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How Do Potholes Form?

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Why do they always happen in the spring?

Picture of a PotholePotholes are holes in the roadway that vary in size and shape. They are caused by the expansion and contraction of ground water after the water has entered into the ground under the pavement. When water freezes, it expands. Think of when ice cubes are made. A tray full of water is put into the freezer, and when you remove the tray from the freezer, you will notice the water has expanded. This same effect happens when water gets into the ground under the pavement. If it has a chance to freeze, it will take up more space under the pavement, and the pavement will expand, bend, and crack, which weakens the material pavement. Then when ice melts, the pavement contracts and leaves gaps or voids in the surface under the pavement, where water can get in and be trapped. If the water freezes and thaws over and over, the pavement will weaken and continue cracking.

As the weight of cars and trucks pass over the weak spot in the road, pieces of the roadway material weaken, which will cause the material to be displaced or broken down from the weight, creating the pothole.

What happens when salt is brought into the picture? Water will freeze at 32 degrees Fahrenheit. When salt is used, it lowers the temperature that water will freeze. This creates an artificial freeze-thaw cycle that permits more occurrences of the damaging cycle to occur. This happens more often in the spring because of the melting that takes place and because the temperatures fluctuating above and below the freezing point very frequently.

How Potholes Form
Rainwater is absorbed Vehicles erode the road Asphalt sinks into eroded portions, cracks Holes filled with patching materials
Rainwater sinks through cracks in old or weakened asphalt. The water is soaked up by the mixture of rock, gravel, and sand that supports the road. Vehicles passing over the road force water through the soggy roadbed, eventually eroding parts of it. Asphalt sinks into the eroded portions of the roadbed and eventually cracks under the continued impact of vehicle tires. Chunks come loose. Holes may be patched with proprietary cold patch or hot patch materials.

For instructions on how to report a pothole, click here.

Last Updated on Thursday, 29 October 2009 11:27  
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