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From the Puckerbrush...

Editor's Column

tex2html_wrap96 Why Seal the Runway?

I received a few queries as to why we need to seal the runway now, or why it wasn't done when it was fresh. I know that several of you have much more knowledge of the workings of asphalt than I do, but here's a rather conventional answer to the questions:

Asphalt is a porous material: it is one of the reasons it is used for paving. The porosity allows the asphalt to expand and contract slightly without breaking up or cracking. Because of the porosity, moisture in the form of water can get into the material causing mechanical breakdown, especially if it freezes and thaws. Over time, breakdown of the asphalt causes it to crack and the surface to deteriorate and get granular. Once this occurs, the deterioration accelerates and the asphalt is soon ruined.

Putting a sealer on the asphalt seals the surface so that water and other liquids will drain off of it rather than penetrate it. The sealer not only helps seal the asphalt, it also replaces some of the oils in the asphalt and helps keep it pliable. Asphalt should be re-sealed periodically. A common statement is ``every 5 years'', but opinions vary as it clearly depends upon the local climate conditions. Here in Arizona, we don't suffer the constant freezing and thawing that a flying field in New York might experience, for example.

Why didn't we do this right away, when the runway was fresh? In general, waiting a year or two is preferred because it allows any periodic roller maintenance (if available) to continue to compact the asphalt, it gives time for the asphalt to settle, and also allows volatiles in the asphalt to evaporate.

Hope that's helpful. If anyone has additional information to add, please send it to me and I'll post it here.


next up previous
Next: The Speed 400 Revolution Up: Front Page Previous: At the Last Meeting...

Craig Kulesa
Fri Dec 1 16:54:18 MST 2000