Why are some highways concrete and others asphalt

[diggleblop]

What are the advantages and disadvantages of each? Is one cheaper than the other? Easier etc... Because I see a lot less concrete roads than asphalt, but the concrete roads seem to be smoother and last longer, true?

[Gary T]

In a nutshell, asphalt costs half as much, concrete lasts twice as long.

[Bearflag70]

Concrete can break in extreme conditions, asphalt is more flexible

[Duckster]

Originally Posted by Gary T

In a nutshell, asphalt costs half as much, concrete lasts twice as long.

With the price of oil these days, are you sure?

[lobotomyboy63]

Someone told me it has a lot to do with the success/failure of the local lobbying groups for the respective products.

[GreasyJack]

I will confess that I once knew a lot more about concrete and asphalt than I do now, but one factor I will throw in is that the local geology will affect the concrete mixture that can be made and thus the affordability and suitability of concrete will vary locally somewhat.

[rbroome]

Originally Posted by diggleblop

What are the advantages and disadvantages of each? Is one cheaper than the other? Easier etc... Because I see a lot less concrete roads than asphalt, but the concrete roads seem to be smoother and last longer, true?

I have been told it depends on two things: this year's budget asphalt is cheaper and so you get more miles done, and second it is easier to repair. It costs a lot more than twice as much to repair a concrete section (with concrete) than it does to repair asphalt. But of course the concrete last longer.

[robby]

Civil engineer here...

Concrete is much more expensive to install and repair. Also, particularly here in the Northeast, concrete gets destroyed by winter conditions and snowplows.

I see a lot more concrete highways down south in Texas than I see up here in New England.

Asphalt, while not as durable, is more flexible and cracks less. It is also cheaper to repair and patch. When a road had degraded to the point of needing to be completely replaced, it is cheaper to grind up old asphalt in a road reconstruction project than to jackhammer out old concrete.

Actually, many of the roads here in the Northeast were originally made of concrete. Many of these roads, when they had degraded to the point of needing replacement were overlaid with asphalt instead of ripping up all of the concrete.

[robby]

P.S. Just to confuse matters, engineers formally refer to asphalt as "bituminous concrete."

(The ordinary concrete is formally referred to as "Portland cement concrete.")

[Ludovic]

Do they have differing characteristics in the rain? It would seem that concrete is more slippery in the rain unless you groove it which would be more annoying in the not-rain and more expensive.

[BobLibDem]

To be quite honest an effort is made to give the concrete producers and the bituminous producers each a piece of the pie. If you went one way or the other you'd put one group out of business and overload the other. If contractors have more work than they can handle, the bids go through the roof.

[Great Dave]

Originally Posted by robby

P.S. Just to confuse matters, engineers formally refer to asphalt as "bituminous concrete."

(The ordinary concrete is formally referred to as "Portland cement concrete.")

Well, both are concretes, as is sedimentary rock. The diffrences are in the "glue" and the size and distribution of aggregate.

Asphalt can be stripped out by a huge road chewing machine, hauled off, broken down into its constituents, and turned back into asphalt. Concrete is much harder to remove, and all you can do with crushed concrete is road beds and jetties.

[Plynck]

Originally Posted by robby

P.S. Just to confuse matters, engineers formally refer to asphalt as "bituminous concrete."

(The ordinary concrete is formally referred to as "Portland cement concrete.")

robby, we seem to cross paths in these types of threads

Just a nitpick, but it looks like Mass Highway (at least) is now revising all their manuals to change from "bituminous concrete" to "hot mix asphalt" (HMA). As I said half-jokingly in a previous thread, it is probably because someone in the State has a brother in the printing business.

And just to confirm what has been said earlier: Bituminous concrete is cheaper and is a flexible pavement, while cement concrete is more expensive and rigid but will last far longer.

Bituminous pavement can be reclaimed (ground up and used either as a roadway base, or recycled into more pavement). It's easy to jackhammer through in order to get to buried utilities, and can be easily repaired by road crews either temporarily (cold patch) or permanently (hot mix). Cement concrete is a bitch to jackhammer through, and tougher to repair because curing takes so long. Cement concrete can be crushed and reused for roadway bases (after all, it's mostly aggregate), but there isn't a lot of that going on right now that I know of.

If you've ever been driving on a bituminous concrete highway, and get that regular rhythmic "bump...bump...bump", it is likely that bituminous was laid over concrete, and your wheels are feeling the expansion joints underneath.

[NinetyWt]

Originally Posted by Duckster

With the price of oil these days, are you sure?

It has historically been so, because of the cost of labor (concrete finishing requires more skilled laborers, and more of them).

However, the cost of asphalt paving (here where I am) is steadily rising.

[K364]

Are expansion joints mandatory with concrete? I know that finished asphalt is a continuous... this makes a big difference up north where in spring and fall there is a freeze/thaw cycle almost every day. This must be very hard on concrete and no problem with asphalt (until it degrades a bit and holes start forming).

We see very little concrete up here.

[Snarky_Kong]

Originally Posted by K364

Are expansion joints mandatory with concrete? I know that finished asphalt is a continuous... this makes a big difference up north where in spring and fall there is a freeze/thaw cycle almost every day. This must be very hard on concrete and no problem with asphalt (until it degrades a bit and holes start forming).

We see very little concrete up here.

Yes. If you don't have joints you'll see concrete "blowups." The blowups happen when thermal expansion causes large stresses in the concrete.

Another thing to note is that the slabs in gas stations will be concrete because spilled gasoline will dissolve asphalt.

[Yllaria]

Originally Posted by Plynck

. . . it looks like Mass Highway (at least) is now revising all their manuals to change from "bituminous concrete" to "hot mix asphalt" (HMA). As I said half-jokingly in a previous thread, it is probably because someone in the State has a brother in the printing business.

Yeah, I've heard that the Superpave program is using HMA. I've been warned that eventually everyone will switch over, but I don't see any sign of CalTrans (California) switching from Asphalt Concrete (AC). Maybe they don't have any relatives in the printing business.

[KlondikeGeoff]

Originally Posted by robby

P.S. Just to confuse matters, engineers formally refer to asphalt as "bituminous concrete."

(The ordinary concrete is formally referred to as "Portland cement concrete.")

Back when I was a pup, asphalt roads were called MacAdam.

[scm1001]

Originally Posted by Duckster

With the price of oil these days, are you sure?

concrete takes a large amount of energy to produce, so prices are liley to rise togther

[BobLibDem]

Originally Posted by KlondikeGeoff

Back when I was a pup, asphalt roads were called MacAdam.

Good Lord, how old are you?

[KlondikeGeoff]

Originally Posted by BobLibDem

Good Lord, how old are you?

I regret to say, 80.

[Civil Guy]

I'll throw in $0.02 here. Beyond the bigger issues mentioned, there are other imponderables. If the portland cement concrete (PCC) was not constructed properly, the cracks can look pretty jagged and unsightly, though the pavement is otherwise okay - so that's a reason for putting asphalt over the concrete. Also, the AC arguably rides better.

As mentioned, the AC takes a lot less time to construct, pretty important for reopening busy roads. Generally, PCC pavement can be thinner, so if there are pipelines close to the road surface (shouldn't be, but stuff happens), that might be an argument for PCC.

PCC holds its surface better, so that's why streets are often constructed with PCC gutters. PCC is also good for spot locations that take a particular beating, like bus landings.

===
When constructed, PCC can be given a moderately rough surface, but over time, it can wear too smooth for traffic safety - at which time, the highway department can cut in grooves.

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Who knew that pavement was so complicated? Or that so many of us have made a study of it?

[Hello Again]

Only semi-related, but I was driving, in rural pennsylvania I believe, and started seeing all these signs -- obviously placed by lobbying groups -- about the concrete vs. asphalt debate.

They said things like "Asphalt: smooth and quiet" and "Concrete kicks asphalt!"

It was unusual passing through a pocket of people who obviously cared intensely about the subject.

[Triskadecamus]

It would be wonderful to believe that government construction choices were made on the basis of engineering concepts. Sadly, the existence of legislators with brother's in law in various industries probably has a lot more to do with it.

Tris

[Quartz]

Originally Posted by Plynck

If you've ever been driving on a bituminous concrete highway, and get that regular rhythmic "bump...bump...bump", it is likely that bituminous was laid over concrete, and your wheels are feeling the expansion joints underneath.

Ah, I've wondered about that from time to time.