Closing a runway at an international airport during the summer months — and milling and paving it under tight deadlines so that it can be reopened quickly — can put a lot of stress on a contractor. Barrett Paving Materials Inc.’s Dayton, OH-based Midwest Central Office recently faced just that kind of challenge and brought to bear new automated grading technology that expedited the milling work and kept runway resurfacing on schedule at the Dayton International Airport.
In July 2010, the City of Dayton awarded Barrett a $4.5 million contract to resurface the 1,700-by-150-foot concrete surface of Runway 18-36. Plans also called for an upgrade to the runway’s underdrainage structures, resurfacing of a 40,000-square-foot blast pad located behind the runway with 6 inches of bituminous base material and 2 inches of bituminous surface and construction of 6½ inches of bituminous base topped by 1½ inches of bituminous surface for a taxiway leading to the runway. In addition, Barrett was contracted to excavate and construct a 12-inch crushed aggregate base and 8-inch asphalt overlay on an 87,500-square-foot terminal shoulder and also was awarded a contract to resurface pavement in front of an aviation center where pleasure craft are stored.
Airport runway resurfacing was a new type of project for Barrett’s Midwest Central Office, which had done paving work at the airport but not runways. Also, this project represented the Barrett Midwest Central Office’s first use of three-dimensional machine control. For the most critical part of the job — milling existing concrete surfaces — Barrett turned to a longtime partner on many highway paving projects: Welfle Inc., Norwalk, OH.
The construction schedule originally called for work to begin in November 2010 around the airport terminal, but temperatures were too low to place silicone joint sealer, noted Nick Meyer, Barrett’s project manager. In mid-May 2011, work began on the east and west shoulders of Runway 18-36. Eight inches of asphalt pavement were milled and 12–14 inches of subgrade were excavated using a Roadtec cold planer to the specified elevation using a high-tech tool that is becoming more common in milling airport pavements.
Combining laser, GNSS
The Topcon Positioning Systems Millimeter GPS+, which made an initial impact in subgrade preparation, increasingly is being used for milling and paving. Just as the system has been used for fine grading, contractors are beginning to use it for “fine milling” — and achieving accuracies within a quarter-inch in contrast to the tenth-of-a foot precision inherent in conventional machine control.
Conventional Global Navigation Satellite System (GNSS) machine control uses satellite signals alone. Such a system uses a rugged antenna mounted to a shock-absorbing, vibration-damping pole along with a GNSS receiver box mounted in a secure location on the machine. Satellites send positioning data to another antenna/receiver combination at a stationary base station. The base station then sends a three-dimensional position and 3D corrections via radio to the mobile or machine control receiver. Positioning data is also sent to the machine.
The stationary base and machine work together to provide real-time kinetic (RTK) position information, revealing the machine’s three-dimensional location on the site. Software compares the machine’s position to the design grade, which was determined using site plans, at a given location. The system also provides visual guidance for machine operators by displaying a site model on an in-cab color monitor, or it automatically adjusts the needed elevation and desired cross-slope of the blade as the operator guides the machine forward.
Millimeter GPS+ combines GNSS and laser. In addition to a GNSS base and rover, the system uses a PZL-1 Lazer Zone transmitter and a PZS-MC machine-control sensor or PZS-1 rover sensor that gets integrated with the contractor’s GNSS receiver.