Figure 11-42.Pneumatic-tired roller.
lifts, a smooth drum is all the compaction equipment
required. The smooth drum compacts lifts of- 4 to 8
inches and seals the surface to allow the excess water to
drain. Unlike the sheepsfoot drum, smooth drum rollers
concentrate the full width of the drum. The total
dynamic force is slightly less, because more of the drum
is in contact with the ground.
The pneumatic-tired rollers are widely used for
compaction of subgrades, bases, bituminous mixes, and
many types of material. They have rubber tires instead
of steel tires or drums and generally feature two tandem
axles, with three or four tires on the front axle and four
or five tires on the rear, as shown in figure 11-42. They
are aligned so the rear tires cover the spaces left between
the tracks of the front tires. The tires are mounted in pairs
that can oscillate, or singly with spring action, so tires
can move down into soft spots that would be bridged by
a steel drum. The rubber tires add to their downward
pressure a kneading effect, as material is pressed
toward spaces between the tires.
Pneumatic-tired rollers can be ballasted to adjust the
weight. Depending on size and type, the weight may
vary from 10 to 35 tons. However, more important than
gross weight is the weight per wheel for the material
Figure 11-43.Action of a pneumatic-tired roller.
Pneumatic rollers ballast with water are top
heavy and are very unstable when operating on