Rea Construction, Charlotte, N.C., recently won a lump-sum bid for 8.1 miles of work on Interstate 77 near Charlotte. Four new asphalt lanes are to be added in the median strip, then the four existing outside lanes are to be milled and resurfaced. Keeping grades as close to theoretical is critical during all stages of the job, says project manager Kipp Cheek, because an extra half-inch of asphalt on the milled surfaces, for example, could amount to $500,000.
While the company was comfortable controlling grades the conventional way, says Cheek, staking and pulling string, it also recognized the potential of automated grade-control systems. So, with some trepidation, says Cheek, Rea contacted Joe McNamara, principal of Spectra Integrated Systems, a local Trimble dealership, and inquired about automated grade control.
"After at least ten meetings with Joe," says Cheek, "we finally had the confidence to turn grade control over to computers. We figured this was the future, and we wanted in on it."
The result is that Rea is now using a Trimble SiteVision GPS (Global Positioning System) package for rough grading the sub-base of the new lanes, and Trimble total robotic stations for fine grading the sub-base, establishing soil-stabilized grades and for controlling the cutting head of the milling machine.
According to Cheek, the consistent grades made possible by automated control are resulting in exceptionally smooth riding surfaces, minimizing material overruns and saving time. Right now, the traffic switch to the new lanes, allowing full-time work on the existing lanes, is estimated to occur about 200 days ahead of schedule. Over all, says Cheek, the technology on site could help trim a full year off the state DOT's original projection.