On Thu, 15 Aug 2002, Met History wrote:

> Why are some roads asphalt and some concrete?  Cost, weather, durability....?

My understanding is that concrete is more expensive, longer lasting, and
generally requires total reconstruction of the roadbed.  Asphalt is
much quicker and cheaper and can be applied on top of earlier efforts.

A newly paved or reconstructed road can be done with asphalt, especially
if it isn't expected to get heavy traffic, or there isn't enough money
available to do it in concrete.

The next step down the scale below asphalt is "seal coating" (maybe a
Michigan term), which involves laying down a sheet of very sticky hot tar,
and then slathering it with a whole lot of pea-sized gravel.  It looks
like a real mess for a day or so, and then suddenly all the pebbles weld
themselves into the tar, and you have an acceptable driving surface that
looks like faded asphalt.  Of course, this presumes that what's underneath
it is basically sound.

East Lansing (Michigan) used to have two beautiful concrete streets dating
back to the 1930s: Charles Street and Butterfield Drive.  (There were
others around town, but those two were in my neighborhood.)  I know they
were laid back then because they show up as brilliant white in old aerial
photos.  Quite possibly they were WPA projects.  Four decades later, there
had been a little spalling here and there, but the streets were still in
very good shape, except along the expansion joints, which had been
repeatedly patched with tar.  The lines of patch were higher than the
street surface, so driving or bicycling along these streets would involve
a periodic bump, bump, bump.

But around 1980, both streets were seal coated, so the old concrete
surface was covered up.

                                  Larry

---
Lawrence Kestenbaum, [log in to unmask]
Washtenaw County Commissioner, 4th District
The Political Graveyard, http://politicalgraveyard.com
Polygon, the Dancing Bear, http://potifos.com/polygon
Mailing address: P.O. Box 2563, Ann Arbor MI 48106

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