نسرین بخشایش اقبالی

Abstract Structural (ECC), also known as engineered cementitious composites, have emerged as a recent trend in construction materials. They require continuous improvement to meet a wide range of applications. While the bond between reinforcement and concrete has been extensively studied in normal- and high-strength concrete, there has been limited attention given to (ECC) concrete, which is the focus of this study. This experimental investigation examines the bond behavior of steel bars embedded in high-strength concrete containing steel fibers and polypropylene fiber. The study considers three different ratios of straight microfibers, hybrid with polypropylene fibers, with a volume content of (0.5%, 1.0%, 1.5%) for steel fiber with 0.5% of polypropylene fiber, compared with self-compacted concrete (SCC). Both block and beam-like specimens are reinforced with deformed steel bars of two diameters (12 or 25 mm). Prior to conducting the mechanical tests, the physical and mechanical properties of the mixes, are examined and compared to the provisions of Model Code 10. The addition of fibers leads to increased concrete density (up to 2377 kg/m3) for ECC mix with 1.5% steel fiber, in terms of compressive strength (except for ECC mix with 1.5% steel fiber) all tested mixes showed an increase in their compressive, and tensile strength in bending (up to 23% improvement over the SCC sample), The preliminary mechanical tests indicate that the ECC concrete mix with 1.0% steel fiber exhibits the highest values, The bond strength tests conducted on the beam-like specimens reveal that the bond strength is significantly influenced by both the bar diameter and the increment of steel fiber. Specifically, larger bar diameters result in lower bond strength. However, the inclusion of steel fibers tends to mitigate the negative effects of bar diameter. An increase in the added fiber ratio is seen to enhance the ultimate pullout load for both block samples reinforced with 25mm and 12.5mm diameter. When 1.5% steel fiber was used, the improvement reached 60% in both cases. Additionally, the block samples reinforced with 25mm and 12.5mm diameter showed the highest displacement values at 17.5mm and 24mm, respectively, for samples including 1.5% steel fiber. Notably, the ECC samples displayed a limited amount of slippage until reaching approximately 83% of the ultimate load. It is evident that the ECC samples with 1.5% steel fiber in beam form exhibited the highest pull-out load compared to the other tested samples. The increases were significant, with a 500% increase compared to SCC, a 34% increase compared to ECC-1.0-S, and a 2% increase compared to ECC-0.5-S. The beam samples reinforced with a 12mm diameter steel bar displayed a slightly different behavior. Notably, the ECC-1.0-S sample achieved the highest pull-out load value, reaching an impressive 43KN. The highest vertical deflection was observed in the SCC beam reinforced with a 25mm diameter at 21mm. Additionally, the ECC-1.5-S reinforced with a 12mm diameter exhibited the highest vertical deflection. These findings are the result of the experimental investigation conducted in this study.