## 4 Flexural Loading Test Results and Discussion  
### Load-Deflection Relationship  
Figure 8a, where the specimens are presented in different colors, shows the relationship between the applied load and deflection at the span center. Figure 8a includes an enlarged figure of the initial loading stage up to 70 kN. As shown by the enlarged figure, the slope in the load-deflection curve of the Type A specimen began decreasing at around 10 kN due to the onset of the crack opening at the interface between the PCa concrete and the joint. This slope decreased significantly at around 155 kN when the strain of all longitudinal reinforcements reached the yield strain. Then, the load gradually increased with the deflection and reached the maximum value at 170 kN at the deflection of 25 mm.  
In the Type B and C specimens, the initial slope of the load-deflection curve decreased at around 40 kN when the crack opening occurred at the interface between the PCa concrete and the joint. This load at the stiffness change was larger than that of the Type A specimen because the tensile bond strength between the PCa concrete and the polymer-based mortar was larger than that between the PCa concrete and plain concrete. Then, the load continued  
Figure 8: (**a**) Relationship between applied load and deflection at span center; (**b**) relationship between applied load and average crack width at bottom of interface between PCa concrete and joint.  
Figure 7: Setup for flexural loading test (Type A).  
to increase until the strain of the longitudinal reinforcement reached its yield strength at around 130-140 kN, whereas the Type A specimen yielded at around 155 kN. This increase in the yield strength in the Type A specimen was due to the dowel effect of the transverse reinforcements inside the loop [24], but the Type B and Type C specimens did not have these reinforcements. From Figure 8a, the maximum load of the Type C specimen was 160 kN at the deflection of 23 mm, while that of the Type B specimen was 148 kN at the deflection of 17 mm. In addition, the decline in the load beyond the maximum load of the Type B specimen was more significant than that of the Type C specimen. These discrepancies were due to the differences in the overlapping lengths of the loop reinforcements; the overlapping length of the Type C specimen was 40 mm longer than that of the Type B specimen. Therefore, a larger overlapping length of loop reinforcements enabled the slab to exhibit a more ductile behavior under flexural loading beyond the maximum load because the large overlapping length increased the concrete area enclosed by the loops and the straight part of the loop reinforcements within the joint. Moreover, the load-deflection curve of the Type C specimen was similar to that of the conventional loop joint of the Type A specimen, and the two maximum loads were close. Thus, the Type C loop joint can be used instead of the conventional loop joint.  
The initial slope of the load-deflection curve of the Type D specimen decreased at around 10 kN load, as was the case with the Type A specimen. Then, the load continued to increase with the deflection until the yield of the loop reinforcement around 110 kN. After reaching the maximum value of 130 kN, the load began to drop sharply at the displacement of 7 mm, showing the non-ductile behavior of the Type D specimen. This was because the Type D joint was narrow and did not have transverse reinforcements; therefore, there was insufficient restraint around the loop reinforcements to resist the tensile force in the transverse direction.