Laying Out Compaction Technology

Intelligent compaction is changing the way grading and excavator contractors do road compaction jobs. While industry experts agree there is no substitution for “old school” skill and touch, intelligent compaction is increasingly coming into play with many states writing the new technologies into their regulations.

According to information from Volvo Construction Equipment, intelligent compaction guidelines were established in Europe in the early 1990s. While dramatic improvements have been made to hardware, the principle of intelligent compaction remains unchanged.

Tim Kowalski, Hamm application support manager for Wirtgen America, notes there have been a lot of changes in the past 20 years in rollers and how they are regarded because of the type of road mixes with which contractors must contend.

“The whole industry is trying to change how we look at testing, because you can’t compare a roller that’s testing load bearing to a density gauge that’s testing density,” he says. “There’s really no correlation between density and load bearing. Ground stiffness and load-bearing capacity is fundamentally different than density.

“When we start looking at load-bearing testing, we’re starting to move into different testing devices that match what the machines are actually measuring. These systems are changing out the whole industry, specifically in quality control and quality assurance.”

Consider the options: Volvo Intelligent Compaction (IC) by Volvo Construction Equipment is expected this fall to introduce real-time density mapping technology designed to eliminate guesswork, improve quality, and increase productivity.

Volvo IC and Volvo IC with Density Direct will initially be available for new Volvo asphalt compactors—the Volvo DD110B, DD120B, and DD140B models sold in North America—with aftermarket availability for Volvo asphalt compactors to follow.

In addition to offering the pass mapping, temperature mapping, and data storage features of the Volvo IC system, Volvo IC with Density Direct includes the industry’s first real-time density mapping technology.

“Density mapping has been described as the ‘holy grail’ of intelligent compaction,” notes Fares Beainy, Volvo Construction Equipment research engineer, adding that the technology is expected to “radically advance the paving industry.

“For years, contractors have relied on IC systems with stiffness calculations (through Compaction Measurement Value or CMV) instead of density, which is not the true metric by which contractors are evaluated and paid,” adds Beainy. “With Density Direct, operators have real-time access to the metric that ultimately determines the success of their work—density.”

Stiffness measures the rigidity of the asphalt surface and provides an output in CMV. Contractors use nuclear gauge measurements and core samples throughout the course of a job to correlate the CMV to the relative density in contrast to Density Direct, offering the operator relative density in real time.

The system includes a display, an accelerometer, front and rear infrared mat temperature sensors, a GPS, a base station, and an optional GPS Rover.

The Volvo IC with Density Direct user interface depicts a density map showing each square foot of rolled asphalt in a color representing density and provides a real-time numerical density reading displayed in the corner of the screen.

Using the cab-mounted Volvo IC system 8-inch by 10-inch color monitor with pinch/zoom and day/night mode, the pass mapping function captures each compactor pass and drum overlap with an individual color so that the operator can easily see gaps and work to maintain uniform coverage.

Temperature mapping provides the operator with a temperature “map” showing the path of the compactor overlaid with the last recorded surface temperature.

The Density Direct system’s calibration screen enables the user to set the project’s target density. Once fully calibrated with data specific to the application, the Volvo Intelligent Compaction with Density Direct system produces a density calculation accurate to within 1.5% of core sampling, providing a real-time reading of density values for over 100% of the mat.

The operator can use the real-time data to make any necessary adjustments while asphalt is being paved. This is designed to reduce the occurrence of inadequate densities that drive up project costs and reduce time spent taking core samples in an effort to improve quality. It also is designed to lead to greater uniformity than offered through nuclear gauge testing.

Calibration information is saved by the machine, enabling operators to assign calibrations to certain job elements and quickly switch back and forth between calibrations to meet the specific job element demands.

Data gathered from pass mapping, temperature mapping, and density mapping is stored on the IC system’s internal 14-GB hard drive for approximately seven months of data logging. Data can be backed up to USB drives in VEDA format, the Freeware system promoted by theFHWA for IC systems.

With optional Differential GPS, the data gathered from Volvo IC is linked to location information accurate to within 0.5 inches. Both Volvo IC packages meet state DOT and FHWA requirements for intelligent compaction specifications.

Caterpillar’s Machine Drive Power (MDP) is designed to measure soil density under broader conditions with improved accuracy. It is designed to work on all soil types, including fine, granular, and cohesive.

MDP is designed to measure the energy necessary to overcome rolling resistance in such a way that is a more tangible and direct measurement of soil stiffness.

“In a very loose, lifted soil, it takes a lot of energy to move that roller through that soil,” says Rawls. “As that dirt becomes more compact and the ground becomes stiffer, it takes less energy to move that machine.”

A compactor has to be operating for an accelerometer to read ground stiffness, whereas an MDP system can be put on static rollers, says Rawls. The MDP has been introduced to Caterpillar’s 815 series four-drum compactors.

MDP works on smooth drums, pad foot drums, and smooth drums equipped with pad foot shell kits. The system works with the vibe system on or off to enable operators to measure during working passes, and shut the vibe system off for proofing passes. It is scalable to meet requirements.

MDP is designed to measure closer to the depth that the machine is able to compact and closer to the thickness of the lift. Its measurements are designed to be more easily correlated to portable measuring devices, such as plate load testing; less affected by the dampening effect of cohesive soils; and not prone to variabilities.

Compaction Meter Value (CMV) is an accelerometer-based measurement system for granular soils available on smooth-drum soil compactors (CS models). The system functions while the drum vibrates, measuring 3–4 feet into the ground to provide the operator with a picture of what’s going on beneath the surface. CMV is designed to reveal to a trained operator the location of hidden anomalies such as buried objects, rocks, clay balls, and areas of poor compaction—or indicate the need for more moisture to aid compaction.

Wacker Neuson offers a compaction display called Compatec. It is a device used to give the operator live feedback regarding the relative compaction and is designed to aid the operator in avoiding unnecessary passes, says Hunt.

Compatec also protects the machine by alerting the operator with flashing LED lights when the machine is operating in an over-compacted situation.

BOMAG Economizer, originally developed for BOMAG plate compactors, is one of the newest technologies expanding the company’s tandem roller line.

“It offers intuitive operation with real-time compaction results easily read from an LED display on the instrument panel,” says Dave Dennison, marketing manager, BOMAG Americas. “Once the roller’s optimum working frequency has been reached, yellow LED lights indicate thelevel material stiffness.

“As compaction increases, more LED lights illuminate on Economizer. When the number of yellow lights stops increasing, the maximum level of compaction has been achieved. If all 10 yellow lights are illuminated, a red LED light illuminates as an indicator to the operator to stop rolling that section. This avoids over-compaction and fracturing of the aggregate, and costly removal and replacement of material.”

Dennison says an added benefit to the Economizer is that it allows the operator to do proof rolling of the area to look for and address weak areas. The Economizer is designed to achieve total surface area compaction control.

The Economizer’s value, simple operation, and relatively low cost “are opening the ability to have real-time compaction results to a broader range of contractors,” says Dennison. “It can be used to improve compaction results on a wide variety of applications, from driveways and parking lots to country roads and highways.”

In the wake of the FHWA initiatives, Wirtgen America has focused on intelligent compaction through its Hamm Compaction Quality (HCQ) system.

The system encompasses a range of products for planning, measuring, controlling, documenting, and analyzing compaction processes.

“We have had intelligent compaction since the mid-1980s, when we started in the soil side, and about 2007 is when we switched over and also added the asphalt portion of it, renamed the system, and updated the software,” says Kowalski, adding that the system is designed to help operators achieve greater consistencies.

“The fixes we now have are totally different from what we had 10 to 20 years ago,” he adds. “If we have a tool in our tool belt that can help produce a better product, it’s better for the taxpayer and everyone.”

CASE Construction Equipment recently introduced its new Tier 4 Interim DV209C and DV210C high-frequency asphalt compactors to its line of high-frequency double-drum models. The compactors are designed to give road builders more control and versatility to dial compaction performance to match the thickness and required density of each lift.

The machines also are equipped with new, high-efficiency Tier 4 Interim engines (Cooled Exhaust Gas Recirculation and Diesel Oxidation Catalyst) with automatic idle control systems to improve fuel efficiency by as much as 10% compared to previous models.

With operating weights of 21,030 pounds and 22,730 pounds, respectively, and a standard drum width of 66 inches on both machines, the DV209C and DV210C are sized to address most mid-size and large road projects.

The new DV209C and DV210C feature a frequency range of 42–55 hertz standard and 46–67 hertz high frequency. The higher frequency range is designed to give operators control over compaction performance based on the thickness and density requirements of the lift.

When combined with variable amplitude settings (0.22–0.6 millimeters on the DV209C, 0.33–0.6 millimeters on the DV210C), the machines can be dialed in to better handle thinner lifts (low amplitude/high frequency) and thicker lifts (high amplitude/low frequency).

Centrifugal force can also be dialed in (15,736–21,582 pounds on the DV209C, 17,535–26,977 pounds on the DV210C) to best match the thickness of the lift and the desired depth of compaction.

Other new features designed into the compactors are increased maneuverability in the operator compartment for greater visibility and a new color monitor and operator interface. Both machines feature large water and fuel tanks to enable longer work hours without the need to stop for fill-up.

The new operator station on the machines is designed to offer more control, visibility, and comfort through “intelligently-placed” controls and monitors. The new operator station is capable of turning and sliding through the entire width of

the cab to give the operator visibility to the drum surfaces and edges as well as the spray bars. Large front and rear mirrors—with optional enclosed cab configuration—help ensure optimal visibility.

A color monitor in the center of the steering wheel offers operators easy access to important operational information as well as controls for speed, frequency, vibration, and sprinkler adjustments. To ensure easy reading and control, the monitor stays in the same position even when the steering wheel is rotating.

Service points on the DV209C and DV210C are accessible from the ground through large side doors and filling and draining points for service fluids are centralized. Both models also are compatible with the CASE SiteWatch telematics system, which helps equipment owners better manage maintenance, equipment utilization, operator performance, equipment security, and overall production.

One of the biggest trends driving the use of intelligent compaction is the verification that the total job site meets compaction requirements, points out Katie Pullen, brand marketing manager, CASE Construction Equipment.

“Intelligent compaction gives operators the ability to target exact areas that have issues, and it helps to take the operator error out of the operation,” she says. “Intelligent compaction also provides less invasive testing techniques as it becomes more accepted.”

Intelligent compaction is ideal for any company that wants to ensure that the job is done right the first time or needs to provide documentation of quality once a job is complete, says Pullen.

Improved productivity—and thus a more significant effect on the bottom line—is its primary benefit, she points out.

“Intelligent compaction generally allows the operator to get to desired compaction levels faster and the ability to determine if there are faults in the base or sub-base materials,” she says. “With that comes improved quality, reduced re-work, and the ability to produce documentation at the end of the job that shows comprehensive results for job sites that require it. CASE intelligent compaction systems vary in complexity based on size and type of machine application.”

Achieving good compaction is about following basic guidelines and executing the job properly, notes Vince Hunt, product application and training specialist for Wacker Neuson.

“Using the proper materials, having the proper moisture content, following the recommended lift heights, and making the required number of passes are the most important factors in achieving good compaction,” he says.

“During Wacker Neuson’s soil compaction training program, we emphasize selecting the right machine for the job,” adds Hunt. “This is based on determining the soil type, job size, and then matching the machine for the best compaction results in the fastest amount of time. These guidelines have not really changed over the years, but the compaction equipment has advanced to help contractors get the best solution for the job.”

Industry experts say many contractors are now utilizing available technology for compaction to augment the “old school” approach of “skill and touch.”

Kowalski says he believes the use of “skill and touch” has gone by the wayside because the technology of rollers has advanced so much.

“Years ago, the seasoned veteran could tell by the seat of their pants when enough rolling was done,” he says. “Nowadays, you try to isolate that feeling from the operator to the machine so they’re more comfortable. With the intelligent compaction, we’re hoping that’s the next step to help them become a better roller machine operator.”

“Today, contractors can’t do it the old school way—maybe smaller contractors can—but regulations are being written around intelligent compaction,” says Rawls, adding that a few dozen states have now done so.

“Typically in the past, if I was putting in a lot of dirt in building up this road, I would really only have to take one density test for every 250 cubic yards of dirt. That’s a type of requirement when you’re doing state and federal work. That density test represents about a square foot of material,” he says.

In essence, that approach is testing a small percentage of the actual material being put in, adds Rawls.

“Now we get 100% testing of all of the material,” he adds. “The operators get a map in their app display. They can see where the roller has been, map those stiffness values and then if they see areas that don’t match the other areas, they can focus their testing guys to that spot to remediate it before they put pavement on it. It’s very cheap to fix something at that point and very expensive to fix after you put pavement on it.”

Newer technologies are offering better consistency throughout the job, points out Rawls. Systems such as the MDP and CMV are useful tools, especially in warranty work and design-build-finance-operate and public-private partnership projects, he adds.

“There’s a lot of exposure out there on the back end of a road job,” he says. “It’s good documentation and a good tool to get consistency.”

“Contractors are interested in on-board compaction gauges primarily to protect their investment,” notes Hunt. “Competec alerts the operator via flashing lights when over-compaction has occurred. The LED indicator also gives feedback regarding maximum compaction for the particular material that is being compacted.”

That said, there is no substitute for experience, says Hunt.

“Skill and operator judgement will always be crucial in achieving proper compaction,” he adds.

Given mandated compaction specifications, the question is whether contractors have all of the technology needed to meet them.

“Primary metrics measured include rebound detection and stiffness. Measur­ing stiffness is said to be a better indicator than density,” says Pullen. “If a company strictly goes off of the data from a nuclear density meter, they’re not getting load-bearing capabilities. A nuclear density test is still required, but it will be more accurate and there will be a higher chance of passing if intelligent compaction is used.”

For jobs involving mandated compaction specifications, a third party is almost always involved in the final determination of compaction values, points out Hunt.

“The tools used by soils experts such as the nuclear density gauge, geogauges, and other devices to measure relative compaction are still indispensable and will always be used for a final determination of the measured compaction,” he adds.

Areas of lack include education and proper machine selection, adds Hunt.

“Proper machine selection for the given application is very important,” he says. “In addition, following basic construction techniques is always crucial.”

Despite the different specifications from state to state, a machine is the same no matter what state in which it is used, points out Kowalski, adding the challenge is getting state officials to better understand what the equipment can do for them.

“In the next three to five years, you’re going to see intelligent compaction become more of a standard in the industry than to be put out on demo or pilot projects because the feds are really pushing the states to start implementing this into their programs and projects,” says Kowalski.

“There are 33 states involved with intelligent compaction and 22 of them currently have some kind of a specification, whether it be on the soil side or the asphalt side and are using them on projects,” he adds. “This year alone, we’re probably going to see more than 200 projects in the US.”

The driving factor comes in the acceptance of the concept that there is a difference between stiffness and density, points out Kowalski.

“Stiffness is more of a resistance of the material where density is the final result of compaction,” he says. “It’s like comparing apples and oranges. What they’ve found out is because we can map our paths out and measure temperature, we’re getting more consistent on our roller patterns and staying within a certain temperature range, so we naturally should

get better density across that, smoother rides, and longer lasting roads. There’s where you see the big benefit.”

In his view, today’s technologies are “long overdue,” notes Rawls.

“I always ask contractors ‘When is the best time to plant the tree?'” The answer: 20 years ago, because you can sit under it and enjoy the shade,” he says. “I can associate these road failures we’re seeing to the compaction map and make clear conclusions between inconsistent baseand road failures.”

Not much attention had been paid to the load bearings underneath the surface, says Rawls.