The enemy of a road, driveway or parking lot is water under the surface.
The inevitable vertical movement of the surface, when a vehicle passes over
it, creates what's called "Pumping" of the dirt under the pavement. It
liquefies dirt, clay or other fine material, removing even more support for
the surface layer with the inevitable cascading result of alligatoring and
pot holes. Compacted and drained stone doesn't lose support for the surface
when moved about by traffic and if the water can be turned away at the
surface level, then the underlying dirt doesn't liquefy. Just as important
as the water-turning ability of the road surface is the ability for the
water that makes it through to escape. That's why there are ditches and
stone underlayment. They're just as important in draining out water under
the roadway as they are to carry off rainwater to prevent roadway flooding.

I know of at least one very long stretch of an Interstate highway where the
designers failed to understand this. The cure was to trench deeply
alongside the concrete roadway of both lanes, on both sides, install drain
tile and then backfill with coarse stone to carry the undersurface water to
ditches.

By the way, expansive soils are also an enemy of roads, just as they are an
enemy of basements. One lady, who was an NCSU graduate engineer, didn't
understand what expansive soils were and approved an entire highway
interchange to be constructed using expansive soil for the ramps. It never
even opened before the concrete began to crack and fail.

Micajah

"Steve B" wrote in message
...

"RogerT" wrote in message
...
The asphalt material is slightly pliable. The surface underneath needs
to be a hard compacted surface -- I think it is compacted modified stone
(or something like that). That creates a solid surface for the asphalt
material. The first layer of asphalt material needs to also be compacted
with at least a 5,000 pound roller and is called a stabilizing layer.
Then a second coat of asphalt goes on top of that and is compacted.

If you don't put something down first and compact it, you will have a
roller coaster surface once traffic has run on it a year or so.

Steve

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