PNEUMATIC-TIRED ROLLERS

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 being compacted.

Figure 11-43.-Action of a pneumatic-tired roller.

CAUTION

Pneumatic rollers ballast with water are top heavy and are very unstable when operating on uneven terrain.

Figure 11-44.-Steel-wheeled roller.

Figure _{11-45 .-Drive wheel rolling action.}

Pneumatic-tired rollers may be equipped with 15-, 17-, 20-, or 24-inch tires. Air pressure in the tires may vary for different types of material, such as 50 to 60 psi to finish asphalt and 100 psi to compact a granular subbase. The tires must be inflated to nearly equal pressure with variation not exceeding 5 psi to apply uniform pressure during rolling.

Figure 11-43 shows the action of a pneumatic-tired roller. Pneumatic-tired rollers are used because the individual wheels can exert a kneading action in small areas that wide, rigid steel drums tend to bridge.