# Evolution Mechanism of Interlayer Properties of CRTS III Slab Track during Construction
## 3 Results and Discussion
### Mechanical Characteristics of Slab Track after Interlayer Damage  
The interlayer damage will directly affect the overall stress state of the track structure. To clarify the impact of interlayer damage on the overall stress characteristics of the slab track, the vertical displacement of key positions of SCC with and without considering damage was extracted, as shown in Figure 15.  
From Figure 15, it can be seen that the vertical displacement characteristics of SCC have significantly changed before and after considering damage. Before 356 h, the vertical displacement was basically the same, but after 356 h, the displacement at the corner of the slab considering damage increased significantly, suddenly reaching about 4.4 mm in just 2 h. The position at the center of the slab also plummeted to about 4.4 mm, and the displacement at these positions remained the same. If the damage is not considered, the vertical displacement at the center of the slab will continue to increase. This is because before 356 h, there was only damage at the corner of the interlayer, and the overall bonding performance still exists. Therefore, non-coordinated deformation occurred under the action of the shrinkage load. After 356 h, rapid cracking occurred at the interlayers, and there was no interface stiffness between the layers to coordinate the deformation of the upper and lower layers of the composite slab. When the cracking area extended to the slab, the bonding between the track slab and SCC had completely disappeared. The track slab and SCC rebounded due to the disappearance of bonding stress, and the disappearance of the bonding surface ultimately made the vertical deformation coordinated and consistent. Therefore, the shrinkage corresponding to 356 h can also be regarded as the critical shrinkage corresponding to an interlayer interface age coefficient of 1. Furthermore, to explain the general law of layer cracking between track slab and SCC, MISES stress distribution diagrams of the lower surface of the track slab with and without damage were extracted, respectively, as shown in Figure 16, to reveal the influence of cracking on the stress distribution of the interlayer.  
Figure 15: Vertical displacement-time curves of SCC with and without damage were considered.  
As shown in Figure 16, it can be seen that the distribution pattern of MISES stress before cracking is basically consistent at different times, with the peaks of \(D_{I}\) concentrated at the edge of the slab and slowly increasing over time. After considering interlayer damage, the stress distribution and magnitude are nearly the same as those without considering damage within 356 h after pouring SCC. However, after 356 h, the stress at the corner of the slab decreased sharply, and the peak of \(D_{I}\) appeared range contracted from the edge to the center of the slab. The MISES stress at the center of the slab did not increase continuously but decreased to 25% at 672 h. This is because the accumulated strain energy overcame the fracture energy, and the strain energy was released. In summary, the interlayer cracking destroys the mechanical properties of the composite slab and changes the force transmission characteristics of the structure. and makes the limit of the multi-layer structural system entirely dependent on the friction force between the track slab and SCC.