For Runway Rubber and Paint Removal:

The traditional method of runway rubber removal has been with chemicals.  In recent years, some of the chemical companies have developed bio-degradable detergents in an effort to reduce the hazardous impact of their products on the environment.  However, when compared to properly engineered, captive waterblasting, the advantages of the waterblasting are both significant and clearly understood. 

Chemical:  There are at least 3 primary factors to be considered when comparing rubber removal with chemicals to rubber removal by captive waterblasting.  They are the Application Process, the Environmental and Infrastructural Impact, and the Cost.

 Application Process:  The cleaning of a runway with chemicals requires at least 3 steps and  sometimes as many as 5.  In any case, the amount of equipment and personnel required for the  process will always be 3 or 4 times as much as required by proper waterblasting.

 1) Initial Flushing: The process sometimes begins with an overall flushing of the runway to bring the  surface temperature to a level recommended by the chemical manufacturer.  This is typically only  necessary in hot climates.

 2) Chemical Application:  The application of the chemical itself requires a specially designed truck or  trailer.  Typically, this equipment incorporates long, boom like outriggers for the spraying of the  chemical across the width of the runway.  Even the largest equipment used for the applying chemicals  requires 2 or mores passes to cover the area being cleaned. 

 3) Brushing:  After the chemical has been given time to soften and breakdown the rubber deposits, the  third step typically involves multiple passes with a rotating, steel bristled broom.  The rotary action of  the broom is meant to separate the softened rubber from the runway surface. 

 4) Rinsing:  The rinsing of the runway is meant to keep the aircraft rubber, now mixed with the  chemical, from settling back into the grooves and pores of the asphalt until the vacuum trucks make  their pass. 

 5) Vacuum Recovery:  The vacuum recovery of the residue that remains on the runway is typically the  last step.  However, vacuum trucks engineered for working on city streets simply are not capable of  lifting the remaining rubber and chemical mix from within the grooves of the runway.  There is a growing  concern that the long term use of chemicals breaks down the bitumen in runway asphalt.  This creates  a softening of the runway surface and ultimately reducing the useful life of the grooves.  

The application process typically requires 3 or more trucks with as many or more operators.  Furthermore, the runway being cleaned is not available for emergency landings during the cleaning process. 

 Environmental Impact:  A critical result of rinsing process is that a large amounts of the rubber and  chemical mix is washed off of the runway and into the adjoining grass ground.  Even if a bio-degradable  detergent is used, when mixed with the petroleum based composition of the rubber, the run off  ultimately is hazardous to any ground water beneath the surface.  A major international airport in the  northeast part of North America is surrounded on 3 sides by water.  Because the large numbers of fish  in the surrounding bodies of  water, this airport is forbidden from using chemicals or detergents for their  runway cleaning by the federal environmental agency.  They are only able to use waterblasting and  representatives from the environmental agency must be on the site when rubber removal is performed.   Several other major airports have on their own accord, determined that runway cleaning by chemical or  detergent is hazardous to the airport environment.                

 Structural Impact:  In the brushing process, he rotary action of the broom is meant to separate the  rubber from the runway surface.  However, it is physically impossible for the steel bristles of a rotary  broom to reach into the grooves of a grooved surface runway.  Consequently, even though the  chemical may breakdown the composition of the rubber deposits in the grooves, the rotary broom is not  capable of lifting the rubber out of the grooves.  Therefore, a measure of the rubber, mixed with the  chemical will always settle, and remain in the grooves.

 A second, long-term impact of the brooms is a polishing effect on the runway aggregate.  This  ultimately reduces the base level friction coefficients for the surface of the runway. 

 Costs:  Studies show that the combined costs of the chemical, the equipment required to support the  process, and the number of employees required to operate the equipment, plus the many hours of time  required to complete the process, all add up to costs that far exceed the cost of waterblasting.  Studies  also show that runways cleaned with chemicals or detergents must be cleaned more frequently then  runways cleaned by properly engineered waterblasting equipment.