Rolling Patterns And Drum-Width-To-Panel-Width RelatIonship
The evolution of double drum vibratory compactors has followed industry needs. Consider this typical application. A paver is laying an HMA panel 12 ft (3.65 m) wide, 3 in. (75 mm) thick. It is being fed by a fleet of haul trucks, delivering sufficient hot mix to the paver to permit 40 ft (12.2 m) per minute continuous speed. In order for any breakdown roller to keep up with this paver, it must be capable of an average rolling speed of 250 ft (76.2 m) per minute when making a five-pass rolling pattern.
To understand how compaction equipment rolling widths have evolved, consider the following examples. For a breakdown roller, there are a number of currently manufactured double drum rollers with rolling widths of approximately 66 in. (1,675 mm), 78 in. (1,980 mm) or 84 in. (2,135 mm) to choose from. The breakdown roller might be any brand of appropriate size and weight. Remember that any compactor’s effective rolling width on the panel may not be the same as its measured drum width.
If a breakdown roller has 66-in. (1,675-mm) wide drums, on most panels its effective drum width is about 10% narrower. Where supported edges require overlap, effective rolling width may be between 60 to 63 in. (1,525 to 1,600 mm) even under the control of the most experienced operators. Therefore, to uniformly cover a paved panel 12 ft (3.65 m) wide, this size roller requires more than two side-by-side effective machine passes to completely cover the paved panel. As depicted in Figures 1, 2, 3, and 4, the center section of the panel is not rolled by the return passes made along left and right sides of the panel. This may require additional rolling through the center of the panel. (By definition, a pass is a roller movement from point A to point B in one direction. Returning to the starting point is a second pass.) The rolling pattern for this compactor is often described as a seven-pass pattern.