The PZL-1 transmitter sends out a wall of laser light 33 feet tall and up to 2,000 feet in diameter. The contractor can link up to four transmitters for a total reach of 8,000 horizontal feet and 132 vertical feet. 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 elevate 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 81-36 in two phases and proved to be a key factor in keeping the construction 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 noted, a 1,000-foot-long section of the runway was closed off. First, one shoulder was excavated and new underdrain was installed. Then, 3½ 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.
The airport had a pavement management study to evaluate all of its pavements. Even though the pavements were determined to be structurally sound, there was another reason why the improvements were needed. A close visual inspection of the existing Runway 18-36 surface revealed why it was time to replace it.
“The big issue that the airport has is FOD (foreign object debris) where debris gets into airplane engines and so forth,” Meyer said. “As the concrete ages, it begins to chip and spall.”
Following the closure of the first runway section — for 40 days, according to the schedule — 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.
The entire project was to be completed in 120 days, meaning sometime in August 2011. Meyer noted that rainy weather had caused work delays, including the day before, when a midday thunderstorm made Millimeter GPS+ operation impossible and shut down the jobsite.
“With this weather, we’ve already taken hits on our underdrain, so we need to make sure that this production is going great,” he said. Another challenge facing Barrett and Welfle was the tolerance on the milling work: a quarter-inch.
Jeff Combs, president of JC Equipment Sales, Cincinnati, made sure to practically live onsite while the high-profile project was underway. He 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, Jeremy Harper, to use; and an MC-R3 GPS receiver, 9169 control box and 9620 cross-slope sensor for mounting on the cold planer. With the customer using the system for the first time, he wasn’t taking any chances.
Combs recalls doing a great deal of preparation for utilizing the system after selling it to Barrett in late 2010. “Between then and now, we did a lot of preparation for the grade control, making sure the control points would match what was out here,” he said. “That preplanning really paid off for us on this job.