Insulation Materials and Thermal Regime in The Pavement Structure

Using insulation layers has become one of the strategies for alleviating and/or preventing the frost-heave problem during winter and thaw-weakening during spring. Surface heave alters the road profile and can negatively affect the road’s ride quality, especially if the heave is differential and uneven. Thaw weakening during spring may result in imposing the spring load restriction (SLR) on low volume road. The subsequent weak subgrade support during thaw season results in higher deflections that cause accumulation of fatigue in the pavement and leads to different types of cracks and deterioration, including alligator cracking. If the insulation layer provides an adequate load bearing capacity for the pavement and does not create an unfavorable moisture regime in the system, using it will result in reducing the depth of frost penetration into the pavement structure. This can enable design engineers to moderate the base/subbase layers’ thicknesses and, thus, limit the depletion of natural aggregate resources and move towards more economical and sustainable design strategies.

Traditionally, polystyrene has been used as insulation material. In recent years, in line with other sectors of society, there has been increased tendency in the pavement community to use more sustainable and environmental friendly practices and materials. Consequently, road highway agencies in cold regions are urged to use waste and recycled materials as an economical insulation layer in an ongoing trial-and-error process. As there are some difficulties associated with the prediction of reliable thermal patterns in pavement structures, also there are concerns regarding long term structural performance of these material, field trials have been initiated. Bottom ash, a waste material produced from the incineration of coal in power plants, has recently been presented as an option for the construction of road embankments. The amount of insulation required will depend on the type of pavement structure, the thermal properties of the different pavement layers, and the climate. As a result, changing the thermal regime in the pavement structure caused by insulation materials should be investigated using proper modeling software to provide an accurate and reliable estimation of required thickness of insulation material to avoid the above-mentioned problems.

In the early 1990’s, the thermal modeling of insulated and uninsulated road was performed by the Alaska Department of Transportation (AK DOT) using an MS-DOS computer program, MUT1D (Multilayer User-Friendly Thermal Model in 1 Dimension).

The software applied one dimensional implicit finite difference techniques for estimating the thermal regime of a multilayered model. Although the MUT1D model yields results with acceptable accuracy, it is limited to producing the depth of phase change along a single line of analysis. The limitation of previous software leads the designer to use TEMP/W (which is one of modules in software Geostudio 2012, GeoSlope International, Calgary, Alberta). This two-dimensional (2-D) finite element program provides heat flow analysis for an entire cross-section and, because it uses 2-D boundary effects, it is more reliable than a 1-D model.