Flexural properties and microstructure of recycled carbon fiber concrete with different morphologies

Green materials can be prepared by incorporating recycled carbon fibers (RCF) into concrete, which is an effective way to realize the recycling of carbon fiber reinforced composite solid waste. In order to investigate the effect of RCF on the flexural properties of concrete, RCF from three different manufacturers were incorporated into concrete at different contents and lengths. Four-point bending tests were carried out to analyze the failure modes, load-deflection curves and flexural strength of recycled carbon fiber reinforced concrete (RCFC). A new method for determining the initial cracking point was proposed, and the flexural toughness was evaluated. The intrinsic causes were explained at the microscopic level in combination with SEM. A new bending strength prediction formula was proposed based on the porosity measured by MIP. The results show that RCF can improve the failure mode and improve the flexural strength and toughness, with a maximum increase of 38.67% in flexural strength and 70.14% in flexural toughness index I₂₀. The effects of different forms of RCFC specimens on the flexural strength, flexural toughness index, equivalent flexural strength and flexural toughness ratio are not the same, which is mainly related to the apparent morphology of RCF. From the perspective of flexural toughness, the best performance is achieved when 1.5 wt% RCF-A with a length of 12 mm is incorporated. The research conclusions and calculation methods can provide reference for the performance enhancement and application of RCFC.