15 May 2001
aggregate and bitumen for the various types of surface treatments. Various other ASTM standards that
are applicable for measuring both bituminous and aggregate quantities are given. The standard lists
recommended grades of various asphalt and tar materials for use with surface treatments. Similar
guidance is also available in the Asphalt Institute publications: ES-11 "Asphalt Surface Treatments-
Specifications" and ES-12 "Asphalt Surface Treatments-Construction Techniques."
(1) Placement. Field construction practices can determine the success or failure of a well-
designed surface treatment; therefore, proper equipment, surface preparation, and construction
techniques are very important.
(2) Equipment. Among the equipment used in placing a surface treatment, the most important
are the asphalt distributor and the aggregate spreader. Aggregate spreaders are used during the
construction of bituminous surface treatments to apply the aggregate to the surface being treated. The
spreader should be designed and calibrated to apply a predetermined amount of aggregate uniformly
over the surface. Some of the aggregate spreaders are self-propelled, while others are propelled by the
truck hauling the aggregate. The self-propelled aggregate spreaders are desirable because they allow
for a more uniform application of material and a smoother operation. Calibration and proper operation of
the distributor and aggregate spreader should be insured.
(3) Surface preparation. Without proper surface preparation the life expectancy of a pavement
will be reduced. Therefore, all soft or failed areas must be repaired and all loose material, dirt, and
vegetation must be removed prior to placing the surface treatment. A bleeding surface may require
either sanding or removal before construction of the surface treatment.
(a) Special attention must be given to the application rates of both binder and aggregate.
Field adjustments to the design application rates may be necessary. Too much binder will cause
bleeding or low skid resistance, and too little binder will result in the loss of cover aggregate. Although
there should be about 5 to 10 percent excess aggregate, too much aggregate will result in a waste of
materials and damage to windshields.
(b) The aggregate must be applied immediately after the binder application in order to
obtain a good bond between asphalt and aggregate. Rolling with a rubber-tired roller immediately after
applying the aggregate will seat the aggregate in the binder and improve the bond.
(a) Since the distributor and aggregate spreader are important for the successful
application of materials, they must be calibrated and checked to insure that the specified application rate
is obtained. ASTM D 2995 offers a method for determining the application rate of asphalt (bituminous)
distributors. In addition, all nozzles should be free and open, the same size, and at the same angle with
reference to the spray bar to produce a uniform fan of asphalt. The height of the spray bar above the
surface is important. A bar too high or too low will produce a variable application in the middle and at
the ends, causing streaking. The height of the spray bar should be such that a double or triple lap of the
spray fan is obtained. ASTM D 5624 offers a method for determining the application rate of aggregate
transversely across the width of the spreader.