Why Are Interstates Concrete Facilities In Urban Areas?

[TheArkansasRoadgeek]

So, I notice this every time I go to Little Rock, on I-40 it turns into a concrete facility near Clarksville, but serveral miles down it's back to asphalt. Near North Little Rock it picks back up being concrete. I wonder why AHTD used concrete there (I assumed it was resurfaced in the 60's or something because that was the concrete era for Interstates). But, yes why is it that most urban areas use concrete facilites for Interstates/ (US/State) Highways? It seems like a waste of money as the years drag on.

[Rothman]

All sorts of reasons.  Durability, soil conditions, you may be on elevated roadways and not realize it...

...and asphalt is still used on highways in urban areas.

[theroadwayone]

All sorts of reasons.  Durability, soil conditions, you may be on elevated roadways and not realize it...

...and asphalt is still used on highways in urban areas.

Example: NJ Turnpike.

[jakeroot]

All sorts of reasons.  Durability, soil conditions, you may be on elevated roadways and not realize it...

I think, chief among these reasons, is durability. Concrete, however noisy it may be, is remarkably more durable than asphalt (assuming US-spec asphalt layering -- I've heard the Germans do it better). Urban areas have more traffic, so concrete is the more logical choice because it can hold up better to the constant battering by commuters and local trucks. Rural areas have lower traffic counts and higher speed limits, so asphalt is preferred in these areas. It's cheaper to install (AFAIK), is quieter at high speeds, plus, it will still last a while because it doesn't take quite the daily beating that urban freeways take.

That all said, I'm not an engineer. My reasons might be rubbish.

[cjk374]

Concrete is better than hot mix (as long as all specs for mixes and applications are met). There is concrete that was poured 25 & 32 years ago on I-20 near me that still looks & drives like brand new today. No way hot mix, even "super-pave" mixes, will ever last that long.

[Beltway]

All sorts of reasons.  Durability, soil conditions, you may be on elevated roadways and not realize it...
...and asphalt is still used on highways in urban areas.

Example: NJ Turnpike.

Properly designed and constructed asphalt roadways, work fine on even the busiest highways in the world.  They need milling and resurfacing about every 8 to 10 years or so.  Concrete pavement goes longer before needing major rehab, but it is far more expensive than the typical asphalt resurfacing project.

[roadfro]

All sorts of reasons.  Durability, soil conditions, you may be on elevated roadways and not realize it...

I think, chief among these reasons, is durability. Concrete, however noisy it may be, is remarkably more durable than asphalt (assuming US-spec asphalt layering -- I've heard the Germans do it better). Urban areas have more traffic, so concrete is the more logical choice because it can hold up better to the constant battering by commuters and local trucks. Rural areas have lower traffic counts and higher speed limits, so asphalt is preferred in these areas. It's cheaper to install (AFAIK), is quieter at high speeds, plus, it will still last a while because it doesn't take quite the daily beating that urban freeways take.

That all said, I'm not an engineer. My reasons might be rubbish.

You're pretty spot on, Jake.

Pavement designs are based on traffic counts, which are converted into equivalent single axle loads or ESALs (passenger cars count as 2 ESALs, but truck traffic is much more based on length and weight). Pavement is then designed to withstand a certain amount of ESALs over the design lifespan given the projected traffic counts. It then comes down to a benefit-cost analysis to figure out whether Portland Cement Concrete (PCC) or asphalt concrete is used. PCC (which most of us refer to as simply "concrete") is a rigid pavement designed typically to last 30+ years without major work, whereas asphalt is a flexible pavement design that is expected to deform slightly over time and need occasional mill & fill and/or overlays over a similar timeframe.

B/c analysis tends to favor PCC pavements in urban areas based on projected ESALs, usually because asphalt is expected to deform more quickly on urban freeways with higher traffic within the design life. B/c also factors in things like rising cost of cement or steel for PCC pavements or rising cost of petroleum or binders for asphalt. So sometimes you might end up with an urban freeway composed of asphalt if there's a lower traffic level expected or if gas prices are on a downward trend.

[Beltway]

<<< PCC (which most of us refer to as simply "concrete") is a rigid pavement designed typically to last 30+ years without major work, >>>

How often does that happen?  Based on over 40 years of observation, that may happen on a segment about 15 or 20% of the time.  Often major patching work (remove and replace slab) starts after 10 to 15 years.

[silverback1065]

i think a major reason is the original interstates were all in concrete (i think this fact is true, but i could be wrong), and the downtown portions are almost always the oldest segments in cities that aren't fixed as often as the suburban segments. 

[ET21]

Long term durability.

[cjk374]

<<< PCC (which most of us refer to as simply "concrete") is a rigid pavement designed typically to last 30+ years without major work, >>>

How often does that happen?  Based on over 40 years of observation, that may happen on a segment about 15 or 20% of the time.  Often major patching work (remove and replace slab) starts after 10 to 15 years.

Right now I know of 4 (maybe 5) places on I-20 in Louisiana that were rebuilt with concrete in the mid 80s & early 90s that are intact with no reworked places. I believe the concrete mixes of the 60s & 70s are not as durable as the mixes of the 80s & 90s.

But to be fair, I have seen concrete fail after less than 10 years due to bad ingredients.

[Road Hog]

Asphalt on Arkansas freeways is a fairly recent development. It was all concrete until the late 1990s and the freeways by then were the roughest in the nation. After the first bond issue passed, asphalt started to be used in rural reconstruction. Asphalt is cheaper, of course. However, for the expanded freeways around Little Rock, concrete was still used.

[AsphaltPlanet]

One of the factors that affects retrofitting concrete highways with asphalt overlays is that asphalt (or flexible) pavement structures typically require much more material than concrete (or rigid) pavements.  The increase in materials means that the height of the pavement will need to be increased, which may not allow for sufficient ground clearance beneath pre-existing grade separations.

In Ontario where I live, a section of the 401 in southwestern Ontario is currently being reconstructed from asphalt to concrete, and one of the benefits of the project are that a number of grade separations that previously had over-height vehicle restrictions will no longer once the highway has been reconstructed.

[Beltway]

i think a major reason is the original interstates were all in concrete (i think this fact is true, but i could be wrong), and the downtown portions are almost always the oldest segments in cities that aren't fixed as often as the suburban segments. 

Depends on the state.  In PA probably about 90% of the mileage was concrete.  In MD and VA it was about equal mileage of each; and no I don't have the exact mileage.  VA I-81 for example was about 90% mileage of asphalt.

[silverback1065]

I wish all interstates were concrete, they always seem to be better. 

[froggie]

<<< PCC (which most of us refer to as simply "concrete") is a rigid pavement designed typically to last 30+ years without major work, >>>

How often does that happen?  Based on over 40 years of observation, that may happen on a segment about 15 or 20% of the time.  Often major patching work (remove and replace slab) starts after 10 to 15 years.

MnDOT experience is generally in the 20-30 year range, depending on specifics.

[DevalDragon]

Long term durability.

What's the deal with the concrete portions of I-94 in western Michigan? There are some sections that were completely rebuild < 10 years ago and are rougher now than they were before.

[cjk374]

I wish all interstates were concrete, they always seem to be better. 

[TheArkansasRoadgeek]

I wish all interstates were concrete, they always seem to be better.

Agreed. There is just something about the Chaffee Crossing area in Fort Smith, (which most, if not all is concrete) it always looks GOOD.

But, one has to argee, the misalgined joints in the concrete as the years go on; living right by a busy street (made of concrete) or highway is rather bothersome. No?

[jakeroot]

I think concrete is attractive because of its longevity. I can't think of any other redeeming features. At least compared to the concrete facilities in Seattle, asphalt is quieter, and it contrasts better with pavement markings. I think those two factors alone raise it above concrete, at least when it comes to how it affects the everyday driver. But, from a technical standpoint, concrete undoubtedly makes more sense, especially in really busy areas where more frequent maintenance (necessary with asphalt) would become a nuisance.

[ET21]

When repairing though, would you rather they cut out the section and replace it with fresh concrete or fill in the hole with asphalt?

[cbeach40]

One of the factors that affects retrofitting concrete highways with asphalt overlays is that asphalt (or flexible) pavement structures typically require much more material than concrete (or rigid) pavements.  The increase in materials means that the height of the pavement will need to be increased, which may not allow for sufficient ground clearance beneath pre-existing grade separations.

In Ontario where I live, a section of the 401 in southwestern Ontario is currently being reconstructed from asphalt to concrete, and one of the benefits of the project are that a number of grade separations that previously had over-height vehicle restrictions will no longer once the highway has been reconstructed.

To clarify, that went from being an asphalt surface on top of concrete, which is the thickest design. The replacement for it gave the contractor the option to bid with either concrete or asphalt. The design for the concrete had a pavement thickness of 260 mm while the asphalt lifts combined for 270 mm in thickness. Asphalt is still thicker, but either option is only a bit more than half of what was previously out there.

And as jakeroot said, the difference is entirely cost. Now, where that cost comes from are typically two things - local availability and life cycle costs. The former speaks for itself, while the latter usually favours concrete. In a busy urban area, where construction staging is much more involved and costly than suburban or rural areas, that skews it even further towards concrete.

In A-B bidding like that, the asphalt bid not only needs to beat a concrete one based on initial construction costs, but also needs to account for the predicted greater life cycle costs.



An as an aside that it doesn't usually apply in terms of freeways, but an asphalt surface is generally easier to do spot cuts and repairs. So if there are utilities under the road that may skew in favour of asphalt as well.

[TheArkansasRoadgeek]

When repairing though, would you rather they cut out the section and replace it with fresh concrete or fill in the hole with asphalt?

AHTD fills in with asphalt. I would like to see repairs done with the same material as the project was built with. I have my suspisions that AHTD will use asphalt for the lane widening on I-630 .

[Rothman]

I am thinking of NY 85, an urban freeway in western Albany.  It was concrete that aged over time.  Due to the enormous expense of replacing the concrete, the very much needed project was delayed a few years until NYSDOT could find finding at the department level.  The decision was made to crack and seat a new asphalt roadway above the pulverized old concrete

The problem with looking at lifecycle of concrete is that, up here, concrete does not age well.  The "panels" go out of alignment; the cracks get milled or filled.  It becomes terrible to drive on and the large expense to replace it does become problematic.

So, you go the asphalt route because it is easier for a NYSDOT region to fit a few-million dollar project into its program to maintain the asphalt than it is to find tens of millions at once when the situation becomes dire with concrete.  It is not like a region can "save up" funds from one year to the next for one big project by bringing the rest of its program to a screeching halt.  "Sorry, we aren't doing much this year to save up for the big concrete replacement" just doesn't fly politically and actually isn't supported by engineering merit, either -- your regional conditions go kaput with that approach.

Just saying that, given all the raving about concrete in here, soil conditions, climate effects and the replacement costs (in terms of how to fit them into a budget) should not be minimized when determining to apply concrete or asphalt to solve a problem.

[Beltway]

When repairing though, would you rather they cut out the section and replace it with fresh concrete or fill in the hole with asphalt?

Depends on the damage.  On the 6-mile long I-64 concrete pavement rehab project just west of I-95, 1) if the damage was light they would remove about 4 inch depth of concrete and then fill over the remaining 4 inch depth of concrete with asphalt base course.  If the damage was heavy and/or extensive, 2) they removed the whole area of damaged concrete full depth and replaced it with new concrete pavement section.  The resident engineer would make the decision at the site as to whether #1 would be adequate or whether #2 was needed.

On this project the rehabbed concrete pavement was overlaid with 5 inch depth of asphalt surface course. 

This info comes from my attending an ASHE (American Society of Highway Engineers) technical meeting where this project was presented.