Asphalt base under concrete road

[digger242j]

It seems like over the past few years, highway jobs around here have been using a base of hot mix asphalt, and then placing concrete on top of that. Often, more blacktop is laid on top of the concrete.

What's the reasoning behind that? :confused:

[Countryboy]

It seems like over the past few years, highway jobs around here have been using a base of hot mix asphalt, and then placing concrete on top of that. Often, more blacktop is laid on top of the concrete.

What's the reasoning behind that? :confused:

They've been doing something kinda like that around here, at the intersections. They use it to try to keep the asphalt from rutting out after thousands of stops at traffic lights and such.

I remember one redlight they just did like that. It was so rutted out before, that cars and other low clearence vehicles were scraping the center where it had risen up. This was on a major multiple lane road. After the repair, I can't see where it is even rutting out the slightest bit.

I know they used the cement to stabilize it but as far as putting asphalt on top, I have no clue. Maybe it sheds water better...:beatsme

[Grader4me]

It seems like over the past few years, highway jobs around here have been using a base of hot mix asphalt, and then placing concrete on top of that. Often, more blacktop is laid on top of the concrete.

What's the reasoning behind that? :confused:


I think CB has the answer with the rutting factor, as concrete won't rut like asphalt, and you see concrete at many intersections. I'm not sure why they would use a base of asphalt, but I know of one section of highway that we have is concrete, and it is a little rougher than blacktop to drive on. So maybe a coat of asphalt over the top to make it smoother? Maybe the combination as you describe would be the answer for longer maintance free highway?:beatsme

Be interesting to hear other views as I'm just guessing..

[digger242j]

I'm not talking about intersections though. I mean miles long stretches of expressway.

It used to be that (in some cases) they'd use concrete, and come back a few years later, when it started to get bad, and overlay the concrete with blacktop.

Now, they're adding a base of blacktop, before they do the concrete.

It's gotta be more expensive than just a compacted stone base (which they still have to have under the blacktop that's under the concrete). I just wonder what, and how big, the adavantages must be to go to that added expense.

[Grader4me]

I just googled this and of course the first link that came up was our discussion on this...fast little buggers aren't they? Here (http://www.mississippiconcrete.com/whitetopping.cfm) is a link where they talk about "white topping" and it being used quite a bit in the states. Is this similar to what you are seeing? This is all new to me!

[JimBruce42]

In Central PA, and even increasingly down here near Philly, they've been completely removing the concrete from the equation. I know back home in central PA area, especially on 80, they are removing the concrete road surface, undercutting another several inches, placing a new subbase then repaving the road with all asphalt, sometimes the entire width, other times just the lanes. I'm not sure the reasoning, but I'm sure it has something to do with $$:beatsme

[CascadeScaper]

I haven't seen anything other than a few bridges paved with concrete, everything is asphalt here.

[CM1995]

Interesting question. Around here I-65 and I-459 has several miles of concrete paving that keeps a cut out and pour crew very busy, it seems like a constant operation. I don't know exactly what went wrong with it but it is horrible to drive on. I do remember, although I was a young kid - but Dad was the type to ignore "road closed" signs:D , that they paved these areas with asphalt and then slipformed the wear surface out of concrete.

What I have seen, only from driving on asphalt overlayed concrete roads, is when you relay asphalt over concrete the expansion joints mirror through to give you a nice " thump.......thump.....thump" ride.

Now I have seen road crews on I-65 in the southern part of the state take one of those "drop hammer" devices and pulverize miles of concrete paving, keep it in place and then relay binder and a wear course over it. I can say that the stretch of I-65 where they done this is as smooth as glass.

I do not know of any new roads where ALDOT has used concrete for the paving surface around my neck of the woods. They are completing I-22 that connects Memphis to Birmingham and it is all asphalt - thick asphalt - in some places 12"-18" thick. Must be an asphalt producer with good political connections.:rolleyes:

[truck608]

The construction company I work for is currently doing work for the new Jet Blue terminal at Kennedy Airport in New York. New tarmac is being put down and the concrete over asphalt method is being used. I was at another job at the airport today and ran into one of our supers. I asked him the reason for this type of subase. He said the reason is for drainage away from the concrete. The asphalt that is put down is not as dense as a base layer or top layer. He referred it as a more "popcorn" type mix, where, if you were to pour water on the surface of the asphalt, it would drain through to the ground. Thus protecting the concrete, especially in the winter months, from frost heaves.
The new job we started at American Airlines at JFK will have the same concrete over asphalt installed with the addition of corrugated pipe under the asphalt, to wick the water away into connected drain systems.
The same method was done on a highway we did about 8 years ago.
Hope this helps. I was very curious as to why this was done also.

[Grader4me]

Thanks for the information. I'm a little curious about the "popcorn' mix of asphalt that is used for the base. I'm also surprised that water will drain down through it. Hummm.. you learn something new every day I guess:beatsme Thanks again :)

[skata]

i've seen that here too recently. they completly tore out a main road, put down gravel, asphalt, then concrete for final surface.
maybe they figure the concrete lasts longer sitting on asphalt??

[truck608]

Thanks for the information. I'm a little curious about the "popcorn' mix of asphalt that is used for the base. I'm also surprised that water will drain down through it. Hummm.. you learn something new every day I guess:beatsme Thanks again :)


Hi Grader,
Glad the info helped. I have delivered this material in the past. With regular asphalt base mix or top mix, there is stone, sand and liquid asphalt and probably more, creating a very dense material. With this 'popcorn' (doubt it is a trade name), mix there appears to be alot less sand and fines in this mix as compared to the others and a higher ratio of stone, creating many voids, allowing the water to drain away. If I can get more info on this I will post it. Hopefully someone on the board is more versed on asphalt than I am. After all, I am only the guy that brings it to you equipment operators. :popcorn

[Grader4me]

I'm used to working with the 1/2" base asphalt mainly, but sometimes we use the sandseal mix asphalt for a smoother finish. I remember once a long time ago I leveled 3/4" base and that was quite course, so it must be close to that mix that they are using. I just never realized that water would drain through it regardless of the mix. Interesting stuff.

[MRM99]

They just put down some of the "Popcorn" asphalt on I45 just north of the causeway. It was concrete, they put a layer of chip on top of the concrete then asphalted over that with the water draining mix. It almost eliminates the water spray when it rains.

[CM1995]

They just put down some of the "Popcorn" asphalt on I45 just north of the causeway. It was concrete, they put a layer of chip on top of the concrete then asphalted over that with the water draining mix. It almost eliminates the water spray when it rains.

The DOT just resurfaced US 280 with this kind of asphalt and it is amazing the difference in the amount of road spray during a rain compared to regular wear course.

[d4c24a]

we have porous asphalt as a wearing course in the UK ,and during rain there is very little spray,but they have had some problems in the frosts with the water freezing and the salt not deicing it .i know the have tried a water salt mix and also doubling the rate of salt spread on these sections i have three sections on my salting run and i have to double the spread rate over thesae sections
thanks graham

[chewy]

I've worked asphalt for 28 years,from all plant opperations to pavers, rollers ect.ect. now as mechanic. truck 608 has it correct, we call it open grade. it's also used as a base for football fields under artificial turf, tennis courts--. base course's use large size stone 3/4 to 1 1/2 AND 3/8 to 1/2 mabey a little sand and liquid asphalt. this mix is not intended direct traffic loads,however works well as pavment drainage. surface mixes are somewhat different in stability(greater) yet provide drainage through and out to the shoulders hence less spray and associated problems. asphalt is considerd 100% recycleable concrete is'nt. that is why you see more full depth asphalt jos popping up. that may change now, with the high cost of liquid ac.

[surfer-joe]

We put "popcorn" asphalt down on Rte 2 & 4 near Lusby, Maryland in 1986. It was a new material for the state to use and it's stated purpose was to drain water more swiftly off the surface to try to eliminate hydro-planing by car tires and improve steering and braking control.

The mix was a failure however and as it was popping loose over the next several months, the state had to go in and remove it. I don't know if they replaced it with some other type.

Placing a thick mat of asphalt under a concrete layer does the same thing -- it allows water to drain down into the sub-base. It also stabilizes the base under the concrete and doesn't subside as does a gravel base sometimes. It's also sometimes used with a poly film or blanket. Seems to be coming a more popular procedure in areas that experience severe frost heaving.

[ForsytheBros.]

forgive me if somebody already mentioned this in the thread.


The crcp (continuously reinforced concrete pavement) that i've seen down in Tx often has an acp layer beneath it, with limestone base beneath that (we have some pretty good limestone base pits in central tx-lots of hydration going on)

I've been told that the acp layer often acts as a bond breaker for the concrete.

Additionally, when set up via a laydown machine, the concrete paving crew has a really sweet all weather surface for close concrete thickness tolerances and bar placement.

Acp on top of concrete...........hard to adequately address that one.

If i've repeated others' responses, please forgive.
thanks

[mclinkus]

interstate 70 from the indiana border heading into illinois for the 1st 20 miles is this way.

there was a 20 year warranty in the orig contract and the powers that be evivdently thought that a black base with crete in the middle and then super pave over the top was the best way to achive 20 maintence free years.. its only been 5 and it still looks pretty good.

i am highly interested to see what it looks like after 10 and 15..

20 years is along time to go w/o miantence.

'link