Roller Marks In Asphalt & What Can Be DonePosted on June 01, 2010 by Rafael Cantillo
Description of the Roller Tracking Problem
Today I wanted to bring up a problem we have seen a lot in the last few years. Roller tracking is something that typically happens during the compaction process, whether you use a vibratory static steel wheel or pneumatic tire type roller, longitudinal line marks or creases can be left in the surface of the hot mix. Once the hot mix has started to cool to a temperature range of about 70C to 60C (160F to 140F), these marks are typically removed by the finish roller. Roller marks are indentations that remain in the surface of the mix after rolling has been completed. Roller marks may also exist in the asphalt surface when any roller is parked on the hot mat for a period of time or when a vibratory roller is vibrated in place. Particularly when used in the breakdown position, pneumatic tire rollers can leave visible longitudinal marks that can still be seen after the finish rolling has been completed. Vibratory washboard marks may be visible if that roller is operated at an improper vibratory amplitude, speed, or frequency setting by a poorly experienced paving contractors as shown in the picture below.
Roller Mark Causes
Roller marks can be an indicator that the proper number of passes have not been made over the hot mix. If the compaction process is stopped before the required amount of compaction rolling has been finished or if the hot mix cools before the compaction process has been finished, the marks or creases made by the rolling process will remain in the surface of the mix. Roller marks left in an asphalt layer also may indicate of a tender mix. The roller operator will normally be unable to remove all the marks left by the compaction equipment if the mix is tender or unstable. A tender mix usually will not support the weight of the finish roller until it has cooled to the point at which the viscosity of the asphalt cement has increased enough to stiffen the mix. By the time the mix has decreased in temperature to this point, however, the required level of density can generally no longer be achieved because the mix has lost its workability. For this reason, the roller marks or indentations left during the breakdown and intermediate roller passes usually cannot be removed during the finish rolling process. All of the asphalt cement, aggregate, and mix properties that contribute to the formation of a tender mix, as discussed above, also contribute to the in-ability of the finish roller to eliminate roller marks. Hasty paving contractors are typically the cause for this type of mistake.
Solutions For Roller Marks
If the cause of roller marks is in fact inadequate compaction, more roller passes should be made with the break-down, intermediate, or finish rollers to properly compact the mix. The solutions for poor compaction related to mix design deficiencies all involve changes to the mix design and to the production of the mix at your asphalt plant. Asphalt cement quality and content, aggregate properties, and characteristics, as well as mix temperature, all play a significant role in the workability and long term stability of the asphalt materials under the compaction roller equipment. Roller marks normally cannot be removed from a tender mix until the mix temperature has lowered to a relatively low level usually less than 70C (160F). Sometimes it is possible, depending on environmental conditions and the properties of the mix, to remove roller crease marks left in the hot mix by using pneumatic tire rollers. If the surface of the mix is hot enough ie 60C (140F) or more, many passes with a pneumatic tire roller can be made to “iron out” the surface of the pavement. Finally, roughness or wash boarding caused by incorrect operation of a vibratory roller should be eliminated by using proper operating techniques with this equipment.
Effects on Performance
Roller marks are normally an indication that the proper level of compaction has not been achieved. In terms of ultimate pavement durability, the air void content or density of the mix is the single most important characteristic that governs the performance of the asphalt mixture under traffic. If the air void content of a dense graded mix is high -- the density is too low--the pavement generally will not perform well under traffic.
About Empire Parking Lot Services
Empire-PLS is one of Southern California best asphalt contractors. We are located in Orange County and service the entire Southern California area. Please call Empire today to discuss your project. Empire offers asphalt repair, concrete repair, seal coating, line painting and many other parking lot maintenance related services to Southern California. Empire can be reached toll free at 877-760-2757 or you can visit our main website at www.empirepls.com information from this blog has been paraphrased by the us army corp of engineers. Please feel free to discuss this and any subject that you have in relation to asphalt repair and maintenance.