Concrete Highways over asphalt highways

[Mergingtraffic]

In CT, there is a project to diamond grind the concrete portion of the CT-25 6-lane expressway.  The DOT says the concrete dates back to the late 1970s.  So, about 36 years later the concrete is getting it's first "repave."  The concrete is smooth and even smoother since the diamond grinding was done.  It feels smoother than asphault.  You glide a long. 

However, most CT expressways were concrete but were paved over with asphalt in the 1980s and have to be repaved almost every 8 to 10 years or so.  So, why weren't the roads left as concrete in the first place?  Considering the concrete requires less maintenance and is smoother with diamond grinding.


http://www.ct.gov/dot/lib/dot/documents/dcommunications/majorprojectupdates/Rt_25_Trumbull_July_2012.pdf

[sp_redelectric]

I've noticed the same thing on I-405 in downtown Portland - most of I-405 was repaved with asphalt, but underneath one overpass (either 4th, 5th or 6th Avenues or Broadway, near the south end of the loop between the Sunset and south I-5/84 interchange) the concrete was simply ground down with no asphalt.  And while it looks questionable, it's absolutely smooth to drive over.

[jjakucyk]

Diamond grinding can't really fix problems with displaced joints (where one slab is a bit higher than the other) because I believe it only takes off about 1/4" to 1/2" of the surface.  So if there's a rough noisy surface, then diamond grinding is the way to go.  But if the concrete is shifting or broken up, or if the joints have widened over time, you can't grind that away. 

That said, if the concrete is thick and has a good sub-base, there's no reason to throw it away.  In fact, here in Cincinnati many roads are reconstructed with a concrete base and asphalt wear surface.  This gets you a solid base, and it's relatively easy to just redo the asphalt overlay as needed.  You can't easily diamond grind a street that's full of manhole covers and such, and I suspect the added expense of doing a proper driving surface on concrete and joint sealing and maintenance is similar to the cost of the asphalt overlay itself.  That's just speculation on my part, but I don't think the city would be doing it if it didn't make sense. 

[CentralCAroadgeek]

I've noticed, in newly repaved asphalt highways, such as 101 in San Jose, they don't pave under overpasses. I can understand bridges, but why don't they lay asphalt under an overpass? It is because it won't dry effectively?

[jjakucyk]

It's usually so they don't change the clearances to the underside of the bridge.  In Indiana they routinely pave under the bridges with concrete even when the rest of the highway is asphalt.  Since the concrete lasts longer they don't have to worry about messing with the bridge clearances as often. 

[DaBigE]

I've noticed, in newly repaved asphalt highways, such as 101 in San Jose, they don't pave under overpasses. I can understand bridges, but why don't they lay asphalt under an overpass? It is because it won't dry effectively?

It's usually so they don't change the clearances to the underside of the bridge.  In Indiana they routinely pave under the bridges with concrete even when the rest of the highway is asphalt.  Since the concrete lasts longer they don't have to worry about messing with the bridge clearances as often.

That's exactly why. Altering clearances is very costly...not only in advanced signing, but also with the time involved for vehicles that have to detour, and the inevitable truck that thinks they can squeeze through (but ends up getting stuck). Very rarely is jacking up the bridge a viable option. Nor is it cheap.

[kphoger]

I wondered that about recent repaving north of Wichita on I-135:  where it crosses under K-96/K-254/I-235, it's still the old pavement.