What causes potholes?

Several factors contribute to the formation of potholes.

Potholes form when water is trapped beneath the pavement surface. As vehicles drive over the saturated base material, the unsupported surface layer collapses, resulting in a hole. The pothole expands as traffic hits the hole.

Water enters the road base through surface cracks and from the sides of the road. During winter’s cold days the water freezes, drawing more water into the base material. The February and March freeze/thaw cycles often cause “frost heaves,” which let in more water. Ice melts from the top down, trapping a pool of water.

Water, salt and ice are enemies of concrete and asphalt. When water freezes, the expansion and contraction that occurs may disturb structural integrity, which may lead to cracks on the surface of the road. Salt can make the cycle worse by keeping trapped water liquified at colder temperatures. With the passage of time and the weight of vehicular traffic, the cracks may gradually become potholes.

What are the two primary methods for patching potholes? What factors determine which is used?

Cold and hot patch procedures. Depending on the time of year, average daily temperature and anticipated weather conditions, a cold (temporary) or hot (permanent) patch will be installed.

The procedure is not as simple as pouring in the filler, patting it down and driving away, is it?

No. First maintenance crews assess the pothole, measuring the size of the affected area and determining the primary cause. Crew members may then use a saw or jackhammer to “square up” the affected area. The next step is for the crew to use a wire brush, hot lance or air compressor to clean and dry the area so the patch material will take hold. The entire process may take less than 60 minutes or as much as several hours, depending on the size of the pothole and why it occurred.

Do MDOT SHA trucks routinely carry materials to repair potholes?

Yes. Temporary cold patch mix material is usually carried on many MDOT SHA truc​ks, especially in the early spring when potholes are likely to develop.