"Blacktop
or asphalt paving is a very interesting surfacing material.
The asphalt industry actually markets the material as a
flexible pavement. This claim arises from the fact that the
asphalt cement, the material that holds together the small
pieces of stone and sand in the blacktop, can remain pliable
for a long period of time. This quality helps the asphalt or
blacktop to resist cracks if installed properly."
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However, asphalt which is exposed to air
and sunlight will begin to loose this flexibility. The
asphalt actually begins to oxidize. Ultraviolet light (UV)
from the sun also helps to breakdown the asphalt cement.
This is where problems begin to happen. If the asphalt
oxidizes, it becomes brittle. The bond between it and the
sand and stone particles (aggregate) begins to fail. The
result of this process is cracking and loosening of
individuals pieces of aggregate. If you live in a
climate that experiences cold weather, this process is
accelerated by water which enters these cracks and then
freezes.
As water permeates cracks in the material
and settles down at the base, the strength of the base is
compromised, resulting in the formation of potholes. Cracks
filled with water are also an open invitation in the North
to damage from freezing. Even in warm climates, grass can
begin to grow up through cracks on the edges of the surface.
Damage from ultraviolet rays and oil/gas spills are other
good reasons for sealing asphalt driveways.
Blacktop sealers block air and sunlight
from attacking the asphalt cement.
