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Our Engineering, Maintenance, and Operations Departments have worked rather collaboratively on this issue, and yes it is a big one.  The FAA requires friction testing and data in order to determine when rubber must be removed.  So, there are two separate and distinct issues; the first being friction, and the second being clarity of markings.

Based on friction testing results we have found that the values that prompt full rubber removal, particularly in touch down areas, is about each 3-5 months depending upon operations.  Our Airport currently utilizes 8,000 – 10,000 psi water blast removal.  Although there are options with chemicals, they are very expensive and can create an environmental hazard.  We found it not to be necessary.  Years ago the pressure utilized by the contractor was well above 20,000 psi.  This tends to remove the fines out of flexible pavements and decreases its life cycle.  By using 8,000 psi the operation is slower, yet effective in keeping friction values into the 80s and above.

The sticking point comes with the clarity of markings for centerlines.  Rubber deposited on centerlines creates a buildup within just a few weeks that obscures runway centerlines.  Although there are multiple markings used for guidance, a Part 139 certificated airport can be cited for failing to keep these markings visible and clear.  The FAA also does not allow painting on top of paint that has rubber deposits.  We developed a schedule where the contractor will come out each five weeks and only do centerlines.  The effort is concentrated on the paint and not the surrounding pavement, and our Maintenance Department comes through the next night and refreshes the centerlines with paint.

Personally, I would never entertain a shot-blast method of removal for two reasons.  First, it’s horribly damaging to the pavement and, secondly you are introducing FOD into the movement area environment.  That’s a huge no-no in our world.  We have found that flexible pavements require rehabilitation in a 10-12 year cycle.  The method we currently employ helps sustain the life cycle of that pavement.  We also have a policy where Operations can request specific areas of rubber removal outside of that cycle if deemed necessary.   I would also never introduce an asphalt binder into the environment, unless it was more of a fog coat that really stays on the surface and does not impact grooving.  The more you consider the grooves, the less effective the fog seal must be.

Friction value testing in itself can be ambiguous.  We have found that the best way to use that tool is relative.  I’m trying to remember, but I think you can see values around 50-60 before it’s an issue.  I believe you should do regular testing and follow trends that show a decline.  Things change when the environment experiences rain as well.