexural tensile stress by 290%, 320%, and 380% at 0.5%, 1%, and 1.5% fiber content, respectively. Compressive strength trends mirrored flexural stress behavior, highlighting the influence of recycling methods on composite performance. This study provides insights into optimizing carbon fiber recycling for enhanced cementitious composite properties.