Based on the changing material stiffness and density, the roller automatically adjusts output energy of the drum. This is accomplished through a "vectoring" process that manipulates the angle of the drum's energy to produce glancing blows where higher density has already been achieved, and direct blows to the material where soft spots exist. The system essentially ensures that no areas are under-compacted, while also avoiding damage from unnecessary over-compaction.
While the BW190AD-4 AM is designed primarily for achieving optimum compaction on asphalt surfaces, JoB has accomplished what it set out to do by also using the machine to proof-roll road base before paving work begins. "We'll start by running a test strip with the roller to show the density of the existing base and define that we have a solid surface to work on," says Hoffman. "At the very least it gives us a point of reference to come back to, and a foot to stand on, should there be any questions or issues with the road at a later time."
That reference point comes in the form of documentation provided by the Asphalt Manager system, which includes an onboard printer to produce a paper record of the achieved compaction results. Job documentation has always been a critical component of the road construction process for contractors, given the extreme financial burden when they must answer for any failure on a completed road. The best that could previously be expected was a thorough sampling of random density tests from multiple spots on a project. With the equipment now automatically providing documentation for JoB, Hoffman acknowledged feeling far more confident about the company's work.
"Without a doubt the roller has already saved us money," says Hoffman. "Now we can come into a job and immediately determine the reliability of the subgrade. And if it isn't built to standard, we can make the argument with the DOT right away. You can't lay asphalt over a mattress and expect it to hold up."
Having the ability to qualify results is obviously important, but the benefits of getting proper compaction the first time go beyond avoiding penalties and fines. It's also about optimizing the use of time and road materials. Over-compaction can ruin thousands of tons of asphalt and cause a contractor to dedicate man-hours to performing the same task a second time.
"Our jobs run in the vicinity of 20,000 tons of asphalt on average," says Hoffman. "Typically our crews are 9 to 12 men strong and are putting down about 1,200 tons in a day," says Hoffman. "All of that can be lost if you don't know what your roller is doing to the material. The roller that we used previously on overlays is just so big and heavy. It's a great roller, but with some of the Superpave mixes we had a tendency to over-roll and crack the material. That basically amounts to wasted asphalt and a wasted work day."
Getting it right
Hoffman's experiences with jobs where asphalt has been over- or under-rolled have led him to believe that the number of passes isn't what matters. Getting it right is what counts. "Being objective for comparison's sake, I can say that I've seen the 190 complete jobs in fewer passes than other rollers, but I've also seen it take an extra pass," says Hoffman. "But the whole point is that quicker is not always better. There can be quite a bit of density variation in different areas of a project after one pass, and the smart roller will eventually even it out. And that's the reason we bought it — to get proper compaction every time."
The benefits provided by the BW190AD-4 AM have quickly led to the roller becoming the primary asphalt compactor in JoB's fleet. "We use it on both commercial and highway jobs," says Hoffman. "Our operator loves it because the maneuverability is outstanding. He can move along the guardrail and position himself easily. And on top of it all, he can watch the monitors and never have to worry about over-rolling or under-rolling the product.
"You'd think that a complex system would provide some operational challenges, but really the most impressive thing about the roller is its simplicity," adds Hoffman. "Whatever the machine is doing, we don't need to think about it. It just goes out and gets the job done."