Shear behavior of polypropylene fiber-reinforced concrete beams containing recycled aggregate and crumb rubber

The growth of unavoidable waste rubber and the demolition of old concrete structures have become a concern for environmental sustainability. The incorporation of crumb rubber and demolished concrete into the new concrete mix is likely to promote environmentally friendly practices. This paper investigates the shear behavior of concrete beams containing crumb rubber (CR), recycled concrete aggregate (RCA), and polypropylene (PP) fiber. A total of fifteen reinforced concrete (RC) beams were prepared with recycled concrete aggregate (RCA) (0%–50%), CR as fine aggregate (0%–10%), and PP fiber fractions (0%–1%). All RC beams made without any shear reinforcement were tested under a four-point bending test up to failure. The ultimate shear strength, crack pattern, post-diagonal cracking, concrete strain, toughness, and deformation behavior of fresh concrete properties were investigated at different combinations. The surface strain of concrete was closely observed by using Digital Image Correlation (DIC) technique. The experimental result suggested that the introduction of CR in the concrete mix negatively affects the ultimate shear strength, post diagonal cracking resistance, toughness, and deformability of the beam. These effects may be remedied and enhanced by inserting PP fiber in the concrete at RCA replacement levels up to 30%. The beam made of 30% RCA along with 5% CR and 1% PP fiber demonstrated the best performance in terms of shear resistance, deformability, and toughness. Interestingly, the application of 50% RCA with or without CR and PP fiber adversely affected the shear strength parameters of concrete. The beam deformability increased with the addition of a small percentage of rubber (up to 5%). The post-diagonal crack resistance increased with the presence of fibers, whereas the response is the opposite with the addition of rubber.