What makes an asphalt driveway durable?
1 of 31: Thick, well-compacted granular base
Eight inches of granular fill
is used for poor-draining
soils, 4 in. for well-draining
soils.
2 of 32: Proper asphalt thickness
A 2-in. layer of
asphalt is spread
after the fill has settled
for several days.
3 of 33: Good asphalt compaction
The asphalt is compacted
with heavy rollers soon
after it's spread. If the
asphalt cools too much
before rolling, it can't be
compacted well.
The first step is finding a reputable contractor
to do the job. The residential asphalt industry
has more than its share of fly-by-nights. The only
advice I can offer is to find one with references from homeowners who are still satisfied with their driveways
after a decade or so. Assuming you find a good contractor,
the rest should take care of itself.
The materials and techniques described here for a quality
driveway are pretty simple. Discuss them with your
potential contractor before signing on the dotted line,
and then stay home to keep an eye on the actual installation
to make sure you’re getting what you paid for.
The secrets of a long-lasting driveway
One of the main design objectives for a durable asphalt
driveway is to provide enough slope for draining water off
and away from the driveway. Water should never pond
on the surface or next to the driveway where it will seep
underneath to weaken the soil or cause frost heaving.
The main component of a long-lasting driveway is the
underlying granular base. It must have the right thickness
and composition. Base materials vary by region and can
be crushed stone or “conbit” (recycled concrete and
asphalt—it’s crushed and reused). Crushed coarse materials
like these have jagged surfaces so they’ll compact and
lock together in a tough, settle-resistant matrix. A binder like cement dust may be added to hold it all together.
Coarse materials also drain water from under the driveway
so ice won’t form and crack the asphalt surface.
Once your old driveway has been torn out, you and
the contractor should closely examine the existing base
(the fill under the asphalt surface) and possibly remove
or add material. Digging into the exposed base will tell
you its type and thickness. Recommended thicknesses
are 8 in. of base over clay soils or 4 in. over well-drained
sandy soils. If your base is inadequate, it must
be upgraded. Low bids may signal that a contractor
isn’t prepared to install a good base. Ask the contractor
about these details before you sign up.
Mechanical compaction of the base, subbase and
asphalt is crucial for a long-lasting driveway. Ideally,
the base should sit for about a week so that natural settling
will augment the mechanical compaction. When
compacting subbases, contractors will use heavy rollers
(or even the tires of the earth-moving equipment) for
large areas and plate compactors for smaller areas. But
when rolling out asphalt, heavy compacting equipment
is needed. Select a contractor who has 1- to 3-ton
rollers for compacting the asphalt itself. Edges are raked
and formed to 45-degree angles, then packed with a hand
tamper.
In most areas of the country, there are two options for
the asphalt itself. The difference is the size of the aggregate
(gravel filler) used. The most common mix for residential
driveways has finer (1/2 in. or smaller) aggregate
and thus forms a smoother surface. Coarser (3/4 in. or
smaller) aggregate mixes are stronger but have a rougher
finish. Parking lots and roads are usually a coarser mix.
Coarser mixes are also recommended for driveways that
get heavier traffic such as RVs, large trucks and tractors.
Both mixes cost about the same.
In most parts of the country, the asphalt laid over a
properly prepared aggregate base should be 2 to 3 in.
thick. If you opt for a 3-in. thick surface, you can use the
coarse asphalt mix for a 2-in. thick bottom layer for
strength, and a 1-in. thick layer of the finer mix on the surface for a better appearance.
