The Rolling Train
Regardless of the job specifics, rolling trains typically consist of breakdown rollers, intermediate rollers and finish rollers. Though the rolling stages may remain the same, it's the details of each of these rollers and how they work with a particular material that requires additional attention to form a proper rolling pattern. Fortunately, crew foremen can simply look back to previous jobs and determine what rollers will work best based on their knowledge and experience with similar mix types. But even with this experience, the remaining variables are too difficult and risky to guesstimate, and a test strip should be used to verify results.

The first roller used in a test strip on a mainline paving operation is the breakdown roller. Typically a double-drum vibratory roller, the breakdown unit immediately follows the paver and works the mat when temperatures range between 270 to 300 degrees Fahrenheit. There are several variables that influence the performance of a breakdown roller including drum width, vibratory frequency, amplitude and overall centrifugal force. Additionally, depending on the application, multiple breakdown rollers may be utilized. Because 90- to 95-percent of compaction should be attained during the breakdown stage, it is of utmost importance that an effective rolling pattern is developed with this equipment.