Water Vapor Movement Through a Drainage Layer In a Freezing Pavement System: Effects On Frost Heave and Pavement Stiffness.

Water ingress in aggregate base materials is a primary cause of pavement deterioration in cold regions.  During winter, the upward movement of water into base layers can lead to frost heave, while the accumulation of meltwater during spring can cause significant thaw-weakening of pavement structures.  To minimize these effects, engineers can specify construction of open-graded drainage layers beneath the base materials.  However, while the drainage layers effectively prevent capillary rise of water into the base materials, they also provide ideal conditions for potentially problematic water vapor movement through the pavement systems. 

The extent to which water vapor moves through such a drainage layer was measured in this research, and its effects on frost heave and pavement stiffness were evaluated.  For comparison, experimental and conventional pavement structures located in Orem, Utah, were each instrumented with several sensors for monitoring temperature, volumetric water content, and matric suction of the base and native subgrade layers.  Between these layers, open-graded and dense-graded subbase layers were constructed in the experimental and conventional pavement structures, respectively.  The experimental section was isolated from all sources of water except upward water vapor movement from the subgrade.  Pavement stiffness, frost heave, and sensor readings in both sections were then monitored during fall, winter, and spring.

Although the structural capacities of the two pavement sections were not significantly different, survey data indicate that frost heave occurred in the experimental section during the coldest periods of winter, while the conventional section remained relatively stable.  Furthermore, sensor data show that, while the volumetric water contents of the base layers doubled in both sections at the onset of fall, the water content of the base material in the experimental section was significantly higher after winter than that of the base material in the conventional section and remained high even after thawing was complete.