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Evaluation of Size-Effect Models for High-Strength Steel Fiber–Reinforced Concrete

In an effort to mitigate crack growth, nine high-strength steel fiber–reinforced concrete (HSSFRC) mixtures were designed in this study, and specimens with various sizes were cast and cured. First, a total of 135 cylinder specimens were tested under the load- and displacement-control apparatus. The crack patterns and size-effect models (size-effect law [SEL], modified SEL [MSEL], multi-fractal scaling law [MFSL], and Sim et al.) were then investigated. The results confirm that with the addition of steel fiber, the rate of crack propagation dramatically decreases, indicating that specimens absorb more energy to break. Accordingly, the effect of size in cylindrical specimens is significantly improved, characterizing a size-independent state. Furthermore, the efficiency of SEL, MSEL, and MFSL models is considerably enhanced when steel fibers are added to the mixtures. For nonfibrous high-strength concrete specimens with brittle nature, SEL and the Sim et al. models are found to be of higher efficacy. Besides, the SEL outperforms the others since it is not only compatible with HSSFRC but also reflects all the characteristics of the specimens in various sizes. Moreover, the results demonstrate that the effect of steel fiber on reducing the size effect compared to other fiber types obtained from various researches is quite noticeable. It is also important to note that there is very little difference between the results of 10 % and 20 % fiber reinforcement; therefore, using 10 % steel fiber reinforcement in concrete is recommended.