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Agencies with frequent winter freeze-thaw cycles suffer from the
most winter potholes. But any area with freezing winter weather
faces the problem of how to deal with repairs as the temperature
drops.
Methods generally used include throw-and-roll,
edge-seal, semi-permanent, and spray injection.
Originally viewed as an expensive method, spray
injection has been gaining favor because the patches are more likely to
remain in place than some other methods, which can actually mean a
lower-cost repair over the long haul.
The conventional method of winter pothole repair
is a temporary method — throw-and-roll, with the crew placing material
in the hole and compacting it by rolling over the repair several times
with truck tires. Unfortunately, this repair may last only weeks, days,
or even hours.
Semi-permanent patching can be done during the
winter, although hot-mix materials cannot be used below 40 degrees F. In
this method, crews remove water and debris from the pothole using a
broom, shovel, compressed air, or other means. They straighten the edges
of the hole, making them as vertical as possible, using a jackhammer,
paving saw, milling machines, or other device. Next, they place the mix
by hand using a shovel and rake. Placement should be in 3-inch or
smaller lifts. The patch is compacted from the center of the repair to
the edges to provide better compaction at the edges and corners. Crews
may use a vibratory plate compactor or single-drum vibratory roller for
this step. The result is a tightly compacted, semi-permanent repair.
Edge seal uses a cold-mix throw-and-roll patch
sealed around the edges with an asphalt-based sealant.
Spray injection is a good winter repair method
because it is highly mechanized. When using a self-contained patcher,
the repair machine operator completes the whole repair job in four
steps, working from a heated cab.
Materials help
High-quality aggregates in repair mixes provide
a common way to improve winter pothole repairs.
In Lawrence, Kansas, crews go a step further,
adding geosynthetics. A small layer of geosynthetic material is placed
in the hole, says Public Works Field Supervisor Bryce Campbell. This
material costs from $1 to $5 a square yard, but can prevent water from
eroding the repair.
After geosynthetic placement, the winter pothole
is filled with a high-quality cold-mix. The average pothole repair cost
is $6.06, including labor and materials.
In Arlington County, Virginia, asphalt-covered
cement bases cause winter potholes because the two materials expand and
contract at differing rates. Repeated pressure from plowing adds to the
stress.
The county also cites winter water-main breaks
as a pothole causer since many local mains are old and made of brittle
cast-iron.
Cold-mix temporary repairs are used until warmer
weather allows for semi-permanent repairs.
In Colorado Springs, a high-performance cold-mix
asphalt patch is used in the winter. It costs five times as much as a
hot-mix patch and lasts a shorter length of time.
Dickinson County, Michigan was one of the
agencies to switch to spray-injected patching soon after its
development. The county uses a self-propelled Rosco (Leeboy) unit that
lets them repair to 30 degrees F.
The method includes four steps:
1. The hole is cleaned. A high-volume blower
provides a blast of air to remove loose rock and debris.
2. A tack coat of hot emulsion is applied to the
area to be patched.
3. Aggregate and hot emulsion are combined with
forced air and shot into the hole.
4. A dust coat of aggregate is applied. Traffic
can be returned to the road immediately. |
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