When an aircraft touches down, the landing gear weels start rotating. The friction forces peel some rubber off the tyres and this process continues until the wheel rotation speed matches the aircraft speed. Therefore, the touchdown zone is prone to rubber deposit accumulation. The adverse effects of these deposits are that they
obliterate the runway markings (which may confuse the pilots)
become slippery when wet (e.g. due to rain) which may contribute to a runway excursion
Methods for removing rubber deposits
Rubber can removed by using one of the following methods:
Chemical solvents. This method consists of spraying the solvent solution on the contaminated area, waiting for a specified period of time and then washing and sweeping. Different chemical agents are used depending on the surface (concrete, asphalt, etc.). Care should be taken during and after application due to the aggressive nature of the cleaning compound. If the chemical is allowed to remain on the surface for too long, the paint and possibly the pavement surface could be damaged. When washing the cleaning compound off the pavement surface, it must be so diluted that it will not harm the surrounding vegetation,drainage system or wildlife, or pollute nearby streams.
High-pressure water blasting. This is a method for mechanical removal of rubber deposits. The equipment ranges from a single, manually operated nozzle (or gun) supplied by pump and water tender, to sophisticated, selfpropelled semi-trailers incorporating a pump, a water tank and a high-pressure water spray bar. This method is reasonably effective on lightly contaminated areas, but its effectiveness decreases as the depth of contamination increases.
A combination of chemical solvents and high-pressure water blasting. A modern practice is to dissolve rubber deposits with chemical solvents followed by thorough flushing with high-pressure water blasting.
Hot compressed air. This technique uses high temperature gases to burn away the rubber deposits. Air-gas mixture is fed into a combustion chamber where burning takes place. The resulting exhaust is emitted at about 400 m/s from orifices at a temperature of approximately 1200°C directly onto the surface. These gases soften and shear off the rubber particles. When a hot compressed air cleaner is used on concrete surfaces, a small amount of carbon deposit is produced. This can be brushed from the surface of the concrete using a normal tractor- or truck-mounted brush machine which most airports already have. It has been claimed that as no mechanical action takes place at the runway surface, there is little danger of the surfacing material becoming loose and causing foreign object ingestion. However, caution should be exercised and the condition of the pavement should be closely monitored when using this technique on asphaltic concrete runways.