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Why would a runway friction measurement that I've just made (with a SARSYS friction tester) give better (condition improved) results than a measurement that I made 6 months ago? The runway has been in use in the interim and no repairs have been made in the interim.

The runway is asphalt and 15 years old. For both measurements, the runway was dry.

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    $\begingroup$ What makes you think it wouldn't be possible? What exactly have you measured, and how? $\endgroup$ – a CVn Apr 10 '18 at 14:12
  • $\begingroup$ @MichaelKjörling Good evening Michael. The measurement was made with SARSYS friction tester! I'm just asking if it's possible to have a better result even if the runway was used all these months! $\endgroup$ – Savvas Markianidis Apr 10 '18 at 18:15
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    $\begingroup$ Please do not attempt to answer the question in the comments. $\endgroup$ – Federico Apr 11 '18 at 7:59
  • $\begingroup$ Did you do the test in exactly the same place on the runway ? $\endgroup$ – Criggie Sep 15 '18 at 0:26
  • $\begingroup$ Is it the same friction tester tool you used 6 months ago or a different one ? $\endgroup$ – Criggie Sep 15 '18 at 0:50
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There could be a number of reasons. Temperature affects asphalt significantly or calibration could be off.

But if higher friction is measured in the touchdown area after significant use I would look to rubber deposited by landing aircraft tires, which is stickier than asphalt. Dragsters do burnouts before their runs to put rubber on their lane. It is just like glue.

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    $\begingroup$ I should add that rubber is sticky when dry, as specified in the question. If it gets wet it is like ice. In fact, the way dragsters initiate a burnout is to put a little water under the tire so they can get it to slip. The FAA has spec for removing said rubber, as grooved concrete is much more grippy when wet than tire rubber. $\endgroup$ – Pilothead Apr 19 '18 at 21:33

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