## 4 Experimental Test Results
### Constant Amplitude Fatigue Loading
#### 4.1.2 Behavior of the C-Jointed Precast FDDP under CAF  
For the tested specimen S3 having C-joint under CAF loading, the compressive strengths of the concrete cylinders on the testing day were 58.10, 57.08, and 54.87 MPa, with an average value of 56.68 MPa. The tested cylinders for the UHPFRC, which were cast ten days before the start of the fatigue testing, resulted in compressive strengths of 168.03, 162.33, 170.54, and 149.22 MPa, with an average value of 162.53 MPa.  
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.  
Figure 7: Static load-deflection curves for slab S1 after being subjected to CAF loading.  
After each 250,000 cycles, the slab was subjected to monotonic loading to observe the change in slab flexural stiffness through deflection measurements. Figure 8(a) 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  
Figure 8: Crack pattern after failure of slabs S1, S3, and S5 having A-joint, C-joint, and Z-joint tested under CAF loading followed by static load test to collapse.  
monotonic load that caused it to collapse. The precast FDDP failed due to punching shear at a jacking load of 973 kN. It can be noted that such a failure load is about 4.67 times the CHBDC factored design wheel load. Figure 8c shows the top view of the slab showing punching shear failure at the footprint of the wheel load, while Figure 8d presents the bottom view of the slab showing a crack pattern after failure. It can be observed that the radial cracks start from the location of the footprint of the wheel load and propagate toward the support line in a fan shape. At failure, concrete spalling appeared in some parts of the bottom side of the slabs on one side of the closure strip as a sign of punching shear failure. However, this concrete spalling did not extend through the closure strip to the adjacent FDDP. Figure 8d shows that a concrete diagonal crack at the end of the bottom perimeter of the punching shear plane appeared, passing through UHPFRC on one side of the closure strip. In addition, fan-shaped cracks at the bottom surface of the slab passed through the UHPFRC but were less intensive than those in the precast slab. Figure 9b depicts the load-deflection relationship for the tested slab under static loading to collapse. Deflection values were recorded at the mid-length of the free edge of the short slab, noted as a \"Free end\" curve that reached 2.54 mm at failure. On the other hand, deflection under the wheel footprint, denoted as \"Point load\", was recorded as 25.98 mm at failure. The deflection at the center of the long precast slab, denoted as \"Mid-span\", was recorded as 17.83 mm. The maximum deflection of the long precast slab at the mid-length of the edge joint, denoted as \"Fixed end\", was recorded as 3.73 mm at failure.  
Figure 9: _Cont._