Condo Media - January 2022 - 37

ASPHALT MIX, REPAIR DESIGN,
PAVING DETERIORATION
So, let us start with the basics. Asphalt
pavement is also called bituminous
concrete. It is called " concrete " because
like cement-based concrete, bituminous
concrete has a mineral aggregate of stone
and sand. This aggregate is held together
with a binder of petroleum derivative asphalt.
Different soil conditions (i.e. sandy
subsurface versus clay) will warrant a different
mix of asphalt paving but this will
be addressed by whoever creates your bid
documents and specifi cations. For planning
purposes, your board should assume
paving will last about 20 years.
Asphalt paved roads, parking areas,
and/or driveways may all require different
repair designs. Typically, roadways
have a sub-base of four to eight inches of
a well-drained compacted soil and gravel
mix. The fi rst layer of paving is called
the binder course and it is one and a half
to two inches thick. This is covered by
a topping coat of one and a half inches.
Driveways and other less traffi cked paving
may allow thinner layers.
If it were not for the sun and water,
asphalt paving would last a long time,
but paving begins to deteriorate as soon
as water begins to penetrate the binder
course and the UV rays remove asphalt
from the topping coat. This can happen
in less than fi ve years. This is why
adding a sealing coat in the fi rst two to
fi ve years following a paving project is
sometimes recommended. It is also an
area of confusion.
SEALING AND MAINTENANCE
Sealing coat materials do not add back
the asphalt lost due to UV deterioration.
It only protects the pavement for a period
of time from further deterioration such
as shrinkage cracks and reveling (loss
of surface aggregate). It does not bridge
large cracks or fi ll in roadway depressions.
If it were not for the sun and water, asphalt paving would
last a long time, but paving begins to deteriorate as soon
as water begins to penetrate the binder course and the
UV rays remove asphalt from the topping coat.
When water begins to infi ltrate the
pavement here in New England the
freeze/thaw cycle takes its toll. The
small cracks become larger in the binder
course and eventually the sub-base
begins to fail. At this point surface cracks,
settlement, alligatoring, and other
surface visible signs make an appearance.
Your maintenance plan should
immediately address these problems by
having crack fi lling as a yearly project.
The cracks should be fi lled with standard
joint fi ller to within one eighth to one
fourth inch of the top of the crack. Similarly,
surface depressions and sink areas
should be annually addressed as well.
After 15 years, more serious paving
repair projects might present themselves.
Sometimes, a major re-surfacing
project can be delayed with judicious
removal of large areas of deterioration
and re-paving with a one and a half inch
binder and a one and a half inch top
coat. If the roadway or parking area
deterioration is judged to be widespread,
the options include a reclamation
project where the top six to
12 inches of pavement and sub-base
is ground into a recycled material that
can be reused for a compacted and
graded foundation for a new paving
surface. This minimizes trucking and
labor costs and extra materials costs.
It takes more than good intentions for a
successful paving project. Timely planning
and a knowledgeable project team
are critical to a successful outcome.
■ JACK CARR, P.E., RS, LEED-AP, IS A
SENIOR CONSULTING ENGINEER FOR
CRITERIUM-ENGINEERS IN FREEPORT,
MAINE. HE IS ALSO A MEMBER OF
THE CONDO MEDIA BOARD .
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January 2022 CONDOMEDIA 37
Condo Media - January 2022

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