Investigation of Asphalt Mixture Balanced Design Method Based on Intermediate Layer Properties

The determination of the optimal asphalt content in aggregate mix design is currently conducted independently of the pavement structure. This approach fails to consider the characteristics of the pavement structure, such as layer positioning and thickness. As a result, there is a significant disconnect between the structural design of asphalt pavements and the material design of the mixtures. This limitation hampers the full and effective utilization of the deformation and crack resistance capabilities of each layer of asphalt mixture. To address this issue, this study focuses on the commonly used AC-20 asphalt mixture in the intermediate layer of asphalt pavements. The Hamburg wheel tracking test (HWTT) and overlay test (OT) were employed to evaluate the high-temperature rutting resistance and low-temperature crack resistance of the mixture, respectively. The effective range of asphalt content was first established through these tests. Additionally, the VESYS rutting prediction model was utilized to obtain the permanent deformation parameters of the asphalt mixture through experimental data. The rutting prediction was calculated based on the deflection values at the top and bottom of the asphalt layer. The optimal range of asphalt content for the intermediate layer was then determined by combining the rutting contribution rate derived from a finite element model with the allowable rut depth value for the intermediate layer. By considering the characteristics of the asphalt layer position and achieving a relative balance between the crack resistance and deformation resistance capabilities of the asphalt mixture, this study proposes a new design method for determining the optimal asphalt content. This method is of great significance for subsequent engineering applications. The feasibility of this design method was demonstrated using the intermediate layer of asphalt pavement on high-grade highways as an example. The research results show that the asphalt content designed by the balanced design method (BDM), based on the rutting resistance performance of the intermediate layer for this pavement structure and material type, is 4.3%–4.6%. In actual engineering practice, it is recommended to use 4.4% as the optimal asphalt content for AC-20.