Rosco CSV - Aggregate Selection

Road preparation before the chip seal work is essential
to producing a uniform surface. The surface should
be well prepared with only minor defects that can be
corrected by the chip seal. Before chip spreading,
perform the following for the best results:
• Repair all holes and depressions.
• Fill and seal cracks.
• Level any pavement bumps and ruts.
• Remove any excess asphalt on patches and joints.
• Clean the full width of the surface to be treated.
NOTE: Patching materials and crack sealants
need time to cure before placing the chip
seal. Whenever possible complete surface
patching well in advance before applying
the chip seal.
Figure 4-23. Chip Spreader Following Binder Truck
There are basically three types of asphalt aggregate
surface treatments used for chip spreading:
• Single-Surface Treatment: This type of treatment
seals minor cracks, prevents wear and aids in
waterproong a surface. It involves a single pass of
sprayed asphalt followed at once by a single layer of
aggregate.
• Multiple-Surface Treatment: This treatment
provides greater surface protection against both
trafc wear and weather. It is made by using two
or more alternating layers of liquid asphalt and
aggregate. Each succeeding layer of aggregate
should be no more than one-half the size of the
aggregate in the preceding layer and sweeping
should be done between applications.
• Sand Seal: This treatment is used to provide a tight
seal against the weather and makes the surface more
skid-resistant. Its construction is similar to a the
single-surface treatment.
Aggregate Selection
Before operating the chip spreader, it is important to
select and understand the compatible sealant and
aggregate materials needed for the job and how they
react with each other. Aggregate (chip rock) selection is
critical for determining which sealant to use, depending
upon the construction project. Aggregate should be
clean, durable and skid-resistant. Larger aggregate is
generally more durable and results in a thicker binder
level. However, if not properly embedded, it can cause
damage to vehicles immediately after application.
Figure 4-24. Aggregate Moving from Conveyor into
Spread Hopper
There are basically three types of asphalt aggregate
surface treatments used for chip spreading:
• Single-Surface Treatment: This type of treatment
seals minor cracks, prevents wear and aids in
waterproong a surface. It involves a single pass of
sprayed asphalt followed at once by a single layer of
aggregate.
• Multiple-Surface Treatment: This treatment provides
greater surface protection against both trafc
wear and weather. It is made by using two or more
alternating layers of liquid asphalt and aggregate.
Each succeeding layer of aggregate should be
no more than one-half the size of the aggregate in
the preceding layer and sweeping should be done
between applications.
• Sand Seal: This treatment is used to provide a tight
seal against the weather and makes the surface more
skid-resistant. Its construction is similar to a the
single-surface treatment.
Most hard aggregates can be used for chip spreading.
Aggregate should meet the following requirements:
Operation
Rosco CSV Variable Width Chip Spreader4-16