Question about I-40 construction/reuse of concrete (required, recycling)

[guest12]

I was on the currently-being-re-paved section of I-40 today (fortify), and it looked like they were actually crushing the concrete they were digging up and reusing it - do they actually do this? I was intrigued by it - never thought about it before, and it seems so...efficient!

Anyway, I figured if anyone knew if they were doing that, it would be someone over here.....

[Poggly Woggly]

Yes, I was aware of this. My assumption is that they were crushing it on the spot and spreading it out as base course for the new pavement. Good idea

[guest12]

Originally Posted by Poggly Woggly

Yes, I was aware of this. My assumption is that they were crushing it on the spot and spreading it out as base course for the new pavement. Good idea

Thanks for confirming....makes sense, but I've never seen it before!

[Poggly Woggly]

Originally Posted by guest12

Thanks for confirming....makes sense, but I've never seen it before!

I think it's the first time I saw it too.

[Sherifftruman]

They actually did something similar when they were widening the I 440 beltline 15 or so years ago. It was brand new then. Still not always done, but laws do require exiting pavement to be reused in some capacity. That's why they typically will mill the existing asphalt down and put it in trucks to take away. It can be fed back into the new asphalt as aggregate at the plant.

[SFspiderman]

Here's an article and video about the Badger Breaker chewing it up to be recycled.

https://apps.ncdot.gov/newsreleases/...s.aspx?r=11391

[Sherifftruman]

Ok that's super interesting. When they did the 440 stuff they used this huge piece of equipment with something like a 40 foot I beam in it with a piece on the end that came down and touched the pavement. They used a motor to cause it to vibrate at its resonant frequency which gave it enough energy to break the concrete up. It could only break maybe an 8-12 inch wide section at a time if I recall. This new thing seems about a thousand times more efficient. I wonder if it's easer due to the structural issues with the concrete in this section which is why they are redoing it.

It was an early version of this. https://youtu.be/cpuJ4csLOkg

[builder24car]

I asked about this three years ago when they started this never ending project.
I had been told that the concrete was the cause for some kind of reaction that
was the cause of this project. If so now they are putting it right back and it
could have been the culprit of this entire mess?

[Sherifftruman]

It's called alkali silica reaction.
https://en.m.wikipedia.org/wiki/Alkali–silica_reaction

It causes the concrete to break apart internally and lose its strength and structure. But it's still just rocks and fine cement particles at its heart. Break it up enough and it's very similar to the ABC stone they put down under roads already. Compact that and put 18" of new concrete on top and it's all good.

As far as the new stuff, they know now how to select proper aggregate and test everything so it doesn't happen.

[SFspiderman]

It's mentioned in the article I linked:

A chemical reaction in the 30-year-old substructure of the roadway was causing it to crumble, and in turn, damaging the road surface. That required constant repairs and led to concerns about ongoing travel disruptions along one of the state’s busiest stretches of highway.

The chemical reaction is stopped during the recycling process, allowing the asphalt to be reused.