Indentations that remain in the mat surface after rolling operations are complete. Most roller marks are removed from the mat surface by finish rolling.
Roller marks may cause an increase in roughness, but by themselves they are not particularly damaging to pavement performance. Roller marks are, however, an indication of inadequate compaction and/or a tender mix.
Causes can be related to compaction, tender mixes or roller operation:
- Inadequate compaction. A mat that is not compacted adequately before it cools to cessation temperature may still contain roller marks.
- Tender mix. A tender mix will generally not be able to support the finish roller’s weight until it has cooled enough to adequately stiffen the mix. By this time, the mix may not be workable enough for the finish roller to remove the breakdown and intermediate roller marks.
- Improper roller operation. Rollers left stationary on a hot mat will tend to sink into the mat with the resulting indentations being difficult to remove. Rollers that are turned quickly may leave a mark as the outside of the leading drum or wheel digs into the fresh mat. Excessively quick stopping can also leave a permanent mark.
Solutions differ depending upon the cause:
- Inadequate compaction. Ensure all compaction is done before the mat cools to cessation temperature.
- Tender mix. Eliminate the causes for tender mixes or develop a compaction sequence and pattern to accommodate the tender mix. Compaction sequence and patterns will depend upon the type of mix tenderness.
- Improper roller operation. Do not let rollers sit stationary on hot mats. Operate rollers at appropriate speeds and avoid sharp turns.