## 3 Experimental Results
### Static Test Results  
#### 3.5.1 Strain Results under Static Load  
Figure 20 shows the load-strain plot of the track slab under static loads both before and after the repeated thermal loading. It can be seen from Figure 19 that under the action of the three-point static load, the track slab is under tension at the beam ends and under compression at the mid-span. After the repeated thermal loading, under the action of the same static load magnitude, the strain at the fixed end section and the mid-span section increased significantly, while the strain change at the sliding end section was relatively insignificant.  
Figure 21 shows the load-strain plot of the CA mortar under static loads in both states of before and after the repeated thermal loading. It can be seen from Figure 21 that under the action of the three-point static load, the CA mortar is under tension at the fixed end section and under compression at the mid-span section and the sliding end section. With respect to the initial state (before the repeated thermal loading), under the same static load magnitude, the strain of the CA mortar at each measuring point increased to different degrees, and the closer to the position of the gap, the greater the increase range.  
The load-strain plot of the track bed under static loads both before and after the repeated thermal loading states is shown in Figure 22, which shows that under the action of the three-point static load, the track bed is under compression at the beam ends and at mid-span. Under the same static load level, after the repeated thermal loading, the strain at the fixed end section and the mid-span section near the position of the gap increases significantly while that at the sliding end section far away from the position of the gap, it is basically unaffected.  
Figure 19: Track- bridge mid-span relative displacement.  
After the repeated thermal loading, under the action of the same static load, the strain of the track structure layers increases to varying degrees. As described above, the track slab strain increase law and the reduction law of the CA mortar strain and the track bed strain are different. According to the analysis, after the initiation of the track slab-CA mortar interlayer gap, the interfacial bond fails, so it cannot withstand tensile force while the compression force can still be withstood. When subjected to the action of the vertical static load, the load effect is transferred to the lower layer through the interlayer extrusion, achieving the harmonized deformation of the track structure. Therefore, under the action of the vertical static load, before and after the repeated thermal loading, the track structure layer strain change trend is consistent, showing an increase.  
Figure 21: Load–strain curve of the CA mortar under static load.  
Figure 22: Load–strain curve of the track bed under static load.  
The linear regression method was used to fit the measured load-strain curve in this experiment, and the linear correlation coefficients were greater than 0.95. Therefore, it can be considered that the load and strain as a whole conform to a linear relationship, and the existing nonlinear trend is ignored. The slope of the load-strain plot is the load required to produce unit strains, which indirectly characterizes the stiffness of the structure. The measured load-strain plot of the track structure layers is linearly fitted to obtain the change in the slope before and after the repeated thermal loading, as shown in Table 3 from which it can be seen that the overall stiffness of the track structure degrades after the repeated thermal loading. This degradation is more significant at the fixed end section and the mid-span section than at the sliding end section of the beam.