fbm3rd
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Runway Question?

Mon Oct 03, 2005 11:01 am

why are some runways all concrete and others asphalt? Is there a logical difference or just a money saving difference? What are the differences when landing for those who are the experts???
 
Slarty
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RE: Runway Question?

Mon Oct 03, 2005 11:08 am

Maybe you should have posted this under the "Tech-ops" forum? Lots of pilots/planners hang out there ... you'd likely get a far better informed post there (unlike mine ...)
 
grrtvc
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RE: Runway Question?

Mon Oct 03, 2005 11:31 am

Some of the decision to use asphalt over concrete is a financial one. But a lot of it has to deal with soil conditions and regional locations.

Most, if not all, runways in the north are concrete. They hold up to the freeze-thaw cycles better then asphalt. Thickness and overall section will vary but I recall in DTW the runways are 17" concrete over 9" asphalt over 14" stone sub-base. This gets it down to the 42" frost line and reduces the effects of the freeze-thaw forces.

Asphalt, up until recently, is generally cheaper then concrete. So many of the runways that are in a region that isn't exposed to the extreme temperature variations like the north are able to use asphalt.

Depending on the MTOW of the aircraft using the runway will also determine its make-up. Asphalt, if engineered correctly, i.e. thicker sections, can handle the weights of a 747.

O&M costs are another factor. Concrete generally doesn't need as much maintenance as an asphalt but again this will depend on the loads and location.

That's sort of it in a nutshell.

GRRTVC
 
kcrwflyer
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RE: Runway Question?

Mon Oct 03, 2005 12:04 pm

Isn't there also something called Bitimus?
 
grrtvc
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RE: Runway Question?

Mon Oct 03, 2005 12:11 pm

Bituminous is an aggregate (stone/gravel) ingredient in asphalt as Portland Cement in concrete.

I believe it is by-product of coal. Not 100% sure on that though.

GRRTVC
 
Boeing7E7
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RE: Runway Question?

Tue Oct 04, 2005 1:49 am

Quoting Fbm3rd (Thread starter):
why are some runways all concrete and others asphalt? Is there a logical difference or just a money saving difference? What are the differences when landing for those who are the experts???

Concerete is generally cheaper (but of late more expensive thanks to China), is a rigid pavement and easier to maintain. Asphalt is flexible and requires a 3-4" overlay about every 5-10 years depending on the number of operations and type of aircraft. There are advantages and disadvantages to both.

Concrete's biggest disadvantage is that it must be replaced at the 20-30 year mark in it's life where Asphalt can simply be overlayed. If you have a single runway airport, you can see the problem. There are several concrete runways in the US which are now covered by Asphalt.

Asphalt's biggest disadvantage is the fact that it's flexible. I've see sections of runway where on a very hot day a large aircraft (777) caught a seam in the overlay and tore a 100' section of runway apart about 4 inches deep and 3 feet wide.

Due to the years of standards establishment, all else is pretty much equal. You can groove both, you can land anything on them and friction is about the same as far as stopping power is concerned.
 
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HAWK21M
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RE: Runway Question?

Tue Oct 04, 2005 11:15 pm

Quoting Boeing7E7 (Reply 5):
Concerete is generally cheaper (but of late more expensive thanks to China

Why thanks.

What about the Aquaplaning problems or rather water draining ability of both types of Runway surfaces.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
Boeing7E7
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RE: Runway Question?

Wed Oct 05, 2005 12:52 am

Quoting HAWK21M (Reply 6):
What about the Aquaplaning problems or rather water draining ability of both types of Runway surfaces.

The issue of grooving is more relevant to this than the surface itself. A runway should have a 1 degree slope (crown) or greater to each side for runoff and ponding avoidance.
 
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HAWK21M
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RE: Runway Question?

Wed Oct 05, 2005 1:45 am

Quoting Boeing7E7 (Reply 7):
A runway should have a 1 degree slope (crown) or greater to each side for runoff and ponding avoidance.

At BOM its quite common to find water on the Runway during the Monsoon.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
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zeke
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RE: Runway Question?

Wed Oct 05, 2005 1:50 am

Quoting Fbm3rd (Thread starter):
why are some runways all concrete and others asphalt? Is there a logical difference or just a money saving difference? What are the differences when landing for those who are the experts???

Concrete need expansion joints, over time you can get subsidence of some slabs of concrete at the expansion joints, getting bumps.

The runway strength is more important for takeoff than for landing, the most weight on wheels is on takeoff, hence the reason why military bases which served strategic bombers had concrete runways as the rigid pavement (concrete) can actually handle more load.

On landing a portion of the weight of the aircraft is still be lifted by the wings until it slows down which reduces the actual load on the runway.

Other difference for landing and rejected takeoff, asphalt I believe is easier to keep grooved, periodic removal of rubber is required on grooved runways to improve the braking performance for landings and rejected takeoffs.

Been told some runways in USA have heating in them also, don’t know if its true or just another tall story.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
Boeing7E7
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RE: Runway Question?

Wed Oct 05, 2005 4:22 am

Quoting HAWK21M (Reply 8):
At BOM its quite common to find water on the Runway during the Monsoon.

It needs a fix.  Smile
 
KBGRbillT
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RE: Runway Question?

Wed Oct 05, 2005 8:33 am

Quoting Slarty (Reply 1):
Maybe you should have posted this under the "Tech-ops" forum?

This is the Tech-ops forum, pay attention before you offer advise!!
 
LimaFoxTango
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RE: Runway Question?

Wed Oct 05, 2005 9:25 am

Quoting KBGRbillT (Reply 11):
This is the Tech-ops forum, pay attention before you offer advise!!

This post was made in Civil Aviation first and was then transfered to Tech Ops.
You are said to be a good pilot when your take-off's equal your landings.
 
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HAWK21M
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RE: Runway Question?

Wed Oct 05, 2005 8:54 pm

Quoting Boeing7E7 (Reply 10):
It needs a fix.

Yeah Fix the Monsoon  Smile

Quoting KBGRbillT (Reply 11):
Quoting Slarty (Reply 1):
Maybe you should have posted this under the "Tech-ops" forum?

This is the Tech-ops forum, pay attention before you offer advise!!



Quoting LimaFoxTango (Reply 12):
Quoting KBGRbillT (Reply 11):
This is the Tech-ops forum, pay attention before you offer advise!!

This post was made in Civil Aviation first and was then transfered to Tech Ops.



How much would the spacing for expansion between Concrete slabs be approx.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
Contact_tower
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RE: Runway Question?

Wed Oct 05, 2005 10:48 pm

Quote:
Quoting Boeing7E7 (Reply 5):
Concerete is generally cheaper (but of late more expensive thanks to China

Why thanks.

Due to the massive economic growth in China, bulilding activity have soared (Some due to the 2008 olympics, and the 3 Rivers Gorge project) to a completely new level, and created a huge demand for all bulding materials.
This has caused a rise in prices on steel and sement in particular.
 
Electech6299
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RE: Runway Question?

Fri Oct 07, 2005 4:09 pm

I suspect local construction practices play a pretty big role too...The contractor/architect with the winning proposal picked the surface. As others have said, either one functions. It should be noted that "asphalt" runways are actually composite, as true asphalt (aka bitumen in other countries- yes, classically a coal product but now available from other sources) is not very strong and subject to distortion in high temperatures. Some thick asphalt roads actually sink 2-3 inches under the weight of bus traffic on a hot summer day, causing lots of problems for smaller vehicles. Then they just resurface it in September.... But layered composite asphalt is much stronger, and doesn't need expansion joints like concrete, and actually (in my opinion) makes a better road/runway surface. (but the incessant thump-thump of the expansion joints in the concrete interstate highways in the Southwest US brings back fond childhood memories...)

The differences in initial cost vs. maintenance have been noted. As to other differences, concrete has a higher compressive strength but is more brittle, asphalt is more flexible. Concrete expands laterally, whereas asphalt is more prone to volumetric expansion (the deck will rise and fall a few inches to absorb the expansion, but not crack like concrete)

Quoting HAWK21M (Reply 13):
How much would the spacing for expansion between Concrete slabs be approx.

That depends a lot on the mixture (lots of different things can go into "concrete", and the proportion makes a big difference in expansion ratios), and a variety of other things including climate, scale, and substrate. In vertical construction (which I am more familiar with), it's not uncommon to see expansion joints every 35-50 feet. (Some buildings use other methods to control expansion and only have joints every 150 feet, but in my experience those buildings usually have water leaks at the joints...)

Flat decks are a whole different ball game, and I see up to about 200 foot spans. I believe the joints at IAD are just slightly more frequent than the runway lights, how are those spaced? 150 feet or so I think. But smaller width runways will require more frequent joints. The lateral expansion means a basically square slab is the best shape to compensate, so figure not more than 1-1/3 the width of the runway if no joints run the length. But I sometimes see smaller airports and municipal roads with a patchwork of square pours not more than 25 feet square with expansion joints. I expect this has to do with the construction method...enough concrete has to be poured at the same time to fill a section, because if you pour a new patch against a section that has already cured without an expansion joint, you risk a stress fracture at that point because new concrete doesn't bond well with existing (cured) material. So smaller projects with limited concrete access (only 5 trucks a day, for example) will pour smaller patches with more (but narrower) expansion joints. This also makes repair and maintenance easier, which is important if corrosives are used during freezing weather. A small patch of concrete is easier to break up and re-pour than a much larger one- although, as has been noted, this means closing that part of the runway until the concrete cures. It is also used for special purpose areas- so you see concrete "islands" around mx and refueling stations in a sea of asphalt. (concrete is a must where mx is performed, as asphalt doesn't have the compressive strength to hold up the heavy jacks.) But you aren't likely to find an asphalt island anywhere in an otherwise concrete facility.
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