Lesson 2/Learning Event 1
formly cover the entire surface of the area. When tack coats are too heavy, they leave a surplus
of asphalt that bleeds into the overlying course. A thin tack coat does no harm to the pavement.
A thin coat will properly bond the courses.
Materials
Tack coat materials may be: (1) a road tar, grade RTCB5-6, RT-6, 7, 8, 9, 10, or 11; (2) an
asphalt cutback such as RC-250, or -800; (3) a diluted emulsion; or (4) an asphalt cement such as
an AP-3 (85-100 penetration) or AP-1 (120-150 penetration).
Quantities to be Applied
Bituminous materials for the tack coat should be applied in quantities not less than 0.05 or more
than 0.25 gallon per square yard. The exact quantity will depend upon the condition of the
surface to be tacked.
Estimation for a Tack Coat
The procedure for estimating the bitumen required for a tack coat is similar to that described for
a prime coat except that the tack coat is applied only over the proposed width of the pavement.
The formulas for a tack coat are:
where;
G = gallons of bitumen
D = drums of bitumen
L = length of treated section in feet
W = width of treated section in feet
ARB = rate of application of bitumen in gallons per square yard
LF = loss factor for bitumen, 5% or 1.05
9 = square feet per square yard conversion factor
53 = gallons per drum
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