Permeability of asphalt mixtures exposed to freeze-thaw cycles

The objective of this research is to assess the permeability of asphalt mixtures exposed to freeze-thaw cycles in the cold region. Three types of asphalt mixtures were produced in a lab environment. A special constant head permeameter following the UNI EN 12697/19 protocol was adopted to evaluate the permeability of asphalt mixtures exposed to freeze-thaw cycles. The permeability of asphalt mixtures mainly focuses on two aspects: regime of flow in asphalt mixtures and hydraulic conductivity of asphalt mixtures. Results showed that the discharge velocity and hydraulic conductivity of asphalt mixtures are aggravated when samples are subjected to freeze-thaw cycles. Accordingly, the critical Reynolds number and corresponding critical hydraulic gradient for each sample decrease when freeze-thaw cycles increase. Results indicated that water can move through the asphalt mixture more easily because of the freeze-thaw cycles, and the scouring effect of water flow on the internal structure of asphalt mixtures becomes more significant. Linear regression equations were utilized on the collected data to determine the susceptibility of permeability growth rate of asphalt mixtures under freeze-thaw cycles to gradation type. Open graded asphalt mixtures exhibited steeper slopes compared with the other mixtures, which indicated their higher susceptibility to freeze-thaw cycles.