Performance bonuses may provide all the incentive a contactor needs for more sophisticated equipment.

“I don’t know many people out that can sit on the job all day, every day,” says Ken Dobey, Highway Paving Superintendent, United Companies. “These machines offer you assurance that what you think you’re doing is really what you’re accomplishing.

“All of our state work is on bonus — bonus for density and often for smoothness. There are penalties for not meeting specs. Documentation becomes important in proving what happened. We know we’re getting density with these rollers and we can prove it. When we run these units in automatic, we also tend to get a smoother finish.”

United Companies has had a Bomag BW190AD-4 with Asphalt Manager for two years. The company added a second 190 with Asphalt Manager last year so they could run the machines as tandem breakdown rollers on state highway jobs in Western Colorado. They also have used the rollers on county road work and airport paving jobs.

BOMAG’s Drum Vectoring
One of the keys to Bomag’s Asphalt Manager intelligent compaction system is a microprocessor-controlled manipulation of the front drum’s energy pattern. Values established during sampling and testing at the start of a job can be used by the system to set a density goal, what Bomag calls an EVIB value, which is the dynamic elasticity modulus of the material being compacted. At the start of the compaction process, the soft material is capable of accepting a lot of energy from the roller drum, so the system projects the energy vertically into the material. As compaction progresses, the microprocessor senses the change in material stiffness through the drum’s reaction to it and begins to redirect, or vector, the angle of the drum’s energy to produce more glancing blows. This is accomplished by controlling an exciter system that incorporates counter-rotating eccentric weights to shift compaction force in a defined direction. As the roller works on the material and density builds, the microprocessor continues to vector the output energy, eventually going from fully vertical impact to fully horizontal impact where the drum is skipping back and forth laterally. The material is receiving little added energy at this time, but additional points of density to the goal value are being achieved without over compaction or the damage that can produce. The amount of force the drum produces never changes, but the direction of the force, and thus, the amount of energy absorbed by the material, does change. Asphalt Manager alerts the operator when the goal value has been achieved.

Eliminates guesswork

Intelligent compaction can eliminate guesswork and get the asphalt mat to density with the fewest number of passes, which could mean less time on the job if the process isn’t too difficult to put into practice in the field. How does Asphalt Manager measure up?

”It’s the home run,” says Hoffman. “It’s very simple to operate. It doesn’t take forever to learn what you need to know. You establish a number and then you run with it. It’s not that complicated.

BOMAG’s Asphalt Manager measures material stiffness and redirects drum energy to get proper density.

The number that Asphalt Manager works with is an elasticity modulus, or EVIB value measured in Mega-Newtons per meter squared. Accelerometers on both sides of the front drum constantly measure material stiffness during compaction. This information is fed to an in-line microprocessor that evaluates the data, comparing it to the goal EVIB value. As the material approaches density, the Asphalt Manager system alters the direction of drum energy through a process called vectoring.

Vectoring is a key to the success of the automated process. At the beginning of the compaction cycle, the material can accept a lot of energy, so the microprocessor projects the energy vertically into the material, which would be the normal operation of a vibratory drum roller. As optimum density approaches, the microprocessor senses the change in the material stiffness or density and reduces the energy output to the material by redirecting or vectoring the drum energy to produce more glancing or horizontal blows, which is unique to Asphalt Manager.

BOMAG’s intelligent compaction system includes asphalt mat temperature sensing directly beneath the roller. A microprocessor calculates the reading and delivers it to the operator. The operator can then adjust the distance between the paver and the roller so that compaction takes place at the right temperature. It’s a feature that can alert the operator to potential problems.

“The plant doesn’t always catch a problem right away,” says Dobey. “Say they get into a wet stockpile for several loads. We get a cooler mix. If you have a roller like this one out there, you’re going to know you have an issue right away.”

BOMAG rollers with Asphalt Manager technology employ accelerometers on both sides of the front drum to measure the load-bearing capacity of the material being compacted. A microprocessor optimizes compaction performance to job-set requirements and displays progress toward density (an EVIB value) on the BOMAG Operational Panel (left). The display also gives the operator the current asphalt surface temperature, roller speed, and the effective amplitude being used in either Metric or English units of measurement (Metric shown). An onboard printer (right) documents the entire process including the EVIB value and mat temperature for job-performance record keeping.