Asphalt Breakdown & Rolling Methods

Method for Thin Lifts

• Lift refers to the thickness of the bituminous layer. Breakdown rolling for thin lifts begins, as is standard, at the mat's edge on the low side of the pavement. The roller then slowly moves forward, following the paver as closely as permitted. Next, the roller reverses along the path it has just passed until it reaches its point of origin. It then repeats this forward-reverse motion by section until the entire width of the mat is covered, after which it goes back to the low side and repeats the whole process. Each section the roller passes over overlaps 3 to 4 inches, ensuring total coverage.

Method for Thick Lifts

• Unlike the procedure for thin lifts, breakdown rolling for thicker layers begins not at the very edge of the low side, but about 12 to 15 inches from the edge. Passes are similar, with the roller moving in a series of forward-reverse motions until it covers the entire width of the mat. With each succeeding pass, the roller progresses further toward the edges. Compaction of the mat's edges is put off until the end to provide confinement for the bitumen, particularly during the first pass. This confinement reduces the amount of lateral movement in the as-yet-uncompressed mix.

Method for Transverse Joints

• A common sight during emergency road repairs, transverse joints are used in instances when paving cannot be performed without interruptions, most often due to traffic. Interruptions exceeding 15 minutes require the construction of transverse joints. Ideally, rollers compact transverse joints transversely, hence the name. However, breakdown rolling may be done longitudinally when necessary, provided that the new mix has enough elevation above the old mix on the cooler side. Uneven joints require immediate scarification and re-rolling to prevent pronounced bumps in the pavement.

Procedure for Longitudinal Joints

• Longitudinal joints run parallel to the direction of traffic. By far the biggest concern in the construction of a longitudinal joint is ensuring nearly-equal density in the cold (previously-paved) lane and the hot (new) lane. The paver deposits the mix adjacent to the joint in a proportion that results in maximum compaction along the joint. As with standard procedures, the roller follows the paver as closely as possible. Rolling begins at the cold side to "pinch" the joint. During breakdown rolling, care is taken to ensure that the hot lane overlaps the cold lane by about 6 inches.