cutbacks are highly flammable, safety precautions must
be carefully followed.
A tack coat should be applied only when the surface
to be tacked is dry; and the atmospheric temperature has
not been below 35°F for 12 hours immediately before
application.
Before applying the tack coat to a surface that is
sufficiently bonded, ensure that all loose material, dirt,
clay, or other objectionable materials are removed from
the surface to be treated.
This operation may be
accomplished with a power broom or blower,
supplemented with hand brooms if necessary.
Immediately following the preparation of the
surface, the bituminous material should be uniformly
applied by means of a bituminous (asphalt) distributor
at the spraying temperature specified. The amount of
bitumen application, known as rate of application
(ROA), for a tack coat should be applied in quantities
not less than 0.05 or more than 0.25 gallon per square
yard. The exact quantity varies with the condition of the
existing pavement being tack-coated. Normally, the
construction project specification denotes the ROA for
the tack coat application; however, when the ROA is not
included in the project specifications, the NCF uses an
ROA of .15 for planning and estimating purposes.
Following the application of bituminous material,
the surface should be allowed to dry until it is in a proper
condition of tackiness to receive the surface course;
otherwise, the volatile substances may act as a lubricant
and prevent bonding with the wearing surface. Clean,
dry sand should be spread on all areas that show an
excess of bitumen to blot up and cure the excess
effectively. After excess bitumen is set, any loose sand
should be lightly broomed from the primed surface
before the wearing surface is laid.
An existing surface that is to be covered by a
bituminous wearing surface should be barricaded to
prevent traffic from carrying dust or mud onto the
surface, either before or after the tack coat is applied.
Should it become necessary for traffic to use the surface,
one lane may be tack-coated and paved, using the other
lane as a traffic bypass. The bypass lane should be
primed and sanded before it is opened to traffic and it
should be swept and reprimed after the adjacent lane is
completed. Doing this preserves the base and acts as a
The formula for a tack coat estimate is as follows:
16-8
Where
ROA =
L =
W =
9
=
WF =
Example:
rate of application of bitumen in gallons
per square yard
length of treated section in feet
width of treated surface in feet
square feet per yard conversion factor
Waste Factor of bitumen = 5% at .05 or
10% at .10. This will depend on the
experience of the asphalt distributor
truck crew.
The specification and other data for a
tack coat application are as follows:
L =
2 miles= 2 x 5280= 10560 feet
W = 12 feet
ROA = 0.5 gal/sq yd
WF = 5% or .05
Calculate the number of gallons of bitumen
necessary to spray a tack coat.
dust palliative (shelter.)