Influence of adding discontinuous and dispersed carbon fiber waste on concrete performance

Abstract

Waste generated in carbon fiber manufactures, such as products in end-of-life, still have limited options of reuse. Therefore, new recycling alternatives are required before expected disposal increases occur in the coming years. This study aims to justify a new carbon fiber recycle method and to understand how carbon fibers corroborate improvements in the transition zone in concrete by controlling crack propagation during mechanical loading. Cylindrical concrete specimens were prepared with cement consumption of 370 kg/m³, water-cement ratio of 0.5, and addition of 2% carbon fiber waste in relation to the cement mass. Despite a lower workability in the fresh state, the mechanical performance of the new composite was improved in compressive strength and tensile strength, as shown by a 28-day test result. In order to explain the relationship of structure and property of the new composite, images of the fibers and fractured surfaces of the concrete were evaluated by scanning electron microscopy (SEM). The carbon fiber acts directly on the concrete cracking mechanism at the moment of rupture, restraining the formation of large cracks from microcracks and maintaining the transition zone of the coarse aggregate adhered to the matrix. The addition of carbon fiber waste into the concrete is potentially positive, for providing mechanical improvements that will reduce the maintenance needs and, consequently, increase the durability of concrete structures and the sustainability of constructions.