Winter is a “hard” time for asphalt pavements, literally. Asphalt pavements are produced and constructed at high temperatures when the asphalt binder is a liquid so it can be easily mixed with the rocks and sand. During the spring, summer, and fall seasons, asphalt is flexible and stretchy in the warm weather, helping to prevent cracks from forming. However, as temperatures decrease during winter, the asphalt becomes harder and stronger, but also more brittle. Extreme cold temperatures can cause pavements to crack, but the most damage to pavements is caused by freeze-thaw cycles.
What is a freeze-thaw cycle?
A freeze-thaw cycle is when the temperature fluctuates from above freezing (32F), to below freezing, and then back to above freezing. This is considered one freeze-thaw cycle, and Minneapolis, Minnesota experiences several freeze-thaw cycles each year.
How do freeze-thaw cycles affect my pavement?
When temperatures are above freezing, rainwater or snowmelt will make its way into any small crack in the pavement. Then, as temperatures drop below freezing, the water within the cracked pavement begins to freeze and expand, causing the crack to expand and grow as well. Water expands approximately 10% when frozen, and has been estimated to exert over 30,000 psi as it expands. In other words, there is no stopping the freezing water from damaging pavements from the inside out. Finally, warming weather re-melts the ice, allowing the water to move deeper into the newly expanded crack, only to freeze and expand again during the next cycle.
Unfortunately, freeze-thaw cycles can do more than expand cracks. Water underneath the pavement is meant to drain away, but during winter it freezes in the base and subgrade materials. Water freezing below the pavement can sometimes cause frost heave to occur. Although not all soils are susceptible, frost heave occurs when water is allowed to freeze and expand in large chunks, called “ice lenses”. The material above these ice lenses is heaved upward with great force, deforming the pavement. Then as temperatures rise, these ice lenses will begin to melt, weakening the base layer and leaving large voids where the ice lenses were formed. Heavy loads can then greatly damage the pavement and even can cause potholes to quickly form.
What can I do to protect my pavement?
When designing and constructing pavements it is important to consider the drainage of water both above and below the asphalt pavement. Sloped pavements quickly direct water off the surface of the pavement into a collection basin. Drain-tile piping below the pavement can prevent frost heave from occurring by removing water in the base and subgrade layers.
After construction, cracksealing of cracks every 2-3 years is the best maintenance practice to preserve pavements. Cracksealing prevents water from entering cracks during the freeze-thaw cycles and from reaching the base and subgrade layers. Once cracking has become widespread, a mill and overlay is another maintenance/rehabilitation practice to restore the surface of the pavement.
Bituminous Roadways, Inc. is the Twin Cities’ most respected and sought-after asphalt pavement company. With more than 70 years in the industry, we provide dependable service and the highest level of quality asphalt paving anywhere. Call us today at 651-686-7001 or request a consultation. We proudly serve the Twin Cities metro and the surrounding area.