Experimental investigation on the mechanical properties of recycled aggregate concrete reinforced by waste carbon fibers

This paper presents the mechanical properties of concrete, which are implemented in three different phases. In the first phase, the natural aggregates were replaced by recycled fine aggregates with the replacement ratio of 0, 30, 50, and 100% and 28-day compressive, splitting tensile and flexural strengths of concretes were tested. As the recycled aggregate concrete with the 30% replacement ratio showed the best mechanical properties, it was chosen for the third phase of this study. In the second and third phases, carbon fiber wastes were, respectively, added to plain concrete and recycled concrete with the volumetric percentages of 0.1, 0.2 and 0.3%. Then mechanical strengths of them were evaluated. This study includes 90 concrete specimens in total which contains 30 cubic specimens (100 × 100 × 100 mm³), 30 concrete cylinders (100 mm × 200 mm) and 30 prismatic beams (500 × 100 × 100 mm³). The SEM images were taken from the fractured surface of the specimens. The results illustrate that the addition of carbon fibers to plain and recycled concrete increases the mechanical properties of concrete and prevents expansion of the initial cracks. It also increases the ductility and the energy absorption of concrete.