Intelligent Compaction Is on a Roll

...change drum movements in real time. European firms have successfully used sensor-equipped rollers for years, but automatic control is still emerging worldwide. Automatic control, researchers note, partly originated as a way to protect machines and operators by stepping down vibrations as the material became stiffer: Too much vibration causes damage, both to the machine and the subgrade material. It also can throw the operator into an unsafe bounce.

But can the safeguard also be used to measure compaction on the fly? One major, federally funded study costing $600,000 over two years looked at the effects of basic instrumented rollers and the more advanced ones. Researchers concluded that while instrumented rollers improved testing quality and QC/QA, “there is not a lot of data that suggests the current IC algorithms improve compaction,” says Mike Mooney, a professor at Colorado School of Mines, Golden, and the study’s lead researcher.

More work needs to be done to determine what, if any, benefit automatic drum controls could have on compaction quality. The idea of “true” intelligence “is in its infancy,” and more data needs to be collected, says Mooney, noting that his final report for the study, titled National Cooperative Highway Research Program “NCHRP 21-09,” is due this fall.

But if intelligence means giving the operator the means to do a better job, then perhaps IC already has proven itself. The impact of instrumentation empowers what typically is a low-skilled operator with the high-skilled task of performing quality-control checks. “We’ve seen operators change their behavior,” says Terry Rasmussen, a marketing supervisor for Peoria, Ill.-based Caterpillar Inc. and former civil engineer for Illinois DOT. In field trials, the instant feedback is forcing roller operators to “slow down, know when they need their water truck or, in the very least, know when they need a geotechnical engineer or inspector so they can tell them, ‘I’ve got a problem, Houston,’” says Rasmussen.

The operator is just one person on the project team whose work is changing. “Twenty years ago, when I was a DOT inspector, we didn’t trust the nuke gauge,” Rasmussen says. “Today, a lot of engineers, especially the younger people, they don’t know—they use the nuke gauge because they grew up with it.” The future of IC may hold more surprises, White adds, “There are going to be new things we haven’t even thought of.”