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By Steve Wilson
Product Development and Support Manager
BOMAG Americas, Inc.

Sometimes what seems to be a case of simple math will be anything but. Let’s say you walk into a grocery store to buy a can of soup. Brand A costs a dollar and Brand B almost a buck-fifty. Which will you choose?

Not so fast. Read the labels. Brand A may satisfy your appetite, but Brand B comes in a time-saving easy opening can. And Brand B pays you a big bonus rebate for each can you eat. You’ll virtually be making money if you continue to eat soup. Now which will you choose?

At this point, put your grocery cart away and consider buying something that weighs thousands of pounds more than a can of soup — a vibratory roller. Roller A gets the job done. Roller B costs more up front because it’s equipped with a system that measures and controls compaction. Like the cans of soup, the math isn’t as simple as subtracting one price tag from the other. It’s important to look down the road (literally) at what each roller can do and what the final cost will be after putting it to work. Costs such as labor, maintenance, fuel, depreciation and penalties (or bonuses) should be considered when reading the “labels” on a new roller.

Level of Intelligence
Before delving into how an intelligent compaction roller impacts the bottom line, it’s important to understand what makes the system so “smart.” The short explanation is that it answers that previously unanswerable question: How does an operator know that he or she has reached targeted density? Nuclear and non-nuclear testing, along with core samples, have offered a way to check, but besides taking extra time, none of these test methods can give a complete report on the entire work area. Areas still can — and do — fail with time. Many contractors looking for more complete, proven results while using standard rollers will hire a full-time technician to perform “real-time” quality control. Such a position — and the high cost that goes along with it — is not needed with intelligent compaction technology.

With intelligent compaction machines, accelerometers automatically measure material stiffness and, in turn, control the drum’s energy output. At first, when the material is soft, most of the drum’s energy is directed into the work surface at a straight vertical, or up-and-down, angle. As the material is compacted, it stiffens and more energy is reflected back into the drum. The accelerometer reads this reactive response and transmits the information to a cab-mounted microprocessor. As the material approaches optimum density, the microprocessor begins to redirect the energy of the drum, causing it to strike with a glancing blow rather than vertically. Eventually, the drum will vector horizontally to the ground, which will cause little direct impact force. In this position, the drum can still detect areas that may need additional compaction while not over-compacting the remaining areas.

The amplitude remains the same throughout each vector angle. The change in force delivered to the ground comes from the angle of the energy output. Think of pounding a nail into a board. A hammer blow square to the nail head will have the most impact as it drives the nail into the wood. Swinging with the same amount of force from an angle won’t have as much affect on the nail.      

As the roller continues over the surface, the microprocessor measures, controls and calculates the value of the drum’s reaction on the subsoil or asphalt. Additionally, a device on the rear axle records the distance the roller travels. Proof of the compaction and density level achieved can be printed and downloaded to a computer, offering documentation that the work was completed according to specifications.