I live near a major roadway that is currently undergoing a major expansion from 2 to 4 lanes (US 119 in Indiana County, PA and I’ve noticed something odd, I think, in the way they’re constructing the new roadway. First they put down a layer of stone, then a layer of asphalt, then they put down metal supports (not like rebar, they are green and sit on the asphalt), then they pour concrete on top of the asphault.
My question is to those of you who know something about highway construction. Is this normal? I’ve seen older concrete highways scraped down and asphalt laid on top, but I didn’t know that they did it this way.
I’m firstborn son the director of planning at the Ohio DOT, and she thinks that her work is interesting to me, therefore I can tell you that “the department is testing and researching concrete against asphault on a few four-mile stretches of roadway over an eight year period.” According to reports she takes some sadistic glee in reading out-loud verbatim to me, concrete is stronger, holds up at least as well, and expands/shrinks less with heat than does asphault. Brakes don’t work quite the same on it, I hear “worse” more often than I hear “better,” but not by much. Also, while it doesn’t sound as loud outside of the car, it “sings” to the driver (a much higher pitched humming noise), which I can say from personal experience is very annoying the first few times you drive on it, but it doesn’t register after a few weeks.
However, it doesn’t resurface anywhere near as easily. You could afford to pave a stretch of road with gold a few dozen times for as much as it costs to resurface concrete. Thus, (in Ohio, at least) it’s going only in areas where noise pollution matters. Beyond that, it’s only going in if there’s a change of political party in office, in order to cause a budget crisis at a later date.
IANACE but will offer this possibility: what looks like asphalt may be ‘crusher run’ or fine stone particles. I’ve used it owing to compaction properties and low cost.
Is it possible that what you are seeing is the old asphalt , after being ground into aggregate sized particles, being used as a base for the new concrete?
They have huge piles of the stuff along the new freeway going in near here.
I agree that what you are likely seeing is aggregate or aggregate/asphalt mix compacted to form the roadbed.
The green “rebar” you are seeing is actually fiberglass rods. They’ll pour one lane or section of concrete, insert the rods half way in, wait for it to set up, then they pour the second, or adjoining lane.
It was explained to me that the rods keep help keep things moving together during expansion and contraction, sorta like a key-way.
Iacob: there are certain types/mthods of using concrete that will last significantly longer than ashpalt (I heard 25-30 years), and not require as much maintenance in the meanwhile. I understand that this method was developed at Northwestern University and was unanimously shot down by everyone they approached with it (what with keeping the guys employed and all). Unfortunately, I live in Chicago which, despite being located next door to NU, has the most advanced system of political corruption seen since the fall of Rome and accordingly, the highway repair is constant to keep the money flowing to the campaign contributors. Every now and then this story pops up and just disappears.
Something else I’ve been told, but can’t vouch for its legitimacy is that the NU process was tried but purposely screwed up to “prove” that the other way is better. Considering the source, I don’t know how true it is, but then again…
Hijack: How is the Autobahn composed? I understand that the contractors bid not only to replace sections, but also must maintain them for 10 years. I imagine that they build them well because 1) liability if some dude going 150 mph spins out because your crew screwed up and 2) fixing those roads every year is expensive.