Freeze-thaw cycles are best known for how they undermine pavement integrity. But when things get really cold, asphalt cracks up in a different way.
Recently, winters in much of the US have been warmer and wetter, particularly in the upper Midwest, than in previous years. But slicing a cold knife into these seemingly mild winters on an almost annual basis are the polar vortexes, the deep penetration of Arctic air fronts that stretch as far south as Texas and northern Florida. These typically last from a few days to one or two weeks.
Paradoxically, the polar vortexes are the result of warmer temperatures in the Arctic. Warmer air there can cause the stratospheric polar vortex – which typically stays in the Arctic latitudes – to weaken and become unstable. Characterized by a band of strong winds, the vortex wobbles, stretches, and even splits, according to NOAA, the National Oceanic and Atmospheric Administration. This allows the Arctic air to spill southward into mid-latitude regions.
In other words, the air temps more typical of Fairbanks visited Chicago, Nashville, and even Dallas in early 2024. Billings, Montana had a temperature reading of -30ºF on January 13. Even Houston had 19ºF on January 16.
This matters in all kinds of ways – including how those exceptionally frigid temperatures, often registering well below zero degrees Fahrenheit, adversely affect pavement. Where freeze-thaw cycles, when the thermometer dances above and below 32 degrees Fahrenheit, are most often blamed for the creation of potholes, deep freeze temperatures wreak their own havoc with asphalt due to a different set of factors and reactions within the structure of the asphalt.
Known as “low-temperature cracking,” the pavement shrinks such that tensile stresses build up. When the tensile stress equals and exceeds the strength of the asphalt concrete mixture, a micro-crack develops at the surface and edge of the pavement structure. With either prolonged very cold temperatures, or from cycles of temperatures at higher levels, the crack penetrates the full depth and width of the asphalt layer.
Those cracks can be damaging enough on their own. But when they allow moisture to penetrate the top layer of the pavement, the freeze-thaw dynamic create a subsurface bubble in the pavement. Whether a semi-tractor trailer, an SUV, or a motorcycle, any vehicle passing over these pavement bubbles turn them into potholes.
So when the weather starts to warm up after a deep freeze, expect a fresh crop of potholes.
