# Application of Mastic Asphalt Waterproofing Layer in High-Speed Railway Track in Cold Regions
## 2 Material Design and Evaluation
### Test Results and Discussion  
The results of all laboratory tests are listed in Table 2. It should be noted that the listed requirements are proposed on the basis of previous work and asphalt pavement specification. The requirements specified for asphalt pavement in cold regions in China Technical Specifications for Construction of Highway Asphalt Pavement [26] were referenced. The Lueer fluidity of designed mastic asphalt at 210 \({}^{\circ}\)C is 10.5 s. In light of previous works [30; 31] and practical experience, this fluidity value allows the fresh mastic asphalt filter into interface during construction and prevents overflow at the same time.  
Air voids of asphalt mixtures are closely related to its waterproof performance. Studies showed that the asphalt mixture becomes impermeable when its air void is less than 3% [32]. The tested air void of the designed mastic asphalt is 1.8%, which is sufficient to ensure good impermeability of the mastic asphalt. The permeability coefficient is another index that is commonly used to directly characterize the impermeability of asphalt concrete, the permeability coefficient value obtained from repeated permeation test, namely 3 mL/min, also indicates the excellent impermeability of the designed mastic asphalt mixture.  
Failure strain in the three-point bending test and dynamic stability in the rutting test are typical indexes used to characterize cracking resistance and high-temperature stability of asphalt mixtures, respectively. As shown in Table 2, the tested values of mastic asphalt fully meet the requirements for pavement asphalt mixture. However, given that the waterproofing layer is only paved on the shoulder and the middle area between track slabs, and mastic asphalt waterproofing layer (MAWL) is not used as a supporting layer under track slab, the working environment for MAWL is much more favorable than asphalt mixture in road pavement. Therefore, the designed mastic asphalt can completely satisfy the requirement of the waterproofing layer of slab track in terms of cracking resistance and high-temperature stability.  
Results of the shear test reveal the bond strength between asphalt waterproofing layer and concrete base plate. Debonding of the interface is one of the main distresses reducing serviceability and durability of slab track systems [33]. The interface bonding between the asphalt waterproofing layer and the concrete base plate is required to be strong enough to secure the structural integrity and durability of the slab track. At present, there are no requirements specified for interface bonding between the asphalt layer and the concrete layer in the slab track structure, so the requirements for asphalt layer-concrete layer interface in pavement structure are referenced in this study to evaluate the interface bonding strength. The work of [PERSON] [21] showed that, due to better dispersion of stress, the train-induced structural stress under the slab track is much lower than that in pavement structure caused by vehicle load. The test results showed that the tested shear strength between asphalt  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Methods** & **Index (Unit)** & **Tested Value** & **Requirements** \\ \hline Lueer test & Fluidity (s) & 10.5 & 5–40 \\ Air voids & Air void (\%) & 1.8 & - \\ Permeation test & Permeability coefficient (ml/min) & 3 & - \\ Three-point bending beam test & Failure strain (\(-\)10 \({}^{\circ}\)C, \(\mu\)\(\epsilon\)) & 5641 & \(>\)3000 \\ Rutting test & Dynamic stability (times/mm) & 2548 & \(>\)2000 \\ Slant shear test & Shear strength (25 \({}^{\circ}\)C, MPa) & 2.01 & - \\ \hline \hline \end{tabular}
\end{table}
Table 2: Results of laboratory tests.  
waterproofing layer and concrete (2.01 MPa) is comparable to the bond strength between structure layers in asphalt pavement [34; 35]. Therefore, the bonding strength was considered to be sufficient to resist possible shear stress caused by train load.