Effect of impurities of steel fibers extracted from shredded tires on the behavior of fiber-reinforced concrete

Production of ductile and environmentally-friendly concrete is a dream come true thanks to the combined usage of recycled fibers and pozzolanic materials in the concrete mixture. The raw recycled steel fibers (RSF) stemmed from shredding waste tires underwent a process of preparation. Secondary products of tire-shredding technique, including recycled steel cords, rubber-attached fibers, tiny steel fibers, and free form of rubber particles, were recognized and removed from raw RSF sample, changing its status from impure to pure. The primary target of this study was to evaluate the contribution of RSF purification to the engineering properties of concrete containing 30% slag powder by weight of the total binder. Based on the results, purifying RSF negatively affected the ultrasonic pulse velocity and led to a less workable mixture with inferior compressive strength (f(c)). Interestingly, the highest fc was attained at 1% impure RSF, indicating a 40% enhancement compared to the plain concrete. The positive effect of RSF purification became visible considering the imperviousness and flexural performance of the mixture. However, a similar impure and pure RSF-reinforced concrete flexural strength could be achieved by doubling the volume of the impure RSF.