Investigation on the utilization of fiber clusters recycled from waste HFRP bars in concrete

The waste fiber reinforced polymer (FRP) bars are difficult to degrade naturally, and inevitably pose a significant challenge to environmental protection, resulting in the recycling of waste FRP bars is of great significance. Compared to chemical recycling and thermal recycling, mechanical recycling processes are more economical and environmental. In this study, the waste Hybrid FRP (HFRP) bars were mechanically recycled into fiber clusters for reinforcing concrete, and the influences of the fiber clusters on the mechanical properties of concrete were studied through compression test, splitting tensile test and four-point bending test. Meanwhile, Fourier transform infrared (FT-IR) spectroscopy and Scanning electron microscopy (SEM) were used to observe the interaction between the fiber clusters and the concrete, and acoustic emission (AE) technique was utilized to monitor the fracture characteristics inside the concrete. Results showed that the performance of mechanically recycled fiber clusters was retained to a certain extent and the alkaline environment of concrete produced slight damage to the fiber clusters. The addition of fiber clusters could obviously improve the mechanical properties of concrete, especially its energy absorption capacity under the splitting tensile and flexural loads. The absorbed energy EH/50 and peak flexural toughness of concrete with 2% fiber clusters were 97.24% and 126.47% higher than those of conventional concrete, respectively, and its flexural toughness index TP,150 was 163.16% higher than that of concrete containing 0.5% fiber clusters. As the volume fraction of fiber clusters increased, the number of AE event localization points and shear cracks mainly caused by fiber clusters pull-out and sliding increased. This study can bring enlightenment for the mechanical recycling of FRP bars into fiber clusters for concrete.