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Comment by save_ferris | Hacker News Reader

That’s interesting. I wonder what goes into reusing old asphalt (i.e. what new chemicals need to be added/removed in order to make old asphalt pliable or whatever the term is to lay it again).

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It isn't just the asphalt that is recycled but many other products are recycled into it as well, shingles, tires, and even glass, can all end up into it.

what they take off the road can be ground and used on site for a layer but mostly its carted off and ground to the same size as the original aggregate and combined into new. since the binding material is still present it reduces the need for more oil byproducts

Super interesting. I always assumed it was a gigantic use of oil globally. Sounds like it doesn’t have to be.

But most of those items are oil originated. At what point can we make asphalt without any new oil?

The term describing this is: RAP (Recycled Asphalt Pavement).

https://www.fhwa.dot.gov/publications/research/infrastructur...

That sounds great for the environment - let’s grind and hide this pile of trash for a few decades, what could go wrong.

Recycling asphalt takes mostly heat. You lose some of it on the process, so you must add some new asphalt, and the new asphalt doesn't have the same composition of the original one (but is still asphalt, or asphalt components).

Generally it's crushed and a percentage of the final mix uses the recycled crushed asphalt. The quality of the asphalt is lower with higher amounts of recycled materials so high traffic roadways like highways may use 30% recycled asphalt. While lower traffic roadways or things like bicycle paths can use a higher percentage with new binder in the mix.

Milled and Crushed, heated, some new aggregates mixed in, new oil, good to go.

You can look up mobile asphalt batch plants if youre interested

I'm sure it goes through some cleaning but generally just heating it up makes it pliable again.

Heat, probably.

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