Renewing the Runway
by Don Talend
January 1, 2010
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A wet summer putreconstruction ofa runway at theMitchell MunicipalAirport behind byabout two weeks, butthe use of machinecontrol technologyregained about aweek, according toJason Bowes of BowesConstruction.
Anyone wanting a glimpse into the future of airport runway site preparation would have found it in South Dakota in late 2009. The sitework for the Mitchell Municipal Airport can be described as cutting-edge for two reasons: a fast-track pavement recycling process and high-speed machine control technology were utilized.
As the dozer levels out the quartzite aggregate, a gyro, compass and inertial sensor take up to 100 readings a second—about five times as many as conventional GNSS machine control systems.
The airport’s 6,700-foot-long Runway 12/30, the longer of two runways at the facility, had an 8-inch-thick concrete layer topped with a total of 9½ inches of asphalt that had built up in many repair projects throughout the years. A technique that is fairly unique to airport construction was used—demolishing and grading half of the runway at a time lengthwise.
First, a Wirtgen milling machine was used to remove the asphalt layer on half of the pavement. A proprietary “guillotine drop” hammer then broke up the concrete. Next, Bowes Construction of Brookings, South Dakota—the grading subcontractor on the project—used a Caterpillar 330 C excavator to feed a Metso LT 1213S mobile track crusher that reduced and blended the millings and broken concrete down to 3-inch-minus size and stockpiled it on the other half of the existing pavement.
Then, largely through the use of a Caterpillar D6R dozer, Bowes Construction excavated 18 inches of soil where the pavement had been and widened the subbase excavation to 134 feet so that the runway could be widened from 100 to 124 feet. The recycled material was then placed in the excavation in uniform lifts to form a 12- to 15-inch-thick subbase. Additional quartzite coarse aggregate was trucked in from Spencer Quarries of Spencer, South Dakota, and placed 18 inches deep in three 6-inch lifts.
“Being that this is more room than we’re used to on a highway job, we worked it in half,” says Jason Bowes, vice president of Bowes Construction. “We mill the asphalt all to one side, level it off, then we take that crusher and run on top of it.” He adds that the use of this process was possible largely because Bowes was allowed to recycle the old pavement onsite instead of hauling it to a central facility. Offsite recycling would have allowed full-width pavement demolition, but that still would have taken longer than the process used, Bowes points out.
The fast-track recycling process aside, a wet summer had put the project behind schedule, according to Bowes. But cutting-edge machine control technology would, in turn, lessen the adverse impact of the weather on scheduling.
Recycled aggregate formed a sub base layer about 15 inches thick and additional material was trucked in to provide an additional 18-inch-thick layer.
The airport, which was initially constructed as a military installation in 1945, received $6.7 million in funding under the American Recovery and Reinvestment Act of 2009 and $450,000 in Federal Aviation Administration and state and local funding for design and construction engineering. Commercial Asphalt of Mitchell, South Dakota, a division of Spencer Quarries, was awarded the contract for reconstructing the runway with a 5½-inch-thick asphalt surface.
Under Phase I, which started in late June 2009, Runway 12/30 was reconstructed at the intersection of two shorter runways. The work included asphalt millings, removal of existing concrete, excavation, subbase and base course construction, asphalt pavement, underdrain, storm sewer piping, drainage improvements, marking, topsoiling and seeding. In early August, Phase 2 work began and included the reconstruction of Runway 12/30 with the construction of 12-foot-wide non-aircraft asphalt shoulders, construction of transition pavement from the runway to one taxiway and the reconstruction of another taxiway to the runway safety area. The work tasks were identical to those in Phase I.
Bowes Construction equipped a second dozer with the Topcon 3D-MC2 system and a machine control-equipped Caterpillar 140H grader followed closely behind and fine-graded the aggregate.
The Topcon 3D-MC2 system’s components include an MC-R3 GNSS controller that works in conjunction with an MC2 sensor (which replaces a slope sensor); a four-color, touchscreen, Bluetooth-capable GX-60 control box; and a conventional GNSS antenna mounted on the dozer blade. The MC2 sensor combines a gyro, compass and inertial sensor to measure the x, y and z position as well as the roll, pitch, yaw and acceleration of the dozer. The technology gives the system the capability to provide blade position readings up to 100 times per second.
Bowes recalled that Topcon had provided him with information about the new system at ConExpo in 2008. “Last spring, my dealer, Steve Salz, called and said that he had a road show in Belle Plaine [Minnesota] and that we should come on out there and check this out. So we did; my dad [company founder Lyle Bowes] and I both went out there and both got to run it and we put her to the test. And we said—we want that.”
The GX-60 monitor shows the precision ofthe dozer blade positioning for operatorLaDuke Palmer.
GNSS machine control is not a new concept to Bowes Construction, although equipping dozers is a new practice. The company has used the systems on graders for years. Following his honorable discharge from the Marine Corps in 1994, Bowes says, “My dad wanted to know what I wanted to do and I said I wanted to learn how to run a blade.” He adds with a laugh, “I didn’t know that that would mean that I would be living in one for the next eight years of my life.”
Around that time, Lyle Bowes installed on a grader an Agtek two-dimensional grading system that utilized slope sensors and sonic trackers, and Jason Bowes used the system on numerous highway projects. (Topcon acquired Agtek around that time.) Starting in 2001, Bowes Construction adopted 3D GNSS machine control and has used the technology on as many as six graders at a time.
According to Salz, Laser Control likes the fact that Bowes Construction wants to be the first customer to use new machine control technologies. “We want to be on the cutting edge, not the bleeding edge,” Bowes says.
After being processed by a mobile track crusher, the recycled pavement is ready for grading.
As Jason Bowes watched, the D6R leveled off piles of quartzite aggregate that had just been trucked in by Spencer Quarries. A Caterpillar 140H grader equipped with Topcon’s System 5 indicate system fine-graded the next swath, just a few feet behind the D6R.
Inside the dozer, operator LaDuke Palmer viewed the dozer’s position and blade placement in real time on the GX-60 in-cab monitor and made necessary adjustments. Although he had operated graders, scrapers and loaders—without the assistance of machine control—Palmer had never operated a dozer before Bowes Construction had hired him the previous May, around the time that the company purchased the 3D-MC2 system for the D6R. His training on high-speed, machine-control-assisted dozer operation consisted of riding alongside Jason Bowes for six hours.
“When you use this system on a dozer, you’re really thinking like you’re operating a [grader],” he says. “You’re really knocking the big rows down so the blade can come in and finish-grade it.” Palmer adds that the machine control system also allows him to keep working without the need for grade-checking interruptions. “We blue-top on the final stage, but there’s no blue-topping in between.” Pointing to the monitor, he noted that the grading tolerances were within tenths of an inch and even in low-precision, the monitor read 0.09, or nine-hundredths of a foot.
“[Machine control] takes human error out of it,” Palmer says. “This is the beginning of the fourth week on this phase. By the end of this week, we’ll have finished the subbase and the base. That’ll be four weeks to do a mile in length and 134 feet wide.”
Bowes imagines how the grading work would be done without machine control. “I’d use the same equipment, but there would be some staking,” he says. After cutting the subgrade excavation, Bowes Construction would check the grade as it was doing when using machine control. But then, Bowes says, “You’d have a survey crew, which would be the engineer’s crew, staking it. And then, after it was staked, after the blue-tops were put in, you’d have to grade the material over the stakes, so there would be another step.”
He says, “That’s probably the biggest difference with this system: scheduling our own work and continuing to move without being held up due to waiting for a staker to get in between each phase, which allows us to keep on moving.”
A design attribute of the system also boosts productivity, Bowes adds. The control box is equipped with magnets so that it can be quickly moved and the GNSS antenna/receiver can be easily switched to another machine. “Flexibility is big in construction and this system has definitely speeded up the process for us,” Bowes says, looking past the severe recession that began in December 2007 with an eye on a possible boom in construction work once stimulus money filters down. “Building isn’t going to stop in the future.”
For more information on Topcon’s 3D-MC2 system, check out these exclusive features at www.siteprepmag.com:
• A Closer Look at the Topcon 3D-MC2 System: A slideshow of Topcon’s latest technology for automated grading with dozers.
• Topcon Opens the Throttle: Three videos recorded at Topcon’s California test site demonstrate how Topcon’s 3D-MC2 technology allows operators to grade at higher speeds.
SIDEBAR: Topcon’s 3D-MC2 Set to Double Productivity
Because of this, the new system has the potential to fundamentally change the way contractors utilize equipment, schedule projects and even bid projects. Double the productivity can mean that a single dozer can replace two that would otherwise be needed on some projects. Theoretically, half the equipment used can equate to half the fuel consumed—not a minor issue given the high fuel costs of 2008 and the economic downturn that began in 2007 and necessitates more scrutiny of profit margins than ever. Finally, twice the productivity can even allow a contractor to take on twice as much work without incurring major additional capital costs.
Don Talend
Don
Talend of Write Results Inc., in West Dundee, Ill., is a print and e-content
developer specializing in covering technology and innovation.
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