# Evolution Mechanism of Interlayer Properties of CRTS III Slab Track during Construction
## 4 Conclusions  
This paper focused on the issue of cracking between the slab track and the SCC of the CRTS III slab track during construction. A time-dependent damage model was established for the interlayer of the slab track during construction while considering time-varying parameters and loads between layers. Interlayer damage evolution and the influence of key factors on damage evolution were systematically analyzed. The conclusions are as follows:  
A time-varying coefficient was proposed that can simultaneously reflect the interfacial strength, stiffness, and fracture energy evolution between track slab and SCC at an early age. Based on this, the bilinear CZM was modified and introduced into the interlayer damage evolution model of the CRTS III slab track during construction using a UFIELD subroutine. This model can better describe the time-dependent damage between the track slab and SCC during construction.  
Figure 19: Typical index at the corner of the slab under different temperatures. (**a**) \(D_{I}\); (**b**) vertical displacement.  
After SCC pouring construction is finished, the corner of the slab is a sensitive area for interlayer cracking, mainly due to the combined effect of longitudinal and transverse shrinkage of SCC as well as significant interfacial stress caused by temperature gradients.  
Under unfavorable conditions of construction load, the interface cracks between the track slab and SCC appear first at the corner of the slab. Gradually, the cracking area extends towards the center of the slab and successively penetrates to the end and the edge of the slab. Interlayer cracking negatively impacts the composite performance and changes the force transmission characteristics of the track structure.  
The interlayer bonding property and SCC shrinkage performance significantly affect the evolution process of interlayer damage. Specifically, the better the interlayer bonding property and the smaller the shrinkage performance of SCC, the later the occurrence of interlayer damage. To reduce the risk of cracking, the bonding and anti-shrinkage properties of SCC can be improved by adding viscosity modifiers, expansion agents, etc.  
Low construction temperatures are less favorable for the interlayer properties of the slab track. Construction in low temperatures below 0 \({}^{\circ}\)C should be avoided as much as possible. During low construction temperatures, it is crucial to take strict insulation measures to prevent the SCC core temperature from dropping too fast and adopt strict and standardized concrete maintenance plans. In addition, to guarantee stable SCC performance, the construction temperature should not exceed 30 \({}^{\circ}\)C.  
Conceptualization, L.G.; methodology, J.W., L.W. and W.Z.; software, J.W., W.Z. and Y.Q.; validation, L.G. and W.Z.; investigation, J.W., L.W. and W.Z.; writing--original draft preparation, W.Z., C.H. and Y.L.; writing--review and editing, J.W., L.W. and Y.Q.; visualization, J.W. and L.W.; supervision, L.G.; project administration, L.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Fundamental Research Funds for the Central Universities (Science and technology leading talent team project, 2022 JBOY009), the Fundamental Research Funds for the Central Universities (No. 2020 JBZD013), the 111 Project (B20040), the Science and Technology Research and Development Project of China State Railway Group Co., Ltd. (P2021G053), and the Research Program of the Shandong Department of Transportation (2021B99).  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.  
The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.