Figure 11-52.—Correct rolling pattern.steel-tired rollers is shown in figure 11-52. The rollingoperation should start from the edge of the hot mat onthe low side with the roller moving forward as closebehind the paver as possible. The second movement ofthe roller should be reversed in the same path until theroller has reached previously compacted material. Atthis point align the roller for pass number three, againstaying as close as possible behind the paver. The fourthmovement is a reversal of the third path and a repetitionof the third operation. After the entire width of the hotmix has been rolled in this fashion, you should swingthe roller back to the low side and repeat the process.With this pattern, on each forward pass the roller onlyneeds to overlap the previous rolled area by 3 to 4 inches.For thick lifts (a lift of 4 inches or more compactedthickness), the rolling process should start 12 to 15inches from the lower unsupported edge and progresstowards the center portion of the hot mix. Theuncompacted edge provides initial confinement duringthe first pass, thus minimizing lateral movement of thehot mix. After the central portion of the hot mix has beenrolled and compacted, the compacted portion of the hotmix will support the roller and allow the edge to becompacted without lateral movement.When using steel-wheeled rollers, the operationshould always progress with the drive wheel forward inthe direction of travel. This is especially important inbreakdown rolling. A primary reason that breakdownrolling should be done with the drive wheel in thedirection of travel is that there is a more direct verticalload applied by this wheel than by the tiller wheel(fig. 11-53).If the breakdown pass of the roller is made with thetiller wheel forward, the pushing force and the weightarc slightly ahead of the downward vertical force,causing material to push up in front of the wheel. Thegreater weight of the drive wheel produces thecompaction, while the turning force tends to tuck the hotmix under the front of the wheel.There are cxceptions to rolling with the drive wheelforward. They usually occur when superelevations arebeing constructed or if the grade on which the asphaltmix is being placed is excessive. The exception occurswhen, due to these high grades, the drive wheel of theroller begins to chatter on the hot mat, causingdisplacement of the hot mix resulting with a very roughFigure 11-53.—Forces acting when tiller wheel or drive wheelis forward.11-28
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business