Insulated Pavement Structures using Alternative Materials: Design and Optimization through FEM

Abstract: Insulated pavement design practices have evolved to address frost-related challenges in cold regions of the United States. Traditional methods typically involve using thick granular material fills or replacing frost-susceptible materials with non-frost-susceptible materials. However, incorporating alternative insulation layers, such as extruded polystyrene, offers a more cost-effective solution for subgrade protection. However, proper construction techniques and design methods are essential to derive optimal performance of XPS boards as insulation material. Hence, such pavement design approaches shall take account of climate conditions, material properties, and the overall thermal balance. State highway agencies in cold regions such as Alaska utilize various methods to characterize materials and determine layer thickness of insulation pavement structures. In general, the insulation material is placed between the base layer and subgrade of pavement to mitigate frost heave. In addition, an additional granular layer above the insulation layer can also help minimize the risk of differential icing. While many states still rely on empirical design methods, there is a growing shift towards mechanistic-empirical design approaches. Pavement design practices vary across states, influenced by freezing regimes, frost susceptibility, and local conditions.
A key parameter in the design of insulated pavements is the freezing index, especially when using extruded polystyrene (XPS) boards as outlined by the UFC (Unified Facilities Criteria). Previous literature proposed an alternative methodology for designing insulated pavements. In their study, they evaluated a UFC-based pavement section using Finite Element method and found that the UFC design lag to meet the updated criteria. To address this, the current study developed thermal criterion-based pavement design approach using Finite Element Method (FEM). This approach utilizing FEM can help further capture and understand the temperature profiles throughout pavement structure due to realistic environmental conditions. It can clearly demonstrate the impact of insulation layer on mitigating frost heave. Furthermore, since there are no available mechanistic-empirical design method for insulated pavements, FEM can be employed to understand their mechanical characteristics. The current study selected Long Term Pavement Performance (LTPP) sections for various cold regions in the U.S., including New Hampshire, New Jersey, Minnesota, and Alaska, exploring alternative insulation materials. Comparative analysis revealed that while XPS insulation exhibited superior thermal performance, it lacked sufficient structural strength. As a result, FEM pavement designs incorporating alternative insulation materials were developed and analyzed for each location. These designs were then ranked based on both thermal and structural performance, providing valuable insights for optimizing insulated pavements across diverse climates and materials.