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Wikipedia list a number of runway pavement. For specific airports, the choice is obvious (e.g. ice, snow). But there are few pavement I cannot figure out how to decide which one use.

Why an airport would choose asphalt over concrete or bitumeous asphalt for the runway pavement? What are the reason for the choice?

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  • $\begingroup$ Asphalt is cheaper and faster to build, but not as strong. $\endgroup$ – Jan Hudec Oct 19 '14 at 9:21
  • $\begingroup$ @JanHudec how much cheaper and faster? what do you mean by "strong"? support heavier aircraft? better absorption of ground movement (e.g. earthquake)? better tolerance to temperature changes? $\endgroup$ – Manu H Oct 19 '14 at 9:46
  • $\begingroup$ I am neither builder nor airport manager, so I don't really know how much cheaper asphalt is compared to concrete (and there are various kinds of each), but it is obviously quite significant since concrete is only used for the highest loaded runways and roads. By stronger I mean that it can support higher load, that is heavier aircraft and/or more of them. Asphalt is slowly deformed by both high loads and repeated moderate loads. It is however more easily repaired than concrete. $\endgroup$ – Jan Hudec Oct 19 '14 at 10:01
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    $\begingroup$ for the not as strong you can look at this answer: essentially because asphalt isn't rigid it will get rutted and potholed eventually. $\endgroup$ – ratchet freak Oct 19 '14 at 19:22
  • $\begingroup$ @JanHudec asphalt also provides a smoother ride (no cracks between the slabs), and is more porous so it's easier to drain rain water. Disadvantage is that it is more easily damaged in icing conditions. $\endgroup$ – jwenting Oct 20 '14 at 6:13
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I am neither builder nor airport manager and can't provide details, but as there is no answer yet, I'll try to summarize the main differences between the materials:

  • Concrete can support highest loads and lasts long. It is however most expensive to build and when it eventually gets damaged, it can't be patched and has to be rebuilt in large slabs. It also requires stable base, because it is rigid. It is built in slabs with spaces between them that are required due to account for thermal expansions and give somewhat bouncy ride.

  • Asphalt. There is a big variation between different kinds of asphalt concrete, but it is generally cheaper than concrete, but can't support as big loads and is susceptible to damage by frost. Asphalt is never completely rigid and slowly deforms under load. This allows using it on unstable base, but it means bumps form by prolonged use reducing the total lifetime. It also easily cracks and when water freezes in the cracks, potholes quickly form. They can however be relatively easily patched. It does not require any thermal expansion gaps and provides smooth ride.

  • Asphalt and concrete can be combined. A concrete with a layer of asphalt on top provides the strength of concrete and smooth ride of asphalt. The asphalt also protects the concrete base from freezing water while itself can be easily patched. This is lately common on roads (where concrete alone is really uncomfortable), not sure how much on runways.

  • Gravel is simple to build; all you need is some stone from nearby quarry and a steamroller. The main disadvantages are risk of foreign object damage by loose stones thrown up by the wheels and need of regular maintenance. So it is used mainly in remote cold places where concrete would be too expensive and asphalt would not last long in prevailing weather conditions.

  • Rolled earth with or without grass is even simpler then gravel, used for small airports where big loads are not needed.

  • When runway is listed as grass, it means it is not even rolled. Usually enough for small airplanes and obviously cheapest.

  • Other surfaces usually as provided by local conditions (snow, salt etc.)

For every particular airport, the investor evaluates the available technologies whether they can handle the expected traffic (to handle large jets like 747 or A380 concrete or concrete-asphalt combination is preferred), whether they are buildable in given location (the ground has to support the weight too) and how much building them will cost and choose the option that satisfies the requirements and they have money for.

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  • $\begingroup$ I think that runway surface is chosen because of the intended traffic. For A380, Airbus requested/directed/lobbied many airports to enhance their runways and other facilities. Your answer does highlight the intended aircraft which a runway can handle. $\endgroup$ – Farhan Oct 20 '14 at 13:30
  • $\begingroup$ At FRA the both main runways 07C/25C (Center) and 07R/25L (South) are made from asphalt and used by large jets (B747-400, B747-800 and A380). I wouldn't say "only concrete will do". en.wikipedia.org/wiki/Frankfurt_Airport#Runways (german wiki says 18 uses mixed concrete and asphalt) $\endgroup$ – Peter Jan 21 '16 at 12:29
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From an engineering perspective, concrete is modeled as a rigid pavement and asphalt is a flexible pavement.

Concrete is harder and more brittle than asphalt. Concrete generally cannot tolerate significant ground movement without cracking. The addition of steel reinforcing to concrete can help to mitigate concrete's brittleness to some extent, but Jan is correct in saying that once concrete has cracked or spalled, it cannot be easily repaired. Generally an entire panel must be completely replaced.

Asphalt is less expensive than concrete to install initially but the surface will degrade over time due to the evaporation of volatile aromatic hydrocarbons so must be maintained on a regular schedule whereas a concrete surface requires no regular maintenance. Asphalt is a weaker material than concrete but can be made to support equal loads by constructing a thicker pavement. Asphalt will soften under high temperatures so warm climates can be a problem for asphalt. Because asphalt is flexible it is a better choice over soils that are prone to movement or over soils that would be too expensive to treat to raise their bearing capacity.

Concrete reflects light better than asphalt so will have better visibility at night. For highways, asphalt is a quieter surface than concrete although that would not be a consideration for aviation purposes.

The choice of whether to use concrete or asphalt must consider all these variables of initial cost vs. long term maintenance, soil condition, visibility, climate, local budgetary considerations, local availability of materials, etc. Each installation will be different.

I have supervised drilling cores from the runway and taxiways at San Diego International Airport (KSAN). It has alternating layers of concrete and asphalt in some locations although the top surface is asphalt. The total thickness varies but is generally at least 18" thick. The airport sits on the former outlet to the San Diego River and is only a short distance from the bay, so the sub soils are weak alluvial silts that are saturated a short distance below grade. Yet the taxiways are mostly concrete. Go figure.

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