## 3 Discussion of Results
### Flexural Strength and Toughness of Un-Cracked Beams in Marine Tidal Zone  
Figure 5 shows the load-vertical deflection diagrams for un-cracked beams in tidal zone at 28, 90 and 180 days. In tidal zone, by the addition of steel fibers to the PC beams, \(P_{\text{max}}(\text{PC})_{\text{28}}\) and \(T_{\text{(PC)28}}\) was increased 46% and 586%, respectively. It was cleared that the role of steel fibers in increasing the \(T_{\text{(PC)}}\) is higher than the \(P_{\text{max}}(\text{PC})\). The slope of PC and SFRC diagram at the beginning was approximately the same. It can be due to the more important role of steel fiber after cracking rather than before concrete cracking. By addition of steel fibers to the un-cracked RC beams in the tidal zone environment, the \(P_{\text{max}}(\text{Un-RC})_{\text{28}}\) and \(T_{\text{(Un-RC)28}}\) were increased 14% and 12%, respectively. It was cleared that the slope of un-cracked (R+S)C and un-cracked RC diagrams is approximately the same. Moreover, by addition of steel fiber to the un-cracked RC beams, the \(S.S_{\text{(Un-RC)28}}\) is increased by about 27%. In the tidal zone at 90 days, \(P_{\text{max}}(\text{Un-SFRC})_{\text{90}}\) was 34% higher than \(P_{\text{max}}(\text{PC})_{\text{90}}\). \(T_{\text{(Un-SFRC)90}}\) was also 516% higher than \(T_{\text{(PC)90}}\). Meanwhile, \(P_{\text{max}}(\text{Un-(R+S)C})_{\text{90}}\) and \(T_{\text{(Un-(R+S)C})_{\text{90}}}\), were about 14% higher than \(P_{\text{max}}(\text{Un-RC})_{\text{90}}\) and \(T_{\text{(Un-RC)28}}\). Moreover, \(S.S_{\text{(Un-(R+S)C})_{\text{90}}}\) was 35% higher than \(S.S_{\text{(Un-RC)90}}\). At 180 days, by addition of steel fibers to the PC beams, \(P_{\text{max}}(\text{PC})_{\text{180}}\) was increased 24% while the \(T_{\text{(PC)180}}\) was increased 514%. It was cleared that the main role of steel fibers in increasing the \(T_{\text{(PC)}}\) is  
Figure 5: Load-vertical deflection diagrams for un-cracked beams in the tidal zone at: (a) 28 days; (b) 90 days; (c) 180 days. PC: Plain Concrete; SFRC: Concrete with Steel fiber Reinforcement; Ti: Tidal zone; Un: Un-cracked beam. higher than the \(P_{max(\text{PC})}\). The slope of PC and SFRC diagram at the beginning was approximately the same. It may be due to the more important role of steel fiber after cracking, rather than before concrete cracking. At 180 days, in tidal zone environment, the \(P_{max(\text{Un-RC})180}\) and \(T_{(\text{Un-RC})180}\) was increased by about 19%. Thus, the positive role of steel fibers in increasing the \(P_{max(\text{Un-RC})}\) and \(T_{(\text{Un-RC})}\) was approximately the same. It was cleared that the slope of diagram related to un-cracked (R+S)C and RC beams, is approximately equaled. Moreover, By the addition of steel fiber to the un-cracked RC beams, the \(S.S_{(\text{Un-RC})180}\) was increased by about 16%. Steel fibers could increase the rigidity by arresting the crack and reducing the crack growth. Generally, in SFRC, The corrosion may act in different manners, with the following different effects: [11] (a) if the fibers strength is reduced noticeably by the corrosion, \(P_{max}\) will be decreased, with an embrittlement behavior after \(P_{max}\); (b) if the crack self-healing happens during marine condition, \(P_{max}\) will be increased due to concrete continuity through the crack. Moreover, the post-peak behavior is expected to rejoin one of the non-croroded beams; and, (c) if the crack healing does not happen, corrosion of the fibers lead to an increase in their friction in the cement matrix. According to mechanisms (a) to (c), the reason for increasing the \(P_{max}\) and \(T\) may be due to the corrosion of steel fibers surface and concrete self-healing. Because of the following reason, the corrosion of steel fibers up to 180 days cannot lead to a decrease of \(P_{max}\): (1) the expansive forces from corrosion of steel fibers are not enough for the concrete detachment because of the little diameter of fibers and the little volume created by the oxides.