When reconstruction of a Mitchell, SD, municipal airport runway fell behind schedule because of rain in summer 2009, Bowes Construction, Brookings, the grading subcontractor, had two weapons at its disposal to make up for lost time: a fast-track pavement recycling process and high-speed machine control technology.
The airport's 6,700-foot-long Runway 12-30, the longer of two runways at the facility, was an 8-inch-thick concrete layer with 9.5 inches of asphalt on top from the many repair projects throughout the years. Bowes demolished and graded half of the runway at a time lengthwise, a technique that is fairly unique to airport construction.
First, Bowes Construction used a Wirtgen milling machine to remove the asphalt layer on half of the pavement. A proprietary guillotine drop hammer then broke up the concrete. Next, a Caterpillar 330C excavator fed a Metso LT 1213S mobile track crusher that reduced and blended the millings and broken concrete into 3-inch pieces and stockpiled it on the other half of the existing pavement. Bowes excavated 18 inches of soil under the old pavement using a Caterpillar D6R dozer and widened the subbase excavation to 134 feet to widen the runway from 100 to 124 feet.
Recycling pavement on-site
The recycled material was placed in the trench in uniform lifts to form a 12 to 15-inch-thick subbase. Additional quartzite coarse aggregate was delivered from Spencer Quarries, Spencer, SD, and placed 18 inches deep in three 6-inch lifts.
"This project had more room than we're used to working on a highway job. We divided the runway in half," said Jason Bowes, vice president of Bowes Construction. "We milled the asphalt all to one side, leveled it, then take that crusher and run on top of it." He added that this process was possible because Bowes Construction was allowed to recycle the old pavement on site instead of hauling the concrete to a central facility. Off-site recycling would have allowed full-width pavement demolition, but that process required more time than the process used.
However, a wet summer delayed the project. Bowes decided to use cutting-edge machine-control technology to reduce the adverse impact of the weather on scheduling.
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.
Phase 2 construction
Commercial Asphalt, Mitchell, SD, a division of Spencer Quarries, received the contract for reconstructing the runway with a 5.5-inch asphalt surface. Under Phase I, which started in late June 2009, Runway 12-30 was reconstructed at the intersection of two shorter runways. Work included asphalt milling, removing existing concrete, excavation, sub-base and base course construction, asphalt pavement, under drain, installing storm sewer pipes, drainage improvements, marking, adding top soil and seeding.
In early August, Phase 2 work began on 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.
On September 1, Bowes reported that Phase 2 site work was about two weeks behind schedule. But Jason Bowes expected the combination of the on-site recycling process and machine-control technology to make up one week's work and complete the project by October 1 instead of September 25 as initially scheduled.
South Dakota, the pheasant-hunting capital of the world, would start its hunting season in November. Large numbers of hunters were expected to fly into the airport in October, which required use of the new runway.
GNSS on two dozers
To make up for lost time, Bowes Construction equipped the second of two dozers, a Caterpillar D8T, with its Topcon 3D-MC2 Global Navigation Satellite System (GNSS) machine-control system for grading the subbase and base. The company had already purchased 3D-MC2 components from Laser Control Inc., Bloomington, MN, and equipped the D6R with this system, which allowed the dozers to move aggregate with minimal interruptions and grade with precision.
The 3D-MC2 system's components include a MC-R3 GNSS controller that works in conjunction with an MC2 sensor that replaces a slope sensor; a four-color, touch screen, Bluetooth-capable GX-60 control box; and a conventional GNSS antenna mounted on the dozer blade. The technology provides blade position readings up to 100 times per second.
GNSS machine control is not new to Bowes Construction, although equipping dozers with GNSS is a new practice. Starting in 2001, the company adopted 3-D GNSS machine control and used the technology on as many as six graders at a time.
The D6R dozer leveled off piles of quartzite aggregate while a Caterpillar 140H grader equipped with Topcon's System 5 indicated grading the next swath 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.
Eliminating human errors
Although he had operated graders, scrapers and loaders without the assistance of machine controls, Palmer had never operated a dozer with the 3D-MC2 system on the D6R. His training on high-speed, machine-control assisted dozer operation consisted of riding with Jason Bowes for six hours.
"[Machine control] takes human error out of the work," said Palmer. "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. The biggest difference with this system is scheduling our own work and continuing to move without waiting for a staker to get in between each phase."
A design attribute of the system also boosts productivity, Bowes added. The control box is equipped with magnets so that it can be moved quickly and the GNSS antenna/receiver can be switched easily to another machine. "Flexibility is big in construction and this system has definitely moved the project forward," said Bowes. "Building isn't going to stop in the future."
Don Talend owns Write Results Inc., a print and e-content developer specializing in construction, technology and innovation.