Fresh and Hardened Properties of Self-Compacting Concrete Reinforced with Hybrid Recycled Steel–Polypropylene Fiber

This paper presents the results of extensive experimental tests on the fresh and hardened properties of self-compacting concrete reinforced with hybrid polypropylene (PP) fiber and recycled steel fiber (RSF) in different fiber volume fractions. In the present paper, RSFs were recovered from waste tires. The mix compositions were reinforced with different combinations of hybrid recycled-steel fiber (0.35, 0.7, and 1.05%) and PP fiber (0.35 and 0.7%). The fresh state of the mix compositions were assessed by using slump flow diameter, T500, and Tv. Moreover, the hardened properties of specimens were characterized by using compressive strength, flexural strength, and impact resistance. Regression analysis was executed on the relatively large amount of gathered experimental data to correlate properties of fresh and hardened states of self-compacting concrete reinforced with hybrid recycled steel–PP fibers. The results showed that adding hybrid recycled steel–PP fiber improves the impact resistance and mechanical properties. Adding recycled steel fiber led to higher improvement in the compressive strength compared to PP fiber. Moreover, increasing the content of PP fiber reduces the effect of recycled steel fiber in improvement of flexural strength.