Field Assessment of Changes in Pavement Moduli Caused by Freezing and Thawing

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Abstract
Three secondary highways with flexible pavements were instrumented for 18 months to monitor changes in pavement moduli caused by seasonal meteorological changes. Temperatures, water contents, and water phase changes in the subsurface as well as meteorological conditions were recorded every 2 hours throughout the study. Pavement moduli were regularly determined by conducting surveys with a falling weight deflectometer and by performing backcalculations using the program Modulus. The moduli of the base and subgrade typically increased 12 to 4 times, respectively, when frost penetrated the subsurface. When the base and subgrade began to thaw, the moduli decreased substantially. The base moduli decreased the most, typically being about 35 percent of the prefreezing values by the end of thaw. Smaller decreases occurred in the subgrade. The subgrade moduli were about 65 percent of their prefreezing values by the end of thaw. The moduli continued to decrease until thaw was complete and then gradually recovered back to the original prefreezing values. Complete recovery required approximately 4 months. Similar changes in moduli were observed regardless of site or year.