## 3 Discussion of Results
However, \(P_{max(\text{Pr-(R+S)C})180}\) and \(T_{\text{(Pr-(R+S)C)180}}\) were 22% higher than \(P_{max(\text{Pr-RC})180}\) and \(T_{\text{(Pr-RC)180}}\). Consequently, with an increasing of age, the role of steel fiber in arresting the cracks will be significant. In water condition, up to 180 days, the effect of steel fiber on increment of \(T_{\text{(Pr-RC)}}\) and \(P_{max(\text{Pr-RC})}\) was approximately the same. By the addition of steel fiber to the pre-cracked RC beam in water environment, the \(S.S_{\text{(Pr-RC)28}}\) was decreased by about 37%. However, at 180 days, the \(S.S_{\text{(Pr-(R+S)C)180}}\) was 38% higher than \(S.S_{\text{(Pr-RC)180}}\). Because of the cracking limitation, as well as delay in the growing of cracks, the role of steel fiber in \(S.S_{\text{(Pr-RC)}}\) at 180 days will be increased. The main reason for decreasing the \(T_{\text{(Pr-RC)}}\) and \(P_{max(\text{Pr-RC})}\) by addition of steel fiber at 28 days may be related to a higher porosity in concrete in primary ages. Increasing \(T_{\text{(Pr-RC)}}\) and \(P_{max(\text{Pr-RC)}}\) at 180 days in water environment may be due to the effect of steel fibers in increasing the bar-to-concrete bond and bridging faces of cracks [19; 24]. Generally, the use of steel fibers in concrete can be efficient in the limitation of cracks at both micro and macro dimensions. At the micro-level, steel fibers prevent the beginning and development of cracks, and after the micro-cracks link with together and change to macro-cracks, steel fibers prepare mechanisms that provide effective bridging and reduce the rate of crack growth, finally enhancing the toughness and ductility [3; 4]. By addition of steel fiber to pre-cracked RC beams in the marine atmosphere environment, the \(P_{max(\text{Pr-RC})28}\) and \(T_{\text{(Pr-RC)28}}\) were decreased 9% and 7%, respectively. With increasing the age, \(P_{max(\text{Pr-(R+S)C})180}\) and \(T_{\text{(Pr-(R+S)C)180}}\) were approximately 27% higher than \(P_{max(\text{Pr-RC})180}\) and \(T_{\text{(Pr-RC)180}}\). Thus, in marine atmosphere environment like to water condition, the steel fiber role in limitation of crack width at 180 days was bolded. According to the Figure 4, at 28 days, the amount of \(P_{max(\text{Pr-(R+S)C})28}\) and \(T_{\text{(Pr-(R+S)C)28}}\) in the water and marine atmosphere condition did not have noticeable differences, while at 180 days, the role of marine atmosphere environment in decrease of \(P_{max(\text{Pr-(R+S)C})28}\) and \(T_{\text{(Pr-(R+S)C)28}}\) will be bolded. In a marine atmosphere environment of up to 180 days, the effect of steel fiber on the growth of \(P_{max(\text{Pr-RC})}\) and \(T_{\text{(Pr-RC)}}\) was approximately the same. By addition of steel fiber to the pre-cracked RC beam, the \(S.S_{\text{(Pr-RC)28}}\) was decreased by about 6%. However, at 180 days, the \(S.S_{\text{(Pr-(R+S)C)180}}\) was 43% higher than \(S.S_{\text{(Pr-RC)180}}\). The reason for the decrease of \(P_{max(\text{Pr-RC})}\) and \(T_{\text{(Pr-RC)}}\) at 28 days by the addition of steel fibers in the marine atmosphere region may be due to an increase in the concrete porosity by steel fiber and a lack of concrete self-healing in early ages. Moreover, a serious deficiency may exist in the transition zone of FRC. Especially in the earlier ages, there is a thick and weak transition zone with a lot of porosity between steel fibers and the paste, which can lead to a decrease in the flexural capacity [25]. However, with increasing the age, decreasing the porosity, and consolidating the transition zone, the role of steel fibers on the enhancement of \(P_{max(\text{Pr-RC})}\) and \(T_{\text{(Pr-RC)}}\) will be increased. Figure 4: Load-vertical displacement diagrams of pre-cracked specimens stored in: (**a**) water condition; (**b**) marine atmosphere zone. RC: Concrete with bar Reinforcement; (R+S)C: Concrete with Steel fiber and bar Reinforcement. Pr: Pre-cracked beam; MA: Marine Atmospheric; W: fresh Water.