Asphalt bubbles

This might be a long shot but at this point I've had no luck anywhere else.
Had my driveway paved about 5 years ago. About 2 or 3 years ago I started getting these little bubbles in it. They grow over about 2 months and will then eventually burst. They look to maybe be some sort of seed pod, but I'm not sure. Anybody ever seen this before? I'm in south central PA if that helps. Just hate to dump another couple thousand dollars to have the driveway torn up and redone if I don't know what's causing the issue.

 

It’s a mushroom, google earth star

 

thats crazy ive never seen one pop through asphalt like that

 

Well that was certainly a quick long shot. Haha.
Now to research the heck out of them and see if I can figure out how to keep it from happening more. Thanks man.

 

What did your contractor put down for an under layment?

Should be compacted crushed limestone, roughly 6" or more.

 

Honestly I can't say 100%. I was at work all day and it was finished when I got home. I will however say that after I had it done I had a few people say that the company I used was maybe a bit shady. And no they were not the lowest bid.

 

Generally, in this area of the country, central Iowa, they will remove the old driveway and undelayment. Dig down to undisturbed soil, compact, lay in 6-8" crushed limestone, compact, final with 2-3" of hot mix asphalt, then rolled.

Personally, I prefer concrete driveways. Yes, more expensive on install and initial cost, but the lifetime far exceeds asphalt.