TACK COAT
CYRUSTR / SHUTTERSTOCK.COM
A good tack coat provides a uniform,
thin, tacky film without running off the
road or causing slippage between the old
and new pavement surface and is used to
bond layers of asphalt together. Essentially,
it is sprayed at a uniform rate by an asphalt
distributor.
“The benefits include a reduction of
slippage between layers of asphalt and
increased structural strength by bond-ing
separate pavement lifts into one,” said
Janssens. “Slippage can cause delamina-tion,
potholes, wheel path cracking, rutting
and premature failures of pavement.”
Blaine Morien, manager, Technical
Services and Innovation at Pounder
Emulsions (a division of Husky Oil
Operations Limited) in Saskatoon, says
tack coats can also reduce the impact of
freeze/thaw cycles, and when applied to
longitudinal and transverse joints during
construction, can also retard cracking in
those areas.
“Until recently, tack coat emulsions re-mained
relatively unchanged for many
years. With the advent of more sophisticat-ed
paving equipment, higher production
rates and advanced paving mixtures, there
has been much more attention paid to tack
coats, their application and their impor-tance
in achieving pavement performance,”
said Morien.
Janssens says tack coats can be used for
any applications – hot or cold – where ad-hesion
between pavement layers is desired
and the products applied do not have suffi-cient
free binder to wet the existing surface
intimately and ensure maximum bond.
“Tack coats are best used when you have
multiple thin layers of asphalt,” he said.
“The thicker the layers, the less likely they
are to unravel or slip between each other.”
Added Morien, “All asphalt paving proj-ects
are improved through the proper ap-plication
of a tack coat. Thinner surface
courses perhaps benefit the most because
the lateral stress between pavement layers
increases as the thickness of the top layer
decreases. A good bond ensures the pave-ment
layers act as one unified system.”
New products
Ania Anthony is the director, Road
Sciences and Environment, Design and
Innovation Division for the Government of
Saskatchewan’s Ministry of Highways and
Infrastructure, in Saskatoon.
She says tack coats are very important
in ensuring that any newly placed asphalt
bonds to previous layers and that all these
layers act together as one when a heavy
load goes over the road.
“Without a good bond, the layers below
the new asphalt don’t contribute as much
as they could to carrying traffic,” she said.
“Tack coat is the glue that helps the asphalt
layers resist cracking under heavy loads. In
extreme cases, the new layers of asphalt can
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