The Efficiency of Intelligent Compaction

Sept. 20, 2019
Innovations in software and sensors have led to highly efficient and productive compaction.

Chances are that today’s operator is unaware that the heavy, vibrating roller machines for compaction were, in fact, decades in the making. Today’s tough workhorse machines have evolved for nearly a century, at first influenced by an expanding car manufacturing market, growing industrial transportation that demanded new and better roads, plus faster modes of application, and later, by innovations in software technology.

In 1929, machinery manufacturers Jacob Blaw and Luther Knox of the Blaw-Knox company had acquired a line of self-propelled asphalt finishers and proceeded to refine the technology. Over the years, products improved, and through numerous sale transactions, this equipment became part of Volvo Construction Equipment. Today’s compaction machine is now available with IC, or Intelligent Compaction, technology, as explained by Volvo product expert Mark Eckert. “Intelligent compaction isn’t really new,” he says, “as it has existed in some version since the 1990s, but in the last decade it has really made great improvements by leveraging technologies available in other markets and adapting them for use in this industry.”

Eckert explains that like many innovations, the concept of using technology to measure and evaluate the compaction work was slow on the uptake in the construction arena. But once users see the ease of use, and realize that it is a user-friendly, simple to use and understand system, “they love the benefits and especially what it can do for them on the job,” he says.

The components that make asphalt compactors “intelligent” are high-precision GPS for machine location; infrared sensors for mat surface temperature; accelerometers for collecting vibration data; an onboard computer and software system; and finally a color monitor to display real-time information for the operator.

When road authorities require “IC rollers” in job specifications, they usually require the break-down roller to be instrumented, but some specs require it on all machines in the roller-train.

Eckert explains that the accelerometer is installed inside of the machine’s vibration isolators to collect raw vibration data. This raw data is sent to the computer for analysis and the operator can compare the displayed information to the project targets. There are also temperature sensors that provide pavement surface temperature. Finally, the operator benefits from being able to see a color pass map to ensure that uniform coverage has been achieved.

Most IC systems on the market display Compaction Measurement Values (CMV) as a method for providing real-time guidance to the operator and quality control for the lift being compacted. The CMV readout, which the operator can see, is an arbitrary set of numbers that starts low and increases as air voids are removed.

So for example, the operator will see a color palette on the screen with associated numbers of increasing value. This scale is not directly correlated with material densities but does typically increase as passes are made. The goal is not to achieve the highest number on the scale, but rather the CMV which correlates to the target density specified for the project.

While Volvo’s system—Compact Assist with Density Direct—does provide CMV, the system differs from anything else on the market because it can be calibrated to provide estimated density in real-time percentages as opposed to the more arbitrary CMV.

Eckert says, “Since we calibrate Density Direct for each lift of material being compacted, the value being displayed relates directly to the density targets for the job. So, it’s much easier for the operator to know exactly how close they are to target density as compared to a system that only displays CMV.”

The company worked with the University of Oklahoma in the development of its density calculation technology, which ultimately became a patented product that delivers consistent and accurate data for compaction.

While having real-time density information is incredibly helpful, temperature also plays a key role in being able to achieve the desired density. The temperature sensors provide the surface temperature of the mat, which is good information for operators when they are instructed to work the material in a determined temperature range, but it also provides data for analysis. For example, the mix may be arriving at the job site too cool; this will reduce the time for compaction.

In addition to all of the real-time benefits for the operator, IC also provides contractors and owners a complete set of data for the entire project. This includes the uniformity of coverage from the pass mapping to be compared with the temperature and compaction values. And, since high precision GPS is used, the data can also be compared with core density tests.

“I think one of the original goals of Intelligent Compaction was to eliminate the need for core density tests because the tests require material to be removed from the compacted lift. These areas can never be effectively compacted which can lead to early pavement failures.”

To date, the industry has not achieved the objective of eliminating core testing. But it has accepted the other benefits received from the use of IC technologies.

In Minnesota, for example, IC must be on your machines to be awarded any road contracts and it only makes sense. They have a short working season, and between cold winters, and the destructive freeze-thaw cycles and impact of studded snow tires, there is never-ending maintenance. But if there is uniformity in density and compaction, the life of these can be extended.

It is not surprising, then, to learn that Scandinavia, along with the rest of Europe, is leading the market, given that between budgets and the taxes required to conduct ongoing repair and maintenance, municipalities want the best road surface at the outset
to mitigate wear and costs.

Minnesota also has been one of the leading states implementing Intelligent Compaction. In fact, in 2018 it was recognized as having 100% adoption of IC on Transportation Pooled Fund Program projects. Another benefit of this technology is to increase the efficiency of the compaction process. Pass mapping optimizes the rolling pattern for uniform and consistent coverage so that under-rolling and over-rolling can be avoided. IC technology continues to evolve and provide more features. As an example, it was originally acceptable to remove data from a system using a USB/flash drive. Now it is a common requirement to have a wireless transfer of the data.

As to the future, Volvo is responding to what the states want. Eckert adds, “We continue to add new features to be compliant with IC specs, but we also look at making improvements to the functionality and performance of our system.”

Trust Me, You’ll Love It
If you hear those words, the first reaction is probably, well, if it’s so good, why do you have to convince me? But that is exactly the type of scenario that occurred when Trimble introduced software for intelligent compacting.

Kevin Garcia, Trimble manager for paving and specialty construction, relates their experiences. “It’s a big ask to go to a
contractor and hope they will believe a benefit when you tell them about something new and different they’ve never seen before. There is no incentive other than your word to try it, and their reaction is skeptical.”

When Trimble developed the technology that would accurately measure stiffness, compaction effort, and temperature, giving contractors verification of their compaction work, he recalls that the reaction was lukewarm.

“They didn’t really see a need for proving anything beyond standard protocols of the day,” explains Garcia. “In this country, once you pass your acceptance test, and the inspection cores say you’ve met your thickness and density, you can get your check. Our warranties here are just a few years, if at all. The road could fall apart tomorrow but basically, you are off the hook. No one would do this purposefully as it would certainly affect any of your new business opportunities, but it is a market reality. There’s not much of an incentive for contractors in the US to deploy these kinds of technologies.”

In Europe, however, he said there is an opposite approach. “Over there, road warranties are 5–10 years and contractors are leading the tip of the spear in technology adoption. Those contractors can’t have enough verification to ensure their product is the best it can be and will last. They actually want the systems to do even more for them,” says Garcia.

He adds that multiple factors come into play that affect a users’ adoption of new systems. “At the beginning when technology emerges, people don’t know what they need, and market penetration is not high. Then all of a sudden the benefits are recognized and it’s everywhere. Think of onboard navigation in passenger cars: nobody thought they needed it; now it’s everywhere, throughout markets. Today in agriculture, for example, you’d rarely find a tractor that didn’t have onboard computers and software assistance. Construction isn’t like that...yet.”

One crucial incentive, however, was when contractors were telling them that the shortage of qualified compacting operators was hurting their business. While they couldn’t solve the personnel staffing, they could leverage technology to create a skilled pool of operators. Eckert relates that “much of our team of operators with decades of experience” has been dwindling. New employees have to learn as they go, and fewer are entering the market, “but with the Trimble technology, new hires can perform well out of the gate,” says Garcia. “We saw this problem as an opportunity to develop a system whereby someone with a low level of experience could learn in a few minutes how to do a superb high-quality compacting job because they had a guidance system that helped them achieve the optimum required levels. So, in a way, we really are helping the skilled labor market for construction.”

Garcia cites the three components that are essential to the compaction knowledge. First is the pass count. In other words, are we touching the same material more than once, or at all? “Then second is temperature: is the asphalt too hot or too cold to be manipulated into its proper shape? And then the third is stiffness. Of course, we’d all love to give an operator the exact density of the material under the drum but that’s simply not possible with today’s technology,” says Garcia.

“Stiffness is the next best indicator as it should mirror what’s happening with the density of the asphalt. To measure stiffness, an accelerometer is mounted on the roller shaft of the compactor to measure the energy being applied to the surface.”

Garcia offers a colorful illustration to explain what this means. “Let’s say I make a fist and repeatedly punch my leg; my knuckles won’t hurt. The energy of the punching is absorbed by my leg, which is a soft material. To translate that to the accelerator that reads on soft material, how most of the energy is absorbed by the ground, so that says, ‘it is not compacted.’ And we know in this case, this is true because my leg is not stiff. So, there is a ‘low energy reading.’ Now, if I make the same fist and punch a table, the energy is rebounded and is not transferring to the table, which is resistant. Again, if the accelerometer gets a reading of high energy transferred to the roller it is saying it’s stiff, it is compacted. So, low energy, low compaction—higher energy reading, higher compaction. This is the point of our technology—to tell the operator when the compaction goals are met with verifiable scientific principles.”

He adds that operators can also figure out how many passes they will need by doing a proof run. If it takes five passes to achieve the desired number then you can forecast how many passes over whatever your length is you will need and can calculate the time required.

Other compaction methods include a power sensor attached to the main drive power for compacting dirt. This has to be mounted to the engine and is created specifically to the machinery. Measuring the resistance of a roller on soil from more to least resistance tells the operator how well the dirt is compacted.

“If you try to ride a bike through mud or the lawn, the tires have a lot of resistance, so it’s the same principle. On soil, it takes a lot of horsepower to compact the first pass, and then less as it becomes easier. For dam projects, or compacting landfill cells, the number becomes lower. Another solution for landfills is measuring the vertical deflection of the machine which tells how much trash is settling, and once there is no change in numbers you know you are achieving the density you need,” explains Garcia.

The Trimble IC technology can go on any roller, and depending on the base level of machine, “We can add technology to do more. In under four hours, we can install and train an operator on the whole system; it is that simple. You set your target, go into your main screen, set your targets, and you are literally good to go.”

As more DOTs require that their contractors use this equipment and phase out the taking of core samples, Garcia says that regardless of your machine fleet, “The investment in compaction technologies will allow you to put more people on the job with the confidence of high-quality results.”

The Inside (Drum) Story
Becoming an apprentice conjures up images of an earlier era where working side by side with a master, one learned those nuances of skill and technique that only firsthand engagement offers. And the opportunity to “earn and learn” serves well, as the innovations of Karl Heinz Schwamborn, founder of German company BOMAG, a world leader in compaction machines, can attest. BOMAG has been privately owned by the French Fayat Group since 2004.

Bert Erdmann, BOMAG’s product manager of compaction, says, “Mr. Schwamborn was an apprentice working on excavation and earthmoving and with this background, he went on to study engineering.”

From the launch of Schwamborn’s first hand-guided rollers in 1957, the company has continued to develop innovative compaction machines that now include small tampers for tight spaces, vibratory plate machines, hand-guided rollers, and radio-controlled compactors, trench compactors, light tandem rollers, heavy tandem rollers, pneumatic tired rollers, embankment compactors, cold milling machines, recycler/stabilizers, asphalt pavers/finishers, and landfill compactors.

The BOMAG current system of intelligent compaction was an outgrowth of this first application “that today we call VARIOCONTROL that automatically adjusts the output of compaction of the drum,” says Erdmann.

“Anybody can measure a rebound, but with our algorithm, it is possible to calculate the stiffness of your material based on the performance of the drum itself. Once the drum starts bouncing, over-compaction occurs, and our sensor technology which is structurally integrated into the machinery itself automatically adjusts the drum. In other words, the machine reacts to the conditions of the material you are rolling on,” explains Erdmann, adding, “VARIOCONTROL is only available on our Single Drum Rollers, which are soil compactors.”

He says that six years ago they introduced ECONOMIZER, a technology that can be used on reversible vibratory plates, trench compactors, single drum rollers, light tandem rollers, and heavy tandem rollers.

As its name says, the ECONOMIZER is an economical means for any contractor to use this optional equipment on their machines and perform correct compacting work, avoiding over- and under-compaction, while saving money on fuel, time, and wear and tear on machinery.

When installed on a roller, the ECONOMIZER sensor is attached to the front drum and the compaction process is monitored as the operator rolls over surfaces. On the control panel, a round tachometer-shaped onboard monitor has a series of LED numbered lights—one to ten—on its circular face, and this tells the operator what’s happening.

When you first start up, a number of the lights will light up, and this is an indication of your base condition. Then, as you make passes, by watching the number of lights on the display, the operator will know the number of passes needed to achieve correct compaction. This reduces operating costs of making extra unnecessary passes and risking over-compaction.

Erdmann says that if the machine detects a risk of over-compaction, a warning light comes on, which indicates to the operator to stop the work and to move on to the next spot. The heavy tandem rollers can also be equipped with a sensor that conveys information to an onboard monitor that displays the temperature of your surface material and an impact-per-feet (IPF) meter.

BOMAG recently offered a new downloadable app on Android that is a GPS mapping device “and it is completely free,” says Erdmann. BOMAP allows mapping and pass counting. “Our thought is that GPS devices have been around for a while so if you introduce something new, people may perceive it as just some gimmick; so, by giving you a chance to try it for free, you can test it out, see if it is for you.” In addition to the free version of BOMAP, higher precision options are available as well.

Although Intelligent Compaction technologies have been around for a while, Erdmann says that they are more widely used—and often mandatory—in Europe and Scandinavia, but their popularity here will inevitably increase.

Having proof via the software capability to generate reports and communicate with cloud-based systems is only going to increase a contractor’s capacity. Being able to prove that you’ve done the job properly and prove the time it took is a valuable asset. Plus, a less skilled operator can do a great job to meet compaction objectives. Using this technology requires a very minimal learning curve and allows operators to get to work quickly and efficiently to meet the compacting objectives of any job.

Diving Into the Ring
When one of the largest landfill owner/operators in North America chose Kentucky-based Carlson Software for their compaction technology needs, the company was beyond thrilled.

“They were looking for a better way to measure compaction, so we saw it as an opportunity to show our solution and demonstrate our responsiveness to our customer’s needs,” says Tim Jones, Director of Machine Control for Carlson Software. He says that Carlson Software is a survey software company that focuses on Survey Software and Hardware applications and Mining and Geology Software for mine planning and scheduling. “Our Laser Measurement Group for laser measurement devices focused on mining and the Machine Control Group.”

Not only can the Carlson Landfill Grade software assist in measuring pass counts or compaction by deflection, but the software also helps the site understand what is happening in real time.

Landfills want to maximize the waste that is being put into their allotted airspace. Using these technologies delivers multiple benefits that can translate to cost savings. The most important benefit is that you can measure your compaction and work to maximize it in landfills; the more trash that can be put into each cubic yard/meter translates to the bottom line. Another major benefit of these systems is building slopes properly to keep water moving so it doesn’t sit on top of garbage, but rather drains more efficiently.

Being a smaller company allows for flexibility “so the Carlson Grade software solutions are designed to be agnostic to any communications system,” says Jones, adding that the customer needs come first. “If you want to use cellular, we can set it up for that. If you want to use it on your radio network, we’ll make it do that also. The company has a team of software developers that are constantly working to improve the product and deliver what you need in your respective situation.”

Another major benefit of the Carlson Solution is engineers and management have real-time views as your machines are working on whatever respective project, be it landfill, mining, or other projects, says Jones, which also helps in troubleshooting as performance can be evaluated remotely and this helps keep the machines working.

He adds that their solution is probably the easiest hardware installation package in the market. “The system consists of a ruggedized computer connected to power, and a cable that runs to a bulkhead to the outside of the compactor, a smart antenna that connects to the bulkhead, and that is it. Then, whatever communication that the site would like to use is installed.”

With so few moving parts, it makes troubleshooting issues easier with the hope of minimizing downtime; any machine downtime is lost economy. Jones says the precision of the GPS reading for compaction work is much more demanding and more sophisticated than the type used for finding your nearest DIY. “These systems require survey-grade GNSS accuracy, to get the most precise measurements off the machine. For example, automotive GPS has an accuracy of around 15 feet. But in compacting we utilize more satellite signals (GPS, GLONASS, Galileo, Beidou) to give us better ground positioning of the machine.”

Using the Carlson Landfill Grade software, a landfill can load in their digital terrain model (DTM) of their allotted airspace and then load in projects for the operators to work to. “Then, as the compacting operator is working, the onboard monitor keeps them working in the right location and helps them to build to the final grade without the need for continuous survey staking, as the Grade software shows the operator how they are working to the final grade of the project,” explains Jones.

Another benefit of the product is that it allows the engineers to put in “warning and watch” zones that can alert the operator of any obstacles or areas that management do not want the machine going near. Using these high precision positioning systems allows for multiple applications. The system also allows you to build your outside slopes properly to the allotted airspace. Jones says, “If you don’t build your outside slope properly and it collapses, it costs a lot of machine time and labor to go back and rework those. The compaction software lets you create the slope correctly the first time around.”