# Effect of SIRRCCs with Varying Steel Fiber Volume Fractions on Flexural Behavior
## 4 Conclusions  
In this study, the flexural behavior characteristics of SIFRCCs were analyzed with respect to variations in fiber volume fraction used to improve the resistance performance of reinforced concrete (RC) structures to unexpected loads such as explosions or impacts. The following conclusions can be drawn from this study:  
1. The load of the SIFRCCs with respect to the fiber volume fraction continuously increased because of the high fiber volume fraction after the initial crack, and sufficient residual strength was obtained after the maximum strength. This sufficient residual strength is expected to bring about positive effects to the brittle fracture of structures when unexpected loads, such as explosion and impact, are applied.
2. The maximum flexural strength at the fiber volume fraction of 6% was about 45 MPa, which is a desirable flexural resistance performance corresponding to approximately 50% of the compressive strength. In contrast, the maximum flexural strength at the fiber volume fraction of 4% was 24 MPa. Thus, a large difference was observed in the flexural strength with respect to the fiber volume fraction.
3. The results of the flexural toughness and flexural strength experiments showed a similar trend, and the fiber volume fraction greatly affected the energy absorption capacity. Furthermore, in the event of a fracture, the fibers also fractured and the fiber-pulling phenomenon occurred on the fracture surface. This suggests that the sufficiently high bond performance between the steel fibers and high-performance slurry increased the fracture energy.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Variables (Fiber Volume Fraction)** & **Flexural Strength (MPa)** & **Flexural Toughness (N-m)** & **Average Flexural Strength (MPa)** & **Average Flexural Toughness (N-m)** \\ \hline \multirow{4}{*}{4\%} & 22.9 & 616.1 & \multirow{4}{*}{22.5} & \multirow{4}{*}{661.8} \\ \cline{2-4}  & 20.2 & 678.8 & & \\ \cline{2-4}  & 24.4 & 690.6 & & \\ \hline \multirow{4}{*}{5\%} & 31.1 & 769.4 & \multirow{4}{*}{31.6} & \multirow{4}{*}{770.4} \\ \cline{2-4}  & 33.2 & 831.3 & & \\ \cline{2-4}  & 30.4 & 710.6 & & \\ \hline \multirow{4}{*}{6\%} & 38.5 & 776.5 & \multirow{4}{*}{42.6} & \multirow{4}{*}{881.7} \\ \cline{2-4}  & 44.6 & 914.0 & & \\ \cline{1-1} \cline{2-4}  & 44.7 & 954.6 & & \\ \hline \hline \end{tabular}
\end{table}
Table 6: Test results of flexural strength and toughness obtained through bending.  
The shapes of the load-deflection curves plotted with respect to the fiber volume fraction were similar. However, the fiber volume fraction had a greater effect on the magnitude of flexural strength. This could be because the composites of steel fibers and high-performance slurry had homogeneous behaviors due to a relatively large number of steel fibers that were included (increasing the high fiber volume fraction); thus, the slurry strength increased.
5. To meet the required performance for increasing resistance to explosions and impact loads, the energy absorption capacity would benefit from maintaining the fiber volume fraction at the highest level through constructions, so as to increase flexural strength and toughness. Furthermore, more economical use of steel fibers requires the determination of the fiber aspect ratio and volume fraction, as it reflects the required characteristics of the structures against impact and explosion loads.  
Conceptualization, S.K., C.P., and Y.K.; methodology, S.K., C.P., and Y.K.; writing--original draft preparation, S.K. and C.P.; writing-review & editing, S.K., C.P., and Y.K. All authors have read and agreed to the published version of the manuscript. This research was supported by a grant (20 SCIP-B146646-03) from the Construction Technology Research Project funded by the Ministry of Land, Infrastructure and Transport of Korea government and by Basic Science Research Program through the National Research Foundation (NRF) of Korea funded by the Ministry of Education (NRF-2019 RI1 TA1A01062942). The authors declare no conflicts of interest.