Section 18: Brooming Excess Aggregate
Introduction
After the aggregate is spread and rolled, there will be some
loose aggregate. This excess aggregate should be removed to prevent
it from being whipped up by vehicle tires. Loose material may act
to dislodge other aggregate under traffic shear forces.
Timing
The excess aggregate should not be broomed off the roadway
as soon as the rolling is finished. The asphalt is still too soft
and must be allowed to stiffen or cure before brooming. Otherwise,
the broom will strip the aggregate away from the binder. If necessary,
light
brooming
may be performed before opening to traffic to remove excess aggregate
that is not embedded in the asphalt. Final
brooming
should be done as soon as the binder is fully cured: on the same
day or the following morning. Best results are obtained by waiting
until the following morning (as early as possible). Temperatures
are lower during the early hours and the aggregate will be held
more firmly in place with only the excess aggregate removed.Equipment
The only equipment needed is a rotary broom or a vacuum sweeper
for curbed roadways. One or two pickup trucks may accompany the
broom, especially if there is a high volume of traffic. One truck
may lead and the other follows the sweeper as a warning to traffic.
Pickup trucks and sweepers must have appropriate warning devices.
Procedures
The sweeper should begin at the centerline and sweep the aggregate
toward the outside edge of the roadway. It is always best to broom
excess aggregate away from traffic. Regardless of how many passes
are required, the objective is to broom the excess aggregate off
the roadway surface.
Inspection
Ensure that all excess aggregate is removed from the roadway
surface including intersections. Extra brooming may be required
at the transverse joints where aggregate tends to overlap. Care
should be taken to ensure that large quantities of aggregate are
not swept onto adjacent private property. In addition, the operation
should be carefully observed to assure that the sweeper is not dislodging aggregate
that is embedded in the binder. Also ensure that sweeping is performed
safely and with minimum interruption or delay of traffic.