Issue 42

A. Jadidi et alii, Frattura ed Integrità Strutturale, 42 (2017) 249-262; DOI: 10.3221/IGF-ESIS.42.27 260 Figure 22 : Load-displacement graph - samples reinforced with 2.5% hybrid steel fibers (L/D=50, L/D=50) on 28-day. Compressive strength results The samples in this research were brought under compressive strength test 28 days after they were constructed. To investigate the impact of the application of steel fibers on the compressive strength of fiber-reinforced concrete, the graph below shows changes in compressive strength for samples reinforced with 1.5%, 2 % and 2.5 % fibers after 28 days. Figure 23 : The impact of steel fiber content on 28-day compressive strength of concrete reinforced with steel fibers. Figure 24 : The impact of steel fiber content on 28-day compressive strength of concrete reinforced with steel fibers Based on Figs. 23 and 24 the compressive strength of mixture designs are to some extent similar to each other. It is worth noting that the use of steel fibers has contributed to concrete long-term compressive strength decrease in some cases. Except the 2.5% crimped steel fibers designs (L/D=50), and 1.5% and 2% hooked steel fibers (L/D=50), the 28-day compressive strength of all samples have increased. Based on these results, the highest 28-day compressive strength exists in samples reinforced with 2.5% hybrid steel fibers (hooked steel fibers L/D=50 and crimped steel fibers L/D=50) with 22.84 compressive strength increase. Further, the highest amount of compressive strength decrease with 6.39% exists in crimped steel fibers (L/D=50).