Intelligent Compaction is on a Roll
...job, proponents say. When poor compaction is found underneath graded aggregate or pavement, “$20,000 gets eaten up pretty fast” when you need to remediate, says Dave Dennison, product manager for Kewanee, Ill.-based roller maker Bomag Americas.
Contractors, which tend to overcompact to save face, see IC as a way to increase profits while helping taxpayers save. “If you can compact your embankments right, these roads will last 25 to 30 years longer,” says Dwayne McAninch, chairman of West Des Moines, Iowa-based earthmover McAninch Corp.
Like building codes that embrace performance-based specifications, using IC on civil earthworks poses a twofold dilemma to contracting authorities: First, each roller measures compaction slightly differently using what typically is a patented combination of accelerometers and algorithms. Writing specs that are technology-neutral, so as not to give any supplier an unfair advantage, is tough when every machine is proprietary. Second, DOTs want to see a direct correlation between IC and performance to ensure real-world results are achieved.
“The only reason why we are going to require something like GPS and IC is because we are confident that it is going to produce savings to the taxpayer,” explains Bill Kramer, foundation and soils engineer for the Illinois Dept. of Transportation. Studies to determine those values are under way. One of the largest IC research projects is TPF-5(128), a three-year, $750,000 pooled fund between Georgia, Indiana, Kansas, Maryland, Minnesota, Mississippi, North Dakota, New York, Pennsylvania, Texas, Virginia and Wisconsin. More details are at www.intelligentcompaction.com.
Artificial Intelligence? Bomag’s parent company in Germany began instrumenting rollers in 1983 and claims to be the first to have introduced “intelligence” with its first automatic drum-control mechanism more than 10 years ago. In the last decade, more than half a dozen IC brands have emerged, as well as bolt-on, aftermarket indicators for existing rollers available at a lower price point than a new machine. Controls for cohesive soils, using non-vibratory, padfoot rollers, are emerging as well.
Just what is “intelligent,” however, is still debatable. While more than half a dozen brands provide measurement, only two—Bomag and Case (a North American rebadge of Swiss maker Ammann)—automatically change drum movements in real time. Automatic control partly originated as a way to protect machines and operators: 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 that. 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.
The idea of “true” intelligence “is in its infancy,” he says, and more data needs to be collected. The final report for his 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. “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, he adds, 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.’”