Continuing developments may bring more sophistication in monitoring and testing your compaction results.
When it comes to new compaction technology on the market, Jimmy Gist of Gist Inc. in Chapin, SC, hesitates. “I’m one of those from the old country. If it’s working the way it is—leave it alone.” Gist does mostly commercial and industrial site work, including some subdivision work in Columbia, SC, and the surrounding region with his 15 workers. Thirty-three years ago he had one backhoe and one dump truck. Now he has 26 pieces of equipment. They do all phases of the job, except for water and sewer lines, and curb, gutter, and asphalt work, which are subcontracted out. The company has a Dynapac smooth-drum roller for setting up stone, as well as an Ingersoll-Rand SD170 smooth drum with sheep’s foot attachment kit, in addition to two Bomag trench rollers. |
PHOTO: SAKAI |
“We haven’t had too many problems relating to our compaction,” says Gist. “I don’t mean to brag, but I have been doing this 40 years and I take pride in knowing what I need to compact, whatever type soil or stone we might be compacting. With the varying types of soils in the Carolinas, we often use both the smooth drum for the sand and then the footed in the clay soil—sometimes nearby.”
Challenges for Gist usually come with his work in clay soil. Moisture, according to Gist, has more impact on clay soil than sand. “The more moisture you have in sand, the better it compacts,” says Gist. “Clay is just the reverse. As a rule of thumb, when I know our winter rainy season is coming on, I go after the sandy jobs because I can go right back to work after the rain. There is hardly any way that sand can get too hard to work, whereas you have to spend extra time and money to dry up the clay.”
Intelligent Compaction
Bomag, along with several other manufacturers, has developed “intelligent compaction.” Bomag’s system evolved from an asphalt compaction system called “Variomatic.” After a second generation of Variomatic was released, the company’s engineers developed “Vario-control” for soil compaction, stiffness, density, and testing.
“We now have an extremely accurate system that can achieve very consistent results able to be both qualified and documented,” says Steve Wilson, manager of marketing services and product manager with Bomag Americas Inc. “It allows the contractor and the operator working for him to define the end result of what he’s achieved and create a paper trail for his work. It functions as a warranty if there is a problem with the job. The contractor then has physical evidence he can use to support his claim that he did what he said he did. We have had some DOT [department of transportation] agencies especially happy with us because they learned that they do not have to test on as regular a basis.”
Jeff Fox, product marketing manager with Ammann America Inc., a company with a full range of compaction equipment, sees things heading in the direction of more machine-verified compaction. Fox recently attended a symposium on intelligent compaction at Auburn University. A number of various state department of transportation directors were in attendance, as were manufacturers. “One of the main areas of discussion at our meeting was that nuclear density testing on asphalt—despite the quality and compaction of the asphalt—is useless, if the base underneath is not compacted adequately,” says Fox. “You will have ‘bridging’ and eventually potholes forming.”
Proper base compaction is a necessity. It is also very expensive and time-consuming, especially since during the evaluation of core samples further erosion and wetting can occur. “Any system such as ‘intelligent compaction’ that gives you recorded density values on the fly is something that various government agencies, including the federal government, are very interested in,” says Fox.
Fox adds that, as more and more agencies become aware of the intelligent compaction systems, it will behoove the various contracting companies to be able to warranty their work. “The contractors eventually will have to be able to supply verifiable and recordable data that is accepted and then say, ‘We did our part,’” says Fox. “The biggest news later this summer [2005], once these various trials start coming online, will be about the new intelligent compaction systems. From a market standpoint I don’t think you’ll see much action on IC this year. But it will start next year. You are going to see orders for this type of equipment. Everyone is going to want to play.”
Ingersoll-Rand is the second largest supplier of compaction equipment in the world and the largest supplier of compactors in North America. Its current machinery incorporates an “intelligent” system that optimizes the performance of the compactor once the amplitude has been manually selected on the basis of layer thickness. The system then automatically controls the machine’s output—i.e., rolling speed, impact spacing of the drum, vibration frequency, vibration on/off, and water spray system on/off.
 |
PHOTO: SAKAI |
“All of those things are done by a microprocessor,” says Dale Starry, marketing manager for compaction at Ingersoll-Rand. According to Starry, US pavers are more interested in productivity—at the expense of sophistication—than their counterparts around the world. The US with its many roads needs speed and productivity. “It really is a situation of comparing apples and oranges. European contractors tend to want rollers that are maneuverable and have pavers that get high density, so the rollers provide finishing to the surface. In the US the roller is what gets density. All manufacturers would love it if we could have one product that satisfied the needs and expectations of contractors around the world. But I have been in this business a long time, and I have yet to see this happen. Work is being done differently throughout the world. “
Starry says that the various state DOTs can now require from the contractors a document of some type that will verify that the contractor’s work satisfies the specific standard. “They don’t have to have people out there watching now. Having worked for a highway department myself, I understand the incentive to go in that direction.”
Denver Area Compaction and Paving
Brad Parker, quality control manager for Denver’s Asphalt Paving Co., says the Colorado Department of Transportation tried to make compaction acceptance density testing the responsibility of the compacting party on an experimental basis. “The job they picked to pilot it on was not very conducive to something like that—a highway out in the middle of nowhere. From the contractor’s standpoint it was cumbersome with all the tests that had to be run. It was shelved here in Colorado. For the time being the DOT does quality assurance and we do our own quality control.” Parker echoes the comments of Ingersoll-Rand’s Dale Starry when he mentions that the best way for contractors in his area to earn bonuses is for them to be out producing roads as quickly and efficiently as possible.
Asphalt Paving Co. employs between 250 and 300 workers during summer months. The bulk of its paving work is done with Cedar Rapids and Caterpillar pavers with some Ingersoll-Rand and Cat compactors. It also runs a Bomag dirt roller. Its largest asphalt roller is an Ingersoll-Rand DD130. “We do jobs for anyone who asks, from 150,000-ton jobs for the highway department to someone’s driveway,” says Parker. “We built a 34-mile segment of E-470 around Denver,” says Parker. “We also just finished a design-built highway job from I-70, west of Denver to Central City in the Rockies. It was a privately funded road. It was also one of the most challenging projects I’ve ever worked on. The climate was different, the aggregates were different, and so the compaction was completely different up there.”
 |
PHOTO: CASE |
Rich Anchustegui, project manager with Lightning Ventures, a 250-employee earthwork contractor in Denver, says that soils in his area of the US are both cohesive and non-cohesive. “We have a wide variety of soil conditions here in the Denver area,” says Anchustegui. “This includes sand, rock, clay stone, sandstone, and expansive and moderately expansive clays. I find that in this area, my greatest challenge on a site is getting the correct moisture content.”
In clay-type soils he finds that the soil moisture being requested on various jobs can be anywhere from a –2 to a +2 or +3 of optimum moisture. “Many commercial projects that we’ve done in the past are asking for a process fill that resembles a stiff mud,” says Anchustegui. “They are adding water to the material to make it swell, so it’s already expanded by the time you build on top of it, and more than anything that is what soil engineers are focused on, the correct moisture. Perhaps the compaction will be the second-most-important criteria they’re focused on.”
Lightning Ventures does everything from smaller foundation backfills to large over-lots, with which the company finds no specific equipment dedicated to compaction. “You might have numerous scrapers, a water tanker, and a tractor pulling a disk to a mixed process of materials,” says Anchustegui. “It’s just a matter of breaking tracks and compaction. Because the compaction equipment is so heavy, getting just the right machinery is not usually an issue.
“One of our most difficult projects was the new Colorado Convention Center project,” says Anchustegui. “That was a phasing nightmare more than anything else, such as getting the right moisture or proper compaction. It also had a road and a rail line right through the middle of the project. This was a downtown site, and the backfills and compaction were tricky because of bricks and debris that had to be removed while some smaller pieces could stay in place.”
The company has both single- and double-drum compactors. They find the smaller-footed drums most useful for smaller backfills such as foundation walls. Caterpillar makes all Lighting Ventures’ equipment.
Compacting in Southern California and Florida
Craig Shirey, owner-operator of Shirey Excavating and Contracting, finds moisture control in the various soils he works with to be the greatest challenge. If the clay is not adequately broken up, the soil will contain voids that can cause problems in the future. “I use vibrating drums in tight spots, and behind walls where I am in close quarters. If I have a big open area, normally I don’t use a vibrating drum.” Shirey uses mostly crawlers and front-end loaders in his work, which is mostly on hillsides in the Los Angeles area with various types of soil. “Malibu tends to have sandy soils,” says Shirey. “San Fernando Valley is silty, while the Santa Monica Mountains have shaley, rocky soils that work together better than the silt. My compaction work all depends on what type of material I find myself in. A footed drum is helpful in the clay soils I work in, helping mix things up. It breaks the clay up and mixes other materials in with it.”
Shirey is on most of his jobs for three to four weeks with his two workers, usually on custom lots containing up to three houses on the hillsides of the region. Some of the homes that he prepares the soil for are 10,000-square-foot homes. “In the course of some projects I have to fill in part of a canyon by taking the soil off the side of the hill,” says Shirey. “I then compact the soil.” Shirey owns three 175 International crawler front-end loaders in his business. For bigger jobs he rents equipment.
On the East Coast, Linda Pelletier of Bob’s Dozer and Backhoe Services Inc. does land clearing, demolition, compaction, and site development in the Daytona Beach area in preparation for housing subdivisions. With Florida’s rapid growth and construction demands, there’s not always time to wait for optimum conditions to return before work needs to start again. Pelletier has a single-drum Caterpillar 433C compactor. “The biggest challenge I have in my area is that the soil, once wet, swiftly turns into muck,” she says. “It is almost like quicksand. There is a gel-like quality to it that is very weird. A lot of times what happens is that I can only do a half pass—only 3 feet at a time—on a variable-compaction schedule. I try to find the right balance between the speed the compactor moves and the amount of vibration, being very careful the whole time I am working so I won’t sink. Sometimes I even have to go back several days later and compact. This is a problem throughout Florida.”
In the summer, during dry conditions, things can also be challenging for Pelletier. “When our sand gets too dried out, it’s just like moving sugar around. You can never get it wet enough to compact. Though I’ve done excavating work for quite a few years, I’ve been doing compaction one year. Out of the 90 properties I recently compacted, 90 of them, when tested, were compacted to an acceptable density.”
According to Bruce Monical, marketing manager at Hamm, soil density and problems with soil moisture are basically one and the same. “There are a half-dozen things that are important to successful compaction,” says Monical. “One of those things is optimum moisture content. You can either have too much or too little moisture, and that can affect compaction. In the case of too much moisture, you will probably need a padfoot roller to drive the soil particles deeper and to help bring the moisture to the surface so it can evaporate away. Too little moisture and the soil particles don’t have enough lubrication to help rearrange and compact the particles. When it comes to soil-moisture problems and compaction, there is no magic bullet; you either have optimum moisture content in the soil you are trying to compact or you don’t. If it’s too wet you have to dry it out. If it’s too dry you have to put some moisture in it.”
 |
PHOTO: BOMAG |
Oscillating and Vibrating
Hamm has a vibratory padfoot roller for such applications just as other manufacturers do. In the mid-1980s, however, Hamm came out with a compaction technology known as oscillation—primarily for asphalt work. It also has machines that use oscillation for earthwork. A standard vibratory compactor applies vertical impaction to whatever surface an operator is working on. With oscillation, instead of having a single eccentric, two sets of eccentrics rotate off of the centerline. They are away from the center of the drum, and they rotate in the same direction but are 180 degrees out of phase of each other. Instead of jumping, the drum rocks back and forth, creating a different kind of compaction.
“The real difference is you aren’t pounding the surface with a hammer, but instead using a back massager,” says Monical. “We use the term non-aggressive compaction. That phrase sums it up. You still generate centrifugal forces and vibrate and rearrange particles, but you’re not aggressively hitting the surface of your material.”
With this method, according to Hamm, there is less destruction of binding material during asphalt compaction, less void formation for the intrusion of water or air to develop potholes, a smoother surface with no “washboard effect,” and less damage to vulnerable structures in the area.
“If I am next to an old church, and the foundation is weak, I am not sending these huge vertical-impact waves of energy into this foundation,” says Monical. “With oscillating there is less damage to existing utilities already in place such as waterlines, or gas, phone, or electric lines. There will not be breakage of those pipes when compacting the sub-base of a new road. Also, when applying an asphalt layer on top of a concrete bridge deck, historically this layer was applied statically to avoid cracking the concrete with the machine’s vibrations. It was a slower process. With oscillation technology you can get the compaction done quicker. You don’t have to worry about cracking the concrete of the bridge deck.” Though this technology has been used in Europe for about 20 years, actual marketing of the technology in North America started in 2003.
“Vibromax invented the first vibratory soil compactor in 1934,” says Tom Meyer, manager of marketing and sales support at Vibromax. The company has recently introduced the new VM Series of single-drum rollers used for soil compaction, from 4.5 metric tons up to 18 metric tons. It also has a new 68-inch tandem asphalt roller, the W10, which is used for road construction and large parking lots.
“We do have a compaction meter that is available on our single-drum rollers,” says Meyer. Vibromax’s compaction-density meter measures the resistance coming off the area that an operator is compacting. “As the material gets stiffer and reaches density, there is more feedback to the drum. A compaction meter will measure density; however, you still have to have some type of independent density check, such as nuclear density testing, to accurately measure density. You just can’t leave it up to the meter on your machine.
“This new equipment also tends to be rather pricey, and our customers have found it to be of marginal benefit. It isn’t anything that necessarily makes the machine work any better. Whether you are going to get density or not is more a factor of the size of the machine and following proper rolling conditions than anything else.”
The top compaction markets at present are California, Florida, Texas, and Pennsylvania. “In the first three states, this is due to their tremendous growth rates,” says Meyer. “For the latter state, it’s because of the population density and the sheer number of miles of roadway in the state.”
Dave Wolf, marketing manager with Case, says the company does not offer any equipment with intelligent compaction in place to date. “All our SV [single vibratory] machines do oscillate,” says Wolf. “We offer four different models, which are tier-two certified with electronically controlled engines to help with fuel efficiency, better responses to load changes, and machine diagnostics. A lower center of gravity in their machinery helps [operators] work better on slopes and drive inclines.” The single-vibratory machines are for soil compaction. Case offers a line of smaller machines (DV, or double vibratory) that are smaller in size and used for asphalt.
For compaction contractors looking for something new or for more sophistication in their equipment, the coming years look to have plenty of equipment to choose from. But for others such as Jimmy Gist, they may be just as pleased to hear that there’s still machinery with fewer changes out there too.