Figure 11-52.—Correct rolling pattern.
steel-tired rollers is shown in figure 11-52. The rolling
operation should start from the edge of the hot mat on
the low side with the roller moving forward as close
behind the paver as possible. The second movement of
the roller should be reversed in the same path until the
roller has reached previously compacted material. At
this point align the roller for pass number three, again
staying as close as possible behind the paver. The fourth
movement is a reversal of the third path and a repetition
of the third operation. After the entire width of the hot
mix has been rolled in this fashion, you should swing
the roller back to the low side and repeat the process.
With this pattern, on each forward pass the roller only
needs to overlap the previous rolled area by 3 to 4 inches.
For thick lifts (a lift of 4 inches or more compacted
thickness), the rolling process should start 12 to 15
inches from the lower unsupported edge and progress
towards the center portion of the hot mix. The
uncompacted edge provides initial confinement during
the first pass, thus minimizing lateral movement of the
hot mix. After the central portion of the hot mix has been
rolled and compacted, the compacted portion of the hot
mix will support the roller and allow the edge to be
compacted without lateral movement.
When using steel-wheeled rollers, the operation
should always progress with the drive wheel forward in
the direction of travel. This is especially important in
breakdown rolling. A primary reason that breakdown
rolling should be done with the drive wheel in the
direction of travel is that there is a more direct vertical
load applied by this wheel than by the tiller wheel
(fig. 11-53).
If the breakdown pass of the roller is made with the
tiller wheel forward, the pushing force and the weight
arc slightly ahead of the downward vertical force,
causing material to push up in front of the wheel. The
greater weight of the drive wheel produces the
compaction, while the turning force tends to tuck the hot
mix under the front of the wheel.
There are cxceptions to rolling with the drive wheel
forward. They usually occur when superelevations are
being constructed or if the grade on which the asphalt
mix is being placed is excessive. The exception occurs
when, due to these high grades, the drive wheel of the
roller begins to chatter on the hot mat, causing
displacement of the hot mix resulting with a very rough
Figure 11-53.—Forces acting when tiller wheel or drive wheel
is forward.
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