Seasonal and diurnal variations of back-calculated layer moduli in flexible pavement and FWD testing guidelines

Abstract

The seasonal and diurnal changes impact the backcalculated layer moduli for flexible pavements in different climatic regions. The HMA layer moduli showed minimal variation in the spring and fall seasons in every climatic area. Also, the HMA layer moduli were consistently higher, based on the deflections measured before noon. However, temperature correction, generally applied to HMA layer moduli, can eliminate the season, time, and temperature impacts of the FWD measurements. Since the base and subgrade layer moduli are backcalculated from the single measured deflection basins on the surface, temperatures and moisture conditions at the time of measurements can affect those material properties. Temperatures may potentially result in layer moduli values that are close to their representative in-field conditions. Based on the results, the preferred temperature ranges for FWD measurements are 55 to 70ᵒF and 65 to 75ᵒF in freeze and non-freeze regions, respectively, during any time of the day.