• It should be as uniform in size as is economical.
Generally, the largest particles should be no more
than twice the size of the smallest particles.
• Aggregates that are one-half inch (13 mm) or less
provide a quieter, smoother road surface. Larger
aggregate provides a more skid-resistant surface but
creates more noise, so it is generally used in non-
populated areas.
• The best aggregate shape is cubical. Flat or
elongated shapes may be completely buried in the
asphalt needed to hold the cubical-shaped aggregate.
The fewer at or elongated shapes in the aggregate,
the better.
• Aggregate must be clean. Coatings of dust, silt or
clay prevent adhesion to the asphalt and interfere with
uniform spreading. Both problems will lessen the life
of the surface treatment.
• Aggregate should also be damp for emulsion use
but dry and warm when using hot binders for better
adherence to the asphalt. Surface treatments are
best applied when the temperature is 50°F (10°C) or
above. The surface being treated should also be dry
and warm.
• Asphalt emulsions for surface treatments and seal
coats are either anionic or cationic, which refers to the
electrical charges surrounding the asphalt particles.
Cationic emulsions have a positive electrical charge
while anionic emulsions have a negative electrical
charge. Cationic emulsions set more quickly in high
humidity or cooler weather, while anionic emulsions
work well in low humidity or warm weather conditions.
Consider the availability of suitable liquid asphalts, and
their electrical charge, before selecting aggregate:
• Anionic emulsions with a negative (-) charge
on the asphalt droplets perform best with
aggregates that have positive (+) surface
charges (such as limestone and dolomite).
• Cationic emulsions with a positive (+) charge
on the asphalt droplets perform best with
aggregates that have negative (-) surface
charges (such as siliceous or granite
aggregates).
Chip Seal Tips
The sequence of chip seal construction is surface
preparation, binder application, aggregate spreading,
rolling (compaction) and sweeping. The following tips
will ensure a successful chip-sealed surface treatment:
• Be sure to have all the aggregate on hand before
starting the surface treatment.
• Follow the asphalt distributor truck closely as the
best results are obtained when spreading aggregate
onto the liquid asphalt within 30 seconds. The chip
spreader should be no more than 100 feet (30 meters)
behind the distributor truck. To see the full line of
Rosco asphalt distributors, visit http://www.leeboy.
com/rosco/products/asphalt-distributors.
• Spread aggregate evenly within 30 seconds of the
asphalt binder application for proper adherence to the
binder. Excess particles can loosen from the adhered
aggregate by trafî›™c and possibly damage vehicles.
• Chip-sealed surfaces are then compacted. Rollers
should follow the aggregate spreading by no more
than 500 feet and should not be operated more than
6 mph (10 kph). Pneumatic-tired rollers, such as the
Rosco Tru-Pac 915, provide even pressure to all
particles with slight depressions in the surface. Steel-
drum rollers crush softer particles and degrade the
surface. For more information, visit www.leeboy.com/
rosco/products/compaction.
• Light sweeping should also be done to clean the
surface of excess aggregate before trafc ow is
restored. Be sure the asphalt surface has had time
to set and bond before sweeping (early morning is
a good time to sweep the surface treated the day
before). To see the full line of Rosco brooms, visit
www.leeboy.com/rosco/products/brooms.
• Refer to Page 4-24 for troubleshooting chip seal
problems.
4
Operation
Rosco CSV Variable Width Chip Spreader 4-17
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