When the local street sweeper comes through your neighborhood, it’s mostly for aesthetic reasons.
Cleaning the runway surface at an airport is for safety.
You probably didn’t know, but airplanes litter every time they land. When the tires touch down, they skid on the surface and leave rubber deposits that need to be cleaned to prevent aircraft from losing traction, which is especially troublesome for aircraft taking off or landing in rain or strong winds.
The tarmac used to pave runways is much coarser than asphalt or concrete used on roads, which makes cleaning tire marks more difficult. One aircraft landing on a fresh layer of tarmac leaves behind about 22 pounds of rubber, according to the operator of Schiphol Amsterdam Airport in The Netherlands. As the runway gets more use and rubber debris builds up, the amount of tire deposits decreases to about 9 to 13 pounds.
Cleaning up all that rubber is no easy task: the tarmac used to pave runways is much coarser than the material used on roads. One aircraft landing on a fresh layer of tarmac leaves behind around 10 kilograms (!!!) of rubber. As the runway is used more frequently, this amount decreases to around 4 to 6 kilograms per landing. In total, we collected 6,500 kilograms of rubber last week. How? By removing it from the tarmac using high-pressure cleaners and hoovering up the bits of loosened material.
Philadelphia International Airport recently outlined in a blog post how it goes about its runway maintenance.
The Pavement & Grounds Department each spring and fall brings in a rubber removal contractor with a specialty semi-truck equipped with an ultra high-pressure power wash unit and a vacuum. Airport operations and pavement personnel inspect and identify the runways to be treated, survey, measure and mark the areas that need to be cleaned.
The pressure washer is capable of 35,000 pounds per square inch. The water pressure strips the rubber from the concrete and the vacuum removes it. Afterwards a friction tester known as the Douglas Mu-Meter Mk6 checks the work. Since the friction equipment doesn’t include a wash unit, friction tests are done during precipitation.
To minimize the impact on airport operations, work is scheduled for overnight. The truck moves slowly and usually runs 6-to-8 hours per night, according to the airport authority. Last fall, Philadelphia’s main two runways had a combined total of 258,000 square feet of rubber removed.
At Schiphol Airport some runways are so long that officials close them down for a week to scrape them off. Other periodic runway maintenance includes repairing cracks in the tarmac, cleaning the gutters along the sides, and adding a fresh coat of paint to runway markings.
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