Ask A Scientist© Engineering Archive

Index Key:   ENG024
Author:      jana hill
Subject:     Causes of potholes.
What causes potholes?

Response #:  1 of 1
Author:      wildman jackson
Potholes are caused by the expansion and contraction of water.  This mainly
occurs during the winter months when temperature is below freezing.  A small
crack must develop in the road surface to allow water to enter.  This water
then freezes (water expands when frozen) causing the road surface to bulge,
and then thaws, returning it to the original position.  Over time, the road
surface weakens and the hole expands in size with wear.
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As soon as the first vehicle crosses it, damage begins accumulating in a
pavement.  Over time, as the pavement is "flexed" by traffic up to 100
million or more times, the pavement will begin to break from fatigue just as
a coat hanger that is repeatedly bent will eventually break.  This damage
typically starts as a single crack where the wheels run on the pavement.
Over time, more of these cracks will appear and eventually join to form a
distinctive cracking pattern that is often referred to as "alligator" or
"chicken-wire" cracking.  Once this type of cracking occurs, if the pavement
is not promptly repaired, the structural integrity of the pavement is lost
and traffic will start knocking the pavement chunks loose.  At this point, a
pothole is born.


Water seeping into the pavement through the cracks can accelerate this
process by softening the soil under the pavement.  Water expanding and
contracting due to freezing can make things even worse.  However, potholes
can form in any unmaintained pavement, even in dry, hot places like Arizona.

Andrew Johnson
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