What Are Those Black Squiggles on Roads?

When asphalt pavement cracks, a squiggle of black sealant can help prevent further damage. Learn more in this episode of BrainStuff, based on this article: https://auto.howstuffworks.com/road-tar-squiggle-drizzle.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff Lauren
vogelbom Here. If you've spent a good amount of time
driving around the United States, especially in rural areas, you've
probably noticed those messy looking black squiggles that cut across
asphalt paved road surfaces and what looks like a paphazard

(00:24):
fashion at best. But arest assured they're not the wasteful
result of some sloppy tarwork, nor drizzles from your local
tar tankred transport. Instead, what you're noticing is crack ceiling.
It's a time honored technique for remedying damaged road surfaces
without inflicting more pain upon taxpayers by tearing up and

(00:46):
repaving the entire road and disrupting traffic while that work
is done. Asphalt is the sticky, binding liquid that sets
around the rocks and stuff that make up our road pavement.
That pavement can take a pounding from heavy traffic, for example,
or from the expansion and contraction that happens during seasonal

(01:08):
changes in temperature. Cracks develop when stress builds up the
surface layer of the pavement that exceeds its tensile strength.
Design and construction flaws such as an adequate drainage for
rainfall or a weak base underneath the road, can also
cause the surface to fail. Cracks are insidious because once

(01:28):
they appear, water can get in not just the cracks
but the base of the road and cause lots more
damage as it expands and contracts with the temperature. In
the arcane, highly technical world of road maintenance, there are
actually a lot of different types of cracking to contend with.
One of the most unsightly is fatigue cracking, a which

(01:50):
turns the highway into something resembling an alligator's hide and
which usually requires an extensive repair job. Another type of damage,
reflection cracking, results from movement between the road's asphalt and
concrete layers and looks more like a jagged gash. There's
also edge cracking, in which rows of wavy, curved cracks

(02:12):
parallel the road shoulder. If you've tried to build a
nice new road every time that stuff happened, it would
be prohibitively expensive. In introduction to crack ceiling, a two
thousand and eight treatise on the subject from the Texas
Engineering Extension Service at Texas A and M University, the

(02:32):
experts note to that ceiling cracks is way cheaper, about
two thousand, five hundred bucks per mile of road compared
to sixty thousand dollars for putting down an overlay surface,
though of course two thousand and eight was a while ago.
In twenty sixteen, the city of Littleton, Colorado, estimated that
crack ceiling cost about five thousand, five hundred dollars per

(02:52):
laane mile, while overlaying cost approximately three hundred and twenty
thousand dollars per laane mile. Trick friends a mile is
about one point six kilometers. These seals aren't actually made
of tar these days, it's more likely to be some
sort of high performance polymer asphalt mix designed to form

(03:13):
a bond that's flexible enough to move with the road
and keep the crack from growing. A cruise apply it
to the fissures with a device that looks vaguely like
a vacuum hose working in reverse. However, although crack ceiling
can keep a road from deteriorating further, it doesn't make
the road any smoother. You might not feel it in

(03:36):
a smooth riding sedan or suv, but some motorcyclists call
the patches tar snakes and contends that they cause damage
to bikes or even accidents. Today's episode is based on
the article what are those wiggles of tar on the
road on howstufforks dot com written by Patrick J. Kiger.

(03:58):
Brainstuff is production by Heart Radio in partnership with HowStuffWorks
dot Com and is produced by Tyler Klang. Four more
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