On many asphalt projects, mat quality determines whether the contractor earns a bonus or incurs a penalty. Any defects in the mat might not only be felt by motorists but contribute to the surface’s premature deterioration.
Asphalt contractors depend on skilled compaction operators and highly reliable compaction machines varying in size and configuration depending on the stage of the compaction process and a given job’s conditions and requirements.
Static or vibratory steel drum rollers follow paving machines, which began the compaction process as they spread and leveled the asphalt mix. Steel drum rollers may feature one, two (tandem) or three drums, with tandem rollers most common. Their roller width typically ranges in size from 35 to 85 inches, 20 to 60 inches in diameter. Machine working weights vary between 1 and 20 tons.
The steel drum rollers make repeated passes in a pattern that minimizes marring from their rollers, driving off the matt and back on, rather than stopping in one place.
Some contractors follow up with pneumatic rollers in a given job’s conditions and type of asphalt mix. A pneumatic roller uses rubber, air-filled tires instead of drums, which are automatically controlled at designated pressures ranging most often from 60 psi to 120 psi to alter their effect. The positions of the tires in the rear row are staggered relative to those in the front row to ensure even coverage. Rather than distribute the machine’s overall weight across a single horizontal line, each tire is a point of contact, increasing density and uniformity of compaction with a kneading action that drives larger aggregate downward in the course, allowing finer grains to rise on top. The goal of using pneumatic-tired rollers is a smoother, longer-lasting surface.
Since hot asphalt sticks to cold rubber, causing tears and imperfections in the mat, the tires are generally not permitted to cool down while in use. Many pneumatic tired rollers feature insulating mats that hang to the ground from the roller’s frame, to prevent the tires from cooling. They are mainly used in finishing work, after steel drums have completed the initial compaction phase.