Breakdown  Rolling

Figure  11-50.—Rolling  a  longitudinal  joint. HOT JOINTS.—  A hot joint is a joint between two lanes of bituminous mix placed at approximately the same  time  by  pavers  working  in  echelon.  This  type  of laydown  produces  the  best  longitudinal  joint,  because both lanes are at, or near, the same temperature when rolled. The material compacts into a single mass under the roller, resulting with little or no difference in density between the two lanes. When you are paving in echelon, the breakdown roller following the lead paver leaves a 3- to 6-inch unrolled edge that the second paver follows. The second paver and roller should stay as close as possible to the first paver to ensure a uniform density is obtained  across  the  joint.  The  roller  following  the second paver compacts the hot joint on its first pass (fig.  11-51). COLD JOINTS.— A cold joint is a joint between two lanes, one of which has cooled overnight or longer before the adjoining lane is placed. Because of the difference  in  temperature  between  the  two  lanes,  there is a difference in density between the two sides of the joint. The longitudinal joint should be rolled directly behind the paver. Breakdown  Rolling Breakdown rolling may be accomplished with static or  vibratory  steel-wheel  rollers.  Breakdown  rolling should start on the low side of the hot bituminous mat, which is usually the outside of the lane being paved, and progress toward the high side. The reason for this is that hot bituminous mixtures tend to migrate towards the low side of the mat under the action of the roller. If rolling is started on the high side, this migration is much more pronounced than if the rolling progresses from the low side.  When  adjoining  lanes  are  placed,  the  same  rolling procedure  should  be  followed,  but  only  after  com- paction  of  the  longitudinal  joint. A  rolling  pattern  that  provides  the  most  uniform coverage of the lane being paved should be used. Rollers vary in width, and a single recommended pattern that applies to all rollers is impractical. For this reason, the best rolling pattern for each roller being used should be worked out and followed to obtain the most uniform compaction across the lane. The rolling pattern not only includes the number of passes but also the location of the first pass, the sequence of succeeding passes, and the overlapping between passes.  Rolling  speed  should  not  exceed  3  mph.  In addition, sharp turns and quick starts or stops are to be avoided. For thin lifts (a lift of less than 2 inches compacted thickness), a recommended rolling pattern for static Figure  11-51.—Rolling  a  hot  longitudinal  joint. 11-27


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