7/12/2012
Reed Hollinshead
ITD Communication
208-334-8881
reed.hollinshead@itd.idaho.gov
Why does ITD seal coat the highways?
BOISE - Every summer, particularly mid- to late-summer, seal coats and chip seals abound throughout the state. The practice always prompts many questions. Here are a few answers from the Idaho Transportation Department.
Click here for picture 1 and picture 2 of recent seal coats.
The short answer is that these applications protect the financial investment taxpayers have made in the road, and
protect drivers. Here are the details:
Is it a seal coat or chip seal, and why are we doing it?
These
two processes may differ slightly in a few minor details, but
it’s mostly a difference in semantics. The principle is the same – apply
a protective layer of rock chips and liquid asphalt to the surface of
the road to extend the life of the roadway surface and to provide better
traction for drivers.It also helpsd seal the surface against penetrating moisture.
The ingredients in the two applications and the functions they serve have led many people to use the terms "seal coat" and "chip seal" almost interchangeably. In fact, a hybrid has recently evolved - the "chip seal coat."
It helps to minimize oxidation of the roadway surface. Oxidation causes the surface to dry out and the “pores” to open up to moisture, said Dave Kuisti, ITD southwest Idaho engineering manager.
“During the freeze/thaw cycles, any
moisture allowed into the road will expand and contract, eventually
causing the surface to crack and deteriorate, which in turn leads to
potholes, broken pavement and repairs. The secondary reason for a seal
coat is to create a rough, traction surface for winter driving,” Kuisti
said.
Seal coating begins by applying a layer of
liquid asphalt, then a cover coat of rock chips on the roadway surface.
The highway is rolled and traffic allowed on to the roadway to help pack
the surface. Like most ITD highway projects, the work is done by a
general contractor with ITD inspecting the work to ensure quality
standards are met. Seal coating helps to defer the cost of repairs that
would be required much sooner without the protective application.
Why do we do it, especially over the top of a new, smooth roadway?
Many
homeowners are dismayed when their new, smooth, blacktop road is seal
coated or chip sealed. The smooth surface is covered with tiny rocks,
eliminating many barefoot jaunts to the mailbox and potentially
increasing the road-rash factor for bicyclists, skateboarders or other
recreationists. However, a properly applied seal coat can add several
years of service to a roadway by sealing the surface against weather and
wear.
It is unfortunate timing that the best time to apply the
seal coat is in the heat of the summer, but the primary
benefit for drivers is greater traction when the snow flies several
months later.
The work is done during the day to allow heat to
help asphalt and rock bond more quickly to the roadway surface,
providing a higher-quality finished product.
How can I avoid rock chips in my windshield or paint job?
Before any seal coat is final, crews "broom" or sweep the roadway surface to remove excess gravel. This is usually done multiple times overnight. In addition, following posted speed limits and increasing following distance will reduce the risk of windshield damage caused by loose gravel. Windshield damage is often attributed to the seal coat but it is frequently caused by impatient drivers going too fast, whose tires fling the rocks indiscriminately at other drivers.
Drivers are also reminded to slow down and watch for equipment and workers. In a confined work area, safety is paramount.