Covering miles at a stretch, the paving train consisted of a Barber-Greene windrow machine, a Cat paver, HYPAC pneumatic-tired intermediate and tandem drum vibratory finish rollers and a BOMAG BW190AD-4 breakdown roller with Asphalt Manager, a unique intelligent compaction system.
The new Asphalt Manager compaction system helps to automate the compaction process and is part of a growing trend in roller technology. The intelligent compaction system not only senses but automatically reacts to the stiffness, or density, of the material being compacted.
This “intelligent” roller employs accelerometers to measure the horizontal and vertical reaction of the drum in correlation to the material it’s compacting. Once the system senses an increase in the mat’s density, it automatically adjusts the roller’s compaction output by vectoring, or redirecting, the drum’s energy, which helps to avoid over-compaction.
When the roller encounters fresh, uncompacted asphalt, the drum’s vibration angle is at a straight up-and-down trajectory, which exerts maximum compaction energy into the mat. As rolling progresses and density increases, Asphalt Manager automatically changes the direction of the vibration, vectoring the drum from full vertical to eventually full horizontal vibration upon approaching optimum density.
“Throughout the process, amplitude remains constant and only the vibration angle of the drum changes,” explains Steve Wilson, manager, marketing services/product manager for BOMAG Americas Inc. “When the drum vibrates horizontally, minimal vibration is exerted on the mat but additional density points are achieved.”
Dobey adds a side benefit to the back-and-forth drum motion. “When we have time to work the mat in full horizontal vibration, we seem to achieve a smoother ride and better profilograph readings.”
At first, United ran the BW190AD-4 as the intermediate roller during test strip evaluations. “Our initial goal was to run the BOMAG in horizontal vibration mode to meet the compaction densities at the joint,” explains Dobey. “It did such a good job, that we had to be careful not to over-compact the mat with our finish roller.”
While the roller easily achieved joint specs, Dobey’s crew discovered the mix had a tender zone that required compaction with a pneumatic-tired roller. “The tender zone is between 180 to 200 degrees F, right when we need to have the intermediate roller on it,” says Dobey.
So Dobey inserted a HYPAC C530AH pneumatic-tired roller as the intermediate roller to get the manipulation and kneading effect the paving crew wanted to achieve with the desired mat quality. This move did not sideline the BOMAG roller. Rather it enabled United to reap the full benefits of the Asphalt Manager system by using it as the breakdown roller.
While the BW190AD-4 had the finesse to maximize joint densities, it also had the power to quickly compact the mat, nearly reaching spec densities during breakdown.
“Density readings behind the BOMAG are 90 to 91 percent,” says Dobey. “We are very happy with these numbers.”
The roller operator set Asphalt Manager to full automatic, which unleashed the front drum’s 55,575 pounds of centrifugal force on the mat. As with any roller, the higher the centrifugal force, the deeper the lifts the drum can compact. On Highways 141 and 145, this high compaction energy allowed the two-inch overlay to be quickly compacted to desired densities.
The breakdown pattern with the new roller included five passes. Only two passes on the edges were made with vibration, and vibration was on for the pass towards the paver and off while rolling away. In full automatic mode, Asphalt Manager vectored vibration angle away from the full vertical position as density increased. “This BOMAG is a hard pounding roller,” comments Dobey.
With this intelligent compaction system, it’s not just operator experience that determines if the roller is achieving optimum densities. Asphalt Manager assists the operator by displaying the changing vibration output values on the cab-mounted microprocessor.
The system also features an on-board printer that provides documentation of jobsite results. “Asphalt Manager gives contractors written proof of the compaction results,” says Wilson. “It’s not just in one spot like with core samples or nuclear gauges but every inch of the mat that the roller covers.”
But for Dobey’s crew, the roller’s versatility is a key component to United’s success on Highways 141 and 145. With the unique compaction management system, the BW190AD-4 could be manually set to full horizontal vibration for working joint density or left in automatic vibration mode to quickly achieve breakdown rolling density goals.
Dobey sums up the roller this way. “The BW190 gives us more options for getting the job done.”