This study aimed to investigate the mechanical performance of early-strength carbon fiber-reinforced concrete (ECFRC) by incorporating original carbon fiber (OCF), recycled carbon fiber (RCF), and sizing-removed carbon fiber (SCF). Compressive, flexural, and splitting tensile strength were tested under three fiber-to-cement weight ratios (5‰, 10‰, and 15‰). The RCF was produced from waste bicycle parts made of carbon fiber-reinforced polymer (CFRP) through microwave-assisted pyrolysis (MAP). The sizing-removed fiber was obtained through a heat-treatment method applied to the OCF. The results of scanning electron microscopy (SEM) analysis with energy dispersive X-ray spectrometry (EDS) indicated the successful removal of sizing and impurities from the surface of the RCF and SCF. The mechanical test results showed that ECFRC with a 10‰ fiber-to-cement weight ratio of carbon fiber had the greatest improvement in its mechanical strengths. Moreover, the ECFRC with 10‰ RCF exhibited higher compressive, flexural, and splitting tensile strength than that of benchmark specimen by 14.2%, 56.5%, and 22.5%, respectively. The ECFRC specimens with a 10‰ fiber-to-cement weight ratio were used to analyze their impact resistance under various impact energies in the impact test. At 50 joules of impact energy, the impact number of the ECFRC with SCF was over 23 times that of the benchmark specimen (early-strength concrete without fiber) and was also greater than that of ECFRC with OCF and RCF.

In the last decade, waste carbon fiber-reinforced plastic (CFRP) products have not been properly recycled and reused, and they sometimes cause environmental problems. In this paper, the microwave-assisted pyrolysis (MAP) technology was utilized to remove the resin from the CFRP bicycle frame, which was recycled into carbon fiber. A scanning electron microscope (SEM) and single filament tensile test were used to observe and compare the difference between recycled carbon fiber and normal carbon fiber. The mechanical performances of carbon fiber-reinforced concrete (CFRC) were investigated with static and dynamic tests under three different fiber/cement weight proportions (5‰, 10‰, and 15‰). Three different kinds of carbon fiber were used in this study, normal carbon fiber, carbon fiber without coupling agent, and recycled carbon fiber. The experimental program was tested according to ASTM C39-01, ASTM C293, and ACI 544.2R standards for compression, flexural, and impact test, respectively. From the experimental results, addition of 10‰ of carbon fiber into the concrete exhibited maximum compressive and flexural strength. The impact performance of recycled carbon fiber improved the highest impact number compared with normal carbon fiber under different impact energy.