Effects of Seasonal Variation on the Load-Bearing Capacity of Pavements Composed of Insulation Layers

Seasonal variation in the subgrade resilient modulus is likely caused by external factors, such as precipitation and freeze–thaw cycles. One of the strategies for minimizing the impact of this variation on the subgrade modulus is to use insulation layers to prevent frost penetration. This study investigated the effects of the use of insulation layers on pavement performance in the fully instrumented Integrated Road Research Facility in Edmonton, Alberta, Canada. Three insulated sections of the test road were comprised of bottom ash (BA) (100 cm) and polystyrene boards of two thicknesses (5 and 10 cm), and the adjacent conventional section was considered the control section (CS). The resilient modulus and the effective modulus of pavement were backcalculated with the data obtained from falling weight deflectometer testing conducted at the test road during a 1-year monitoring period, from July 2014 to July 2015. Temperature and moisture probes, installed across the depth of the sections, were used to determine the frozen, thawed, or recovering condition of the pavement. The study results revealed that polystyrene boards protected subgrade soil from freezing and thawing effects. The minimum ratio of the backcalculated subgrade modulus of each test to the resilient modulus of the test performed in September was 0.94 in the BA section, and the ratio of the CS could decrease to 0.88 in the recovering period. Comparison of the load-bearing capacity of insulated sections and the CS indicated that, unlike BA, polystyrene boards significantly decreased the load-bearing capacity of the pavement.