Effect of macro-synthetic fibers on the fracture energy and mechanical behavior of recycled aggregate concrete

In order to achieve sustainability in construction industry, recycling of construction and demolition wastes in new concrete is gaining a lot of attention. However, extensive research is needed to explore the complete behavior of resulting recycled aggregate concrete (RAC). This study aims to investigate the fracture behavior, mechanical performance and microstructure of macro-synthetic fiber reinforced RAC. For this purpose, notched beam specimens were produced using three different replacement ratios of recycled concrete aggregates (RCA) (i.e., 0, 50% and 100%) and three different dosages of macro-synthetic fibers (i.e., 0, 0.5% and 1% of volume of RAC). Three-point bending and other mechanical tests were performed to investigate the post peak behavior (residual flexural tensile strength, fracture energy and toughness) and mechanical properties (compressive strength, flexural strength and split tensile strength) of macro-synthetic fiber reinforced normal and RAC. Fracture surface analysis was also performed to develop the empirical relationships between number of fibers and post peak behavior of fiber reinforced RAC. Furthermore, microstructure characteristics of macro-synthetic fiber reinforced normal and RAC were also investigated using scanning electron microscopy (SEM). Results showed that reduction in mechanical properties of concrete was observed with the increase in RCA replacement ratio. However, increase in mechanical properties particularly split tensile strength of normal and RAC was observed with the increase in dosage of macro-synthetic fibers. Concrete specimens also showed increase in residual flexural tensile strengths with the increase in dosage of macro-synthetic fibers. RAC reinforced with 1% dosage of macro-synthetic fibers showed increase in fracture energy and toughness by 380% and 129%, respectively. A strong influence of number of fibers on residual flexural tensile strength and fracture energy of concrete mixtures was observed during the study. Microstructural analysis also showed the existence of bond between mortar paste and macro-synthetic fiber, which improved the mechanical properties and post peak behavior of macro-synthetic fiber reinforced concrete. Based on this study, it can be concluded that macro-synthetic fibers improve the fracture energy and mechanical properties of RAC leading towards higher ductility and better energy dissipation. Moreover, number of fibers strongly influences the residual flexural tensile strength and fracture energy of RAC.