Evaluation of Recycled Carbon Fiber Reinforced Concrete

Concrete is the most widely used building material in the world and has many different applications and uses, all requiring specific properties and mix designs. While concrete is an incredibly valuable and versatile material for construction, it has a major drawback in the form of low tensile strength compared to its compressive strength. One solution for this is Fiber-Reinforced Concrete (FRC), where short fibers are randomly dispersed into the concrete during mixing to carry the tensile loads in the concrete. Many fibers have been used, with steel being one of the most common; however, carbon fiber shows particular promise due to its superior mechanical properties. Recycled carbon fiber is of particular interest due to its comparable mechanical properties to virgin carbon fiber but at a potentially much lower cost and additional sustainability benefits, potentially making this a novel form of reinforcement for FRC.

In this study, ultra-high-performance concrete reinforced with recycled carbon fiber was evaluated for its mechanical performance and compared with two commercially available carbon fiber types and steel fibers using the same concrete mix. Additionally, high-resolution micro X-ray computed tomography was performed on the concrete samples to investigate microstructure features of interest spatially including defects such as pore size distribution which can compromise the structural integrity of the concrete. Scanning electron microscopy were performed to investigate failure mechanism of the tensile concrete samples. Important properties including thermal stability of the carbon fibers and fiber density are reported.

The study further investigated the mechanical performance and effectiveness of recycled carbon fiber when mixed into high strength, structural lightweight and ultra lightweight concrete. The mechanical performance of the recycled carbon fiber reinforce concrete was compared to steel fibers. This study showed that recycled carbon fiber can significantly improve the tensile and flexural strength of neat concrete serving as a potential replacement for steel fiber reinforced concrete in certain applications. This study will help provide critical information for the development of process-structure relationships for recycled carbon fiber reinforced concrete for structural applications.