Runway Rubber and 5 Ways to Remove It

Summer officially started last week. With the warmer weather, airports must be extra attentive to rubber build up on runways. When airplanes land on hot runways, the rubber on the tires gets deposited in long black stripes. This is due to friction and thus excess heat and pressure caused when the stationary tires touch down onto the pavement and for the next 1000 feet have to spin up to reach the speed of the moving aircraft. Amazingly, approximately 1.4 pounds of rubber from each tire of a large aircraft like a Boeing 747 is deposited each time that aircraft lands (Source). A Boeing 747 has 18 tires, so that would be 18*1.4 = 25.2 pounds of rubber per landing.

Courtesy of Waterblasting Technologies

The rubber tends to build up in mostly the same areas on each end of the runway until eventually, the friction coefficient (for braking) becomes too low and the rubber must be removed to prevent slide offs and overruns. (See my article about Safety Areas.) The rubber also covers up the paint markings on the runway until at worst, the center line stripes are completely invisible.



The FAA has put out a guideline on how often runways should be tested with CFME (Continuous Friction Measuring Equipment) to determine friction coefficients (AC 150/5320-12C). Rubber should be removed from runways based on the outcomes of the friction tests. Many Large airports remove the rubber twice a year in the spring and fall.


NUMBER OF DAILY
MINIMUM TURBOJET
AIRCRAFT LANDINGS   
PER RUNWAY END
   MINIMUM
   FRICTION  
   SURVEY  
 FREQUENCY
LESS THAN 15
1 YEAR
16 TO 30
6 MONTHS
31 TO 90
3 MONTHS
91 TO 150
1 MONTH
151 TO 210
2 WEEKS
GREATER THAN 210
1 WEEK

What does the rubber removal process look like? Generally, the airport operator schedules a closure either for a full 3-5 days or closures on and off for throughout the day, for a number of days, as to not deprive Air Traffic Control and the airlines a runway at peak times. (So, the runway may be closed overnight until a certain time in the morning, then open for four hours, and then close for 6 hours, then close again for the night.) When the runway closes for more than a designated amount of time (generally 2 or more hours), airport operations or maintenance will put out a runway Lighted Visual Aid (AC 150/5345-55A) or "Lighted X" at each end of the runway. Then the maintenance crew or a contracted runway rubber removal crew go to town removing the many thousands of pounds of rubber.

Courtesy of Wanco

 There are five different ways to remove the deposits. I found most of this information from a presentation titled Airfield Rubber Removal and another titled Rubber Removal Techniques.


1. High-Pressure Water Blasting

Water is sprayed out of a rotary device at 2,000-15,000 PSI and removes at least 10,000 sq. ft. of rubber perhour. The machines use about 30 gallons of water/minute, but by using water, it makes this technique cost effective. While the machine is clearing the rubber, it also improves the friction characteristics as it passes. A great benefit is that the runway can be cleared very quickly in case of an emergency as there are no chemicals to be removed; a sweeper truck can simply go over the area right after the water blasting vehicle, and both can be off of the runway in minutes. This method can be used in any weather condition. Disadvantages include: The machine being loud requiring hearing protection, requirement to properly dispose of the waste, the loosening of surface matrix, a cleaning rate of one run is only 70%, and it can damage asphalt and grooved pavement over time.


2. Ultra High Pressure Water Blasting

Water is sprayed out of a truck mounted rotary device at 40,000 PSI and can remove 10,000 sq. ft. of rubber per hour. This sounds similar to the High-Pressure water blasting, but the benefit of this machine is that it only uses 8 gallons of water/minute. A disadvantage of some of these types of machines is that they use such a high pressure, that it actually causes the pavement underneath it to become smoother, and overtime can create a polished surface that ultimately decreases braking coefficients. A machine called a TrackJet, claims to remove almost 100% of the rubber without damaging the micro or macro texture of the pavement. Additionally the TrackJet uses less water and fuel to operate than traditional machines of this type. The TrackJet removes slightly less rubber per hour, about 8600 sq. ft.  Any of these machines allow for quick exit in case of an emergency.

TrackJet©


3. Chemical Removing

Environmentally safe chemicals are sprayed onto the runway and then brushed and worked into the rubber for and left to sit for at least four hours.  Crews then come out and use high pressured water to push the gelatinous rubber debris off the sides of the runway. Unfortunately, the chemically altered rubber cannot be swept up by a machine because the machines have many parts made of rubber and the chemical would ruin them. Thus, clean up beyond spraying the debris to the shoulders is difficult and could cause future environmental and costly issues. Benefits of this method are that the pavement surface is not altered and that an expensive water blasting machine used in methods 1 and 2 above is not needed, however the chemicals can be quite expensive. An obvious disadvantage is that the runway is not usable while the chemical is present.


4. High Velocity Impact Removal (Shotblasting)

A self-contained shotblaster propels abrasive particles onto the pavement blasting away contaminants. The shotblaster can be adjusted to achieve different surface textures and on non-grooved surfaces, and it can collect debris from the runway surface and recycle the steel shot for re-use. Most shotblasters are used for retexturing pavement surfaces like roads, and are small riding units that cut up to 20" per pass (good for paint removal). Atlanta uses a machine called the a Skidabrader that cuts six feet in a single pass and re-textures the pavement to boot (at a rate of greater than 10,000 sq. ft./hour). Click here for a link to a Skidabrader Brochure, it does not include a price, but apparently is expensive to buy and operate. Another example of this is called the Blastrac. These machines also have the ability to quickly clear from a runway. One possible issue is that the steel shot can become embedded in the pavement and then dislodged later causing a FOD (Foreign Object Debris) hazard.


5. Mechanical Removal

This process involves grinding or milling the runway surface to achieve removal of bumps, high areas due to joints/slabs shifting, and to mill asphalt for overlay. A byproduct of this method is the removal of rubber deposits. It also improves pavement friction, but unfortunately, because it removes a surface layer up to 3/16th deep, it decreases the depth of grooved surfaces (which provide water drainage) requiring the pavement to be redone sooner. It can also cause micro-cracking of the pavement structure leading to accelerated aging and FOD.




What did I miss, get incorrect or need to clarify? Please tell me in the comments below.
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