To illustrate the intelligent-compaction (IC) roller’s potential to increase production, Kevin Garcia—road and paving construction segment manager for Trimble Navigation—relates an experiment Trimble conducted when testing one of its IC systems:
“On a highway paving job, we covered the monitor for the roller’s IC system, then asked a seasoned operator to go about his job. He covered 316,000 square feet in 21 hours and made from two to 13 passes over any given area. With the cover removed, and using the system’s pass-counting function, the operator covered 380,000 square feet in 18 hours. The paver stopped only once for the roller to catch up, but had to stop four times when the monitor was covered.”
Cost of Ownership
Size (metric ton)
to 1.7 $27,575 $14.07 1.8-2.9 $45,214 $23.94 3.0-4.9 $61,985 $32.10 5.0-7.9 $145,788 $66.88 8.0-11.2 $162,490 $76.62 11.3 & above $207,252 $92.67
Size (metric ton)
to 2.9 $57,895 $24.69 3.0-4.9 $84,175 $32.20 5.0-7.9 $128,323 $46.24 8.0-11.9 $151,024 $56.64 12.0-14.9 $187,800 $68.71 15.0 & above $233.176 $82.90
*Hourly rate represents the monthly ownership costs divided by 176, plus operating cost. Unit prices used in this calculation: diesel fuel, $3.46 per gallon; mechanic’s wage at $52.33 per hour; and money costs at 2.125 percent.
The increased production, says Garcia, resulted from the roller operator being able to graphically monitor the number of passes made over a given area; when the set number of passes—determined by a pre-job test strip—were completed, he immediately moved on.
Proponents of intelligent compaction say that the technology’s essential value is its ability to bring improved consistency to the compaction process, whether soil or asphalt, by providing a means for exercising continuous quality control over virtually every square foot of the project. Without IC, quality control relies on taking a limited number of nuclear-gauge readings or asphalt corings and then inferring compaction quality for large areas from those few spot checks.
Also, say proponents, the technology allows proof- rolling base materials to find and correct weak spots before paving, thus avoiding costly rework.
Defining Intelligent Compaction
Intelligent compaction has been on the industry’s radar for two decades or more, and though IC rollers are widely accepted in Europe, they have been slow catching on in the U.S. market. Interest here is increasing, however, as more state DOTs specify IC rollers in bids.
According to www.intelligentcompaction.com (a helpful website for learning about IC), 23 states now include specifications for IC machines—either asphalt or soil, or both. Specifications range from two pages to nearly 30 pages, depending on the state, but all address to some degree the capabilities expected of the IC roller.
Most specifications require that the roller be able to evaluate its compaction effort and that a satellite-based positioning system provide mapping for pass counts, compaction levels, and, in asphalt applications, temperature. This information is to be available in real time for the operator on a color-coded in-cab monitor and is also to be stored for later documentation and analysis using Veda software, defined on the above website as a “map-based tool for viewing and analyzing geospatial data.” Veda, says the website, is “currently funded by the MnDOT [Minnesota DOT].”
Trimble’s Garcia notes further that some IC systems are compatible with total-station-based positioning systems, allowing use of IC technology in areas where satellite coverage is hindered, such as urban areas with tall buildings.
Katie Pullen, brand marketing manager, Case Construction Equipment, reminds roller buyers that the term “intelligent compaction” today covers a broad range of technology, from simple meters that use LED-light displays to indicate a material’s degree of compaction, to systems providing recommended settings for the roller as it works against a pre-determined compaction benchmark. More advanced systems, says Pullen, can adjust drum force in relation to a target compaction level, which typically is identified as a compaction measurement value (CMV) or ICMV, the “I” for intelligent.
ICMV versus density
The ICMV is basically a measure of a material’s load-bearing capacity—its resistance to deformation under load—or, in short, its “stiffness.” By comparison, “density” is a measure of a material’s air-void content—the fewer the air voids, the greater the density—and this measurement typically is among a state DOT’s primary evaluators of job quality. (Some suggest that stiffness is a better indicator of compaction quality than density.)
On most rollers, the ICMV is determined by an accelerometer, a sensor that measures the travel of a vibrating drum as it rebounds from material being compacted—the stiffer the material, the greater the rebound. The resulting electronic signals are processed by the manufacturer’s proprietary software, which calculates what most manufacturers describe as a “dimension-less” or “unit-less” value. BOMAG, however, assigns a definite value to its ICMV, “Evib,” saying it is a force measured in Mega-Newtons per square meter (MN/m2).
A job-specific ICMV is determined by running the roller over a test strip already compacted to the project’s target density and verified via nuclear gauge or asphalt coring. The ICMV produced as the roller traveres the test strip then can be used to correlate with the project’s density number—to some degree—allowing the operator to use the ICMV as a benchmark.
Tim Kowalski, applications support manager, Wirtgen America, reminds users of IC rollers on asphalt projects that the validity of ICMV-to-density correlation requires uniformity: “We need to make sure the material lift thickness and the temperature stay consistent, and also that the underlying base is consistent.”
Todd Mansell, training consultant, Caterpillar Paving Products, reinforces the need for consistency: “Change any of the parameters, and you will alter the conditions that produced the ICMV target value, thus invalidating it. In order to make best use of the ICMV, the operator must try to maintain the conditions that produced that target value initially.”
Dynapac’s Tim Hoffman, product manager, heavy compaction, says that quickly spotting inconsistencies is a distinct advantage of the IC system if established ICMV parameters are applied everywhere on the job site: “The contractor can immediately rule out improper compaction if a weak spot emerges, because the data, combined with real-time mapping, ensure that the operator made the same number of passes at the same settings and temperature as the rest of the project—reducing the culprits to improper prep work or improper mix design.”
Most of the industry is still investigating a more direct link between the ICMV and density: “Agencies were hoping that FHWA studies comparing stiffness with density would actually result in a system to provide density on the fly,” says Wirtgen’s Kowalski, “making it not only a quality-control tool for the contractor, but also a quality-assurance tool for the agency.”
Volvo Construction Equipment, however, says that its new Density Direct system, available for certain of its asphalt rollers, can provide immediate density readings.
“Volvo’s intelligent compaction system with Density Direct provides operators with real-time density calculation of the surface being compacted,” says Mark Eckert, product manager for compaction. “Once fully calibrated with data specific to the application, [the system] produces a density calculation that is accurate to within 1.5 percent of core sampling, providing a real-time reading of density values over 100 percent of the mat.”
Markets, then and now
Some 20 years ago, European-based companies, such as BOMAG and Geodynamik, already had advanced IC systems up and running in Europe. Geodynamik, for example, had a system that changed the drum’s amplitude and frequency, as well as the machine’s speed, as material stiffened. Interest in the system waned, however, given the cost of electronics at the time.
At least 10 years ago, BOMAG had versions of its present Asphalt Manager and VarioControl (soil) systems available in North America. These systems introduced the company’s drum-vectoring technology, which allows the exciter mechanism to rotate through a 90-degree arc to change the direction (vector) of the drum’s force from vertical to horizontal as material becomes stiffer.
“When BOMAG introduced its intelligent-compaction systems some 20 years ago in Europe,” says Bert Erdmann, director of engineering/product manager for heavy compaction, “we defined ‘intelligence’ as the drum’s ability to regulate amplitude in order to avoid over-compaction and to prevent the drum from jumping when its energy could no longer be absorbed. But the industry, especially in the United States, has shifted away from that definition to more of a mapping-function definition—reporting pass counting, temperature, and perhaps stiffness values.”
A wider view of roller intelligence, however, is still being pursued. Caterpillar Paving Products, for instance, will soon launch its Auto Adjustable Compaction (AAC) system for certain of its asphalt machines. According the company’s Mansell, “the system senses the level of compaction and adjusts the amplitude to optimize the amount of energy that goes into the mat, decreasing amplitude as the mat becomes more compact.”
Construction Equipment asked a number of manufacturers to comment on the present state of the market for intelligent-compaction rollers:
“At this point, most contractors are taking a cautious approach to adopting this technology until they are convinced that the benefits justify the costs. There is, however, a growing understanding of the value these systems add in terms of efficiency and damage avoidance by preventing over-compaction.”—Steve DePriest, product specialist, Hyundai Construction Equipment Americas.
“While a few contractors have seen the value in terms of efficiency and job quality that intelligent-compaction machines can provide, the market at present is largely driven by agency specifications.”—Todd Mansell, Caterpillar.
“Sales seem to be driven primarily by road-agency specifications requiring intelligent-compaction rollers, but as more agencies require intelligent-compaction machines, and as more contractors begin to understand the value of these machines and add them to their fleets, we will see the market continue to develop.” —Mark Eckert, Volvo.
“Some contractors understand the value that intelligent compaction can bring to them and their projects. They’re the ones who are usually leading the industry in the adoption of new technology. At present, however, most contractors using IC machines are doing so only because the state has put the requirement in the bid for a project. This, I think, will change once more projects requiring IC are let and as more states adopt some kind of IC specifications.” —Tim Kowalski, Wirtgen.
According to Ed Conlin, asphalt specialist, Sakai America, IC systems typically are offered as options on certain of a manufacturer’s roller models and a “full-blown” system might add 20 percent to the price of a typical machine—“but much less,” he notes, “if the user doesn’t require all the available technology.” The manufacturer’s systems are usually scalable, says Conlin, with options that provide different types of information.
According to Trimble’s Garcia, most aftermarket IC systems also are scalable, with simple systems perhaps providing only pass-count information, but allowing the addition of such features as temperature sensing, compaction-value reporting, and on-site connectivity. The latter allows information in one roller to be shared with other roller operators (providing collective pass counting in some instances) and also allows this information to be remotely available via laptops and phones.
The cost of aftermarket systems is estimated to range from a “bare-bones” pass-counting system at around $15,000, to systems with “all the bells and whistles” that come in at around $40,000. Some in the industry suggest that these systems, as well as factory-installed systems, can have a short return-on-investment interval, given their potential to increase production and to help contractors avoid project-warranty penalties—and conversely, to help increase the prospect of receiving bonuses.
Case’s Pullen makes the observation that compaction equipment has always been a popular rental item, but given the yet-uncertain demand for IC machines, rental firms might be hesitant to invest in these more expensive models.
Pullen’s observation is well taken, and some in the industry speculate that this dynamic could, at least in the near term, encourage the sale of IC machines to end-users as more specifying agencies mandate the use of these units. For some contractors, equipping an existing machine with an after-market IC system, such as the Topcon C-63 Compaction Management System or Trimble CCS900 Compaction Control System, might be a viable alternative.