blacktop/macadam

[James A. Landau]

In a message dated 12/10/02 9:57:13 AM Eastern Standard Time,
jsmithjamessmith at YAHOO.COM writes:

> Then there's the term "asphalt concrete", which is
>  used in many bid specifications for asphalt.  It
>  confused me the first time I saw it, wondering if it
>  was offering an option between concrete or asphalt at
>  the bidders discretion.

It's a technical term among civil engineers.  "Asphalt concrete" is blacktop.
 The stuff that is poured out of concrete mixers is "cement concrete".  The
base term "concrete" here is in a sense which the MWCD10 dates as 1656: "a
mass formed by concretion or coalescence of separate particles of matter in
one body."

The layman's meaning of "concrete" is MWCD10 sense 2 "a hard strong building
material made by mixing a cementing material (as Portland cement) and a
mineral aggregate (as sand and gravel) with sufficient water to cause the
cement to set and bind the entire mass".  The referent, though not the word,
goes back to Roman times---the Romans made a concrete using pozzolana instead
of Portland cement, which was not invented until 1824.

By the way, "aggregate" is also a technical term in civil
engineering---MWCD10 sense 2b "any of several hard inert materials (as sand,
grael, or slag) used for mixing with a cementing material to form concrete,
mortar, or plaster".  Note that this definition uses the layman's rather than
the civil engineer's definition of "concrete".

Martin Marietta Aerospace (now Lockheed-Martin) owned (and maybe still owns)
of all things an "Aggregate Division" which sold sand and/or gravel.  A few
years ago, when Martin Marietta's contract here at the Tech Center was about
to expire, the running joke was "Don't worry.  Martin will give you a job in
the Aggregate Division."  (Happy ending, too---the ex-Martin people got jobs
with 8a contractors).

        - James A. Landau
          systems engineer
          FAA Technical Center (ACB-510/BCI)
          Atlantic City Int'l Airport NJ 08405 USA

P.S.  I too have heard "tarnac" used only in reference to airports.