Editing Runway (section)

==Surface==
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[[File:Pista Congonhas03.jpg|thumb|Runway surface at [[Congonhas Airport]] in [[São Paulo]], [[Brazil]]. The grooves increase friction and reduce the risk of [[Hydroplaning (tires)|hydroplaning]].]]
The choice of material used to construct the runway depends on the use and the local ground conditions. For a major airport, where the ground conditions permit, the most satisfactory type of pavement for long-term minimum maintenance is [[concrete]]. Although certain airports have used reinforcement in concrete pavements, this is generally found to be unnecessary, with the exception of [[expansion joint]]s across the runway where a [[dowel]] assembly, which permits relative movement of the concrete slabs, is placed in the concrete. Where it can be anticipated that major settlements of the runway will occur over the years because of unstable ground conditions, it is preferable to install [[asphalt concrete]] surface, as it is easier to patch on a periodic basis. Fields with very low traffic of light planes may use a sod surface. Some runways make use of salt flats.

For pavement designs, borings are taken to determine the subgrade condition, and based on the relative [[bearing capacity]] of the subgrade, the specifications are established. For heavy-duty commercial aircraft, the pavement thickness, no matter what the top surface, varies from {{cvt|10|to|48|in|cm}}, including subgrade.

Airport pavements have been designed by two methods. The first, ''Westergaard'', is based on the assumption that the pavement is an elastic plate supported on a heavy fluid base with a uniform reaction [[coefficient]] known as the [[Hooke's law|K value]]. Experience has shown that the ''K'' values on which the formula was developed are not applicable for newer aircraft with very large footprint pressures.

The second method is called the ''[[California bearing ratio]]'' and was developed in the late 1940s. It is an extrapolation of the original test results, which are not applicable to modern aircraft pavements or to modern aircraft [[landing gear]]. Some designs were made by a mixture of these two design theories. A more recent method is an analytical system based on the introduction of vehicle response as an important design parameter. Essentially it takes into account all factors, including the traffic conditions, service life, materials used in the construction, and, especially important, the dynamic response of the vehicles using the landing area.

Because airport pavement construction is so expensive, manufacturers aim to minimize aircraft stresses on the pavement. Manufacturers of the larger planes design landing gear so that the weight of the plane is supported on larger and more numerous tires. Attention is also paid to the characteristics of the landing gear itself, so that adverse effects on the pavement are minimized. Sometimes it is possible to reinforce a pavement for higher loading by applying an overlay of asphaltic concrete or [[portland cement]] concrete that is bonded to the original slab. Post-tensioning concrete has been developed for the runway surface. This permits the use of thinner pavements and should result in longer concrete pavement life. Because of the susceptibility of thinner pavements to [[Frost heaving|frost heave]], this process is generally applicable only where there is no appreciable [[Weathering#Frost weathering|frost action]].

===Pavement surface===
[[File:Mahan Air A310 EP-MNO.jpg|thumb|A [[Mahan Air]] [[Airbus A310]] using [[reverse thrust]] in rainy weather at [[Düsseldorf Airport]]]]

Runway pavement surface is prepared and maintained to maximize friction for wheel braking. To minimize [[hydroplaning (tires)|hydroplaning]] following heavy rain, the pavement surface is usually grooved so that the surface water film flows into the grooves and the peaks between grooves will still be in contact with the aircraft tyres. To maintain the macrotexturing built into the runway by the grooves, maintenance crews engage in [[airfield rubber removal]] or [[hydrocleaning]] in order to meet required [[FAA]], or other aviation authority friction levels.

===Pavement subsurface drainage and underdrains===
Subsurface underdrains help provide extended life and excellent and reliable pavement performance. At the Hartsfield Atlanta, GA airport the underdrains usually consist of trenches {{cvt|18|in|cm}} wide and {{cvt|48|in|cm}} deep from the top of the pavement. A perforated plastic tube ({{cvt|15|cm|order=flip}} in diameter) is placed at the bottom of the ditch. The ditches are filled with gravel size crushed stone.<ref>[https://www.ntnu.no/ojs/index.php/BCRRA/article/view/2723/2786] Design, Construction and Maintenance of Concrete Pavements at the  | World's Busiest Airport  | W. Charles Greer, Jr., P.E. | AMEC Environment & Infrastructure, Inc., Alpharetta, GA, USA | Subash Reddy Kuchikulla | Materials Managers and Engineers, Inc., Atlanta, GA, USA | Kathryn Masters, P.E. | Hartsfield | Jackson Atlanta International Airport, Atlanta, GA, USA | John Rone, P.E. | Hartsfield | Jackson Atlanta International Airport, Atlanta, GA</ref> Excessive moisture under a concrete pavement can cause pumping, cracking, and joint failure.<ref>[http://www.dot.state.mn.us/materials/pvmtdesign/docs/2007manual/Chapter_5-4_5.pdf] Minnesota | Dept. of Transportation| Pavement Manual | 5-4.02 Subsurface Drainage</ref>

==={{anchor|surface_types}} Surface type codes===
[[File:Grass airstrip at badminton england arp.jpg|thumb|The grass airstrip on the Badminton estate, [[Badminton, Gloucestershire|Badminton]], [[South Gloucestershire]], [[England]]. The strip is very simple: no lighting, no centerline, and no approach aids. The edge is marked by simple posts.]]

In [[aviation]] charts, the surface type is usually abbreviated to a three-letter code.

The most common hard surface types are asphalt and concrete. The most common soft surface types are grass and gravel.

{| class="wikitable"
! Abbreviation !! Meaning
|-
| ASP
| [[Asphalt concrete|Asphalt]]
|-
| BIT
| [[Bitumen|Bitumin]]ous asphalt or tarmac
|-
| BRI
| [[Brick]]s (no longer in use, covered with asphalt or concrete now)
|-
| CLA
| [[Clay]]
|-
| COM
| Composite
|-
| CON
| [[Concrete]]
|-
| COP
| Composite
|-
| COR
| [[Coral]] (fine crushed coral reef structures)
|-
| GRE
| Graded or rolled earth, grass on graded earth
|-
| GRS
| [[Grass]] or earth not graded or rolled
|-
| GVL
| [[Gravel]]
|-
| ICE
| [[Ice]]
|-
| LAT
| [[Laterite]]
|-
| MAC
| [[Macadam]]
|-
| PEM
| Partially concrete, asphalt or bitumen-bound macadam
|-
| PER
| Permanent surface, details unknown
|-
| PSP
| [[Marston Matting]] (derived from pierced/perforated steel planking)
|-
| SAN
| [[Sand]]
|-
| SMT
| [[Sommerfeld Tracking]]
|-
| SNO
| [[Snow]]
|-
| U
| Unknown surface
|-
| WAT
| [[Water]]
|}