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Material of Choice
Airports and airbases are becoming increasingly essential to the wellbeing of Europe's economy and security. Whether it is the movement of passengers or freight, the need to keep airports open for business will not diminish as the global trade and next day delivery becomes a way of life.
Operators of airports are under increasing pressure therefore to ensure that the network of runways, taxiways and aprons remain free from maintenance works to simply accommodate more aircraft and keep dealys to a minimum.
Pavements at airports undergo some of the heaviest loading and are subjected to some of the most extreme operating environments in the transport area.
The requirement of the safe operation of airports extends to all areas of airport technology and infrastructure, including the pavements that make up the runways, taxiways and aprons. It is for this reason that concrete is the material of choice for airports.
One of the key concerns for airport operators is loose stones and debris rising from deteriorating pavements. This debris is collectively known as Foreign Object Debris or FOD. The problem is that FOD ingested into a jet engine can cause serious damage with obvious consequences for high-speed aircraft.
Resistance to fuel spillage is a key issue - passenger aircraft do not refuel anywhere else and so the refuelling operation with its risks of spillage is continuously carried out on aircraft stands.
Asphalt binders soften under fuel spillage, aggregates pluck and a FOD hazard is introduced. The damage that can be sustained by an aircraft engine through FOD can run to 10's of millions of euros - not a risk worth taking.
Resistance to jet blast is equally pertinent - take off thrust from a Boeing 747 for instance results in wind speeds of over 400 km/hr (250mph) at 38°C (100F) - enough to lift loose, or semi-embedded aggregate.
This is why runway thresholds tend to be in concrete as the aircraft sits there and fires its engines up before take off.
Resistance to Impact
For the passengers, when their aircraft finally arrives at its destination, it's time to disembark. However, for the ground crews it is only just the beginning of a frenetic bout of activity. This includes refuelling tankers, baggage trolleys, cargo loaders and containers, ground power servicing units, cabin cleaning vehicles, gallery servicing vehicles, tugs and air bridges.
These activities commonly result in surface impact and as such the pavement surface must be tough enough to accept this environment. This is another reason why concrete is the favoured surface for aprons.
High Pressure Tyres
Aircraft have very high tyre pressures, typically 1,4 N/mm² (200psi) and beyond. These high tyre pressures demand a surface material that has the stiffness levels necessary to avoid indentation and rutting. It is for this reason that USAF has recently replaced asphalt taxiways with concrete at RAF Lakenheath, Mildenhall and Fairford due to the very high tyre pressures [in excess of 2 N/mm² (300psi)] of the military jet range.
Strength and Quality
Airfields are environments where pavement strength and quality are taken to another level. These pavements must be constructed to exacting tolerances due to the very shallow gradients required by aircraft. The quality of construction to avoid future FOD problems is imperative.
A material that can deal with freezing conditions and thermal shock when de-icing agents are applied is also necessary to avoid generation of FOD through pot-holes.
With aircraft weights increasing, such as with the introduction of the Airbus A380, a material with the flexural strength necessary to give long lasting structural performance becomes essential to busy airports. The material of choice is therefore concrete.
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