Intelligent Compaction Is on a Roll

Smart machines pose a radical change in project delivery and could save taxpayers $100 billion a year in infrastructure costs

By Tudor Van Hampton

Researchers test a ‘smart roller.’ (Photo: Courtesy of Iowa State University.)

Nationwide research is firming up the case for “intelligent” compaction, or IC, a construction method three decades in the making that could save billions of dollars a year in potholed roads, cracked bridges, broken dams and blown-out tires. But as it represents a huge cultural shift in project delivery, the industry is struggling to find a standard way to roll it out.

David White, a professor at Iowa State University, Ames, and director of the school’s Earthworks Engineering Research Center, estimates that the stiffness of soil, sand and aggregate—the building blocks of road embankments, building pads and bridge abutments—cost the public up to $100 billion a year due to poor construction.

“There is something like $50 billion a year for vehicle maintenance because of poor road conditions,” he says. “Those poor road conditions are tied to what they are sitting on.” At the very least, improper compaction costs taxpayers $1 billion a year in wasted diesel fuel, construction labor, equipment maintenance, rework, rehabilitation, litigation and other inefficiencies.

advertisement

IC in its simplest form is an onboard measuring device that shows roller operators whether they are overcompacting, undercompacting or right on target in soil, aggregate and asphalt. Some machines go another step by automatically changing frequency, amplitude or other characteristics of the drum. How users define “intelligence” is still up for debate, but the construction industry is investing millions of dollars to validate IC.

Government agencies are working to write specifications so they can let contracts enabling IC. So far, Minnesota is the only state to do so, though its specification is still under regular revision and is careful not to mandate IC due to the high up-front cost to contractors.

Louder Drumbeats Originally pioneered and adopted in Europe, IC recently has grown out of automated machine guidance, or AMG, which grew out of the increased use of the Global Positioning System in the U.S.

IC puts roller operators directly in charge of ground control, enabling them to inspect their own work before turning it over to the owner for verification and payment. The increasing use of IC onexperimental highway projects over the past five years is steadily giving state departments of transportation more confidence the technology can cut construction waste and extend the life of roads and other infrastructure. Though IC likely will not render traditional inspection instruments, such as the nuclear-density gauge, obsolete, IC is in a position to grow as a 21st-century quality-control/quality-assurance tool.

So far, smart compaction machinery is turning out to be excellent for “proof” rolling, engineers say. “We are trying to measure and predict how [roads] will behave when a truck runs over the material,” explains John Siekmeier, a senior research engineer for the Minnesota Dept. of Transportation. “The roller is really a better simulation of how well that material will behave over the long term, over the itty-bitty, nuclear-density gauge.”

The instrumented rollers cost about 20% more than their non-instrumented counterparts but can pay off in the first 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-based earthmover McAninch Corp.

Three rollers face off in a field trial. Such tests across the U.S. are under way, focusing on evaluating the benefits of “intelligent” rollers, often pitting brands against each other. (Photo: Iowa State University.)

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 Illinois DOT. 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.

Some engineers believe a machine is not truly intelligent unless it can operate automatically without input from the operator to improve compaction quality. (Photo: Courtesy of Iowa State University.)

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 change 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.’”