## 4 Experimental Test Results
### Constant Amplitude Fatigue Loading  
#### 4.1.1 Behavior of the A-Jointed Precast FDDP under CAF  
For the tested specimen S1 under CAF loading, the compressive strength of the concrete cylinders taken from the concrete mix were 60.76, 59.83, and 54.26 MPa, with an average value of 58.28 MPa. The tested cylinders for the UHPFRC resulted in compressive strengths of 161.94, 163.30, 170.54, and 159.20 MPa, with an average value of 161.48 MPa.  
Figure 6: View of the test setup for fatigue loading and the monotonic loading for the FDDP system.  
During the initiation of the fatigue pre-cracking procedure, at a static load of 220.5 kN, the flexural crack propagated from underneath the mid-point of the wheel footprint about 100 mm towards the middle shear pockets shown at the middle of the precast slab segment. When the applied load increased to 275.625 kN, the flexural crack propagated further another 300 mm. However, when the applied load reached 330.75 kN, the flexural crack propagated diagonally from underneath the mid-point of the wheel footprint to the closest corner of the middle shear pocket. The maximum recorded flexural crack width at that point measured 80 \(\upmu\)m. No more flexural cracks were observed during the CAF test that lasted over 16 days.  
After each 250,000 cycles, the slab was subjected to monotonic loading to observe the change in slab flexural stiffness through deflection measurements. Figure 7a depicts the load-deflection relationship for the slab at the center of the footprint of the wheel load. It can be observed that the slope of the curves after each group of fatigue cycles appeared unchanged and stayed linear. After the 4 million fatigue cycles, the slab was subjected to a monotonic load that caused it to collapse. The precast FDDP failed due to punching shear at a jacking load of 930.92 kN. Figure 7b depicts the recorded slab deflection at the mid-length of the free edge of the short slab shown as the location of LVDT 1 in Figure 2c, noted as the \"Free end\" curve in Figure 7b. Such deflection reached 10.68 mm at failure. On the other hand, deflection under the wheel footprint shown as the location of LVDT 2 in Figure 2c, denoted as \"Point load\" in Figure 7b, was recorded as 23.05 and 23.88 mm at failure since two LVDTs were installed at this location. The deflection at the center of the long precast slab shown at the location of LVDT 3 in Figure 2c, denoted as \"Mid-span\" in Figure 7b, was recorded as 13.09 mm. The maximum deflection of the long precast slab at the mid-length of the edge joint shown as the location of LVDT 4 in Figure 2c, denoted as \"Fixed end\" in Figure 7b, was recorded as 6.80 mm at failure.  
Figure 7: Cont.  
Interestingly, such a failure load is about 4.47 times the CHBDC factored design wheel load. Figure 7(a) presents the top view of the slab showing punching shear failure at the footprint of the wheel load. Figure 7(b) shows the bottom view of the slab showing a crack pattern after failure due to the fan mechanism. One may observe the radial cracks starting from the location of the footprint of the wheel load and propagating toward the support line in a fan shape. At failure, concrete spalling appeared in some parts of the bottom side of the slabs as signs of punching shear failure. However, such concrete spalling appeared only in the large FDDP slab, but it did not extend to the short FDDP segment on the other side of the closure strip.