# Effect of SIRRCCs with Varying Steel Fiber Volume Fractions on Flexural Behavior
## 3 Experimental Results and Analysis  
### Flexural Behavior Characteristics  
Figures 3-5 show the load deflection curve with respect to the fiber volume fraction. The experimental results with a fiber volume fraction of 6% revealed a desirable flexural resistance performance at the maximum load of 149 kN. In addition, the residual strength continued increasing after the maximum strength was reached. This suggests that when extreme loads such as unexpected explosions and impacts are applied, the collapse of structures due to brittle fracturing can be prevented by obtaining additional residual strength.  
Figure 3: Load-mid span deflection curve at a fiber volume fraction of 6%.  
The experimental results showed maximum loads of 111 and 81 kN for the fiber volume fractions of 5% and 4%, respectively, which were approximately 75% and 55% of the maximum load for the fiber volume fraction of 6%. Thus, the maximum load decreased with decreases of the fiber volume fraction. Accordingly, the flexural strength of steel-fiber-reinforced cementitious composites with a high fiber volume fraction were observed to decrease sensitively with respect to the steel-fiber density inside the specimen. Furthermore, the residual strengths for the fiber volume fractions of 6% and 5% were similar after a certain deflection. This suggests that the steel-fiber density variation on the fracture section was insignificant above a certain steel-fiber volume fraction and did not greatly affect the residual strength.  
The experimental results of flexural behavior characteristics with respect to the fiber volume fraction showed that the load of SIFRCCs tended to continuously increase with respect to fiber volume fraction after the initial crack until they reached the maximum load. Furthermore, the maximum load of every variable occurred at around 2.5 mm of deflection, regardless of the fiber volume fraction. This implies that the dynamic properties were improved so that the cementitious composites could resist loads (such as an impact) by absorbing sufficient energy even after the initial crack through the bridging effect with respect to high fiber volume fractions. Furthermore, the high-performance slurry increased the steel-fiber bond strength, and the failure mode of the fiber fracturing at the fracture surface occurred along with the fiber-pulling phenomenon.  
As described above, owing to the high volume fraction of steel fibers, the specimens showed continuous load resistances with no sudden failures, indicating a desirable deformation capacity. Generally, after failure, fiber volume fraction has a greater effect on flexural toughness rather than on flexural strength. Although the load-deflection curves of the fiber volume fraction were similar in general, the flexural strength showed distinct differences with respect to fiber volume fraction.  
Figure 4: Load-mid span deflection curve at a fiber volume fraction of 5%.  
Figure 5: Load-mid span deflection curve at a fiber volume fraction of 4%.  
This could be because the composites of steel fibers and the slurry showed homogeneous behaviors owing to the inclusion of relatively large numbers of fibers and the high strength of the slurry due to the high volume fraction of steel fibers. The increase in the fiber volume fraction of SIFRCCs improves the mechanical strength, the residual strength, and especially the toughness. The use of fine aggregates in the binder matrix reduces the water demand of the fresh matrix and increases the flexural strength and brittleness of SIFRCCs. The use of steel fibers in SIFRCCs increases bending tension and shear strength, and makes concrete sufficiently ductile. Thus, SIFRCCs can be considered UHPC.