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My elementary school playground was made of asphalt and had a track painted on with white lines. While walking on the track, I noticed that cracks in the asphalt often followed the paint.

The conclusion I came to and that I still hold is that the white tape on the black asphalt causes a temperature difference due to the different amounts of sunlight absorbed and that this difference accounts for the cracking.

Is this correct? Is there more to the story?

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Interesting hypothesis. Just thinking out loud. If your hypothesis were true, would there be a preference in bends for the cracks to be on the inside or on the outside? –  Bernhard Jun 16 '13 at 11:48
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Another explanation might be that cracks in/under the white lines/tape (especially if they run along with them) are more visible and stick out more than cracks elsewhere in the black asphalt concrete, thus giving you a false impression of correlation. For roads there are even more possible explanations (besides the one given by Olin), but I don't see those quite working for playgrounds. –  Glen The Udderboat Jun 16 '13 at 17:05
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2 Answers

I don't know what is going on with your playground, but I do know what caused a similar problem elsewhere.

Over the last decade or so, the pavement of Interstate 495 northwest of Boston was wearing out quickly under the dashed white stripes used to delineate lanes. For a while it seemed like it could be coincidence, but then it became obvious something was degrading the pavement just under the stripes.

It turns out that the contractor that did the last repaving used the wrong paint. Apparently there are two predominant types of roadway paint, one for concrete and one for asphalt. They used the concrete paint on asphalt, which contains a solvent that seeped a bit into the asphalt and degraded it. The solvent was long gone by the time the problems appeared, but the degradation due to the weakened asphalt under where this paint was applied continued.

Many many asphalt roadways have had white paint applied, so we know it is possible to do this without any apparent harm. If differential thermal expansion was a problem, then we should see it in lots more places, given the very large number of test cases for this experiment.

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Just curious: which paint was specified, and which was cheapest? –  User58220 Jun 16 '13 at 19:09
    
I don't know the details. I remember noticing the issue on I-495 and mentioning it to a friend, and he said there was a Boston Globe article on it recently. That was probably a couple of years ago. What I reported was heresay from the friend who claims to have read the article, but I have no reason to suspect he wasn't reporting what he believed to be true. I've probably given enough details that some quality time with Google or Bing can uncover the story. –  Olin Lathrop Jun 16 '13 at 22:06
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It's usually caused from the paint being laid too thick (especially oil based paints) and when the paint dries it shrinks pulling itself to the centre of the line. Because the paint has such a good hold of the asphalt it pulls the asphalt as well causing the crack. Most line markers now use a water based paint.

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