The PZL-1 transmitter can operate multiple machines equipped to accept its signals. The GNSS component of the system plots the location of the machine while the laser component guides the grader to position and elevates the blade precisely. The system “knows” the three-dimensional position of the laser transmitter and the three-dimensional position of the machine and is then able to calculate the vertical angle from the laser up to the sensor on the machine and provide a vertical correction.
After the project was awarded, Barrett purchased a Millimeter GPS+ system and let Welfle alternately mount the system on the motor grader for fine dirt grading, and a Roadtec RX-60 cold planer for milling existing concrete runway surfaces. The cold planer went to work on Runway 18/36 in two phases, a key factor in keeping the team on a tight schedule.
Up and running
In late May 2011, Barrett’s project superintendent, Jay Shawver, watched through fog and drizzle as the cold planer milled the existing concrete surface and conveyed the broken material into a dump truck that crawled along the runway at the same pace. During this first phase, he notes, a 1,000-foot long section of the runway was closed off. First, one shoulder was excavated and new under-drain was installed. Then, 3-½ inches of concrete were milled off of the runway adjacent to the excavated shoulder while excavation work took place on the opposite shoulder. The cold planer then was to mill 5¼ inches off of the taxiway leading to Runway 18-36 but only 4 inches along a joint for an adjacent taxiway, which was not being resurfaced.
Following the closure of the first runway section for 40 days to provide a buffer zone for the still-active intersecting Runway 6L/24R, the remaining 700 feet were to be resurfaced in the same fashion. Runway 6L/24R actually was to be closed in two 10-day phases while the second section of Runway 18-36 was resurfaced.
Jeff Combs, president of JC Equipment Sales, Cincinnati, had sold Barrett the Millimeter GPS+ system, which included a PZL-1; a HiPer Lite+ base station; a 915-MHz RE-S1 spread-spectrum radio repeater set up in the middle of the runway and running off of a pickup truck battery; a PZS-1 rover receiver for Barrett’s grade checker; and an MC-R3 GPS receiver, 9169 control box and 9620 cross-slope sensor for mounting on the cold planer. Combs had contacted several Topcon dealers whose customers had used the Millimeter GPS+ system for airport runway milling.
Says Combs, “There was a lot of preplanning on this job — I can’t stress that enough. You have to have it all right and you have the people trained so that when it starts going, it goes off correctly and there are no problems. One thing we’ve learned is that the system works only as well as the control.” With this in mind, Combs suggested that the official surveyor on the project, Luis G. Riancho & Associates, Englewood, OH, set control points every 250 feet. “With those control points in that kind of proximity, we have checks and balances on either side of the machine as we go up the runway.”
The cold planer was making two passes on each swath on the runway, first taking off 2-½ inches, then a nominal 1-½ inches. “The variable depth — that’s one advantage to having the Millimeter GPS+,” Shawver says. “It’s telling us what to cut and where to cut.” Avoiding overmilling would allow Barrett to minimize asphalt use when it came time to pave the milled areas.
The Millimeter GPS+ system passed its first test, with the milled surface on the first 1,000 feet of Runway 18/36 and the entire surface was within tolerance, except for one spot that was 4/100ths high. This was a much better scenario for Barrett than having overmilled. The motor grader also graded the blast pad within tolerances throughout. “What we don’t want to have happen is for [Riancho] to come out and tell us that it’s wrong so that we have to tear it up,” says Meyer. “That impacts material costs; but the system also minimizes any mistakes that could occur, from stringlining to putting markings down.”
Besides savings on materials, the system also provided savings in surveying costs. Combs points out that the cost of having a licensed surveyor constantly checking elevation and grade behind the cold planer can add up fast.
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