How does it fit into the paving business?
By Jeff Winke
For many asphalt paving companies, the old Big Joe Turner tune made famous by Bill Haley & His Comets in the 1950’s could be updated to more aptly reflect current compaction roller practices. Bear this out… if “Shake, Rattle and Roll” can be emblematic of vibratory compactor rollers, then “Shake, Rattle, Oscillate and Roll” may be the new tune.
Oscillation technology for drum compaction paving rollers was introduced in Germany in 1983 as a solution to over compaction. That’s a good 30 years after teens were dancing to Bill Haley at sock hops.
Compactors with oscillation drum rollers were initially developed to provide faster, more effective compaction. Tandem rollers with one vibrating drum in the front and an oscillation drum in the rear, achieve at least the same degree of compaction as double vibrating drum rollers, but with fewer passes.
“Oscillating drums are traditionally activated by two exciters which are timed to rotate at exactly 180 degrees offset, which causes the drum to ‘oscillate,’ or to rock back and forth,” said Bert Erdmann,
product manager for heavy compaction,
BOMAG Americas, Inc., Ridgeway, S.C. “Compactors with oscillating drums are best used where standard vibrating drums are either not beneficial or permitted. Oscillating drums are also more effective than rolling in static mode, without any vibration at all. Oscillating compactors are ideal for finish rolling, joint compaction, and rolling on bridges or near buildings and structures.”
Drum roller oscillation is said to improve compaction results.
“Oscillation is achieved through a rapid forward/backward motion of the drum, which differs from standard vibratory rollers in that the oscillation drum stays in contact with the surface at all times,” stated Jeremy Dulak, product and marketing manager, CASE Construction Equipment, Racine, Wis. “Additionally, the dynamic force being applied to the substrate is on an angle—not vertical like you would get with standard vibration. This significantly reduces the potential for over-compaction and provides a smoother finish with fewer passes.”
There are productivity advantages to using asphalt compactors with oscillation drum rollers.
Vijay Palanisamy, director of product marketing and communications, for Dynapac North America LLC, Fort Mill, S.C. described five:
1. Able to compact faster and reach better density results closer to buildings, where traditional vibration rollers might affect the structures.
2. Able to compact faster and reach better density results at bridge decks, where traditional vibration rollers are not permitted in vibration mode.
3. Can extend the compaction time when working with special asphalt mix designs or in colder climates.
4. Improves density results especially on longitudinal joints when paving adjacent to existing pavement.
5. Effective in thin lift paving applications with smaller aggregate sizes. The oscillation roller could help by not crushing the material, which can be an issue with high-amplitude vibratory compaction.
The expectation is that the more even and high-quality the asphalt compaction is, the more durable and long-lasting the pavement will be. More asphalt paving projects, especially road projects, are being tendered with demands for detailed, comprehensive compaction measurement.
“There are ways to measure, monitor, document and control compaction and compaction processes,” stated Matt Graves, director of marketing, for Wirtgen America, Antioch, Tenn., which offers HAMM compaction equipment. “There are technologies that use a GNSS receiver to continuously determine the position of the rollers and combines this data with the measured values that have been collected. A panel PC with a touchscreen in the operator’s platform then displays all the data in a single package in the form of a real-time ‘compaction map’ – this includes additional parameters such as current speed, amplitude and frequency, as well as process data such as the number of passes, asphalt temperature and stiffness value.”
In comparison to other methods, compactors with oscillation drum rollers have a place and serve a distinct role.
“Standard vibration has the best/most effective compaction force,” stated Erdmann. “The higher the vibration amplitude and the static linear load of a roller the higher the compactive force.
“For breakdown compaction and hard to compact materials, standard vibration is more suitable then oscillation. Oscillation is considered to be ‘gentle compaction,’ since it does not impact the material. It makes it ideal for joint compaction, because the drum won’t ‘bounce’ off the cold mat while compacting the hot mat. In a sense, the oscillating motion manipulates the material and sort of pushes the asphalt into place and reduces air voids.”
Erdmann continued: “The same is true for finish rolling; since the oscillating drum won’t ‘bounce’ on the cooling hot asphalt mat, it can’t break the aggregate and yet achieve additional density as long as the material is still pliable enough. Static steel drum rollers are becoming more and more a thing of the past. Usually, static rollers were used in applications where standard vibration could no longer be used. Oscillation and horizontally directed vibration have additional benefits over static rolling, since the material manipulation has a positive side effect of sealing the asphalt finish. This is probably the reason for the trend why oscillating rollers are more and more replacing static steel drum rollers.”
Think about it, oscillation is a non-vertical force that applies compaction energy without impact. In other words, there is no up-and-down vibration movement. The drum stays in contact with the surface, and there are no repeated impacts to the surface for compaction. The technology creates horizontal motion only. This provides more compaction force than static rolling, but less force than traditional vibration.
The needs of the compaction project will dictate the best solution.
“It really comes down to the application and/or the needs of the job,” Dulak stated. “Vibratory rollers have a high vertical compaction force that penetrates deeper in the substrate. Oscillating rollers are designed to reduce amplitude—this provides the compaction and finish desired, while minimizing potentially damaging vibratory forces to the mat or any nearby structures.”
Mat temperature will also be a factor.
“As rule of thumb compaction mat temperatures will vary depending on the material but are usually between 200- and 280-degreesF, from start to finish,” Palanisamy said. “With oscillation rollers, matt temperatures can be as low as 150-degreesF.”
In addition to advantages in close proximity to structures, addressing longitudinal pavement joints, and on bridge decks, oscillation compaction is said to be good for achieving target densities with special mix designs where vibratory compaction doesn’t yield the desired results and when pushing production into the colder seasons where compaction is needed.
Areas the paving contractor needs to be aware of with oscillation drum rollers is the wear life of the oscillation drum and regular maintenance.
“Oscillation rollers feature a thinner drum for the oscillation to create the back and forth movement–which raises the question of how long the drum will last,” stated Palanisamy. “Contractors are advised to work with manufacturers who have the best drum material that prolongs the wear life and also the best extended warranty protection, in case of early wear or unanticipated failure.
“Additionally, contractors should consider how easy routine maintenance can be performed. For instance, can the belts that drive the eccentric weights be changed out in the field or does the machine need to be brought into the shop for service? Maintenance needs can have a direct impact on uptime.”
In summary, oscillatory compaction systems can be used on all phases of the compaction process. It delivers the best results on thin asphalt layers – less than 2-inches, compaction of materials with sensitive substructure or next to buildings, or on bridge decks or overpasses. In addition to excelling in urban city vibration sensitive areas, asphalt roller oscillation succeeds with joint compaction, such as longitudinal joints, where it prevents damage to existing pavements while pressing the joint between lanes tightly, and transverse joints, where its massaging action creates a tighter joint.
Oscillation compaction truly holds a respected place in the asphalt paving contractor’s arsenal of productive tools.
Jeff Winke is a business and construction writer based in Milwaukee, Wisconsin. He can be reached through email@example.com