cover the surface uniformly. After the binder cools and
cures, it should bind the aggregate tightly to prevent
dislodgement by traffic.
Individual aggregate stones
should be pressed into the binder but must not be
covered by the binder. Approximately one half of the
individual aggregate stones should be exposed to traffic.
The ROA for the binder material should be between 0.25
and 0.30 gallon of aspalt per square yard.
For a single-surface treatment, the bitumen must be
heated and applied to the surface while hot. The
aggregate must be spread and rolled before the bitumen
cools. Under no circumstances is traffic permitted to
travel upon uncovered fresh bitumen. The distributor
should NOT apply bitumen until the aggregate is on
hand and ready for application. When the distributor
moves forward to spray the asphalt, the aggregate
spreader should start right behind it. The bitumen
should be covered within 1 minute if possible;
otherwise, the increase in asphalt viscosity may prevent
good binding of aggregate.
Aggregate Application. The size and amount of
aggregate, used for surface treatments, are important.
You must use a size that matches the bitumen application
rate. For a single-surface treatment, one-half inch to
sieve number 4 is needed. The amount of aggregate
should be 25-30 pounds per square yard.
When aggregate is distributed properly, very little
hand work is required.
At longitudinal joints, the
aggregate cover is stopped 8 inches from the edge of the
bitumen to ensure ample overlap of the bitumen coat.
All bare spots should be covered by hand spreading, and
any irregularities of the distribution should be corrected
with hand brooms. Excess aggregate in limited areas
should be removed immediately with square-pointed
shovels. When the aggregate spreader is properly set
and operated, handwork is reduced to a minimum.
Rolling. The aggregate is usually rolled by
pneumatic-tired rollers. Steel-wheeled rollers are not
recommended by themselves. If used, they should make
only one pass (one trip in each direction). The rolling
operation should then be completed with the
pneumatic-tired rolls. Steel-wheeled rollers produce
maximum compaction but must be used with care to
prevent excessive crushing of the aggregate particles.
Also, these rollers will bridge over smaller size particles
and small depressions in the surface and will fail to press
the aggregate in these places in the asphalt.
Faulty rolling can be eliminated or minimized if you
adhere to the following procedures:
1. Rolling should be parallel to the center line of
the roadway to reduce the number of times the roller
must change direction.
2. Succeeding passes should overlap one half of the
wheel width of the roller. This action ensures that the
aggregate becomes well embedded in the bitumen.
3. Rolling should be completed before the bitumen
hardens. This will ensure that the aggregate becomes
well embedded in the bitumen.
4. Succeeding passes should be made from the low
side to the high side of the surface. This operation
maintains the surface crown and prevents feathering at
5. Rolling should be done at a slow speed.
6. Rollers should be only wet enough to prevent
bitumen from sticking to the wheels.
7. The power wheel of the roller should pass over
the unrolled surface before the steering wheel(s) of the
After rolling and curing, the surface is ready for
traffic. When the surface is used as an airfield, excess
aggregate must be swept from the surface to avoid
damage to aircraft. This practice is also recommended
MULTIPLE-SURFACE TREATMENT. A
multiple-surface treatment is essentially the same as the
single-surface treatment. However, the multiple-
surface treatment consists of two or more successive
layers of binder and aggregate.
This type of treatment is done in stages. Each stage
is accomplished in the same manner as a single-surface
treatment. The only difference is that each additional
layer of aggregate should be about one half of the size
of the previous layer. This allows the smaller aggregate
to interlock with the larger aggregate when rolled.
Equipment, used in asphalt pavement construction,
are aggregate spreaders, asphalt distributors and their
associated hand sprayers and spray bars, asphalt kettles,
asphalt haul trucks, and asphalt pavers.
When a spreader is operated properly, it will
conserve aggregate and produce a uniform spread.
Spreaders range from a type attached to a truck tailgate
to a highly efficient self-propelled machine.